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[72] Bezerra MA, Lacerda CF, Gomes-Filho E, Abreu CEB, Prisco JT. Physiology of cash‐ ew plants grown under adverse conditions. Brazilian Journal of Plant Physiology

[73] Ferreira-Silva SL, Silveira JAG, Voigt EL, Soares LSP, Viégas RA. Changes in physio‐ logical indicators associated with salt tolerance in two contrasting cashew rootstocks.

[74] Abreu CEB, Bezerra MA, Enéas-Filho J, Prisco JT, Gomes-Filho E. Physiological and biochemical changes occurring in dwarf-cashew seedlings subjected to salt stress.

[75] Alvarez-Pizarro JC, Alencar NLM, Prisco JT, Gomes-Filho E. Salt-induced changes on

[76] Lima MA, Bezerra MA, Gomes-Filho E, Pinto CM, Enéas-Filho J. Gas exchange in leaves of sun and shade of cashew in different water regimes. Revista Ciência Agro‐

[77] Amorim AV, Gomes-Filho E, Bezerra MA, Prisco JT, Lacerda CF. Physiologic re‐ sponses of precocious dwarf cashew at different levels of salinity. Revista Ciência

[78] Dombroski LD, Praxedes SC, Freitas RMO, Pontes FM. Water relations of Caatinga trees in the dry season. South African Journal of Botany 2011; 77: 430–434.

[79] Santos MG, Ribeiro RV, Machado EC, Pimentel C. Photosynthetic parameters and leaf water potential of five common bean genotypes under mild water deficit. Biolo‐

[80] Trovão DMB, Fernandes PD, Andrade LA, Dantas-Neto J. Seazonal variations of physiological aspects of Caatinga species. Revista Brasileira de Engenharia Agrícola

[81] Souza RP, Machado EC, Silva JAB, Lagôa AMMA, Silveira JAG. Photosynthetic gas exchange, chlorophyll fluorescence and some associated metabolic changes in cow‐ pea (*Vigna unguiculata*) during water stress and recovery. Environmental and Experi‐

[82] Santos MG, Ribeiro RV, Machado EC, Pimentel C. Photosynthetic parameters and leaf water potential of five common bean genotypes under mild water deficit. Biolo‐

[83] Chaves MM, Maroco JP, Pereira JS. Understanding plant responses to drought-from

genes to whole plant. Functional Plant Biology 2003, 30: 239-264.


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Growth Regulation 2009; 59 (2): 125-135.

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2007; 19 (4): 449-461.

94 Responses of Organisms to Water Stress

H+

Allan Klynger da Silva Lobato, Elaine Maria Silva Guedes, Douglas José Marques and Cândido Ferreira de Oliveira Neto

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/53765

## **1. Introduction**

The silicon (Si) is an abundant element in terrestrial superficie [1], however its availability to plants is normally low [2]. According to Matichenkov & Calvert [3], the chemically active Si forms in soil are represented by soluble monosilicic acid (Si(OH)4) that is soluble and weakly adsorbed, as well as acid polisilicic, which are compound organosilicates.

Si is considered an benefic element to higher plants [4], being that the absorption process must be active or passive [5], and deposition in cell walls of several organs such as leaf and stem can promote beneficial effects [6], and for this reason has been frequently linked to physiological, morphological, nutritional, and molecular aspects in plants [7-10].

In plants this nutrient is assimilated mainly by roots, and capacity to accumulate in tissues is variable [11], being several monocots such as *Oryza sativa* and *Triticum aestivum* considered silicon accumulator, with absorption active by root system, and it present leaf levels normal‐ ly higher that 10.0 g kg-1 of Si [12]. In other hand, many dicots like as *Phaseolus vulgaris* and *Glycine max* are characterized as not accumulator of silicon, and its presents passive absorp‐ tion, with leaf tenors minors that 5.0 g kg-1 of Si [13].

In tissues, about of 99% of silicon is found in silic form and less than 1% is colloidal or ionic form, which is the soluble form [14]. Therefore, the storage sites of silicon in plants normally are responsible to improve leaf and plant architectures and also others metabolic processes like as gas exchanges [15], photosynthetic pigments [16], and antioxidant system [17], in

which it results in better performance linked to growth, development, and yield parameters [18] (Figure 1).

justment [22], modifications in physiological parameters as water potential, stomatal closing [23], and decrease in photosynthesis rate [24], besides reduction in cell metabolism with neg‐

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97

Gas exchanges like as leaf water potential, stomatal conductance, and transpiration rate has been used mainly to explain mechanisms affected during drought [25]. When the water availability in soil decrease, normally the water potentials of soil and leaf also are reduced, and it will provoke as consequence turgescence loss in plant cells, mainly in leaf, causing

The water potential describes the water amount, in which the water is moved in direction to potentials more negatives, and it differences of potential reveal water flux in soil-plant-at‐ mosphere system [27]. In general, the leaf water potential is depending to soil water poten‐

Attenuation of negative effects induced by the silicon application has been frequently de‐ scribed in plants exposed to water deficiency, such as Hattori et al. [2] investigating *Sorghum bicolor* plants related interference on gas exchanges. Results obtained by Ahmad & Haddad [29] working *Triticum aestivum* plants revealed influence positive on antioxidant enzyme ac‐ tivities. In addition, Lobato et al. [30] studying *Capsicum annuum* plants reported maximiza‐

Aims of this chapter is to define (i) silicon and water deficit, to explain (ii) on silicon sources, uptake system and transporters into plant, and detection form in tissue, and to present (iii) the silicon action on gas exchanges and photosynthetic pigments in plants exposed to water

The silicon uptake using metal salts of silicic acid normally requires their hydrolysis prior to their uptake. In either case they would affect the ionic balance of the system. The proposed mechanism for the solubilization of silica by PNO or MNO is novel and probably involves polarization of surface silica layer through interaction with the oxygen of the pyridine Noxides. In the solubilization, PNO and MNO are regenerated, as evidenced by the fact that clear water containing freshly prepared PNO/MNO-silica complexes slowly deposits granu‐

Based in overview related, a research was conduced by Ranganathan et al. [33] with *Oryza sativa* plants exposed to pyridine N-oxide (PNO), 4-morpholino pyridine N-oxide (MNO), and sodium metasilicate (SMS) aiming to test silicon sources on their ability to enhance the

ative consequences on growth and production.

stomatal closing and limiting the gas exchanges [26].

tial, water flux in system, and transpiration rate [28].

tion in proline synthesis.

**2. Objective**

restriction.

**3. Silicon sources**

lar silica [31-32].

plant silicon content.

**Figure 1.** Effects of Si-treatment on growth of cvs. Hinohikari, Oochikara and lsi1 mutant. Aspects of wild type rice cvs. Hinohikari (a, d), Oochikara (b, e) and lsi1 mutant (c, f) were observed after control nutrient treatment of rice seedlings (a, b, c) and 14-day silicic acid treatment of rice seedlings (d, e, f) [7].

Drought is one of the key sources of abiotic stress, since it induces smaller growth and de‐ velopment rates, flower aborting, and decreases crop yields during the vegetative, repro‐ ductive, and maturation stages [19]. Usually, drought consequences on plants are studied in controlled/artificial conditions through water restriction.

Vascular plants present several strategies to minimize the negative effects induced by water deficiency, being morphological modifications like increase in root size [20] and reduction in leaf area [21]. Other responses are frequently reported, such as reductions in CO2 assimila‐ tion by leaf through stomatal closing, membrane damage and disturbed activity of various enzymes, especially those of CO2 fixation and adenosine triphosphate (ATP) synthesis. En‐ hanced metabolite flux through the photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen species. Injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deter‐ rents to growth.

The stress occasioned by lower water supply to plant is defined as water deficit, being re‐ sponsible to active responses in plant such as over-expression of genes linked to osmotic ad‐ justment [22], modifications in physiological parameters as water potential, stomatal closing [23], and decrease in photosynthesis rate [24], besides reduction in cell metabolism with neg‐ ative consequences on growth and production.

Gas exchanges like as leaf water potential, stomatal conductance, and transpiration rate has been used mainly to explain mechanisms affected during drought [25]. When the water availability in soil decrease, normally the water potentials of soil and leaf also are reduced, and it will provoke as consequence turgescence loss in plant cells, mainly in leaf, causing stomatal closing and limiting the gas exchanges [26].

The water potential describes the water amount, in which the water is moved in direction to potentials more negatives, and it differences of potential reveal water flux in soil-plant-at‐ mosphere system [27]. In general, the leaf water potential is depending to soil water poten‐ tial, water flux in system, and transpiration rate [28].

Attenuation of negative effects induced by the silicon application has been frequently de‐ scribed in plants exposed to water deficiency, such as Hattori et al. [2] investigating *Sorghum bicolor* plants related interference on gas exchanges. Results obtained by Ahmad & Haddad [29] working *Triticum aestivum* plants revealed influence positive on antioxidant enzyme ac‐ tivities. In addition, Lobato et al. [30] studying *Capsicum annuum* plants reported maximiza‐ tion in proline synthesis.

## **2. Objective**

which it results in better performance linked to growth, development, and yield parameters

**Figure 1.** Effects of Si-treatment on growth of cvs. Hinohikari, Oochikara and lsi1 mutant. Aspects of wild type rice cvs. Hinohikari (a, d), Oochikara (b, e) and lsi1 mutant (c, f) were observed after control nutrient treatment of rice seedlings

Drought is one of the key sources of abiotic stress, since it induces smaller growth and de‐ velopment rates, flower aborting, and decreases crop yields during the vegetative, repro‐ ductive, and maturation stages [19]. Usually, drought consequences on plants are studied in

Vascular plants present several strategies to minimize the negative effects induced by water deficiency, being morphological modifications like increase in root size [20] and reduction in leaf area [21]. Other responses are frequently reported, such as reductions in CO2 assimila‐ tion by leaf through stomatal closing, membrane damage and disturbed activity of various enzymes, especially those of CO2 fixation and adenosine triphosphate (ATP) synthesis. En‐ hanced metabolite flux through the photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen species. Injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deter‐

The stress occasioned by lower water supply to plant is defined as water deficit, being re‐ sponsible to active responses in plant such as over-expression of genes linked to osmotic ad‐

(a, b, c) and 14-day silicic acid treatment of rice seedlings (d, e, f) [7].

controlled/artificial conditions through water restriction.

[18] (Figure 1).

96 Responses of Organisms to Water Stress

rents to growth.

Aims of this chapter is to define (i) silicon and water deficit, to explain (ii) on silicon sources, uptake system and transporters into plant, and detection form in tissue, and to present (iii) the silicon action on gas exchanges and photosynthetic pigments in plants exposed to water restriction.

## **3. Silicon sources**

The silicon uptake using metal salts of silicic acid normally requires their hydrolysis prior to their uptake. In either case they would affect the ionic balance of the system. The proposed mechanism for the solubilization of silica by PNO or MNO is novel and probably involves polarization of surface silica layer through interaction with the oxygen of the pyridine Noxides. In the solubilization, PNO and MNO are regenerated, as evidenced by the fact that clear water containing freshly prepared PNO/MNO-silica complexes slowly deposits granu‐ lar silica [31-32].

Based in overview related, a research was conduced by Ranganathan et al. [33] with *Oryza sativa* plants exposed to pyridine N-oxide (PNO), 4-morpholino pyridine N-oxide (MNO), and sodium metasilicate (SMS) aiming to test silicon sources on their ability to enhance the plant silicon content.

The suggestion that enhanced silica deposition is linked to the ability of the rice plant to combat abiotic and biotic stresses is further supported by SEM and EDX analysis of silicon distribution in the rice leaves. In the absence of added silicon, the leaves exhibited a scat‐ tered profile of silicon distribution (Figure 2). The leaves treated with MNO, PNO or SMS showed enhanced silicon content and localization of silicon bodies in leaf bundle sheath cells, particularly in the primary and secondary cell wall.

Electron microscopy and in situ X-ray analysis of rice leaves reflect the differences in silicon distribution and cell wall structure between silicon treated and untreated plants [34-36]. The SEM pictures show that PNO and MNO enhanced the silica deposition on the leaves of rice plants concomitant with the localization of silicon bodies in leaf bundle sheath cells and in

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99

For decades, rice has been known as the most effective silicon-accumulating species, al‐ though the mechanisms involved in high silicon uptake are poorly understood. One of the reasons is, unlike other minerals, the genotypic difference in silicon concentration of rice is too small to be utilized for comparative study on silicon uptake by rice roots [8]. With finali‐ ty to resolve this problem, a research conduced by Ma et al. [8] working low-silicon mutant (*lsi1*) and wild-type of *Oryza sativa* plants revealed that there are least two transporters in‐

**Figure 3.** Concentration of silicon in the symplastic solution of *Oryza sativa* root tips (A), and concentration of silicon in the xylem sap (B) of rice cultured in silicon solution at various concentrations. Seedlings (26 d old) of wildtype (WT) and mutant (*lsi1*) rice were cultured in half-strength Kimura nutrient solution containing various concentrations of sili‐ con. The stem was severed after 8 h, and the xylem sap was collected for 30 min. Values are means 6 SD of three repli‐

A kinetic study showed that the silicon concentration in the root-cell symplast increased with increasing silicon concentration in external solution but saturated at a higher silicon concentration in both lines (Figure 3 A). Again, there was no significant difference in the sili‐ con concentration of symplastic solution between the wild type and the mutant. These re‐ sults suggest that silicon transport from the external solution to the root cortical cells is mediated by a type of transporter and that the transporter of the mutant is identical to that

Other kinetic study on xylem loading of silicon was then conducted in the wild-type and mutant rice. In contrast to the silicon concentration in the root cortical cell symplast, the sili‐

volved in silicon transport from nutritive solution to the xylem (Figure 3 and 4).

**A B**

the primary and secondary cell walls [33].

cates [8].

of the wild type [8].

**4. Uptake system and transporters linked to silicon**

**Figure 2.** Scanning electron micrograph of silicon mapping (right) and its corresponding bundle sheath cells (left). Ap‐ plication of A - 150 mg kg-1 MNO, B - 150 mg kg-1 sodium silicate, C - control, and D - 150 mg kg-1 PNO [33].

Electron microscopy and in situ X-ray analysis of rice leaves reflect the differences in silicon distribution and cell wall structure between silicon treated and untreated plants [34-36]. The SEM pictures show that PNO and MNO enhanced the silica deposition on the leaves of rice plants concomitant with the localization of silicon bodies in leaf bundle sheath cells and in the primary and secondary cell walls [33].

## **4. Uptake system and transporters linked to silicon**

The suggestion that enhanced silica deposition is linked to the ability of the rice plant to combat abiotic and biotic stresses is further supported by SEM and EDX analysis of silicon distribution in the rice leaves. In the absence of added silicon, the leaves exhibited a scat‐ tered profile of silicon distribution (Figure 2). The leaves treated with MNO, PNO or SMS showed enhanced silicon content and localization of silicon bodies in leaf bundle sheath

**Figure 2.** Scanning electron micrograph of silicon mapping (right) and its corresponding bundle sheath cells (left). Ap‐

plication of A - 150 mg kg-1 MNO, B - 150 mg kg-1 sodium silicate, C - control, and D - 150 mg kg-1 PNO [33].

cells, particularly in the primary and secondary cell wall.

98 Responses of Organisms to Water Stress

For decades, rice has been known as the most effective silicon-accumulating species, al‐ though the mechanisms involved in high silicon uptake are poorly understood. One of the reasons is, unlike other minerals, the genotypic difference in silicon concentration of rice is too small to be utilized for comparative study on silicon uptake by rice roots [8]. With finali‐ ty to resolve this problem, a research conduced by Ma et al. [8] working low-silicon mutant (*lsi1*) and wild-type of *Oryza sativa* plants revealed that there are least two transporters in‐ volved in silicon transport from nutritive solution to the xylem (Figure 3 and 4).

**Figure 3.** Concentration of silicon in the symplastic solution of *Oryza sativa* root tips (A), and concentration of silicon in the xylem sap (B) of rice cultured in silicon solution at various concentrations. Seedlings (26 d old) of wildtype (WT) and mutant (*lsi1*) rice were cultured in half-strength Kimura nutrient solution containing various concentrations of sili‐ con. The stem was severed after 8 h, and the xylem sap was collected for 30 min. Values are means 6 SD of three repli‐ cates [8].

A kinetic study showed that the silicon concentration in the root-cell symplast increased with increasing silicon concentration in external solution but saturated at a higher silicon concentration in both lines (Figure 3 A). Again, there was no significant difference in the sili‐ con concentration of symplastic solution between the wild type and the mutant. These re‐ sults suggest that silicon transport from the external solution to the root cortical cells is mediated by a type of transporter and that the transporter of the mutant is identical to that of the wild type [8].

Other kinetic study on xylem loading of silicon was then conducted in the wild-type and mutant rice. In contrast to the silicon concentration in the root cortical cell symplast, the sili‐ con concentration in the xylem sap was much higher in the wild type than in the mutant (Figure 3 B). In the mutant, the silicon concentration in sap increased gradually with increas‐ ing silicon concentration in the external solution without saturation. In the wild-type rice, the silicon concentration in the xylem sap also increased with increasing silicon concentra‐ tion in the external solution (Figure 3 A), but it was saturated at a higher concentration [8].

ning microscopy have been broadly applied for analysis of silica bodies and other elements

Silicon: A Benefic Element to Improve Tolerance in Plants Exposed to Water Deficiency

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101

Therefore, study carried out by Isa et al. [7] optimized a technique for silica body specific stain‐ ing to visualize silica deposits in rice tissue by bright field microscopy and a technique for deter‐

The samples were fixed in FAA solution, and fixed samples were transferred and incubated in accordance with the methods of Kaufman et al. [46] and Morikawa & Saigusa [47], with minor modifications. Benzene-equilibrated samples were stained in 0.1% crystal violet lac‐

Silica bodies were observed in the motor cells of the leaf blades of cv. Hinohikari at the max‐ imum tillering stage (Figure 5 A), and silica opal was also observed in the blades (Figure 5 B). In enlarged images of silica cells located along the vascular bundles of cv. Hinohikari treated with silicic acid for 14 days, accumulation of silica was observed as clear X shapes

**Figure 5.** Crystal violet lactone staining of motor cell and silica body in leaf blade of cv. Hinohikari. A, motor cell and silica bodies in cross-section of leaf blade; B, rice opals in motor cells of leaf blade; C, a line of X-shaped silica bodies in leaf sheath. Rice opals in motor cells and silica bodies in epidermis cells were stained with crystal violet actone using leaf blade of cv. Hinohikari in paddy field at the maximum tillering stage. Motor cells and X-shaped silica bodies are

mining the in situ content of elements, including silica, by X-ray scanning microscopy.

tone solution (in benzene) to visualize the silica bodies.

indicated by lines and arrow heads, respectively [7].

in rice tissues [42-45].

(Figure 5 C) [7].

The silicon concentration in the xylem sap of the wild type was higher than 30 mM at 0.9 mM silicon supply (Figure 3 B). This concentration was much higher than that in root-cell symplast (Figure 3 A), suggesting that silicon is transported from the root cells to the xylem also against a concentration gradient. The curve of Figure 2 B also suggests that the release of silicon into the xylem is mediated by a type of transporter in the wild type [8].

**Figure 4.** Schematic representation of the silicon uptake system in rice roots. SIT1, Silicon transporter from external solution to cortical cells. SIT2, Silicon transporter for xylem loading [8].

Above results suggest that at least two transporters are involved in the silicon uptake by rice roots (Figure 4). One is located on the plasma membrane of root cortical cells (SIT1, silicon transporter 1), which transport silicon from external solution to the root cortical cells. The other is located on the plasma membrane of xylem parenchyma cells (SIT2, silicon transport‐ er 2), which is responsible for releasing silicon into the xylem. These transporters may have different affinities for silicic acid (Figure 3). Our results also clearly showed that the mutant is defective in xylem loading of silicon rather than transport of silicon from the external sol‐ ution to the root cell [8].

### **5. Detection technique**

Despite the abundance of studies of the effects of Si fertilizers and electron-microscopic ob‐ servations of silica depositions within plants[13, 37-39], few of the morphological analysis of silica deposition in rice tissues have used histochemical staining and conventional micro‐ scopic techniques available to field researchers.

Although there are a few reports using X-ray scanning analytical microscopy, which descri‐ bed silica deposition detected in a dicot plant such as *Arabidopsis halleri* [40-41], X-ray scan‐ ning microscopy have been broadly applied for analysis of silica bodies and other elements in rice tissues [42-45].

con concentration in the xylem sap was much higher in the wild type than in the mutant (Figure 3 B). In the mutant, the silicon concentration in sap increased gradually with increas‐ ing silicon concentration in the external solution without saturation. In the wild-type rice, the silicon concentration in the xylem sap also increased with increasing silicon concentra‐ tion in the external solution (Figure 3 A), but it was saturated at a higher concentration [8]. The silicon concentration in the xylem sap of the wild type was higher than 30 mM at 0.9 mM silicon supply (Figure 3 B). This concentration was much higher than that in root-cell symplast (Figure 3 A), suggesting that silicon is transported from the root cells to the xylem also against a concentration gradient. The curve of Figure 2 B also suggests that the release

**Figure 4.** Schematic representation of the silicon uptake system in rice roots. SIT1, Silicon transporter from external

Above results suggest that at least two transporters are involved in the silicon uptake by rice roots (Figure 4). One is located on the plasma membrane of root cortical cells (SIT1, silicon transporter 1), which transport silicon from external solution to the root cortical cells. The other is located on the plasma membrane of xylem parenchyma cells (SIT2, silicon transport‐ er 2), which is responsible for releasing silicon into the xylem. These transporters may have different affinities for silicic acid (Figure 3). Our results also clearly showed that the mutant is defective in xylem loading of silicon rather than transport of silicon from the external sol‐

Despite the abundance of studies of the effects of Si fertilizers and electron-microscopic ob‐ servations of silica depositions within plants[13, 37-39], few of the morphological analysis of silica deposition in rice tissues have used histochemical staining and conventional micro‐

Although there are a few reports using X-ray scanning analytical microscopy, which descri‐ bed silica deposition detected in a dicot plant such as *Arabidopsis halleri* [40-41], X-ray scan‐

solution to cortical cells. SIT2, Silicon transporter for xylem loading [8].

ution to the root cell [8].

100 Responses of Organisms to Water Stress

**5. Detection technique**

scopic techniques available to field researchers.

of silicon into the xylem is mediated by a type of transporter in the wild type [8].

Therefore, study carried out by Isa et al. [7] optimized a technique for silica body specific stain‐ ing to visualize silica deposits in rice tissue by bright field microscopy and a technique for deter‐ mining the in situ content of elements, including silica, by X-ray scanning microscopy.

The samples were fixed in FAA solution, and fixed samples were transferred and incubated in accordance with the methods of Kaufman et al. [46] and Morikawa & Saigusa [47], with minor modifications. Benzene-equilibrated samples were stained in 0.1% crystal violet lac‐ tone solution (in benzene) to visualize the silica bodies.

Silica bodies were observed in the motor cells of the leaf blades of cv. Hinohikari at the max‐ imum tillering stage (Figure 5 A), and silica opal was also observed in the blades (Figure 5 B). In enlarged images of silica cells located along the vascular bundles of cv. Hinohikari treated with silicic acid for 14 days, accumulation of silica was observed as clear X shapes (Figure 5 C) [7].

**Figure 5.** Crystal violet lactone staining of motor cell and silica body in leaf blade of cv. Hinohikari. A, motor cell and silica bodies in cross-section of leaf blade; B, rice opals in motor cells of leaf blade; C, a line of X-shaped silica bodies in leaf sheath. Rice opals in motor cells and silica bodies in epidermis cells were stained with crystal violet actone using leaf blade of cv. Hinohikari in paddy field at the maximum tillering stage. Motor cells and X-shaped silica bodies are indicated by lines and arrow heads, respectively [7].

Crystal violet lactone staining was an effective method of visualizing various shapes of silica opals and silica bodies deposited on the walls of the epidermal cells of leaf blades and stems, forming X-shaped silica cuticles along the vascular bundles (Figure 5 C) [7].

**Figures** 

**0.00**

**0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4**

**Transpiration**

**Figure 6:** 

**(mmol m-2 s-1)**

 **rate** 

**Stomatal** 

**(mmol m-2 s-1)**

**conductance**

**control 0.00 µM Si 0.25 µM Si 1.00 µM Si 1.75 µM Si + deficit + deficit + deficit + deficit**

**a**

**a**

**a a a**

**c**

**b**

by the Scott-Knott test at 5% of probability. The bars represent the mean standard error [15].

**b**

**Figure 6.** Leaf relative water content (A), stomatal conductance (B), and transpiration rate (C) in two pepper cultivars treated with silicon and exposed to water deficiency. Means followed by the same letter are not significantly different

The Si application attenuated the effects of water deficit, indicating intermediary levels in relation to stomatal conductance, and consequently, possible maintenance in gas exchange. A fall in this parameter will affect directly water relations, limiting the assimilation of car‐

**c**

**c**

**b**

**b**

**<sup>b</sup> <sup>c</sup>**

**b**

**a**

**C**

**B**

**a**

**c**

Silicon: A Benefic Element to Improve Tolerance in Plants Exposed to Water Deficiency

**e**

**d**

**c**

**A**

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103

**Treatments**

**0.05**

**0.10**

**0.15**

**0.20**

**0.25**

**a**

**b**

**a**

**0.30**

**0**

**20**

**Leaf relative water content**

**40**

**60**

**(%)**

**80**

**b**

**a**

**100**

**Ikeda Vermelho Gigante**

**d**

**d**

**c**

**f**

Successful staining reactions for observing silica bodies in plant tissues have been devel‐ oped; they involve the use of methyl red, silver amine chromate, and crystal violet lactone [46, 48]. In accordance with the reactivity of the silanol groups on the surfaces of the silica bodies, the crystal violet lactone dye stains the silica bodies exclusively, clearly allowing their shapes to be observed [7].

## **6. Attenuation of negative effects produced by silicon in physiological parameters of plants exposed to water limitation**

Benefits of silicon actuation recently reported on physiological parameters such as transpira‐ tion [10], stomatal conductance [49], and photosynthesis [50] were reported in several spe‐ cie. In addition, pepper crops, more specifically *Capsicum annuum* exercises strong influency on Brazilian market, and there is necessacity to investigate silicon action on this crop. A study aiming to respond these questions was organized with five water and silicon combi‐ nations (control, deficit + 0.00, deficit + 0.25 deficit + 1.00, and deficit + 1.75 µM Si) applied to two cultivars (Ikeda and Vermelho Gigante) with a total of 10 treatments.

The water deficit promoted a decrease in leaf relative water content in two cultivars, and 0.25, 1.00, and 1.75 µM Si did not consistently increase this variable for Ikeda, although it was maintained at levels closer to the deficit. Leaf relative water content in Vermelho Gi‐ gante for all Si concentrations was slightly higher than the deficit + 0 µM Si (Figure 6 A).

Stomatal conductance was significantly reduced due to water deficit in both cultivars, com‐ pared with the control. Ikeda applied with 1.00 and 1.75 µM Si had higher stomatal conduc‐ tance compared with deficit + 0 µM Si, while Vermelho Gigante had higher values at 0.25 and 1.75 µM Si (Figure 6 B).

The water deficit caused significant reduction in transpiration in Ikeda and Vermelho Gi‐ gante cultivars (Figure 6 C). Exogenous application of 0.25, 1.00, and 1.75 µM Si promoted attenuation of symptoms induced by water deficit. The treatments with added silicon were not statistically different.

The leaf relative water content of treatments under silicon application was maintained at levels closer to the control treatment, and this is linked to silicon action that was probably absorbed by plant, and deposited mainly in epidermal cell wall [51]. Additionally, the Si can contribute to higher resistance of xylem vessels [8], which are structures responsible by wa‐ ter transport into plant [52]. Therefore, plants with firmer xylem vessel walls can potentially avoid problems in these structures during drought or extreme heat, besides increasing water volume assimilated by plants [53]. Romero-Aranda et al. [54] investigating silicon effects on *Lycopersicon esculentum* plants under salt stress corroborate the data in this investigation.

2

**Figures** 

Crystal violet lactone staining was an effective method of visualizing various shapes of silica opals and silica bodies deposited on the walls of the epidermal cells of leaf blades and

Successful staining reactions for observing silica bodies in plant tissues have been devel‐ oped; they involve the use of methyl red, silver amine chromate, and crystal violet lactone [46, 48]. In accordance with the reactivity of the silanol groups on the surfaces of the silica bodies, the crystal violet lactone dye stains the silica bodies exclusively, clearly allowing

**6. Attenuation of negative effects produced by silicon in physiological**

Benefits of silicon actuation recently reported on physiological parameters such as transpira‐ tion [10], stomatal conductance [49], and photosynthesis [50] were reported in several spe‐ cie. In addition, pepper crops, more specifically *Capsicum annuum* exercises strong influency on Brazilian market, and there is necessacity to investigate silicon action on this crop. A study aiming to respond these questions was organized with five water and silicon combi‐ nations (control, deficit + 0.00, deficit + 0.25 deficit + 1.00, and deficit + 1.75 µM Si) applied to

The water deficit promoted a decrease in leaf relative water content in two cultivars, and 0.25, 1.00, and 1.75 µM Si did not consistently increase this variable for Ikeda, although it was maintained at levels closer to the deficit. Leaf relative water content in Vermelho Gi‐ gante for all Si concentrations was slightly higher than the deficit + 0 µM Si (Figure 6 A).

Stomatal conductance was significantly reduced due to water deficit in both cultivars, com‐ pared with the control. Ikeda applied with 1.00 and 1.75 µM Si had higher stomatal conduc‐ tance compared with deficit + 0 µM Si, while Vermelho Gigante had higher values at 0.25

The water deficit caused significant reduction in transpiration in Ikeda and Vermelho Gi‐ gante cultivars (Figure 6 C). Exogenous application of 0.25, 1.00, and 1.75 µM Si promoted attenuation of symptoms induced by water deficit. The treatments with added silicon were

The leaf relative water content of treatments under silicon application was maintained at levels closer to the control treatment, and this is linked to silicon action that was probably absorbed by plant, and deposited mainly in epidermal cell wall [51]. Additionally, the Si can contribute to higher resistance of xylem vessels [8], which are structures responsible by wa‐ ter transport into plant [52]. Therefore, plants with firmer xylem vessel walls can potentially avoid problems in these structures during drought or extreme heat, besides increasing water volume assimilated by plants [53]. Romero-Aranda et al. [54] investigating silicon effects on *Lycopersicon esculentum* plants under salt stress corroborate the data in this investigation.

**parameters of plants exposed to water limitation**

two cultivars (Ikeda and Vermelho Gigante) with a total of 10 treatments.

stems, forming X-shaped silica cuticles along the vascular bundles (Figure 5 C) [7].

their shapes to be observed [7].

102 Responses of Organisms to Water Stress

and 1.75 µM Si (Figure 6 B).

not statistically different.

**Figure 6: Figure 6.** Leaf relative water content (A), stomatal conductance (B), and transpiration rate (C) in two pepper cultivars treated with silicon and exposed to water deficiency. Means followed by the same letter are not significantly different by the Scott-Knott test at 5% of probability. The bars represent the mean standard error [15].

The Si application attenuated the effects of water deficit, indicating intermediary levels in relation to stomatal conductance, and consequently, possible maintenance in gas exchange. A fall in this parameter will affect directly water relations, limiting the assimilation of car‐

2

bon dioxide (CO2) and water flux (H2O) through stomata[55]. The stomatal mechanism will reduce the CO2 assimilation, causing a reduction in photo-assimilate production and losses in yield [56]. Similar results were observed by Gong et al. [57] evaluating the silicon effects on *Triticum aestivum* plants under water deficit, with stomatal conductance being kept at in‐ termediary levels in relation to control plants.

Water deficiency occasioned significant decrease in total chlorophyll evaluated in both culti‐ vars (Figure 7 C). Silicon in concentrations of 0.25, 1.00, and 1.75 µM Si induced a progres‐ sive increase in total chlorophyll. The better result was obtained in treatment exposed to

Silicon: A Benefic Element to Improve Tolerance in Plants Exposed to Water Deficiency

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105

The reduction in chlorophyll a for both cultivars is a consequence of water restriction, in which will induce probably the production of peroxidative enzymes, and these enzymes are associated to degradation of chlorophyll a in thylakoid membrane [67]. In cultivars exposed to water deficit, silicon application proportioned increase in levels of chlorophyll a, indicat‐ ing synthesis of new pigments, and maintenance of chlorophyll a previously existing. Done‐ ga [68] also affirmed that silicon uses promotes improvement in plant architecture and increase in photosynthesis. In other hand, the deposition of silicon in cell wall increased your tissue resistance, and it will keep plants with better performance linked to leaf position and interception of light [69-70]. Results of this research are similar and corroborate study carried out by Lobato et al. (2009a) investigating *Capsicum annuum* plants under water defi‐ cit, as well as Ahmad & Haddad [29] working with *Triticum aestivum* plants under water de‐

Water deficiency occasioned decrease chlorophyll b due to water restriction in substrate. Chlorophyll b was positively affected by silicon application, and this fact is associated to Si accumulation in epidermal cells localized in shoot, in which it will promote indirect protec‐ tor effect on photosynthetic apparatus, and consequently decrease in damages provoked by water restriction in this parameter. The reduction in chlorophyll b in plants under water de‐ ficiency probably is resulting of disorders in chloroplast and modifications in relation pro‐ teins/lipids responsible by formation of pigment-protein complex [71-72]. Similar results on increase in chlorophyll b were observed by Locarno et al. [63] studying *Rosa* spp. plants un‐

Results obtained in total chlorophyll indicate that plants under water deficit and treated with silicon presented increase in this parameter, and a relationship observed (data not shows) between leaf water potential and total chlorophyll can explain this fact, because ade‐ quate water amount in leaf tissue works probably maintaining stability of chloroplasts and consequently the functions carried out by the chlorophylls like as absorption and transport

In other hand, plants exposed to water deficit presented decrease, being probably linked to decrease in nitrogen absorption, in which is an essential element in formation of chlorophyll molecules. Plants under nitrogen application presented increase in chlorophyll amounts [64], as well as silicon promotes modifications on nitrogen metabolism [73]. Water works as vehicle responsible by nitrogen conduction and other nutrients during absorption through root system [74]. In other hands, during situations of water deficiency can there lower water assimilation, producing a negative interference linked to nitrogen assimilation. Therefore, this fact will generate minor amount of δ-aminolevulinate, which is chlorophyll precursor [75]. Tranaviciene et al. [76] investigating *Triticum aestivum* plants under different nitrogen levels observed that level of chlorophyll increased in consequence of increase in amount of

concentration of 1.75 µM Si, and this treatment is statistically equal to control.

ficiency and silicon utilization reported similar results.

der silicon application.

of energy.

nitrogen applied.

Silicon promoted attenuation in symptoms linked to water deficiency in transpiration rate, because during plant absorption in form of monosilicic acid (H4SiO4) [58], silicon accumu‐ lates in the leaf, forming a layer double of silicon. This accumulation promotes a reduction in transpiration and decrease water loss by the plant [59-60], but still contributing to mainte‐ nance of adequate transpiration rate. In addition, the transpiration process in plants is car‐ ried out by the stomatal present in leaf and cuticle normally in stem [61]. Agarie et al. [62] found improvement linked to transpiration rates in *Oryza sativa* plants cultivated with Si. Similar results on maintenance of transpiration were reported previously by Lobato et al. (2009a) studying the protective action of silicon in *Capsicum annuum* under water deficit.

## **7. Silicon promotes increase in chlorophylls of plants exposed to water deficit**

Study conducted by Locarno et al. [63] described increase in level of chlorophyll a, and con‐ sequent repercussion on amount of chlorophyll total. Ávila et al. [64] investigating interac‐ tion between silicon and nitrogen reported also increase in level of chlorophyll a in *Oryza sativa* plants. In other hand, the drought normally promotes significant decrease in photo‐ synthetic pigments [65-66].

Therefore, there is limited information linked to silicon action on chlorophyll levels in plants submitted to water deficit. Based in previous results described, Silva et al. [16] carried out an experiment with *Lycopersicon esculentum* plants submitted to water deficiency and silicon, being five water and silicon combinations (control, deficit + 0.00, deficit + 0.25, deficit + 1.00, and deficit + 1.75 µM Si) applied to two cultivars (Super Marmande and Santa Cruz) totaliz‐ ing 10 treatments. This study had aim of explain silicon action on chlorophylls.

Water deficit promoted reduction not significant in relation to level of chlorophyll a in con‐ trol treatment for Super Marmande, while Santa Cruz presented significant reduction (Fig‐ ure 7 A). Applications of silicon in treatments deficit + 0.25, deficit + 1.00, and deficit + 1.75 µM Si promoted an increase in levels of chlorophyll a to both cultivars.

Cultivars evaluated under water deficit presented a reduction in chlorophyll b (Figure 7 B), when compared to control plants. Silicon applications in concentrations of 0.25, 1.00, and 1.75 µM Si provoked oscillations in this parameter. In treatments exposed to silicon, the lev‐ els of chlorophyll b presented better performances in concentrations of 1.00 and 1.75 µM Si for Super Marmande and Santa Cruz cultivars, respectively, being these treatments statisti‐ cally equals to control to both cultivars.

Water deficiency occasioned significant decrease in total chlorophyll evaluated in both culti‐ vars (Figure 7 C). Silicon in concentrations of 0.25, 1.00, and 1.75 µM Si induced a progres‐ sive increase in total chlorophyll. The better result was obtained in treatment exposed to concentration of 1.75 µM Si, and this treatment is statistically equal to control.

bon dioxide (CO2) and water flux (H2O) through stomata[55]. The stomatal mechanism will reduce the CO2 assimilation, causing a reduction in photo-assimilate production and losses in yield [56]. Similar results were observed by Gong et al. [57] evaluating the silicon effects on *Triticum aestivum* plants under water deficit, with stomatal conductance being kept at in‐

Silicon promoted attenuation in symptoms linked to water deficiency in transpiration rate, because during plant absorption in form of monosilicic acid (H4SiO4) [58], silicon accumu‐ lates in the leaf, forming a layer double of silicon. This accumulation promotes a reduction in transpiration and decrease water loss by the plant [59-60], but still contributing to mainte‐ nance of adequate transpiration rate. In addition, the transpiration process in plants is car‐ ried out by the stomatal present in leaf and cuticle normally in stem [61]. Agarie et al. [62] found improvement linked to transpiration rates in *Oryza sativa* plants cultivated with Si. Similar results on maintenance of transpiration were reported previously by Lobato et al. (2009a) studying the protective action of silicon in *Capsicum annuum* under water deficit.

**7. Silicon promotes increase in chlorophylls of plants exposed to water**

Study conducted by Locarno et al. [63] described increase in level of chlorophyll a, and con‐ sequent repercussion on amount of chlorophyll total. Ávila et al. [64] investigating interac‐ tion between silicon and nitrogen reported also increase in level of chlorophyll a in *Oryza sativa* plants. In other hand, the drought normally promotes significant decrease in photo‐

Therefore, there is limited information linked to silicon action on chlorophyll levels in plants submitted to water deficit. Based in previous results described, Silva et al. [16] carried out an experiment with *Lycopersicon esculentum* plants submitted to water deficiency and silicon, being five water and silicon combinations (control, deficit + 0.00, deficit + 0.25, deficit + 1.00, and deficit + 1.75 µM Si) applied to two cultivars (Super Marmande and Santa Cruz) totaliz‐

Water deficit promoted reduction not significant in relation to level of chlorophyll a in con‐ trol treatment for Super Marmande, while Santa Cruz presented significant reduction (Fig‐ ure 7 A). Applications of silicon in treatments deficit + 0.25, deficit + 1.00, and deficit + 1.75

Cultivars evaluated under water deficit presented a reduction in chlorophyll b (Figure 7 B), when compared to control plants. Silicon applications in concentrations of 0.25, 1.00, and 1.75 µM Si provoked oscillations in this parameter. In treatments exposed to silicon, the lev‐ els of chlorophyll b presented better performances in concentrations of 1.00 and 1.75 µM Si for Super Marmande and Santa Cruz cultivars, respectively, being these treatments statisti‐

ing 10 treatments. This study had aim of explain silicon action on chlorophylls.

µM Si promoted an increase in levels of chlorophyll a to both cultivars.

termediary levels in relation to control plants.

104 Responses of Organisms to Water Stress

**deficit**

synthetic pigments [65-66].

cally equals to control to both cultivars.

The reduction in chlorophyll a for both cultivars is a consequence of water restriction, in which will induce probably the production of peroxidative enzymes, and these enzymes are associated to degradation of chlorophyll a in thylakoid membrane [67]. In cultivars exposed to water deficit, silicon application proportioned increase in levels of chlorophyll a, indicat‐ ing synthesis of new pigments, and maintenance of chlorophyll a previously existing. Done‐ ga [68] also affirmed that silicon uses promotes improvement in plant architecture and increase in photosynthesis. In other hand, the deposition of silicon in cell wall increased your tissue resistance, and it will keep plants with better performance linked to leaf position and interception of light [69-70]. Results of this research are similar and corroborate study carried out by Lobato et al. (2009a) investigating *Capsicum annuum* plants under water defi‐ cit, as well as Ahmad & Haddad [29] working with *Triticum aestivum* plants under water de‐ ficiency and silicon utilization reported similar results.

Water deficiency occasioned decrease chlorophyll b due to water restriction in substrate. Chlorophyll b was positively affected by silicon application, and this fact is associated to Si accumulation in epidermal cells localized in shoot, in which it will promote indirect protec‐ tor effect on photosynthetic apparatus, and consequently decrease in damages provoked by water restriction in this parameter. The reduction in chlorophyll b in plants under water de‐ ficiency probably is resulting of disorders in chloroplast and modifications in relation pro‐ teins/lipids responsible by formation of pigment-protein complex [71-72]. Similar results on increase in chlorophyll b were observed by Locarno et al. [63] studying *Rosa* spp. plants un‐ der silicon application.

Results obtained in total chlorophyll indicate that plants under water deficit and treated with silicon presented increase in this parameter, and a relationship observed (data not shows) between leaf water potential and total chlorophyll can explain this fact, because ade‐ quate water amount in leaf tissue works probably maintaining stability of chloroplasts and consequently the functions carried out by the chlorophylls like as absorption and transport of energy.

In other hand, plants exposed to water deficit presented decrease, being probably linked to decrease in nitrogen absorption, in which is an essential element in formation of chlorophyll molecules. Plants under nitrogen application presented increase in chlorophyll amounts [64], as well as silicon promotes modifications on nitrogen metabolism [73]. Water works as vehicle responsible by nitrogen conduction and other nutrients during absorption through root system [74]. In other hands, during situations of water deficiency can there lower water assimilation, producing a negative interference linked to nitrogen assimilation. Therefore, this fact will generate minor amount of δ-aminolevulinate, which is chlorophyll precursor [75]. Tranaviciene et al. [76] investigating *Triticum aestivum* plants under different nitrogen levels observed that level of chlorophyll increased in consequence of increase in amount of nitrogen applied.

**8. Final considerations**

in plants exposed to water restriction.

**Acknowledgements**

**Author details**

Paragominas, Brazil

**References**

459-466.

Allan Klynger da Silva Lobato1

Cândido Ferreira de Oliveira Neto1

AKS.

This chapter was structured with novel informations that can represent an important source to students, teachers, researchers, scientists and farmers on silicon action linked to attenua‐ tion of water deficit in higher plants. It revealed results and concepts on water deficiency and your consequences on plants, as well as silicon utilization with finality to improve toler‐ ance during inadequate water supply. In addition, it presented a simple and efficient techni‐ que to carry detection of element beneficial in tissue. Based in recent results, was also demonstrated as silicon is assimilated, transported, and accumulated in several plant or‐ gans. Besides to prove positive interference on gas exchanges and photosynthetic pigments

Silicon: A Benefic Element to Improve Tolerance in Plants Exposed to Water Deficiency

http://dx.doi.org/10.5772/53765

107

This chapter had financial support from Conselho Nacional de Pesquisa (CNPq/Brazil) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES/Brazil) for Lobato

, Elaine Maria Silva Guedes1

1 Núcleo de Pesquisa Vegetal Básica e Aplicada, Universidade Federal Rural da Amazônia,

[1] Pereira HS, Korndörfer GH, Moura WF, Corrêa GF. Extractors of available silicon in

[2] Hattori T, Inanaga S, Araki H, An P, Morita S, Luxová M, Lux A. Application of sili‐ con enhanced drought tolerance in *Sorghum bicolor*. Physiologia Plantarum 2005;123

[3] Matichenkov VV, Calvert DV. Silicon as a beneficial element for sugarcane. Journal

slags and fertilizers. Revista Brasileira de Ciência do Solo 2003;27 265-274.

American Society of Sugarcane Technologists 2002;22 21-30.

2 Departamento de Ciência do Solo, Universidade Federal de Lavras, Lavras, Brazil

, Douglas José Marques2

and

**Figure 7.** Chlorophyll a (A), chlorophyll b (B), and total chlorophyll (C) in two tomato cultivars treated with silicon and exposed to water deficiency. Means followed by the same letter are not significantly different by the Scott-Knott test at 5% of probability. The bars represent the mean standard error [16].

## **8. Final considerations**

This chapter was structured with novel informations that can represent an important source to students, teachers, researchers, scientists and farmers on silicon action linked to attenua‐ tion of water deficit in higher plants. It revealed results and concepts on water deficiency and your consequences on plants, as well as silicon utilization with finality to improve toler‐ ance during inadequate water supply. In addition, it presented a simple and efficient techni‐ que to carry detection of element beneficial in tissue. Based in recent results, was also demonstrated as silicon is assimilated, transported, and accumulated in several plant or‐ gans. Besides to prove positive interference on gas exchanges and photosynthetic pigments in plants exposed to water restriction.

## **Acknowledgements**

This chapter had financial support from Conselho Nacional de Pesquisa (CNPq/Brazil) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES/Brazil) for Lobato AKS.

## **Author details**

Allan Klynger da Silva Lobato1 , Elaine Maria Silva Guedes1 , Douglas José Marques2 and Cândido Ferreira de Oliveira Neto1

1 Núcleo de Pesquisa Vegetal Básica e Aplicada, Universidade Federal Rural da Amazônia, Paragominas, Brazil

2 Departamento de Ciência do Solo, Universidade Federal de Lavras, Lavras, Brazil

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**Figure 7.** Chlorophyll a (A), chlorophyll b (B), and total chlorophyll (C) in two tomato cultivars treated with silicon and exposed to water deficiency. Means followed by the same letter are not significantly different by the Scott-Knott test

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106 Responses of Organisms to Water Stress


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search Journal of Biological Sciences 2009b;4 1048-1055.

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Botany 1989;67 2356-2363, 1989.

thology 2002;92 1095-1103.

2003;93 535-546.

110 Responses of Organisms to Water Stress


[58] Richmond KE, Sussaman M Got silicon? The non-essential beneficial plant nutrient. Current Opinion in Plant Biology 2003;6 268-272.

short-term drought stress followed by recovery. Plant Biotechnology Reports 2007;1

Silicon: A Benefic Element to Improve Tolerance in Plants Exposed to Water Deficiency

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[73] Watanabe S, Fujiwara T, Yoneyama T, Hayashi H. Effects of silicon nutrition on me‐ tabolism and translocation of nutrients in rice plants. Developments in Plant and Soil

[74] Santos RF, Carlesso R. Water deficit and morphologic and physiologic behavior of the plants. Revista Brasileira de Engenharia Agrícola e Ambiental 1998;2 287-294.

[75] Siqueira SC, Moreira MA, Mosquim PR, José IC, Ferreira FA, Sediyama CS. Simula‐ tion of the transgenic soybean tolerant to glyphosate through explant cultivation.

[76] Tranaviciene T, Urbonaviciute A, Samuoliene G, Duchovskis P, Vaguseviciene I, Slie‐ saravicius A. The effect of differential nitrogen fertilization on photosynthetic pig‐ ment and carbohydrate contents in the two winter wheat varieties. Agronomy

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[73] Watanabe S, Fujiwara T, Yoneyama T, Hayashi H. Effects of silicon nutrition on me‐ tabolism and translocation of nutrients in rice plants. Developments in Plant and Soil Sciences 2002;92 174-175.

[58] Richmond KE, Sussaman M Got silicon? The non-essential beneficial plant nutrient.

[59] Freitas LB, Coelho EM, Maia SCM, Silva TRB. Foliar fertilization with silicon in

[60] Datnoff LE, Snyder GH, Korndörfer GH. Silicon on Agriculture. Elsevier Science,

[62] Agarie S, Hanaoka N, Ueno O, Miyazaki A, Kubota F, Agata W, Kaufman PB. Effects of silicon on tolerance to water deficit and heat stress in rice plants (*Oryza sativa L.*)

[63] Locarno M, Fochi CG, Paiva PDO. Influence of silicate fertilization on chlorophylls of

[64] Ávila FW, Baliza DP, Faquin V, Araujo J, Ramos SJ. Silicon-nitrogen interaction in rice cultivated under nutrient solution. Revista Ciencia Agronomica 2010;41 184-190.

[65] Lobato AKS, Costa RCL, Neto MAM, Oliveira Neto CF, Santos Filho BG, Alves GAR, Freitas JMN, Cruz FJR, Marochio CA, Coimbra GK. Responses of the photosynthetic pigments and carbon metabolism in *Vigna unguiculata* cultivars submitted to water

[66] Oliveira Neto CF, Lobato AKS, Gonçalves-Vidigal MC, Costa RCL, Santos Filho BG, Alves GAR, Maia WJMS, Cruz FJR, Neves HKB, Lopes MJS. Carbon compounds and chlorophyll contents in sorghum submitted to water deficit during three growth

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112 Responses of Organisms to Water Stress


**Chapter 6**

**Water Stress in Small Ruminants**

Lina Jaber, Mabelle Chedid and Shadi Hamadeh

Small ruminants are an integral part of farming systems in the marginal arid regions of the world. These areas are characterized by water scarcity and fluctuating precipitation; under the effect of global warming and unpredictable weather, rainfall is becoming even more irregular and water availability more limited. Along with water accessibility, feed and other resources will be markedly affected by climate change. Livestock that are able, in open range, to select high quality forage to maintain a relatively similar basal diet quality from season to season, will have their intake significantly reduced in extremely dry seasons when forage biomass and its quality are low [1]. Hence, selection of adapted animal breeds is very valuable for sustaining animal production under an increasingly

Breeds of ruminants which are well adapted to arid environments demonstrate a greater ca‐ pability than non-desert breeds to endure the stressful environmental effects [3]. Although small ruminants in hot arid and semi-arid regions may survive up to one week with little or even no water, water deficiency is proved to affect animals' physiological homeostasis lead‐ ing to loss of body weight, low reproductive rates and a decreased resistance to diseases [4]. In addition, under natural conditions, water scarcity often occurs at times of high environ‐ mental temperature and low feed quality and availability. Therefore, the effects of these

In this review, the effects of various degrees and forms of dehydration on small ruminants are presented. The findings are based on previous literature on the subject as well as the re‐ sults of original research by the authors on water restriction in Awassi sheep. The major changes in physiological indicators and blood parameters are presented, in addition to the interaction of dehydration with physiological status. Finally, a brief overview of new ap‐

> © 2013 Jaber et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

© 2013 Jaber et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/53584

challenging environment [2].

three constraints are often confounded.

proaches for water stress alleviation, through drugs, is exposed.

**1. Introduction**

## **Chapter 6**

## **Water Stress in Small Ruminants**

Lina Jaber, Mabelle Chedid and Shadi Hamadeh

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/53584

## **1. Introduction**

Small ruminants are an integral part of farming systems in the marginal arid regions of the world. These areas are characterized by water scarcity and fluctuating precipitation; under the effect of global warming and unpredictable weather, rainfall is becoming even more irregular and water availability more limited. Along with water accessibility, feed and other resources will be markedly affected by climate change. Livestock that are able, in open range, to select high quality forage to maintain a relatively similar basal diet quality from season to season, will have their intake significantly reduced in extremely dry seasons when forage biomass and its quality are low [1]. Hence, selection of adapted animal breeds is very valuable for sustaining animal production under an increasingly challenging environment [2].

Breeds of ruminants which are well adapted to arid environments demonstrate a greater ca‐ pability than non-desert breeds to endure the stressful environmental effects [3]. Although small ruminants in hot arid and semi-arid regions may survive up to one week with little or even no water, water deficiency is proved to affect animals' physiological homeostasis lead‐ ing to loss of body weight, low reproductive rates and a decreased resistance to diseases [4]. In addition, under natural conditions, water scarcity often occurs at times of high environ‐ mental temperature and low feed quality and availability. Therefore, the effects of these three constraints are often confounded.

In this review, the effects of various degrees and forms of dehydration on small ruminants are presented. The findings are based on previous literature on the subject as well as the re‐ sults of original research by the authors on water restriction in Awassi sheep. The major changes in physiological indicators and blood parameters are presented, in addition to the interaction of dehydration with physiological status. Finally, a brief overview of new ap‐ proaches for water stress alleviation, through drugs, is exposed.

© 2013 Jaber et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Jaber et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## **2. General characteristics of small ruminants in arid and semi-arid regions**

Small ruminants in the Middle East and North Africa region are mostly reared under exten‐ sive and traditional pastoral farming systems, centuries-old, relying on natural pastures and mobility to secure water and feed year round. Giger-Reverdin and Gihad (1991) [5] reported that the water requirement for maintenance of goats in temperate climates is 107ml/kg BW0.75; they also indicated that the water requirements under different ambient tempera‐ tures, based on previous work, range between 3.15 kg/kg DM (at 23o C) to 4.71 kg/kg DM (at 35o C). However, the effect of ambient temperature should be viewed in combination with the particular breed origin and adaptability, since wide differences in response to heat have been reported in different breeds [6].

during the dry season while sheep showed less selectivity to high quality feed. Drinking behavior is also affected by water restriction whereby water deprived sheep and goats tend to drink large volumes of water in one bout upon watering. This capacity is more

Water Stress in Small Ruminants http://dx.doi.org/10.5772/53584 117

Timing of reproduction is another adaptive feature of sheep living in semi-arid areas: partu‐ rition is timed to a favorable period of the year to ensure offspring survival [21]. Seasonality in small ruminants is commonly observed. Reproductive cycles are thought to be regulated by environmental cues, most importantly photoperiod. Research has demonstrated that nu‐ trition and the general body score are also important factors for normal cyclicity. Under-nu‐ trition (below 40-60% of maintenance requirement) is reported to cause an immediate retardation in follicular growth [22]. In addition, prolonged under-nutrition induces a delay in estrous behavior that lasts for a shorter period, as compared to normally fed animals. Similarly, fasting was reported to cause major changes in the concentrations of reproductive hormones and ovulation rate [23, 24]. Since water deprivation is often accompanied by feed intake reduction, the same effects on ruminant reproductive cycles can be expected. Indige‐ nous sheep living in the tropical and sub-tropical regions tend to breed throughout the year; however, their sexual activity may be limited, to a degree, during the summer season when the environmental temperature is elevated and feed is lacking [25]. In arid and semi-arid re‐ gions, where differences in daylight, as well as in food and water availability are well marked, the breeding season usually spans from June to November [26, 27]. Consequently, kidding and lambing mostly occur between February and April, when food and climate be‐

Ruminants are usually classified as grazers, browsers or intermediate feeders. Sheep are usually classified as grazers feeding mainly on grasses while goats are intermediate feeders which can use grasses as well as shrubs [28]. These observed preferences in feed selection have been linked to underlying morphological and physiological digestive differences. These include larger rumen and long feed passage time for grazers to allow them to digest their high fiber diet, while browsers have simple and smaller digestive system with profuse saliva production to effectively process their feed high in cell solubles [28]. However, other scientists have argued that the observed differences in feed selection are related more to body size than to actual differences in the digestive anatomy and physiology [29]. Other morphological differences are also noted in relation to the mouth anatomy with goats hav‐ ing a mobile upper lip, while sheep are characterized by a cleft upper lip, features that allow them to best use the available vegetation. In addition, goats have the capacity to assume a bipedal position thus they are capable of browsing higher vegetation that is beyond the reach of sheep [30]. This area of research relating morphology, diet selection and utilization and response to changes in the available vegetation is still in need of further exploration [29, 31] as it is affected by the climatic changes and drought spells that put pressure on the vege‐

pronounced in goats than in sheep [5].

come more hospitable for the newborns.

tation cover and the animals that feed on it.

**2.2. Morphological adaptations**

Sheep breeds differ in their capacity to overcome water limitation; experiments show a vari‐ ety of results: Yankasa sheep survived 5 days of water restriction but with several physio‐ logical changes [7, 8]. Jaber et al. (2004) [9] concluded that Awassi females can withstand more than one month of watering every 2 days without significant changes, while a regime of watering once every five days causes important physiological perturbations. The Austral‐ ian Merino sheep survived 10 days without water [10], and the desert bighorn sheep with‐ stood water deprivation up to 15 days [11; 12], while the Barki sheep in Egypt did not endure 3 days without drinking [11].

Similarly, variations in water deprivation tolerance are observed in goat breeds. Ahmed and El Kheir (2001) [13] report that desert goats raised under traditional systems may be watered only once every 3-6 days, when water is scarce. The Black Bedouin and the Barmer goats are another example of adapted breeds that can live on a once every four days watering regime [14; 15].

Review papers are numerous on this subject, indicating differences between adapted and non-adapted sheep and goat breeds in tolerating water deprivation and the general arid conditions [6, 16].

Indigenous small ruminants are able to thrive despite extreme temperatures and limited wa‐ ter through their behavioral adaptations in combination with both morphological and phys‐ iological adaptations [17].

## **2.1. Behavioral adaptations**

Feeding behavior is affected by environmental constraints. Nocturnal feeding has been documented in bighorn sheep [18] in order to avoid high temperatures during the day. Similar behavior is also reported in goats [16]. The author also indicated that feeding fre‐ quency is modified in some adapted goats which resort to more frequent and shorter meals in order to reduce heat production associated with rumen fermentation. Langhans et al. (1991) [19] further observed that feed intake is less affected by water deprivation in adapted breeds such as pygmy goats as compared to non-adapted breeds. Furthermore, Lechner-doll et al. (1995) [20] observed that adapted goats can select high quality feed during the dry season while sheep showed less selectivity to high quality feed. Drinking behavior is also affected by water restriction whereby water deprived sheep and goats tend to drink large volumes of water in one bout upon watering. This capacity is more pronounced in goats than in sheep [5].

Timing of reproduction is another adaptive feature of sheep living in semi-arid areas: partu‐ rition is timed to a favorable period of the year to ensure offspring survival [21]. Seasonality in small ruminants is commonly observed. Reproductive cycles are thought to be regulated by environmental cues, most importantly photoperiod. Research has demonstrated that nu‐ trition and the general body score are also important factors for normal cyclicity. Under-nu‐ trition (below 40-60% of maintenance requirement) is reported to cause an immediate retardation in follicular growth [22]. In addition, prolonged under-nutrition induces a delay in estrous behavior that lasts for a shorter period, as compared to normally fed animals. Similarly, fasting was reported to cause major changes in the concentrations of reproductive hormones and ovulation rate [23, 24]. Since water deprivation is often accompanied by feed intake reduction, the same effects on ruminant reproductive cycles can be expected. Indige‐ nous sheep living in the tropical and sub-tropical regions tend to breed throughout the year; however, their sexual activity may be limited, to a degree, during the summer season when the environmental temperature is elevated and feed is lacking [25]. In arid and semi-arid re‐ gions, where differences in daylight, as well as in food and water availability are well marked, the breeding season usually spans from June to November [26, 27]. Consequently, kidding and lambing mostly occur between February and April, when food and climate be‐ come more hospitable for the newborns.

## **2.2. Morphological adaptations**

**2. General characteristics of small ruminants in arid and semi-arid**

tures, based on previous work, range between 3.15 kg/kg DM (at 23o

been reported in different breeds [6].

endure 3 days without drinking [11].

days watering regime [14; 15].

conditions [6, 16].

iological adaptations [17].

**2.1. Behavioral adaptations**

Small ruminants in the Middle East and North Africa region are mostly reared under exten‐ sive and traditional pastoral farming systems, centuries-old, relying on natural pastures and mobility to secure water and feed year round. Giger-Reverdin and Gihad (1991) [5] reported that the water requirement for maintenance of goats in temperate climates is 107ml/kg BW0.75; they also indicated that the water requirements under different ambient tempera‐

C). However, the effect of ambient temperature should be viewed in combination with the particular breed origin and adaptability, since wide differences in response to heat have

Sheep breeds differ in their capacity to overcome water limitation; experiments show a vari‐ ety of results: Yankasa sheep survived 5 days of water restriction but with several physio‐ logical changes [7, 8]. Jaber et al. (2004) [9] concluded that Awassi females can withstand more than one month of watering every 2 days without significant changes, while a regime of watering once every five days causes important physiological perturbations. The Austral‐ ian Merino sheep survived 10 days without water [10], and the desert bighorn sheep with‐ stood water deprivation up to 15 days [11; 12], while the Barki sheep in Egypt did not

Similarly, variations in water deprivation tolerance are observed in goat breeds. Ahmed and El Kheir (2001) [13] report that desert goats raised under traditional systems may be watered only once every 3-6 days, when water is scarce. The Black Bedouin and the Barmer goats are another example of adapted breeds that can live on a once every four

Review papers are numerous on this subject, indicating differences between adapted and non-adapted sheep and goat breeds in tolerating water deprivation and the general arid

Indigenous small ruminants are able to thrive despite extreme temperatures and limited wa‐ ter through their behavioral adaptations in combination with both morphological and phys‐

Feeding behavior is affected by environmental constraints. Nocturnal feeding has been documented in bighorn sheep [18] in order to avoid high temperatures during the day. Similar behavior is also reported in goats [16]. The author also indicated that feeding fre‐ quency is modified in some adapted goats which resort to more frequent and shorter meals in order to reduce heat production associated with rumen fermentation. Langhans et al. (1991) [19] further observed that feed intake is less affected by water deprivation in adapted breeds such as pygmy goats as compared to non-adapted breeds. Furthermore, Lechner-doll et al. (1995) [20] observed that adapted goats can select high quality feed

C) to 4.71 kg/kg DM (at

**regions**

116 Responses of Organisms to Water Stress

35o

Ruminants are usually classified as grazers, browsers or intermediate feeders. Sheep are usually classified as grazers feeding mainly on grasses while goats are intermediate feeders which can use grasses as well as shrubs [28]. These observed preferences in feed selection have been linked to underlying morphological and physiological digestive differences. These include larger rumen and long feed passage time for grazers to allow them to digest their high fiber diet, while browsers have simple and smaller digestive system with profuse saliva production to effectively process their feed high in cell solubles [28]. However, other scientists have argued that the observed differences in feed selection are related more to body size than to actual differences in the digestive anatomy and physiology [29]. Other morphological differences are also noted in relation to the mouth anatomy with goats hav‐ ing a mobile upper lip, while sheep are characterized by a cleft upper lip, features that allow them to best use the available vegetation. In addition, goats have the capacity to assume a bipedal position thus they are capable of browsing higher vegetation that is beyond the reach of sheep [30]. This area of research relating morphology, diet selection and utilization and response to changes in the available vegetation is still in need of further exploration [29, 31] as it is affected by the climatic changes and drought spells that put pressure on the vege‐ tation cover and the animals that feed on it.

Morphological characteristics such as body shape and size help reducing heat loads and minimizing water losses; it is noted that goat breeds of arid and semi-arid regions are rela‐ tively smaller than their European counterparts [6]. Smaller animals benefit from a relatively larger surface area which allows them to better dissipate heat to the environment. Fleece is another feature that plays a major role in controlling body temperature, serving as a thermal barrier that reduces the effects of the ambient temperatures through the formation of a mild‐ er microclimate within the fleece [32]. In addition, fleece and hair color of small ruminants play a role in reflecting solar radiation with light colors absorbing less heat that the darker ones thus leaving the underneath skin relatively cooler [33]. Therefore, thermostability could be maintained without directly resorting to evaporative cooling (panting) which leads to high water loss [34]. Location of body fat also affects heat dissipation rates: arid-adapted sheep exhibit highly localized fat storage [35], such as in the fat-tail, as opposed to high sub‐ cutaneous fat in non-adapted breeds; this again facilitates heat conductance to the periphery for dissipation [34]. Moreover, fat-tails are important energy reserves that help in buffering long-term dietary shortfalls to maintain survival and productivity [36, 37]. The Awassi sheep, as a representative breed adapted to arid regions, presents a medium body size, with a large fat-tail and carpet type fleece. The carpet-type wool of the Awassi allows convective heat loss from the skin to the environment [34]. Their large ears are another anatomical adaptation that is thought to help in convective heat loss [34]. Finally, as mentioned above, the localization of the fat stores in the fat-tail facilitates body heat dissipation and serves as energy reservoir for times of scarcity.

well-coordinated mechanisms of saliva recycling and high water and Na+ retention in the kidneys, slow rehydration is achieved without causing water toxicity and with minimal water losses. These processes are detailed in [15]. Small increases in body temperature are also observed during the hottest parts of the day, followed by body cooling at night through conduction and radiation. The capacity to tolerate this increase in temperature

Water Stress in Small Ruminants http://dx.doi.org/10.5772/53584 119

Studies show a close relation between water intake and feed consumption [3, 43, 44]. Rumi‐ nant feeding behavior can be affected by the changes in osmolality of body fluids [45]. Feed intake causes hypovolemia and hyperosmolality due to the secretion of saliva and gastric juices. These mechanisms can urge ruminants, as well as other animals, to drink while eat‐ ing, or alternatively not to eat when severely dehydrated [45]. Moreover, an adequate level of water intake is necessary for proper digestive functions [46]. On the other hand, Kay (1997) [33] states that drinking water is not needed for swallowing and moistening feed, since water can be circulated from the blood to maintain high salivation. However, water is needed to replace the inevitable water loss by excretion and evaporation. A possible explan‐ ation for the physiological mechanism behind the reduction in feed intake under water re‐ striction, mainly through the reduction in meal size, may be attributed to the postprandial

The co-occurrence of decrease in feed intake along with water restriction renders the dif‐ ferentiation between water versus feed shortage related effects difficult. Previous work has shown that Awassi sheep under 3-4 days intermittent watering regime reduced their voluntary feed intake to approximately 60% of the control [9, 47]. Similar rates are re‐ ported in [48] in different domestic ruminants subjected to dehydration, especially when combined with heat stress. The drop in feed intake under dehydration is also dependent on the type of feed that is available to the animals. Water restricted goats reduced their feed intake by 18.8% when offered legume hay compared to 21.21% when offered grass hay with lower crude protein content [49]. Therefore the negative effect of water restric‐ tion is more pronounced on low versus high quality forage [16]. This reduction in feed intake is partially compensated for by a slower feed movement and longer retention time in the digestive tract [46, 50, 51]. This is thought to lead to an increase in digestibility and nutrient utilization, as longer time is available for the microflora in the digestive tract to act on the feed [49, 52]. However, this hypothesis needs further research as re‐ ports seem inconclusive. Further drop in feed intake was recorded with increasing the degree of water restriction in South African indigenous goats [52]; but an improved nu‐ trient utilization was also reported by the same author. Concomitantly, Ahmed Muna and El Shafei Ammar (2001) [49] reported an improvement in digestibility of Lucerne hay under water restriction in desert goats, and similarly, higher organic matter digesti‐

means that less water is needed for evaporative cooling [33].

**3. Physiological changes in response to water stress**

**3.1. Effect on feed intake and body weight**

hyperosmolality of the ruminal fluid [19].

#### **2.3. Physiological adaptations**

Physiologically, ruminant breeds of arid regions show many adapted mechanisms to con‐ serve water in times of heat and drought. Adapted breeds resort to reduction of urine vol‐ ume and fecal moisture. The production of more concentrated urine is related to the length of Henlé loops located in the medulla of the kidney [38]. The thickness of the medulla is rel‐ ative to kidney size, and is frequently used as an index of kidney concentrating ability [38, 39]. For instance, the desert bighorn sheep exhibits a medulla nearly twice thicker than that of other domestic sheep and thus produces highly concentrated urine of 3900 mOsm/liter H2O [40, 41]. The Awassi sheep demonstrated a similar ability to highly concentrate urine (up to 3244 mOsm/Kg H2O) under dehydration, and to drink large volumes upon rehydra‐ tion without disrupting their homeostasis [42].

Urea renal retention is similarly increased under dehydration leading to increased urea concentration in the blood, on the other hand, urea recycling from the blood in to the gut is often observed under these conditions and is thought to contribute as a nitrogen source in times when the quality of the offered feed is low in protein [33]. The rumen is another organ that plays an important role in maintaining homeostasis under dehydra‐ tion in adapted ruminants, particularly goats. Due to its relatively large volume, it acts as an important water reservoir providing most of the water lost during prolonged dehy‐ dration to maintain blood volume. It also allows the intake of large volumes of water upon rehydration which is temporarily sequestered in the rumen. Through efficient and well-coordinated mechanisms of saliva recycling and high water and Na+ retention in the kidneys, slow rehydration is achieved without causing water toxicity and with minimal water losses. These processes are detailed in [15]. Small increases in body temperature are also observed during the hottest parts of the day, followed by body cooling at night through conduction and radiation. The capacity to tolerate this increase in temperature means that less water is needed for evaporative cooling [33].

## **3. Physiological changes in response to water stress**

#### **3.1. Effect on feed intake and body weight**

Morphological characteristics such as body shape and size help reducing heat loads and minimizing water losses; it is noted that goat breeds of arid and semi-arid regions are rela‐ tively smaller than their European counterparts [6]. Smaller animals benefit from a relatively larger surface area which allows them to better dissipate heat to the environment. Fleece is another feature that plays a major role in controlling body temperature, serving as a thermal barrier that reduces the effects of the ambient temperatures through the formation of a mild‐ er microclimate within the fleece [32]. In addition, fleece and hair color of small ruminants play a role in reflecting solar radiation with light colors absorbing less heat that the darker ones thus leaving the underneath skin relatively cooler [33]. Therefore, thermostability could be maintained without directly resorting to evaporative cooling (panting) which leads to high water loss [34]. Location of body fat also affects heat dissipation rates: arid-adapted sheep exhibit highly localized fat storage [35], such as in the fat-tail, as opposed to high sub‐ cutaneous fat in non-adapted breeds; this again facilitates heat conductance to the periphery for dissipation [34]. Moreover, fat-tails are important energy reserves that help in buffering long-term dietary shortfalls to maintain survival and productivity [36, 37]. The Awassi sheep, as a representative breed adapted to arid regions, presents a medium body size, with a large fat-tail and carpet type fleece. The carpet-type wool of the Awassi allows convective heat loss from the skin to the environment [34]. Their large ears are another anatomical adaptation that is thought to help in convective heat loss [34]. Finally, as mentioned above, the localization of the fat stores in the fat-tail facilitates body heat dissipation and serves as

Physiologically, ruminant breeds of arid regions show many adapted mechanisms to con‐ serve water in times of heat and drought. Adapted breeds resort to reduction of urine vol‐ ume and fecal moisture. The production of more concentrated urine is related to the length of Henlé loops located in the medulla of the kidney [38]. The thickness of the medulla is rel‐ ative to kidney size, and is frequently used as an index of kidney concentrating ability [38, 39]. For instance, the desert bighorn sheep exhibits a medulla nearly twice thicker than that of other domestic sheep and thus produces highly concentrated urine of 3900 mOsm/liter H2O [40, 41]. The Awassi sheep demonstrated a similar ability to highly concentrate urine (up to 3244 mOsm/Kg H2O) under dehydration, and to drink large volumes upon rehydra‐

Urea renal retention is similarly increased under dehydration leading to increased urea concentration in the blood, on the other hand, urea recycling from the blood in to the gut is often observed under these conditions and is thought to contribute as a nitrogen source in times when the quality of the offered feed is low in protein [33]. The rumen is another organ that plays an important role in maintaining homeostasis under dehydra‐ tion in adapted ruminants, particularly goats. Due to its relatively large volume, it acts as an important water reservoir providing most of the water lost during prolonged dehy‐ dration to maintain blood volume. It also allows the intake of large volumes of water upon rehydration which is temporarily sequestered in the rumen. Through efficient and

energy reservoir for times of scarcity.

tion without disrupting their homeostasis [42].

**2.3. Physiological adaptations**

118 Responses of Organisms to Water Stress

Studies show a close relation between water intake and feed consumption [3, 43, 44]. Rumi‐ nant feeding behavior can be affected by the changes in osmolality of body fluids [45]. Feed intake causes hypovolemia and hyperosmolality due to the secretion of saliva and gastric juices. These mechanisms can urge ruminants, as well as other animals, to drink while eat‐ ing, or alternatively not to eat when severely dehydrated [45]. Moreover, an adequate level of water intake is necessary for proper digestive functions [46]. On the other hand, Kay (1997) [33] states that drinking water is not needed for swallowing and moistening feed, since water can be circulated from the blood to maintain high salivation. However, water is needed to replace the inevitable water loss by excretion and evaporation. A possible explan‐ ation for the physiological mechanism behind the reduction in feed intake under water re‐ striction, mainly through the reduction in meal size, may be attributed to the postprandial hyperosmolality of the ruminal fluid [19].

The co-occurrence of decrease in feed intake along with water restriction renders the dif‐ ferentiation between water versus feed shortage related effects difficult. Previous work has shown that Awassi sheep under 3-4 days intermittent watering regime reduced their voluntary feed intake to approximately 60% of the control [9, 47]. Similar rates are re‐ ported in [48] in different domestic ruminants subjected to dehydration, especially when combined with heat stress. The drop in feed intake under dehydration is also dependent on the type of feed that is available to the animals. Water restricted goats reduced their feed intake by 18.8% when offered legume hay compared to 21.21% when offered grass hay with lower crude protein content [49]. Therefore the negative effect of water restric‐ tion is more pronounced on low versus high quality forage [16]. This reduction in feed intake is partially compensated for by a slower feed movement and longer retention time in the digestive tract [46, 50, 51]. This is thought to lead to an increase in digestibility and nutrient utilization, as longer time is available for the microflora in the digestive tract to act on the feed [49, 52]. However, this hypothesis needs further research as re‐ ports seem inconclusive. Further drop in feed intake was recorded with increasing the degree of water restriction in South African indigenous goats [52]; but an improved nu‐ trient utilization was also reported by the same author. Concomitantly, Ahmed Muna and El Shafei Ammar (2001) [49] reported an improvement in digestibility of Lucerne hay under water restriction in desert goats, and similarly, higher organic matter digesti‐ bility was observed in water-restricted dairy cows [53]. These adaptations allow the ex‐ ploitation of grazing areas which are distant from water sources, and prevent erosion especially in regions where water is scarce and grazing pressure is high. In contrast, oth‐ ers [46, 48, 54] found no changes in feed digestibility in water-restricted sheep and goats. It was suggested that the elevated digestibilities usually observed are rather the result of dry matter accumulation rather than "a real increase in fermentation or digestion" [50].

**Physiological status Water restriction regime Drop in**

1L on day 4 and 3L on day 8 of 12-day water restriction

> 1L on day 4 of 7-day water restriction

**Table 1.** Effect of water restriction on body weight of Awassi sheep.

\*Water restricted animals received water every 3 days;

**weight (%) Age Ambient temp.**

10.4 mature 18-21

3-day-restriction 9.98 mature 27-30 [62]

4-day-restriction 3.32 mature 15-32 [9]

Non-lactating 2-day-restriction 0.84 mature 15-32 [9]

Lactating 3-day-restriction 26.2 mature 27-31 [47]

Weight loss (%) 9.98 5.7 [62]

**3.2. Fat metabolism: Fat cell diameter, cholesterol, glucose, fatty acids, leptin and insulin**

The fat deposited during the periods of pasture abundance is mobilized and utilized for maintaining the body and sustaining production during periods of scarcity [67, 68]. The spe‐ cialized fat depot represented in the fat-tail of many indigenous sheep, serves as a readily available source of energy to circumvent variation in dietary energy intake. This was well described in the Barbarine sheep subjected to long periods of undernutrition [37] as well as in the Awassi which showed a reduction in the fat-tail adipocyte diameter following an in‐ termittent watering regime [64]. Ermias et al. (2002) [68] highlighted the importance of the location of fat depots as adaptive features to periodic fluctuations in nutrition. They noted that the rump and fat-tail depots are the most responsive under such conditions. On the oth‐ er hand, Atti et al. (2004) [37] noted that subcutaneous fat is the first energy depot to be mo‐

Feed restricted animals had free access to water but received 60% feed of the ad libitum intake.

**Table 2.** Effect of water restriction versus feed restriction on body weight in Awassi ewes.

**Water restriction Feed restriction**

**(°C)**

16.8 mature 23-28 [63] 16.7 mature 27-31 [47] 26.2 2 years 30-31 [64]

22.13 mature 25-35 [61]

16.8 mature 23-33 Chedid et al.

**Treatment\* Reference**

17.9 8.2 [63]

**Reference**

121

Water Stress in Small Ruminants http://dx.doi.org/10.5772/53584

(unpublished)

The drop in feed intake puts an additional burden on the water stressed animal. In fact, in order to survive such regimes, adapted ruminants are thought to resort to lowering their metabolic rate in order to reach a new body condition with lower maintenance requirements [55]. Consequently, the effects of this decrease in dietary intake should be considered along with the effects of dehydration. Feed restriction of 50% for only a 3-day period is enough to cause metabolic changes in lactating dairy Sarda ewes [56]. It has also been reported that the depleted body condition during periods of energy deficiency reduces heat tolerance [57], which in turn affects the reproductive potential of sheep [58, 59].

As reported in [9, 47, 60-64] the most obvious physiological consequence of water restriction with the concomitant reduction in feed intake is weight loss. Many trials on dry and lactat‐ ing Awassi ewes recorded a drop in weight ranging between 0.84% and 26% (Table 1). Be‐ sides the effect of the water regimen, other factors contribute to body weight variation such as the physiological status of the animal (lactating or dry), its age, and the prevailing climat‐ ic conditions during the experiment (ambient temperature). It is clear in Table 1 that water‐ ing every two days did not cause a mentionable weight loss in Awassi ewes even if the temperature reached up to 32°C. The highest weight loss (26.2%) was recorded in young sheep (2-year-old ewes) and in lactating animals. Reported results lead to one conclusion that dry Awassi have a high adaptation to dehydration, and can tolerate 3-day water restric‐ tion regime, up to one month with losing only 16.8% of their body weight (Chedid et al., unpublished).

Significant weight loss is documented in other breeds of sheep and goats subjected to feed and water stress [6, 65]. Part of this weight reduction is due to body water losses [9] while the other part is caused by the consequent mobilization of fat (and possibly muscle) used for energy metabolism to compensate the decrease in dietary intake [9, 66]. Furthermore it was observed that water restriction leads to more weight loss as compared to feed restriction alone [49, 62-63] although the difference was not always statistically significant.

The following table (Table 2) presents the effect of water and feed restriction on body weight of adult dry Awassi ewes [62, 63].

Results in both studies are in compliance: water restricted animals lost more weight (ap‐ proximately two fold) than those drinking every day but receiving less feed; however, large individual variations were recorded within each of the experimental groups (N=8). There‐ fore, further research is needed for conclusive results on the difference between water and feed restriction impact on weight loss.


**Table 1.** Effect of water restriction on body weight of Awassi sheep.


\*Water restricted animals received water every 3 days;

bility was observed in water-restricted dairy cows [53]. These adaptations allow the ex‐ ploitation of grazing areas which are distant from water sources, and prevent erosion especially in regions where water is scarce and grazing pressure is high. In contrast, oth‐ ers [46, 48, 54] found no changes in feed digestibility in water-restricted sheep and goats. It was suggested that the elevated digestibilities usually observed are rather the result of dry matter accumulation rather than "a real increase in fermentation or digestion" [50].

The drop in feed intake puts an additional burden on the water stressed animal. In fact, in order to survive such regimes, adapted ruminants are thought to resort to lowering their metabolic rate in order to reach a new body condition with lower maintenance requirements [55]. Consequently, the effects of this decrease in dietary intake should be considered along with the effects of dehydration. Feed restriction of 50% for only a 3-day period is enough to cause metabolic changes in lactating dairy Sarda ewes [56]. It has also been reported that the depleted body condition during periods of energy deficiency reduces heat tolerance [57],

As reported in [9, 47, 60-64] the most obvious physiological consequence of water restriction with the concomitant reduction in feed intake is weight loss. Many trials on dry and lactat‐ ing Awassi ewes recorded a drop in weight ranging between 0.84% and 26% (Table 1). Be‐ sides the effect of the water regimen, other factors contribute to body weight variation such as the physiological status of the animal (lactating or dry), its age, and the prevailing climat‐ ic conditions during the experiment (ambient temperature). It is clear in Table 1 that water‐ ing every two days did not cause a mentionable weight loss in Awassi ewes even if the temperature reached up to 32°C. The highest weight loss (26.2%) was recorded in young sheep (2-year-old ewes) and in lactating animals. Reported results lead to one conclusion that dry Awassi have a high adaptation to dehydration, and can tolerate 3-day water restric‐ tion regime, up to one month with losing only 16.8% of their body weight (Chedid et al.,

Significant weight loss is documented in other breeds of sheep and goats subjected to feed and water stress [6, 65]. Part of this weight reduction is due to body water losses [9] while the other part is caused by the consequent mobilization of fat (and possibly muscle) used for energy metabolism to compensate the decrease in dietary intake [9, 66]. Furthermore it was observed that water restriction leads to more weight loss as compared to feed restriction

The following table (Table 2) presents the effect of water and feed restriction on body weight

Results in both studies are in compliance: water restricted animals lost more weight (ap‐ proximately two fold) than those drinking every day but receiving less feed; however, large individual variations were recorded within each of the experimental groups (N=8). There‐ fore, further research is needed for conclusive results on the difference between water and

alone [49, 62-63] although the difference was not always statistically significant.

which in turn affects the reproductive potential of sheep [58, 59].

unpublished).

120 Responses of Organisms to Water Stress

of adult dry Awassi ewes [62, 63].

feed restriction impact on weight loss.

Feed restricted animals had free access to water but received 60% feed of the ad libitum intake.

**Table 2.** Effect of water restriction versus feed restriction on body weight in Awassi ewes.

#### **3.2. Fat metabolism: Fat cell diameter, cholesterol, glucose, fatty acids, leptin and insulin**

The fat deposited during the periods of pasture abundance is mobilized and utilized for maintaining the body and sustaining production during periods of scarcity [67, 68]. The spe‐ cialized fat depot represented in the fat-tail of many indigenous sheep, serves as a readily available source of energy to circumvent variation in dietary energy intake. This was well described in the Barbarine sheep subjected to long periods of undernutrition [37] as well as in the Awassi which showed a reduction in the fat-tail adipocyte diameter following an in‐ termittent watering regime [64]. Ermias et al. (2002) [68] highlighted the importance of the location of fat depots as adaptive features to periodic fluctuations in nutrition. They noted that the rump and fat-tail depots are the most responsive under such conditions. On the oth‐ er hand, Atti et al. (2004) [37] noted that subcutaneous fat is the first energy depot to be mo‐ bilized when energy intake is deficient. This is true for the fat-tailed sheep such as the Barbarine on which they conducted their study, as well as other ruminants. However, the fat-tail provided an adaptive advantage by being slowly mobilized when undernutrion is extended over a long period thus allowing long-term survival by using up this important energy store.

**3.3. Hematology: PCV and hemoglobin**

**3.4. Blood chemistry**

*3.4.1. Total protein, globulin and albumin*

like the skeletal muscle are available [95].

Urea is mainly synthesized in the liver using NH4

*3.4.2. Creatinine and urea*

tribute body water after a long water deprivation period [87].

Dehydration in warm weather conditions reduces plasma volume as water is taken up by the tissue [82]. Although some authors reported and agreed that increased PCV and Hb con‐ centration are good indicators of dehydration [42, 61, 71, 83, 84] results on these two param‐ eters have been inconclusive. Even though levels of hematocrit were found to increase in Awassi [42, 60] and Merinos [61] subjected to water stress in some experiments, no variation was remarked in Yankasa [7, 8], Awassi [9] and Australian whether sheep [85] under similar watering conditions. Similar contradictory results were reported regarding hemoglobin: whilst an elevation of hemoglobin level was attributed to a decrease in plasma volume due to water loss [47, 61, 85] others did not report any variation [7-9]. These undetermined re‐ sults may be an indication that adapted sheep can maintain plasma volume [86] and redis‐

According to Caldeira et al. (2007a, b) [88, 89], serum total protein, globulin and particularly albumin are good indicators for predicting the animal's protein status. A drop in serum al‐ bumin concentration is observed in ruminants with low dietary protein intake [88, 90], fol‐ lowed by a decrease in globulin concentration when this dietary insufficiency is prolonged [88]. Many authors reported an increase in blood albumin and globulin in sheep under wa‐ ter restriction [9, 61, 74, 91, 92]. The high protein concentration is explained by the reduced plasma volume due to dehydration [93]. However, reduction in total protein and albumin was noticed after 3 days of water deprivation in Awassi [47] and in Barki sheep under water stress [94] suggesting that low feed intake is behind this reduction and that circulating pro‐ teins are being used in order to compensate for the dietary shortfall. Accordingly, maximum values of total serum protein were recorded on the 8th day of water restriction in Awassi fol‐ lowed by a decline at the end of the experiment (12 days) [61]. Serum albumin is a major labile protein reservoir, but it is also very important in the maintenance of body osmoregu‐ lation. Consequently, some variations in serum albumin levels can occur, but the mainte‐ nance of normal levels has to be re-established as soon as amino acids from other sources

+

and is released to the blood [96]. Urea is excreted by the kidneys to rid the body of the ex‐ cess N intake that was not used for maintenance or production [90], or it is recycled through saliva or by reabsorption into the rumen to be utilized by rumen microflora [96, 97]. Creati‐ nine is produced in the muscles and excreted by the kidneys in proportion to the muscle mass and the rate of proteolysis [88, 97]. The transfer function of the kidney is altered under water stress [98] with slower glomerular filtration and higher urea re-absorption [6, 8, 99]. Water stress induces a decrease in urine output and the production of dry faeces under the

, the end product of protein catabolism,

Water Stress in Small Ruminants http://dx.doi.org/10.5772/53584 123

Fat mobilization under water restriction is further denoted by high levels of cholesterol [69] and Free Fatty Acids (FFA) in the blood [61, 64]. The increase in plasma cholesterol follow‐ ing water scarcity is attributed to the decrease in energy intake, along with fat metabolism [70]. These results were recorded in different ruminant species submitted to water depriva‐ tion such as Awassi [9, 47] and Yankasa ewes [8]. Furthermore, the high level of FFA out‐ lined in water restricted Awassi [61, 64] and the Sudanese desert sheep [71] reflects lipid mobilization within the adipocyte, thus permitting lipid stores to be used as fuel when feed intake is limited [72]. Similarly, FFA levels in the blood of lactating goats correlated positive‐ ly with fat mobilization in times of under nutrition [73].

Reports about the changes in glucose levels in water restricted sheep are contradicting: while no significant change was recorded by some authors [8, 9, 61, 74], a decrease in plas‐ ma glucose level was observed in Merino sheep after 24 and 48 hours of fasting [75], and in intermittently watered Awassi, although the change was not significant [47]. Glucose metab‐ olism decreases due to the decline of propionate (the major precursor for gluconeogenesis) production in the rumen caused by low feed intake [76]. Although ruminants derive most of their energy requirements from volatile fatty acids resulting from rumen fermentation of carbohydrates, they still have an absolute need for glucose, necessitating a good homeostatic control of this compound [77].

Fat mobilization seems to be coordinated by underlying changes in the levels of key hor‐ mones. In dry Awassi ewes, subjected to an intermittent watering once every four days, FFA were negatively correlated with insulin and leptin as highlighted in [64]. The de‐ crease in plasma insulin is probably caused by the decline in feed intake, insulin secre‐ tion being accelerated by feeding [78]. Insulin levels are thought to remain low during fasting periods in order to facilitate lipolysis [79]. Similarly, the decrease in leptin levels in dehydrated and undernourished ruminants is well documented and explained by the decrease of the metabolic status which inhibits the adipose tissue from secreting leptin [80]. Moreover, a strong correlation between leptin concentration and fat-tail adipocyte diameter was noted in [64] highlighting the relation between the secretion of leptin by the adipose tissue and body fatness [81]. Chilliard et al. (2000) [36] proposed a model whereby insulin, cortisol and leptin interact in the process of adaptation to underfeeding and re-feeding in ruminants such as experienced also under intermittent watering. The drop in leptin following undernutrition leads to a chain of events that includes stimula‐ tion of re-feeding and decrease of energy expenditure and insulin-sensitivity, that serves to re-establish homeostasis by preventing excessive lipolysis that would yield toxic levels of fatty acids, and preserve body stores to prolong survival [36, 81].

## **3.3. Hematology: PCV and hemoglobin**

Dehydration in warm weather conditions reduces plasma volume as water is taken up by the tissue [82]. Although some authors reported and agreed that increased PCV and Hb con‐ centration are good indicators of dehydration [42, 61, 71, 83, 84] results on these two param‐ eters have been inconclusive. Even though levels of hematocrit were found to increase in Awassi [42, 60] and Merinos [61] subjected to water stress in some experiments, no variation was remarked in Yankasa [7, 8], Awassi [9] and Australian whether sheep [85] under similar watering conditions. Similar contradictory results were reported regarding hemoglobin: whilst an elevation of hemoglobin level was attributed to a decrease in plasma volume due to water loss [47, 61, 85] others did not report any variation [7-9]. These undetermined re‐ sults may be an indication that adapted sheep can maintain plasma volume [86] and redis‐ tribute body water after a long water deprivation period [87].

## **3.4. Blood chemistry**

bilized when energy intake is deficient. This is true for the fat-tailed sheep such as the Barbarine on which they conducted their study, as well as other ruminants. However, the fat-tail provided an adaptive advantage by being slowly mobilized when undernutrion is extended over a long period thus allowing long-term survival by using up this important

Fat mobilization under water restriction is further denoted by high levels of cholesterol [69] and Free Fatty Acids (FFA) in the blood [61, 64]. The increase in plasma cholesterol follow‐ ing water scarcity is attributed to the decrease in energy intake, along with fat metabolism [70]. These results were recorded in different ruminant species submitted to water depriva‐ tion such as Awassi [9, 47] and Yankasa ewes [8]. Furthermore, the high level of FFA out‐ lined in water restricted Awassi [61, 64] and the Sudanese desert sheep [71] reflects lipid mobilization within the adipocyte, thus permitting lipid stores to be used as fuel when feed intake is limited [72]. Similarly, FFA levels in the blood of lactating goats correlated positive‐

Reports about the changes in glucose levels in water restricted sheep are contradicting: while no significant change was recorded by some authors [8, 9, 61, 74], a decrease in plas‐ ma glucose level was observed in Merino sheep after 24 and 48 hours of fasting [75], and in intermittently watered Awassi, although the change was not significant [47]. Glucose metab‐ olism decreases due to the decline of propionate (the major precursor for gluconeogenesis) production in the rumen caused by low feed intake [76]. Although ruminants derive most of their energy requirements from volatile fatty acids resulting from rumen fermentation of carbohydrates, they still have an absolute need for glucose, necessitating a good homeostatic

Fat mobilization seems to be coordinated by underlying changes in the levels of key hor‐ mones. In dry Awassi ewes, subjected to an intermittent watering once every four days, FFA were negatively correlated with insulin and leptin as highlighted in [64]. The de‐ crease in plasma insulin is probably caused by the decline in feed intake, insulin secre‐ tion being accelerated by feeding [78]. Insulin levels are thought to remain low during fasting periods in order to facilitate lipolysis [79]. Similarly, the decrease in leptin levels in dehydrated and undernourished ruminants is well documented and explained by the decrease of the metabolic status which inhibits the adipose tissue from secreting leptin [80]. Moreover, a strong correlation between leptin concentration and fat-tail adipocyte diameter was noted in [64] highlighting the relation between the secretion of leptin by the adipose tissue and body fatness [81]. Chilliard et al. (2000) [36] proposed a model whereby insulin, cortisol and leptin interact in the process of adaptation to underfeeding and re-feeding in ruminants such as experienced also under intermittent watering. The drop in leptin following undernutrition leads to a chain of events that includes stimula‐ tion of re-feeding and decrease of energy expenditure and insulin-sensitivity, that serves to re-establish homeostasis by preventing excessive lipolysis that would yield toxic levels

of fatty acids, and preserve body stores to prolong survival [36, 81].

ly with fat mobilization in times of under nutrition [73].

control of this compound [77].

energy store.

122 Responses of Organisms to Water Stress

#### *3.4.1. Total protein, globulin and albumin*

According to Caldeira et al. (2007a, b) [88, 89], serum total protein, globulin and particularly albumin are good indicators for predicting the animal's protein status. A drop in serum al‐ bumin concentration is observed in ruminants with low dietary protein intake [88, 90], fol‐ lowed by a decrease in globulin concentration when this dietary insufficiency is prolonged [88]. Many authors reported an increase in blood albumin and globulin in sheep under wa‐ ter restriction [9, 61, 74, 91, 92]. The high protein concentration is explained by the reduced plasma volume due to dehydration [93]. However, reduction in total protein and albumin was noticed after 3 days of water deprivation in Awassi [47] and in Barki sheep under water stress [94] suggesting that low feed intake is behind this reduction and that circulating pro‐ teins are being used in order to compensate for the dietary shortfall. Accordingly, maximum values of total serum protein were recorded on the 8th day of water restriction in Awassi fol‐ lowed by a decline at the end of the experiment (12 days) [61]. Serum albumin is a major labile protein reservoir, but it is also very important in the maintenance of body osmoregu‐ lation. Consequently, some variations in serum albumin levels can occur, but the mainte‐ nance of normal levels has to be re-established as soon as amino acids from other sources like the skeletal muscle are available [95].

#### *3.4.2. Creatinine and urea*

Urea is mainly synthesized in the liver using NH4 + , the end product of protein catabolism, and is released to the blood [96]. Urea is excreted by the kidneys to rid the body of the ex‐ cess N intake that was not used for maintenance or production [90], or it is recycled through saliva or by reabsorption into the rumen to be utilized by rumen microflora [96, 97]. Creati‐ nine is produced in the muscles and excreted by the kidneys in proportion to the muscle mass and the rate of proteolysis [88, 97]. The transfer function of the kidney is altered under water stress [98] with slower glomerular filtration and higher urea re-absorption [6, 8, 99]. Water stress induces a decrease in urine output and the production of dry faeces under the action of vasopressin, and increased water reabsorption from the gastro-intestinal tract [100]. Urine volume dropped by 75% and fecal water output was 37% lower in desert sheep subjected to 5 days of water restriction [101]. Consequently, urea reabsorption by the kidney is also expected to increase as reflected by increased concentration in the blood [102], which was confirmed by several trials on Merinos [65], Yankasa [7, 8] and Awassi sheep [9, 42]. When Yankasa sheep were submitted to two consecutive periods of five-day water stress, an increase in urea and creatinine concentration was observed after the first period but only creatinine levels remained high after the second [8]. Thus the author suggested that urea is being re-circulated from the blood system into the digestive tract. This is consistent with the observations that urea conservation at the level of the kidneys and recycling into the gut is increased when dietary nitrogen intake is low [102].

ieve homeostasis under the imposed treatment. The observed return to normal values in protein and albumin concentrations could indicate that these compounds are being used up from the blood in replacement of the deficient dietary intake, or this could also denote the mobilization of water from the extracellular fluid and the rumen into the blood stream [47]. Similarly, the decline in urea at the end of the treatment could be related to the above men‐ tioned urea recycling mechanism, while creatinine concentrations remained relatively high as previously observed in [8]. The figure also illustrates that lactating and dry animals had similar responses to water restriction with no effect of lactation (2-3 months in lactation) on

Analyzing osmolality is a good approach for monitoring the hydration status. It has been proved that osmolality and electrolytes levels are largely affected by water deprivation: the reduced plasma volume causes hyperosmolality inducing consequently an increase in elec‐

small ruminant breeds, which allows the maintenance of sodium balance in the body. Ashour and Benlemlih (2001) [87] attributed the increased renal retention to the influence of aldosterone, whereas McKinley et al. (2000) [107] added the effect of vasopressin secretion. Dehydration causes an increase in plasma vasopressin levels in both lactating goats [108-110] and non-lactating ones [108, 111]. According to Yesberg et al. (1970) [112] urinary vasopressin excretion rate is directly related to urinary osmolality and inversely related to urine flow rate. This explains why dehydrated goats and sheep decrease their urine volume while the osmolality and vasopressin levels augment. Olsson (2005) [113] noted that thermo‐ regulation and fluid balance, as regulated by thirst control, vasopressin secretion, sodium balance and other osmotic and cardiovascular signals, seem to be centrally regulated at the hypothalamic level, particularly the preoptic and anterior hypothalamic neurons. Silanikove (1994) [15] presents a detailed account of the dynamics of major electrolytes under dehydra‐ tion in connection with water conservation and homeostatic mechanisms in ruminants. In

dehydrated animals but its osmolality is increased. In parallel, the ruminants resort to utilize the large volume of water present in the gut through active transport of Na+ across the ru‐ men wall. This transport necessitates the presence of a minimal amount of volatile fatty acids in the rumen, hence the importance of sustaining some feed intake during dehydra‐ tion. The hyperosmotic fluid absorbed from the rumen needs to be desalted the salivary

Rehydration is an equally challenging situation for ruminants that can lead to hemolysis in non-adapted or severely dehydrated animals. Many studies reported the slow return to nor‐ mal levels of blood volume, osmolality and other blood components after the rehydration of ruminants, although the animals drank large amounts of water at once [42, 92, 114]. The mechanisms allowing the slow release of the ingested water from the rumen into the blood

were reported in different breeds of sheep and goats [10, 63, 71, 91, 103, 107].

and chloride Cl-

is a physiological response to water restriction in different

[60, 105, 106]. These results

Water Stress in Small Ruminants http://dx.doi.org/10.5772/53584 125

, saliva secretion is decreased in

these blood parameters.

*3.4.3. Electrolytes and osmolality*

Increased renal retention of Na+

trolytes concentration [104] mainly sodium Na+

addition to the increased renal retention of water and Na+

flow to the rumen has to be maintained in order to preserve homeostasis.

On the other hand, creatinine levels in lambs were not affected by 48-hour water restriction [103], while others observed an increase of this parameter in water restricted animals [47, 91]. The creatinine concentration is influenced by the level of reliance on proteolysis and en‐ dogenous N sources [88, 98] as well as by higher kidney retention due to decreased glomer‐ ular filtration rate. In turn, these factors are related to the degree of protein/N intake deficiency that the animal is experiencing as well as the level of dehydration.

**Figure 1.** Changes in some serum chemistry indicators of dry (◊) and lactating (♦) Awassi ewes subjected to daily wa‐ tering (―) or to water restriction (- - - -). (Adapted from [47])

Figure 1, adapted from [47], illustrates the changes over repeated cycles of three days water restriction on major blood chemistry parameters of dry Awassi ewes. This figure shows that the response to the watering regime tends to decrease over time after it reaches a certain peak. This underlines the adaptation mechanisms that the animals activate in order to ach‐ ieve homeostasis under the imposed treatment. The observed return to normal values in protein and albumin concentrations could indicate that these compounds are being used up from the blood in replacement of the deficient dietary intake, or this could also denote the mobilization of water from the extracellular fluid and the rumen into the blood stream [47]. Similarly, the decline in urea at the end of the treatment could be related to the above men‐ tioned urea recycling mechanism, while creatinine concentrations remained relatively high as previously observed in [8]. The figure also illustrates that lactating and dry animals had similar responses to water restriction with no effect of lactation (2-3 months in lactation) on these blood parameters.

#### *3.4.3. Electrolytes and osmolality*

action of vasopressin, and increased water reabsorption from the gastro-intestinal tract [100]. Urine volume dropped by 75% and fecal water output was 37% lower in desert sheep subjected to 5 days of water restriction [101]. Consequently, urea reabsorption by the kidney is also expected to increase as reflected by increased concentration in the blood [102], which was confirmed by several trials on Merinos [65], Yankasa [7, 8] and Awassi sheep [9, 42]. When Yankasa sheep were submitted to two consecutive periods of five-day water stress, an increase in urea and creatinine concentration was observed after the first period but only creatinine levels remained high after the second [8]. Thus the author suggested that urea is being re-circulated from the blood system into the digestive tract. This is consistent with the observations that urea conservation at the level of the kidneys and recycling into the gut is

On the other hand, creatinine levels in lambs were not affected by 48-hour water restriction [103], while others observed an increase of this parameter in water restricted animals [47, 91]. The creatinine concentration is influenced by the level of reliance on proteolysis and en‐ dogenous N sources [88, 98] as well as by higher kidney retention due to decreased glomer‐ ular filtration rate. In turn, these factors are related to the degree of protein/N intake

**Figure 1.** Changes in some serum chemistry indicators of dry (◊) and lactating (♦) Awassi ewes subjected to daily wa‐

Figure 1, adapted from [47], illustrates the changes over repeated cycles of three days water restriction on major blood chemistry parameters of dry Awassi ewes. This figure shows that the response to the watering regime tends to decrease over time after it reaches a certain peak. This underlines the adaptation mechanisms that the animals activate in order to ach‐

deficiency that the animal is experiencing as well as the level of dehydration.

increased when dietary nitrogen intake is low [102].

124 Responses of Organisms to Water Stress

tering (―) or to water restriction (- - - -). (Adapted from [47])

Analyzing osmolality is a good approach for monitoring the hydration status. It has been proved that osmolality and electrolytes levels are largely affected by water deprivation: the reduced plasma volume causes hyperosmolality inducing consequently an increase in elec‐ trolytes concentration [104] mainly sodium Na+ and chloride Cl- [60, 105, 106]. These results were reported in different breeds of sheep and goats [10, 63, 71, 91, 103, 107].

Increased renal retention of Na+ is a physiological response to water restriction in different small ruminant breeds, which allows the maintenance of sodium balance in the body. Ashour and Benlemlih (2001) [87] attributed the increased renal retention to the influence of aldosterone, whereas McKinley et al. (2000) [107] added the effect of vasopressin secretion. Dehydration causes an increase in plasma vasopressin levels in both lactating goats [108-110] and non-lactating ones [108, 111]. According to Yesberg et al. (1970) [112] urinary vasopressin excretion rate is directly related to urinary osmolality and inversely related to urine flow rate. This explains why dehydrated goats and sheep decrease their urine volume while the osmolality and vasopressin levels augment. Olsson (2005) [113] noted that thermo‐ regulation and fluid balance, as regulated by thirst control, vasopressin secretion, sodium balance and other osmotic and cardiovascular signals, seem to be centrally regulated at the hypothalamic level, particularly the preoptic and anterior hypothalamic neurons. Silanikove (1994) [15] presents a detailed account of the dynamics of major electrolytes under dehydra‐ tion in connection with water conservation and homeostatic mechanisms in ruminants. In addition to the increased renal retention of water and Na+ , saliva secretion is decreased in dehydrated animals but its osmolality is increased. In parallel, the ruminants resort to utilize the large volume of water present in the gut through active transport of Na+ across the ru‐ men wall. This transport necessitates the presence of a minimal amount of volatile fatty acids in the rumen, hence the importance of sustaining some feed intake during dehydra‐ tion. The hyperosmotic fluid absorbed from the rumen needs to be desalted the salivary flow to the rumen has to be maintained in order to preserve homeostasis.

Rehydration is an equally challenging situation for ruminants that can lead to hemolysis in non-adapted or severely dehydrated animals. Many studies reported the slow return to nor‐ mal levels of blood volume, osmolality and other blood components after the rehydration of ruminants, although the animals drank large amounts of water at once [42, 92, 114]. The mechanisms allowing the slow release of the ingested water from the rumen into the blood stream are not fully understood. The production of hypotonic saliva is dramatically in‐ creased following rehydration [15] thus allowing the recycling of absorbed water and Na+ from the blood back into the rumen to prevent a sudden drop in blood osmolality. In paral‐ lel, the kidney sustains its water/Na+ conservation activity to prevent the loss of the ingested water which is vitally needed in anticipation of a future dehydration cycle. Rehydration also activates appetite and thermoregulatory mechanisms that allow the final restoration of ho‐ meostasis and normal functioning in up to 24 hours after rehydration or more.

a new homeostasis by activating water mobilization and conservation mechanisms to re‐

Finally, blood pH, a critical parameter for normal enzymatic and metabolic functions, seems to be well maintained in intermittently watered Awassi [9, 47, 61].Increase in pH was only recorded in highly restricted Awassi following a once in a five days intermittent watering regime [9], this could be related to a combination of the high dehydration state and environmental heat which leads to hyperventilation and consequently to respiratory alkalosis as observed in other heat stressed animals

**Blood Na+**

**(mmol/L)**

048 12

Water Stress in Small Ruminants http://dx.doi.org/10.5772/53584 127

048 12

**Days**

10

Figure 2. Effect of water restriction (---) on dry Awassi ewes with (▲) and without (■ ) vitamin C

**Figure 2.** Effect of water restriction (- - -) on dry Awassi ewes with (▲) and without (■ ) vitamin C supplementation

Cortisol is a hormone secreted in order to deal with stress. It is released due to the activation of the hypothalamo-pituitary-adrenal axis by stress. Although it plays a major role in main‐ taining the balance of water and electrolytes [120, 121], its mechanism is not very clear yet [122]. Dehydration had no effect on serum cortisol levels of Awassi [9, 61] and Clun forest sheep [123] which is consistent with the results obtained under laboratory conditions in sheep deprived of feed and water for 48h [124]. On the other hand, Kataria and Kataria (2004) [98] suggested that the increase in cortisol levels in dehydrated Marwari sheep (for 6 days) is a sign that the animals are under stress; they also reported that cortisol levels did not return to normal even after 72 hours of rehydration. Working on the same subject, Li et al. (2000) [85] reported plasma cortisol variation with fasting while water restriction had no additional effect on this parameter. A decline in serum cortisol was recorded in intermittent‐ ly watered Awassi along the experimental period [47]. Concurring with [125], it is suggested that cortisol could be a good parameter in assessing acute stress response in small ruminants

Figure 2 is an illustration of the effect of a 12 days water restriction episode on Awassi dry ewes. The animals were offered 1 liter of water on day 4 and 3 liters on day 8 only. In this trial, the treatment had no significant effect on blood pH and K+ concentration, while Na+ and Cl- were significantly increased under the restriction regime. The trial also included a group of water restricted animals that received 2.5g/d of vitamin C, the effect of which is discussed below (vitamin C section). It is worth noting here that the levels of Na+ and Cl- seem to have reached a peak after which they started to show a slight decline. This observation reinforces the previously proposed idea of adaptation to the restriction regime to reach a new homeostasis by activating water mobilization and

90

100

**Blood Cl-**

**(mmol/L)**

110

120

130

Cortisol is a hormone secreted in order to deal with stress. It is released due to the activation of the hypothalamo-pituitary-adrenal axis by stress. Although it plays a major role in maintaining the balance of water and electrolytes [120, 121], its mechanism is not very clear yet [122]. Dehydration had no effect on serum cortisol levels ofAwassi [9, 61] and Clun forest sheep [123] which is consistent with the results obtained under laboratory conditions in sheep deprived of feed and water for 48h [124]. On the other hand, Kataria and Kataria (2004)[98] suggested that the increase in cortisol levels in dehydrated Marwari sheep (for 6 days) is a sign that the animals are under stress; they also reported that cortisol levels did not return to normal even after 72 hours of

store the blood volume and composition.

due to the increased elimination of CO2 [119].

7.3

5.5

4

4.5

**Blood K+(mmol/L)**

5

7.35

7.4

**Blood pH**

7.45

7.5

supplementation (Ghanem et al., 2008, unpublished data)

048 12

**Days**

048 12

*3.5. Cortisol and other hormones* 

but not chronic stress such as dehydration.

(Ghanem et al., 2008, unpublished data)

**3.5. Cortisol and other hormones**

conservation mechanisms to restore the blood volume and composition.

Studies on different sheep breeds [115, 116] showed a negative correlation between Na+ and K+ in plasma. Concurrently, blood K+ was reported to decrease in water-deprived sheep [9, 65] probably due to the intra-erythrocytic diffusion of K+ or loss of these ions in urine in ex‐ change of Na+ re-absorption [8]. However, others observed an elevation in plasma K+ under water restriction [7, 117], while [8, 47, 61] did not report a variation in K+ levels in Yankasa and Awassi sheep, respectively. These inconclusive results about K+ alteration under water restriction do not make of potassium a reliable indicator of the hydration status; on the con‐ trary they warrant further studies about the role played by this blood parameter during de‐ hydration.

Chloride Cl is the major anion in extra cellular fluids (ECF). It functions primarily in trans‐ port processes integral to cation and water balance and as a conjugate anion in acid-base metabolism. Several findings reported that dehydration leads to an increase in plasma chlor‐ ide levels in parallel to sodium levels [8, 9, 47, 74] as Cl is passively distributed in relation to the electrical gradients established by active Na+ transport [118]. This increase may be at‐ tributed to many phenomena such as the hemoconcentration resulting from a lower blood water level [74], and the increase in aldosterone and vasopressin concentrations [87] leading to increased renal retention.

Calcium plays an important role in regulating ion gating and as a co-factor for intermediary metabolism reactions. However, studies did not report variation in Ca++ under water depri‐ vation in the Awassi [9, 47] nor in Comisana sheep [74].

Finally, blood pH, a critical parameter for normal enzymatic and metabolic functions, seems to be well maintained in intermittently watered Awassi [9, 47, 61]. Increase in pH was only recorded in highly restricted Awassi following a once in a five days intermittent watering regime [9], this could be related to a combination of the high dehydration state and environ‐ mental heat which leads to hyperventilation and consequently to respiratory alkalosis as ob‐ served in other heat stressed animals due to the increased elimination of CO2 [119].

Figure 2 is an illustration of the effect of a 12 days water restriction episode on Awassi dry ewes. The animals were offered 1 liter of water on day 4 and 3 liters on day 8 only. In this trial, the treatment had no significant effect on blood pH and K+ concentration, while Na+ and Cl were significantly increased under the restriction regime. The trial also included a group of water restricted animals that received 2.5g/d of vitamin C, the effect of which is discussed below (vitamin C section). It is worth noting here that the levels of Na+ and Clseem to have reached a peak after which they started to show a slight decline. This observa‐ tion reinforces the previously proposed idea of adaptation to the restriction regime to reach

a new homeostasis by activating water mobilization and conservation mechanisms to re‐ store the blood volume and composition. well maintained in intermittently watered Awassi [9, 47, 61].Increase in pH was only recorded in highly restricted Awassi following a once in a five days intermittent watering regime [9], this could

Finally, blood pH, a critical parameter for normal enzymatic and metabolic functions, seems to be

be related to a combination of the high dehydration state and environmental heat which leads to hyperventilation and consequently to respiratory alkalosis as observed in other heat stressed animals

Figure 2. Effect of water restriction (---) on dry Awassi ewes with (▲) and without (■ ) vitamin C supplementation (Ghanem et al., 2008, unpublished data) **Figure 2.** Effect of water restriction (- - -) on dry Awassi ewes with (▲) and without (■ ) vitamin C supplementation (Ghanem et al., 2008, unpublished data)

The animals were offered 1 liter of water on day 4 and 3 liters on day 8 only. In this trial, the

#### Figure 2 is an illustration of the effect of a 12 days water restriction episode on Awassi dry ewes. **3.5. Cortisol and other hormones**

due to the increased elimination of CO2 [119].

stream are not fully understood. The production of hypotonic saliva is dramatically in‐ creased following rehydration [15] thus allowing the recycling of absorbed water and Na+ from the blood back into the rumen to prevent a sudden drop in blood osmolality. In paral‐ lel, the kidney sustains its water/Na+ conservation activity to prevent the loss of the ingested water which is vitally needed in anticipation of a future dehydration cycle. Rehydration also activates appetite and thermoregulatory mechanisms that allow the final restoration of ho‐

meostasis and normal functioning in up to 24 hours after rehydration or more.

K+

change of Na+

hydration.

Chloride Cl-

and Cl-

to increased renal retention.

in plasma. Concurrently, blood K+

126 Responses of Organisms to Water Stress

65] probably due to the intra-erythrocytic diffusion of K+

ide levels in parallel to sodium levels [8, 9, 47, 74] as Cl-

vation in the Awassi [9, 47] nor in Comisana sheep [74].

Studies on different sheep breeds [115, 116] showed a negative correlation between Na+

re-absorption [8]. However, others observed an elevation in plasma K+

is the major anion in extra cellular fluids (ECF). It functions primarily in trans‐

water restriction [7, 117], while [8, 47, 61] did not report a variation in K+ levels in Yankasa and Awassi sheep, respectively. These inconclusive results about K+ alteration under water restriction do not make of potassium a reliable indicator of the hydration status; on the con‐ trary they warrant further studies about the role played by this blood parameter during de‐

port processes integral to cation and water balance and as a conjugate anion in acid-base metabolism. Several findings reported that dehydration leads to an increase in plasma chlor‐

the electrical gradients established by active Na+ transport [118]. This increase may be at‐ tributed to many phenomena such as the hemoconcentration resulting from a lower blood water level [74], and the increase in aldosterone and vasopressin concentrations [87] leading

Calcium plays an important role in regulating ion gating and as a co-factor for intermediary metabolism reactions. However, studies did not report variation in Ca++ under water depri‐

Finally, blood pH, a critical parameter for normal enzymatic and metabolic functions, seems to be well maintained in intermittently watered Awassi [9, 47, 61]. Increase in pH was only recorded in highly restricted Awassi following a once in a five days intermittent watering regime [9], this could be related to a combination of the high dehydration state and environ‐ mental heat which leads to hyperventilation and consequently to respiratory alkalosis as ob‐

Figure 2 is an illustration of the effect of a 12 days water restriction episode on Awassi dry ewes. The animals were offered 1 liter of water on day 4 and 3 liters on day 8 only. In this trial, the treatment had no significant effect on blood pH and K+ concentration, while Na+

group of water restricted animals that received 2.5g/d of vitamin C, the effect of which is

seem to have reached a peak after which they started to show a slight decline. This observa‐ tion reinforces the previously proposed idea of adaptation to the restriction regime to reach

discussed below (vitamin C section). It is worth noting here that the levels of Na+

were significantly increased under the restriction regime. The trial also included a

served in other heat stressed animals due to the increased elimination of CO2 [119].

was reported to decrease in water-deprived sheep [9,

or loss of these ions in urine in ex‐

is passively distributed in relation to

and

under

and Cl-

treatment had no significant effect on blood pH and K+ concentration, while Na+ and Cl- were significantly increased under the restriction regime. The trial also included a group of water restricted animals that received 2.5g/d of vitamin C, the effect of which is discussed below (vitamin C section). It is worth noting here that the levels of Na+ and Cl- seem to have reached a peak after which they started to show a slight decline. This observation reinforces the previously proposed idea of adaptation to the restriction regime to reach a new homeostasis by activating water mobilization and conservation mechanisms to restore the blood volume and composition. *3.5. Cortisol and other hormones*  Cortisol is a hormone secreted in order to deal with stress. It is released due to the activation of the hypothalamo-pituitary-adrenal axis by stress. Although it plays a major role in maintaining the balance of water and electrolytes [120, 121], its mechanism is not very clear yet [122]. Dehydration had no effect on serum cortisol levels ofAwassi [9, 61] and Clun forest sheep [123] which is consistent with the results obtained under laboratory conditions in sheep deprived of feed and water Cortisol is a hormone secreted in order to deal with stress. It is released due to the activation of the hypothalamo-pituitary-adrenal axis by stress. Although it plays a major role in main‐ taining the balance of water and electrolytes [120, 121], its mechanism is not very clear yet [122]. Dehydration had no effect on serum cortisol levels of Awassi [9, 61] and Clun forest sheep [123] which is consistent with the results obtained under laboratory conditions in sheep deprived of feed and water for 48h [124]. On the other hand, Kataria and Kataria (2004) [98] suggested that the increase in cortisol levels in dehydrated Marwari sheep (for 6 days) is a sign that the animals are under stress; they also reported that cortisol levels did not return to normal even after 72 hours of rehydration. Working on the same subject, Li et al. (2000) [85] reported plasma cortisol variation with fasting while water restriction had no additional effect on this parameter. A decline in serum cortisol was recorded in intermittent‐ ly watered Awassi along the experimental period [47]. Concurring with [125], it is suggested that cortisol could be a good parameter in assessing acute stress response in small ruminants but not chronic stress such as dehydration.

10

for 48h [124]. On the other hand, Kataria and Kataria (2004)[98] suggested that the increase in cortisol levels in dehydrated Marwari sheep (for 6 days) is a sign that the animals are under stress; they also reported that cortisol levels did not return to normal even after 72 hours of Thyroid hormones (Triiodothyronine T3 and Thyroxine T4) play a major role in many phys‐ iological events such as thermoregulation and metabolic homeostasis of energy and proteins [126-128]. T3 and T4 concentration is affected by many factors like reproductive status, cli‐ matic conditions [127, 129] nutrition, age and gender [130, 131]. Water restriction [64] and nutrient limitation [132] were found to lower the levels of T3 and T4 in dry Awassi ewes and pregnant Whiteface Western ewes, respectively. Similarly, Caldeira et al. (2007a) [88] noticed a decrease in these hormones with decreasing body score of ewes. They concluded that T3 is a good indicator of the metabolic state of the animal. On the other hand, variable T3 and T4 responses to seasonal variations and/or dehydration were reported in literature from vari‐ ous ruminants [133]. The concentrations of these two hormones were found to be strongly correlated (R2 =0.568; P=0.000) [64]. The authors suggested that this decline in T3 under water restriction reflected the declining metabolic state due to dehydration and decreased feed in‐ take while the declining T4 concentration was probably a response to the thermal stress ex‐ perienced by the animals in that experiment. Similarly, T4 concentrations were reported to vary with the season while T3 is affected by both the season and the physiological status of the sheep [134]. The reduction of thyroid hormone activity under dehydration is associated with the animal's attempt to minimize water losses by reducing general metabolism [135].

which increase during late gestation. Research on the Matebele goat showed that a low nu‐ trition level during late pregnancy had little effect on kid birth weight [139]. Similarly, a twice weekly watering regime imposed for a prolonged period had no effect on birth weight of desert adapted Magra and Marwari sheep [140]. On the other hand, pregnant Chokla ewes watered every 4 days gave birth to lambs of lower weight compared to ewes that were watered daily or every three day; however, at 12 weeks of age, lambs' weight were similar between the differently watered groups [136]. Working on goats, Mellado et al. (2006) [141] highlighted the importance of goat birth weight and weight gain at 25 days of age on their future reproductive performance under intensive conditions in hot arid environments. On the other hand, in a recent study prenatal feed restriction in the last trimester resulted in lower male offspring weight in goats, but had no effects on later behavior and growth [142]. Further studies are needed to assess the long term consequences of dehydration and/or in‐ termittent watering during gestation on the growth and later performance of the offspring.

Water Stress in Small Ruminants http://dx.doi.org/10.5772/53584 129

Significant weight loss was recorded in lactating water-stressed Awassi [47] and Comisana ewes [74] as compared to control animals. Weight loss during lactation is due to body water loss caused by less water and feed intake combined with energy deficit that drives lactating

Physiologically, lactating animals show lower hemoglobin concentration than dry ones [47]. According to [120], the decrease in hemoglobin concentration in lactating ewes is ex‐ plained by the high water content and plasma volumes due to increased water mobiliza‐ tion to the mammary glands. It was found in [47] that lactation did not affect levels of serum glucose or those of cholesterol in Awassi ewes in their second to third month of lactation. Concurrently, no significant changes were recorded in glucose level caused by lactation beyond the first month [144]. Moreover, lactation did not affect blood total pro‐ tein, albumin and globulin concentration of Awassi ewes in their mid-lactation [47]; no change in albumin was also reported in [145], however an increase in the gammaglobulin fraction was noticed. El-Sherif and Assad (2001) [94] observed a return to normal total protein levels on the fourth week of lactation most probably caused by a fall in globulin concentrations. The same authors reported that lactation significantly increased plasma albumin, albumin to globulin ratio and blood creatinine in Barki ewes under semi-arid conditions. No alteration was caused by lactation on serum urea and creatinine levels in Awassi ewes [47] and Corriedal [138]. Working with lactating Comisana subjected to 60% water deprivation, Casamassima et al. (2008) [74] reported significant elevations in serum concentration of triglycerides, albumin, total proteins and cholesterol. Intermittently wa‐ tered Ethiopian Somali goats, exhibited similar physiological responses to those described in other breeds, namely increased osmolality, AVP secretion and blood protein concentra‐ tion [110]. The authors also noted a significant capacity to fluctuate rectal temperature in

the activation of a water saving mechanism following the first cycle of water restriction,

C daily change in some animals; they also observed

animals to strongly depend on their body reserves [143].

response to heat stress reaching 5o

**4.2. Lactation**

## **4. Changes in relation with physiological status**

As seen above, small ruminants in arid and semi-arid regions face many constraints related to fluctuating temperatures as well as shortages in feed and water sources. Pregnancy and lactation increase the needs for adaptive mechanisms due to the greater need for food, water and electrolytes in order to meet the requirements of the fetus and the mammary glands [113]. Water requirements could increase up to 50% by late pregnancy (around 160 ml/kg BW0.75) while the requirement for milk production is stated as 165 ml/kg BW0.75 for a milk production level of 148g milk/kg0.75 [5]. Pregnant and lactating animals have 40-50% higher water turnover rates than dry animals [17]. However, Degen (1977) [35] recorded a small difference in water turnover between control and pregnant Awassi and Merinos sheep.

#### **4.1. Pregnancy**

The reported physiological changes vary according to the degree of water restriction and stage of pregnancy. Chokla pregnant ewes submitted to intermittent watering (every 72 and 96 hours) under semi-arid conditions showed significant hemocentration and reduction in extracellular fluid space as compared to pregnant Chokla receiving water daily [136]. Simi‐ larly, Olsson et al. (1982) [137] reported increases in plasma osmolality and Na+ concentra‐ tion in pregnant goats dehydrated for 30h accompanied by a decrease in glomerular filtration rate, while plasma protein and hematocrit did not change with dehydration. Inter‐ estingly, it was observed that pregnant goats [137] and sheep [138] have a lower capacity to concentrate urine in response to dehydration. Authors in both studies suggested that the ap‐ parent reason for this observation is a decreased sensitivity to Arginin-Vasopressin (AVP) which in turn, could be partially due to the effects of high prostaglandin concentrations which increase during late gestation. Research on the Matebele goat showed that a low nu‐ trition level during late pregnancy had little effect on kid birth weight [139]. Similarly, a twice weekly watering regime imposed for a prolonged period had no effect on birth weight of desert adapted Magra and Marwari sheep [140]. On the other hand, pregnant Chokla ewes watered every 4 days gave birth to lambs of lower weight compared to ewes that were watered daily or every three day; however, at 12 weeks of age, lambs' weight were similar between the differently watered groups [136]. Working on goats, Mellado et al. (2006) [141] highlighted the importance of goat birth weight and weight gain at 25 days of age on their future reproductive performance under intensive conditions in hot arid environments. On the other hand, in a recent study prenatal feed restriction in the last trimester resulted in lower male offspring weight in goats, but had no effects on later behavior and growth [142]. Further studies are needed to assess the long term consequences of dehydration and/or in‐ termittent watering during gestation on the growth and later performance of the offspring.

#### **4.2. Lactation**

Thyroid hormones (Triiodothyronine T3 and Thyroxine T4) play a major role in many phys‐ iological events such as thermoregulation and metabolic homeostasis of energy and proteins [126-128]. T3 and T4 concentration is affected by many factors like reproductive status, cli‐ matic conditions [127, 129] nutrition, age and gender [130, 131]. Water restriction [64] and nutrient limitation [132] were found to lower the levels of T3 and T4 in dry Awassi ewes and pregnant Whiteface Western ewes, respectively. Similarly, Caldeira et al. (2007a) [88] noticed a decrease in these hormones with decreasing body score of ewes. They concluded that T3 is a good indicator of the metabolic state of the animal. On the other hand, variable T3 and T4 responses to seasonal variations and/or dehydration were reported in literature from vari‐ ous ruminants [133]. The concentrations of these two hormones were found to be strongly

restriction reflected the declining metabolic state due to dehydration and decreased feed in‐ take while the declining T4 concentration was probably a response to the thermal stress ex‐ perienced by the animals in that experiment. Similarly, T4 concentrations were reported to vary with the season while T3 is affected by both the season and the physiological status of the sheep [134]. The reduction of thyroid hormone activity under dehydration is associated with the animal's attempt to minimize water losses by reducing general metabolism [135].

As seen above, small ruminants in arid and semi-arid regions face many constraints related to fluctuating temperatures as well as shortages in feed and water sources. Pregnancy and lactation increase the needs for adaptive mechanisms due to the greater need for food, water and electrolytes in order to meet the requirements of the fetus and the mammary glands [113]. Water requirements could increase up to 50% by late pregnancy (around 160 ml/kg BW0.75) while the requirement for milk production is stated as 165 ml/kg BW0.75 for a milk production level of 148g milk/kg0.75 [5]. Pregnant and lactating animals have 40-50% higher water turnover rates than dry animals [17]. However, Degen (1977) [35] recorded a small difference in water turnover between control and pregnant Awassi and Merinos sheep.

The reported physiological changes vary according to the degree of water restriction and stage of pregnancy. Chokla pregnant ewes submitted to intermittent watering (every 72 and 96 hours) under semi-arid conditions showed significant hemocentration and reduction in extracellular fluid space as compared to pregnant Chokla receiving water daily [136]. Simi‐ larly, Olsson et al. (1982) [137] reported increases in plasma osmolality and Na+ concentra‐ tion in pregnant goats dehydrated for 30h accompanied by a decrease in glomerular filtration rate, while plasma protein and hematocrit did not change with dehydration. Inter‐ estingly, it was observed that pregnant goats [137] and sheep [138] have a lower capacity to concentrate urine in response to dehydration. Authors in both studies suggested that the ap‐ parent reason for this observation is a decreased sensitivity to Arginin-Vasopressin (AVP) which in turn, could be partially due to the effects of high prostaglandin concentrations

**4. Changes in relation with physiological status**

=0.568; P=0.000) [64]. The authors suggested that this decline in T3 under water

correlated (R2

128 Responses of Organisms to Water Stress

**4.1. Pregnancy**

Significant weight loss was recorded in lactating water-stressed Awassi [47] and Comisana ewes [74] as compared to control animals. Weight loss during lactation is due to body water loss caused by less water and feed intake combined with energy deficit that drives lactating animals to strongly depend on their body reserves [143].

Physiologically, lactating animals show lower hemoglobin concentration than dry ones [47]. According to [120], the decrease in hemoglobin concentration in lactating ewes is ex‐ plained by the high water content and plasma volumes due to increased water mobiliza‐ tion to the mammary glands. It was found in [47] that lactation did not affect levels of serum glucose or those of cholesterol in Awassi ewes in their second to third month of lactation. Concurrently, no significant changes were recorded in glucose level caused by lactation beyond the first month [144]. Moreover, lactation did not affect blood total pro‐ tein, albumin and globulin concentration of Awassi ewes in their mid-lactation [47]; no change in albumin was also reported in [145], however an increase in the gammaglobulin fraction was noticed. El-Sherif and Assad (2001) [94] observed a return to normal total protein levels on the fourth week of lactation most probably caused by a fall in globulin concentrations. The same authors reported that lactation significantly increased plasma albumin, albumin to globulin ratio and blood creatinine in Barki ewes under semi-arid conditions. No alteration was caused by lactation on serum urea and creatinine levels in Awassi ewes [47] and Corriedal [138]. Working with lactating Comisana subjected to 60% water deprivation, Casamassima et al. (2008) [74] reported significant elevations in serum concentration of triglycerides, albumin, total proteins and cholesterol. Intermittently wa‐ tered Ethiopian Somali goats, exhibited similar physiological responses to those described in other breeds, namely increased osmolality, AVP secretion and blood protein concentra‐ tion [110]. The authors also noted a significant capacity to fluctuate rectal temperature in response to heat stress reaching 5o C daily change in some animals; they also observed the activation of a water saving mechanism following the first cycle of water restriction, resulting in lower physiological changes in subsequent cycles. A similar trend was also noted in lactating Awassi ewes subjected to intermittent watering [47].

stressors with the longest lasting effect since they may prevail for months. For example, heat stress and elevated ambient temperature are considered major risks affecting sheep per‐ formance [85; 158]. The negative impact of heat is translated into increased body tempera‐ ture, higher respiration and heart rates followed by a drop in feed intake, redistribution in blood flow and alteration in endocrine function [158]. Low temperatures or cold leads to an equally stressful situation which affects sheep performance by increasing the metabolic rate [85,160]. Furthermore, different environmental constraints often come together such as the situation in arid and semi-arid areas during the dry season when heat stress is combined

Water Stress in Small Ruminants http://dx.doi.org/10.5772/53584 131

Animal producers and researchers have looked for ways to alleviate the negative effects of common stressors. Stress alleviation strategies are numerous, and their availability to pro‐ ducers depend on the access to water and energy, the price they are able to pay and the adopted farming system [153]. These strategies vary from simple on-farm practices such as modifying the feeding pattern, feed composition [160], water management, cooling systems and environmental modifications like shading [153, 161], protection from solar radiation [153], the use of micro-sprinklers, spray jets and ventilation [162] to more scientific proce‐

In this quest for stress alleviation in domestic animals, researchers have tested special drugs and/or nutritional supplements. Trials showed that a pre-transportation administration of ascorbic acid to goats facilitates the transition from depression to excitation; it exhibited po‐ tential depression amelioration after road trips [163] and significantly decreased weight loss caused by transportation under unfavorable thermal conditions [164]. Ali et al. (2005) [156] reported that a single dose of the anti-stressor xylazine administered to sheep and goats be‐ fore road transportation considerably ameliorated the effects induced by the stressful stimu‐ lus; whereas a pretreatment with sodium betaine (a test compound) had no significant effects. Electrolyte therapy was also found effective in reducing stress of transportation in

market cattle allowing a better meat quality and a reduction in live weight loss [157].

In this review we will focus on two compounds that appear to have a good potential for stress remediation in domestic animals: Vitamin C which is tolerated at high doses without apparent side effects [165] and aspirin which showed some potential advantages warranting

Although ruminants biosynthesize ascorbic acid under normal conditions and do not need any additional supplementation [45], and even though vitamin C administration is not a common practice in adult livestock nutrition [169] scientists however, decided to study the effect of Vitamin C administration to sheep under water-stress conditions [60, 61, 64, 92] and goats facing the stress of transportation [163, 164]. These trials were encouraged by promis‐ ing results obtained on weaned pigs [170], Japanese quails [171], rabbits [172] and broilers

with water scarcity and low pasture quality.

dures like genetic selection [161] and others.

further investigation [166-168].

**5.1. Vitamin C**

[173] under stress.

Concerning the effect of lactation on blood pH, Hamadeh et al. (2006) [47] reported signifi‐ cantly higher blood pH in water restricted lactating Awassi ewes as compared to dry ones. This increase in pH is correlated to the decrease in plasma Ca++ and K+ levels due to their need for milk production [47] and to the increase in plasma Na+ and Cl since Na+ is used for nutrient transport [146]. As for cortisol, lactating Awassi ewes tended to have high levels as compared to dry counterparts. However, more work is needed in order to elucidate the adaptive mechanisms of pregnant and lactating ewes to water restriction.

#### **4.3. Milk production and composition**

Water needs are reported to be the highest during lactation as compared to other physiolog‐ ical statuses [109]. Dehydration leads to a reduction in the blood flow to the mammary gland however, enough supply for milk production may still be achieved as supported by the sustained milk production in dehydrated goats [113] and sheep [74]. During dehydra‐ tion, milk volume is generally decreased [109, 110, 147], although the Bedouin goats could maintain their milk production when watered every second day [108]. Dahlborn et al. (1997) [148] suggested that the drop in milk volume observed in some dehydrated animals was mainly the result of lack of water as such and not a reflection of the consequent decrease in feed intake; furthermore the authors suggested that this drop could be related to the altera‐ tion in casein production observed under dehydration. In fact, Silanikove (2000) [6] showed that stress leads to a chain of events including increased cortisol secretion leading the activa‐ tion of the plasmin system resulting in the release of a proteose peptone with channel block‐ ing activity (PPCB) from β-casein and interfering with lactose secretion into the lumen of the mammary gland and consequently causing a drop in production. Previous studies have in‐ dicated an increase in milk osmolality, lactose and density following water deprivation for 48 hours [109, 149, 150]. Milk osmolality is strictly controlled to keep it isotonic with plasma; the increase in lactose under water restriction, being the major osmotic component of milk, is probably a response to the increase in serum osmolality under water restriction [149]. Nonetheless, milk can be less concentrated in fat and non-fat solids and more rich in water. Alamer (2009) [150] noted a decrease in fat content of milk of 25% water restricted goats but not in those that were 50% restricted. The increase in water content [151, 152] is thought to be a form of adaptation allowing the offspring to receive the adequate quantity of water when water is not available.

#### **5. Stress alleviation drugs**

Domestic animals are routinely faced with different stressors. Most stressful conditions, in‐ cluding diseases [153] and farming practices such as milking [143], isolation [154], introduc‐ tion to a new flock [155], road transportation [156, 157] last for only a short period ranging between hours to days. On the other hand, harsh environmental factors are probably the stressors with the longest lasting effect since they may prevail for months. For example, heat stress and elevated ambient temperature are considered major risks affecting sheep per‐ formance [85; 158]. The negative impact of heat is translated into increased body tempera‐ ture, higher respiration and heart rates followed by a drop in feed intake, redistribution in blood flow and alteration in endocrine function [158]. Low temperatures or cold leads to an equally stressful situation which affects sheep performance by increasing the metabolic rate [85,160]. Furthermore, different environmental constraints often come together such as the situation in arid and semi-arid areas during the dry season when heat stress is combined with water scarcity and low pasture quality.

Animal producers and researchers have looked for ways to alleviate the negative effects of common stressors. Stress alleviation strategies are numerous, and their availability to pro‐ ducers depend on the access to water and energy, the price they are able to pay and the adopted farming system [153]. These strategies vary from simple on-farm practices such as modifying the feeding pattern, feed composition [160], water management, cooling systems and environmental modifications like shading [153, 161], protection from solar radiation [153], the use of micro-sprinklers, spray jets and ventilation [162] to more scientific proce‐ dures like genetic selection [161] and others.

In this quest for stress alleviation in domestic animals, researchers have tested special drugs and/or nutritional supplements. Trials showed that a pre-transportation administration of ascorbic acid to goats facilitates the transition from depression to excitation; it exhibited po‐ tential depression amelioration after road trips [163] and significantly decreased weight loss caused by transportation under unfavorable thermal conditions [164]. Ali et al. (2005) [156] reported that a single dose of the anti-stressor xylazine administered to sheep and goats be‐ fore road transportation considerably ameliorated the effects induced by the stressful stimu‐ lus; whereas a pretreatment with sodium betaine (a test compound) had no significant effects. Electrolyte therapy was also found effective in reducing stress of transportation in market cattle allowing a better meat quality and a reduction in live weight loss [157].

In this review we will focus on two compounds that appear to have a good potential for stress remediation in domestic animals: Vitamin C which is tolerated at high doses without apparent side effects [165] and aspirin which showed some potential advantages warranting further investigation [166-168].

#### **5.1. Vitamin C**

resulting in lower physiological changes in subsequent cycles. A similar trend was also

Concerning the effect of lactation on blood pH, Hamadeh et al. (2006) [47] reported signifi‐ cantly higher blood pH in water restricted lactating Awassi ewes as compared to dry ones. This increase in pH is correlated to the decrease in plasma Ca++ and K+ levels due to their

nutrient transport [146]. As for cortisol, lactating Awassi ewes tended to have high levels as compared to dry counterparts. However, more work is needed in order to elucidate the

Water needs are reported to be the highest during lactation as compared to other physiolog‐ ical statuses [109]. Dehydration leads to a reduction in the blood flow to the mammary gland however, enough supply for milk production may still be achieved as supported by the sustained milk production in dehydrated goats [113] and sheep [74]. During dehydra‐ tion, milk volume is generally decreased [109, 110, 147], although the Bedouin goats could maintain their milk production when watered every second day [108]. Dahlborn et al. (1997) [148] suggested that the drop in milk volume observed in some dehydrated animals was mainly the result of lack of water as such and not a reflection of the consequent decrease in feed intake; furthermore the authors suggested that this drop could be related to the altera‐ tion in casein production observed under dehydration. In fact, Silanikove (2000) [6] showed that stress leads to a chain of events including increased cortisol secretion leading the activa‐ tion of the plasmin system resulting in the release of a proteose peptone with channel block‐ ing activity (PPCB) from β-casein and interfering with lactose secretion into the lumen of the mammary gland and consequently causing a drop in production. Previous studies have in‐ dicated an increase in milk osmolality, lactose and density following water deprivation for 48 hours [109, 149, 150]. Milk osmolality is strictly controlled to keep it isotonic with plasma; the increase in lactose under water restriction, being the major osmotic component of milk, is probably a response to the increase in serum osmolality under water restriction [149]. Nonetheless, milk can be less concentrated in fat and non-fat solids and more rich in water. Alamer (2009) [150] noted a decrease in fat content of milk of 25% water restricted goats but not in those that were 50% restricted. The increase in water content [151, 152] is thought to be a form of adaptation allowing the offspring to receive the adequate quantity of water

Domestic animals are routinely faced with different stressors. Most stressful conditions, in‐ cluding diseases [153] and farming practices such as milking [143], isolation [154], introduc‐ tion to a new flock [155], road transportation [156, 157] last for only a short period ranging between hours to days. On the other hand, harsh environmental factors are probably the

and Cl-

since Na+

is used for

noted in lactating Awassi ewes subjected to intermittent watering [47].

adaptive mechanisms of pregnant and lactating ewes to water restriction.

need for milk production [47] and to the increase in plasma Na+

**4.3. Milk production and composition**

130 Responses of Organisms to Water Stress

when water is not available.

**5. Stress alleviation drugs**

Although ruminants biosynthesize ascorbic acid under normal conditions and do not need any additional supplementation [45], and even though vitamin C administration is not a common practice in adult livestock nutrition [169] scientists however, decided to study the effect of Vitamin C administration to sheep under water-stress conditions [60, 61, 64, 92] and goats facing the stress of transportation [163, 164]. These trials were encouraged by promis‐ ing results obtained on weaned pigs [170], Japanese quails [171], rabbits [172] and broilers [173] under stress.

Ascorbic acid is known for its function as an antioxidant mainly due to its redox properties; it acts as a free radical scavenger in numerous cellular oxidation processes [174] and has been demonstrated to be helpful for young ruminants in acclimatizing to cold stress [175]. Ascorbic acid plays an important role in modulating the immune response by enhancing neutrophil function and minimizing free radical damage [176] and by improving antibody response to antigen [177]. Concurrently, Minka and Ayo (2007) [164] reported that adminis‐ tering Vitamin C to Red Sokoto goats before transportation reduced the post-journey effect to a minimum or eliminated it completely; however the impaired animals' homeostasis was rapidly recovered after the trip.

creases fat mobilization [172], it is also essential in carnitine formation, which upon reacting with acetyl CoA forms acetylcarnitine that transports fatty acids into the mitochondria to be

Reports on the effect of Vitamin C on osmolality are scarce. However, Karnib (2009) [63] and Hanna (2006) [106] observed increased osmolality in water-stressed vitamin C supplement‐ ed Awassi ewes, but the mechanism of such phenomenon is still not well understood. Re‐ sults obtained on the effect of Vitamin C on blood electrolytes are not very clear and need more elaborated work. Ghanem et al. (2008) [60] reported that Vitamin C administration al‐

thors attributed this observation to the role of vitamin C in norepinephrine formation, which affects the kidney function and therefore water and electrolytes dynamics. On the other hands, [72] reported an opposite result in one experiment while in a second experiment Na+

Benefits of Vitamin C in decreasing stress hormones was reported by several authors: some [181] observed that ascorbic acid intake resulted in a drop in adrenal and plasma corticoster‐ one levels, others showed that vitamin C eliminated the secretion of cortisol in animals sub‐ jected to stress [182]. Still others did not observe any effect of Vitamin C administration on cortisol concentrations in stressed animals [61, 122, 124]. Serum cortisol is a better marker for acute stress than for chronic stress [125]. While Vitamin C and cortisol interact, the anti-

Concluding with Vitamin C, it has been shown that the most important parameter in high‐ lighting the role of Vitamin C in counteracting the effect of water deprivation on sheep is the observed decrease in weight loss. Consequently, further work is warranted in order to eluci‐ date the mechanisms of action of Vitamin C, and to determine the best dose recommenda‐ tions that would increase the adaptive capacities of shepherds and flock keepers to the

Acetyl-salicylic acid ASA or aspirin has been used for ages as an antipyretic and analgesic agent [183]. New studies have emphasized the role of aspirin in the treatment of some types of cancer [168] and cardio-vascular diseases [184] although data on the effect of aspirin in animal production is contradictory. On one hand, supplementation of 20ppm of ASA to lay‐ er chicken under hot climates improved the number of eggs as well as their weight; it in‐ creased feed intake, improved fertility and hatchability [185]. On the other hand, chronic feeding of ASA had detrimental results to layer breeders with concerns for early hen livabil‐ ity and egg quality [186]. In mammals, aspirin reduced scouring and improved growth rate when supplemented to weanling pigs at a level of 125 or 250 ppm [166]. It also reduced plas‐ ma cholesterol levels in rats [167], and protected rats from colon cancer [168]. Recently, the

The role of aspirin in alleviating stress has been investigated in adult Awassi ewes subjected to water and feed restriction has been studied [62]. Treated animals with a daily dose of

role of aspirin in the protection from oxidative stress has been highlighted.

were the same between supplemented and un-supplemented water restricted ewes.

and Cl-

(Figure 2). The au‐

Water Stress in Small Ruminants http://dx.doi.org/10.5772/53584 133

leviated the effect of water restriction as reflected in lower Na+

cortisol role of Vitamin C is still unclear and needs more research.

changing weather and increasing global warming.

oxidized [60].

and Cl-

**5.2. Aspirin**

A daily dose of Vitamin C was reported to decrease weight loss in adult female Awassi subjected to a water-restricted regime [61, 63] while this effect was not significant in oth‐ er trials [63, 64, 92]. The alleviation of body weight loss can be explained by improved feed intake [92] and better feed conversion, also observed in other animals in stressful conditions and supplemented with vitamin C [164, 171, 178]. The ameliorated effect of ascorbic acid on weight loss during short-term transportation of goats in hot weather [164, 179] proves the advantage of Vitamin C supplementation in order to maintain an adequate live body weight for slaughter.

Vitamin C supplementation to sheep alleviated the effect of dehydration on PCV [61] but not on hemoglobin [61, 63]; while in goats submitted to transportation under unfavorable climate conditions, Vitamin C significantly decreased levels of both PCV and Hb [164]. It was also found that supplementing Vitamin C to deficient pigs increased hemoglobin levels probably due to increased iron absorption [180].

Lower serum protein concentrations were reported in Vitamin C administered water-re‐ stricted Awassi as compared to non-supplemented counterparts [61], while others found no significant differences in total protein and globulin levels due to Vit C [92]. The effect of vi‐ tamin C on albumin levels is inconclusive as well: although some [61] noted lower concen‐ trations in treated ewes, others [47] reported higher values of albumin in treated animals. The daily Vitamin C dose also plays a considerable role on blood parameters: a daily dose of 5g significantly increased serum creatinine and urea concentrations as compared to 3g and to control [92]. This might be considered as an enhancement to the adaptive mechanisms of Awassi sheep to water restriction. However, in other experiments no effect of Vitamin C was observed on creatinine levels [63] warranting further investigations on the role of Vita‐ min C in urea and creatinine dynamics during dehydration.

In an experiment conducted in order to study the effect of Vitamin C on fat mobilization un‐ der water stress, Jaber et al. (2011) [64] reported no significant effect of this drug administra‐ tion on adipocyte diameter, fat mobility and weight loss in water deprived sheep. Authors speculated that a daily dose of Vitamin C (3g or more) may be more helpful in increasing fat mobilization under water stress than single high dosages; they agreed that more work would be essential to confirm the observed trends.

A tendency for higher cholesterol levels was observed under Vitamin C administration [60, 61, 63]. Vitamin C interferes in norepinephrine formation, an important hormone that in‐ creases fat mobilization [172], it is also essential in carnitine formation, which upon reacting with acetyl CoA forms acetylcarnitine that transports fatty acids into the mitochondria to be oxidized [60].

Reports on the effect of Vitamin C on osmolality are scarce. However, Karnib (2009) [63] and Hanna (2006) [106] observed increased osmolality in water-stressed vitamin C supplement‐ ed Awassi ewes, but the mechanism of such phenomenon is still not well understood. Re‐ sults obtained on the effect of Vitamin C on blood electrolytes are not very clear and need more elaborated work. Ghanem et al. (2008) [60] reported that Vitamin C administration al‐ leviated the effect of water restriction as reflected in lower Na+ and Cl- (Figure 2). The au‐ thors attributed this observation to the role of vitamin C in norepinephrine formation, which affects the kidney function and therefore water and electrolytes dynamics. On the other hands, [72] reported an opposite result in one experiment while in a second experiment Na+ and Cl were the same between supplemented and un-supplemented water restricted ewes.

Benefits of Vitamin C in decreasing stress hormones was reported by several authors: some [181] observed that ascorbic acid intake resulted in a drop in adrenal and plasma corticoster‐ one levels, others showed that vitamin C eliminated the secretion of cortisol in animals sub‐ jected to stress [182]. Still others did not observe any effect of Vitamin C administration on cortisol concentrations in stressed animals [61, 122, 124]. Serum cortisol is a better marker for acute stress than for chronic stress [125]. While Vitamin C and cortisol interact, the anticortisol role of Vitamin C is still unclear and needs more research.

Concluding with Vitamin C, it has been shown that the most important parameter in high‐ lighting the role of Vitamin C in counteracting the effect of water deprivation on sheep is the observed decrease in weight loss. Consequently, further work is warranted in order to eluci‐ date the mechanisms of action of Vitamin C, and to determine the best dose recommenda‐ tions that would increase the adaptive capacities of shepherds and flock keepers to the changing weather and increasing global warming.

#### **5.2. Aspirin**

Ascorbic acid is known for its function as an antioxidant mainly due to its redox properties; it acts as a free radical scavenger in numerous cellular oxidation processes [174] and has been demonstrated to be helpful for young ruminants in acclimatizing to cold stress [175]. Ascorbic acid plays an important role in modulating the immune response by enhancing neutrophil function and minimizing free radical damage [176] and by improving antibody response to antigen [177]. Concurrently, Minka and Ayo (2007) [164] reported that adminis‐ tering Vitamin C to Red Sokoto goats before transportation reduced the post-journey effect to a minimum or eliminated it completely; however the impaired animals' homeostasis was

A daily dose of Vitamin C was reported to decrease weight loss in adult female Awassi subjected to a water-restricted regime [61, 63] while this effect was not significant in oth‐ er trials [63, 64, 92]. The alleviation of body weight loss can be explained by improved feed intake [92] and better feed conversion, also observed in other animals in stressful conditions and supplemented with vitamin C [164, 171, 178]. The ameliorated effect of ascorbic acid on weight loss during short-term transportation of goats in hot weather [164, 179] proves the advantage of Vitamin C supplementation in order to maintain an

Vitamin C supplementation to sheep alleviated the effect of dehydration on PCV [61] but not on hemoglobin [61, 63]; while in goats submitted to transportation under unfavorable climate conditions, Vitamin C significantly decreased levels of both PCV and Hb [164]. It was also found that supplementing Vitamin C to deficient pigs increased hemoglobin levels

Lower serum protein concentrations were reported in Vitamin C administered water-re‐ stricted Awassi as compared to non-supplemented counterparts [61], while others found no significant differences in total protein and globulin levels due to Vit C [92]. The effect of vi‐ tamin C on albumin levels is inconclusive as well: although some [61] noted lower concen‐ trations in treated ewes, others [47] reported higher values of albumin in treated animals. The daily Vitamin C dose also plays a considerable role on blood parameters: a daily dose of 5g significantly increased serum creatinine and urea concentrations as compared to 3g and to control [92]. This might be considered as an enhancement to the adaptive mechanisms of Awassi sheep to water restriction. However, in other experiments no effect of Vitamin C was observed on creatinine levels [63] warranting further investigations on the role of Vita‐

In an experiment conducted in order to study the effect of Vitamin C on fat mobilization un‐ der water stress, Jaber et al. (2011) [64] reported no significant effect of this drug administra‐ tion on adipocyte diameter, fat mobility and weight loss in water deprived sheep. Authors speculated that a daily dose of Vitamin C (3g or more) may be more helpful in increasing fat mobilization under water stress than single high dosages; they agreed that more work

A tendency for higher cholesterol levels was observed under Vitamin C administration [60, 61, 63]. Vitamin C interferes in norepinephrine formation, an important hormone that in‐

rapidly recovered after the trip.

132 Responses of Organisms to Water Stress

adequate live body weight for slaughter.

probably due to increased iron absorption [180].

min C in urea and creatinine dynamics during dehydration.

would be essential to confirm the observed trends.

Acetyl-salicylic acid ASA or aspirin has been used for ages as an antipyretic and analgesic agent [183]. New studies have emphasized the role of aspirin in the treatment of some types of cancer [168] and cardio-vascular diseases [184] although data on the effect of aspirin in animal production is contradictory. On one hand, supplementation of 20ppm of ASA to lay‐ er chicken under hot climates improved the number of eggs as well as their weight; it in‐ creased feed intake, improved fertility and hatchability [185]. On the other hand, chronic feeding of ASA had detrimental results to layer breeders with concerns for early hen livabil‐ ity and egg quality [186]. In mammals, aspirin reduced scouring and improved growth rate when supplemented to weanling pigs at a level of 125 or 250 ppm [166]. It also reduced plas‐ ma cholesterol levels in rats [167], and protected rats from colon cancer [168]. Recently, the role of aspirin in the protection from oxidative stress has been highlighted.

The role of aspirin in alleviating stress has been investigated in adult Awassi ewes subjected to water and feed restriction has been studied [62]. Treated animals with a daily dose of 100mg of ASA lost more weight than the untreated animals. However, the difference was not statistically considerable. Similar results had been reported in broilers [187] and wean‐ ling pigs [166].

and nutritional manipulations to alleviate water stress, with special attention to the longterm effects of such approaches on overall productivity and welfare. The identification of breeds that show high adaptability to arid and semi-arid regions with an acceptable level of

Water Stress in Small Ruminants http://dx.doi.org/10.5772/53584 135

Department of Animal and Veterinary Sciences, Faculty of Agricultural and Food Sciences,

[1] Migongo-Bake W. Rumen dry-matter digestive efficiency of camels, cattle sheep and goats in a semi-arid environment in eastern Africa. Rome, Italy: FAO, The comple‐

[2] Iñiguez, L. Small ruminant breeds in West Asia and North Africa. ICARDA Caravan 2005; Issue 22. http://www.icarda.org/Publications/Caravan/Caravan22/Focus\_3.htm

[3] Silanikove N. Effects of water scarcity and hot environment on appetite and diges‐ tion in ruminants: a review. Livestock Production Science 1992;30: 175-194.

[4] Barbour E, Rawda N, Banat G, Jaber L, Sleiman FT, Hamadeh S. Comparison of im‐ munosuppression in dry and lactating Awassi ewes due to water deprivation stress.

[5] Giger-Reverdin S, Gihad EA. Water metabolism and intake in goats. In: Morand-Fehr P. (ed.) EAAP 1991: Goat Nutrition: proceedings of EAAP, 24–26 April 1991, Pudoc

[6] Silanikove N. The physiological basis of adaptation in goats to harsh environments.

[7] Aganga AA, Umunna NN, Oyedipe EO, Okoh PN. Influence of water restriction on some serum components in Yankasa ewes. Small Ruminant Research 1989;2: 19–26.

[8] Igbokwe IO. Haemoconcentration in Yankasa sheep exposed to prolonged water

mentarity of feed resources for animal production in Africa; 1992.

Veterinary Research Communications 2005;29(1) 47-60.

Small Ruminant Research 2000;35: 181– 193.

deprivation. Small Rumin. Res. 1993;12: 99–105.

productivity is also important.

Lina Jaber, Mabelle Chedid and Shadi Hamadeh\*

(accessed 15 August 2012).

Wageningen, Wageningen.

\*Address all correspondence to: shamadeh@aub.edu.lb

American University of Beirut, Riad el Solh, Beirut, Lebanon

**Author details**

**References**

Aspirin did not have any effect on rectal temperature; perhaps these results highlight the ca‐ pacity of Awassi to remain thermostable even under dehydration [10, 35]. No changes were detected in PCV and hemoglobin levels [62] confirming that salicyclates do not usually alter these two parameters [188]. Moreover, results of the experiment revealed that aspirin has no effect on plasma concentrations of proteins, globulin and albumin. Similarly, no significant differences in the levels of urea, creatinine and osmolality were observed between treated and untreated animals. Furthermore, no significant effect of aspirin was observed on any fat mobilization indicator i.e. cholesterol, insulin, free fatty acids and leptin.

Other studies investigating the role of aspirin in water and feed stressed ruminants are not found. The available literature covers stress resulting from transportation and exposition to new environment [189] and physical pain caused by tail docking [190].

Further studies using different doses of aspirin could be done. Additional experiments might also help clarify the antioxidant property of aspirin and its effect on the ruminant im‐ mune system which might be compromised under stress.

## **6. Conclusion**

This review helped in highlighting the adaptability of indigenous small ruminant breeds to water stress and the changes it induces under different physiological statuses. Most small ruminants respond to water stress by decreasing their feed intake, resulting in weight reduc‐ tion due to water and body mass loss. The rumen plays an important role as water reservoir both in times of dehydration, to maintain blood volume, and upon rehydration to prevent hemolysis. Similarly, modulating saliva production and osmolality is an important mecha‐ nism for facing dehydration and rehydration cycles.

A ten-year research track on the Awassi demonstrated the key mechanisms that this breed activates in facing water stress. Strong water conservation is achieved at the level of the kid‐ ney, as reflected by a drop in urine output and increased blood Na+ , albumin and urea along with hyperosmolality. Furthermore, the Awassi seems to adapt to an intermittent watering regime after a couple of cycles by re-adjusting its blood volume and constituents to a new status tending toward control levels. Finally, the Awassi mobilizes its fat stores, including the fat-tail, to overcome the shortfall in dietary energy intake. This breed could be main‐ tained, during the hot months and in times of severe water shortage, on short intermittent watering regimes. However, severe dehydration will ultimately result in detrimental effects on milk production, reproductive success, lambs' weight gain and disease resistance, partic‐ ularly during gestation and peak lactation.

Stress alleviating supplements such as vitamin C show some promise in decreasing the ef‐ fects of dehydration. Many tracks still need to be explored in future research such as feeding and nutritional manipulations to alleviate water stress, with special attention to the longterm effects of such approaches on overall productivity and welfare. The identification of breeds that show high adaptability to arid and semi-arid regions with an acceptable level of productivity is also important.

## **Author details**

100mg of ASA lost more weight than the untreated animals. However, the difference was not statistically considerable. Similar results had been reported in broilers [187] and wean‐

Aspirin did not have any effect on rectal temperature; perhaps these results highlight the ca‐ pacity of Awassi to remain thermostable even under dehydration [10, 35]. No changes were detected in PCV and hemoglobin levels [62] confirming that salicyclates do not usually alter these two parameters [188]. Moreover, results of the experiment revealed that aspirin has no effect on plasma concentrations of proteins, globulin and albumin. Similarly, no significant differences in the levels of urea, creatinine and osmolality were observed between treated and untreated animals. Furthermore, no significant effect of aspirin was observed on any fat

Other studies investigating the role of aspirin in water and feed stressed ruminants are not found. The available literature covers stress resulting from transportation and exposition to

Further studies using different doses of aspirin could be done. Additional experiments might also help clarify the antioxidant property of aspirin and its effect on the ruminant im‐

This review helped in highlighting the adaptability of indigenous small ruminant breeds to water stress and the changes it induces under different physiological statuses. Most small ruminants respond to water stress by decreasing their feed intake, resulting in weight reduc‐ tion due to water and body mass loss. The rumen plays an important role as water reservoir both in times of dehydration, to maintain blood volume, and upon rehydration to prevent hemolysis. Similarly, modulating saliva production and osmolality is an important mecha‐

A ten-year research track on the Awassi demonstrated the key mechanisms that this breed activates in facing water stress. Strong water conservation is achieved at the level of the kid‐

with hyperosmolality. Furthermore, the Awassi seems to adapt to an intermittent watering regime after a couple of cycles by re-adjusting its blood volume and constituents to a new status tending toward control levels. Finally, the Awassi mobilizes its fat stores, including the fat-tail, to overcome the shortfall in dietary energy intake. This breed could be main‐ tained, during the hot months and in times of severe water shortage, on short intermittent watering regimes. However, severe dehydration will ultimately result in detrimental effects on milk production, reproductive success, lambs' weight gain and disease resistance, partic‐

Stress alleviating supplements such as vitamin C show some promise in decreasing the ef‐ fects of dehydration. Many tracks still need to be explored in future research such as feeding

, albumin and urea along

mobilization indicator i.e. cholesterol, insulin, free fatty acids and leptin.

new environment [189] and physical pain caused by tail docking [190].

mune system which might be compromised under stress.

nism for facing dehydration and rehydration cycles.

ularly during gestation and peak lactation.

ney, as reflected by a drop in urine output and increased blood Na+

ling pigs [166].

134 Responses of Organisms to Water Stress

**6. Conclusion**

Lina Jaber, Mabelle Chedid and Shadi Hamadeh\*

\*Address all correspondence to: shamadeh@aub.edu.lb

Department of Animal and Veterinary Sciences, Faculty of Agricultural and Food Sciences, American University of Beirut, Riad el Solh, Beirut, Lebanon

## **References**


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**Chapter 7**

**Water Stress and Agriculture**

Suzelei de Castro França

http://dx.doi.org/10.5772/53877

**1. Introduction**

inhabitants of the planet?

cessible agricultural land [1].

Sonia Marli Zingaretti, Marielle Cascaes Inácio, Lívia de Matos Pereira, Tiago Antunes Paz and

Additional information is available at the end of the chapter

ban areas has occurred in the last decades. From the 50th´

Climate changes and water availability cause an important impact in agriculture, food disposal and consequently in human health. According to the U.S. Census Bureau, the total population of the World is now over 7,032 billion, and all growth projections for developed and undeveloped countries show that a total of 9 million of inhabitants will be reached before 2050. As a result, the demand for food and fuel will increase signifi‐ cantly. How agriculture will move on to guarantee continuous provision of food for all

As a consequence of the population growth the scenario has changed and an increase of ur‐

4 to 11% in Africa, 33 to 52% in Asia, 9 to13% in Latin America, and decreased from 38 to 15% in Europe, from 15 to 6% in Northern America. Growth forecasts for 2050 are 54, 32.5 and 6.8% increase in Asia, Africa and Latin America respectively. Increasing urban areas make less cropland available for fuel and food production. Croplands are not expanding in the same rate as population in the last half a century and salinity and desertification have also contributed to the fact that less useful areas remain proper for agriculture. According to FAO about 12% of globe´s land surface is used for crop production and most of remaining world agricultural land are covered by forest and protect by environmental laws. Brazil, Bo‐ livia, Argentina, Colombia, Sudan and Democratic Republic of the Congo retain 90% of ac‐

The climate changes in agriculture and human life can be considered under different as‐ pects: the biological effects on crop yields; the resulting impacts on outcomes including pri‐ ces, production and consumption and also the impact on per capita calorie consumption and

> © 2013 Zingaretti et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2013 Zingaretti et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

s

urban population increased from

## **Chapter 7**

## **Water Stress and Agriculture**

Sonia Marli Zingaretti, Marielle Cascaes Inácio, Lívia de Matos Pereira, Tiago Antunes Paz and Suzelei de Castro França

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/53877

## **1. Introduction**

Climate changes and water availability cause an important impact in agriculture, food disposal and consequently in human health. According to the U.S. Census Bureau, the total population of the World is now over 7,032 billion, and all growth projections for developed and undeveloped countries show that a total of 9 million of inhabitants will be reached before 2050. As a result, the demand for food and fuel will increase signifi‐ cantly. How agriculture will move on to guarantee continuous provision of food for all inhabitants of the planet?

As a consequence of the population growth the scenario has changed and an increase of ur‐ ban areas has occurred in the last decades. From the 50th´ s urban population increased from 4 to 11% in Africa, 33 to 52% in Asia, 9 to13% in Latin America, and decreased from 38 to 15% in Europe, from 15 to 6% in Northern America. Growth forecasts for 2050 are 54, 32.5 and 6.8% increase in Asia, Africa and Latin America respectively. Increasing urban areas make less cropland available for fuel and food production. Croplands are not expanding in the same rate as population in the last half a century and salinity and desertification have also contributed to the fact that less useful areas remain proper for agriculture. According to FAO about 12% of globe´s land surface is used for crop production and most of remaining world agricultural land are covered by forest and protect by environmental laws. Brazil, Bo‐ livia, Argentina, Colombia, Sudan and Democratic Republic of the Congo retain 90% of ac‐ cessible agricultural land [1].

The climate changes in agriculture and human life can be considered under different as‐ pects: the biological effects on crop yields; the resulting impacts on outcomes including pri‐ ces, production and consumption and also the impact on per capita calorie consumption and

© 2013 Zingaretti et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Zingaretti et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

child malnutrition [2]. In other words their effects on agriculture will induce changes in pro‐ duction and prices, altering economic system, crop mix, production, food demand and con‐ sumption. Unfortunately those changes are already occurring and the projections on annual mean temperature for the next 20 to 30 years point to great economic losses due to decline in productivity for cereals like maize, wheat and rice as well. It is well known that most of our important crops will decrease yield with temperature above 30°C, as they growth faster in high temperature they have less time to accumulate carbohydrates, proteins and oil. Increas‐ ing temperature will perhaps make some areas available for agriculture, but will it be enough to replace the areas that will certainly be lost?

**2. Physiological aspects of water stress**

severe some will not recover at all.

**Figure 1.** Physiological mechanisms induced by water stress.

It is well known that plant growth and development can be affected by abiotic agents such as salinity, high temperatures, radiation, flood and water deficit. Exacerbate action of those environmental conditions can led to great losses in productivity due to crop stress. When subjected to water deficit plants go through a cascade of metabolic alterations started with reduction in photosynthetic pigments concentration. Physiological mechanisms of plant re‐ sponse to water stress are summarized in Figure 1. Facing a water deficit situation plant re‐ sponses can be species/genotype specific, under rehydration after a mild water deficit almost every plant can return to normal growth, but if the stress intensity was moderated or

Water Stress and Agriculture http://dx.doi.org/10.5772/53877 153

Recently, it was discussed the physical and economic consequences of climate changes con‐ sidering temperature rising in Europe over four different factors such as agriculture, river floods, coastal systems and tourism [3]. Considering four different temperature increases from 2.5 to 5.1°C and five Europe regions (Southern, Central South, Central North, British Isle and Northern). Yield change (%) would affect Southern Europe (Portugal, Spain, Italy, Greece and Bulgaria) more than any other region with temperature increase. Northern Eu‐ rope (Sweden, Finland, Estonia, Latvia, and Lithuania) instead would benefit from positive yield changes. River floods are natural disasters anywhere it happens, resulting in very large economic losses due to properties and agriculture damage. An increase on river flood is expected with global warming [4]. As a consequence of increasing temperature river floods would affect 250,000-400,000 additional people in Europe in the 2080s, specially West‐ ern Europe, British Isle and Central Europe regions. All the costal systems across Europe would suffer with people flooded. Tourism in Europe would be impacted as well. Accord‐ ing to bed night's percentage measures the effects will be a decrease in Southern Europe and an increase in all other areas such as Central and Northern Europe. But not only tempera‐ ture would have importance to agriculture, fluctuation in seasonal precipitation is also ex‐ tremely relevant and as well as increasing evaporation rates [3].

The effects of climate change on rainfed and irrigated crops for developing and devel‐ oped countries were also discussed [2]. Percentage change in yield for irrigated and rainfed crops like maize, rice and wheat were analyzed using Decision Support System for Agrotechnology Transfer (DSSAT) crop-simulation model with and without CO2 fer‐ tilization in 2050 scenario. The observed effects on rainfed were attributed to changes in temperature and precipitation index, while for irrigated areas the effects were only relat‐ ed to temperature variation. In general, yields in developed countries were less affected than those in developing countries, where for most crops without CO2 fertilization the yield declines. The stress imposed by climate changes on agriculture will certainly inten‐ sify the disparities among regions.

Nevertheless, prices for major grain crops like rice, wheat, maize and soybean will increase up to 60 to 70 %, over the next few years, even without climate changes. Bearing in mind the predicted weather changes an additional of 32 to 37% for rice, 52 to 55% for maize, 94 to 111% for wheat and 11 to 14% for soybean can be expected [2].

## **2. Physiological aspects of water stress**

child malnutrition [2]. In other words their effects on agriculture will induce changes in pro‐ duction and prices, altering economic system, crop mix, production, food demand and con‐ sumption. Unfortunately those changes are already occurring and the projections on annual mean temperature for the next 20 to 30 years point to great economic losses due to decline in productivity for cereals like maize, wheat and rice as well. It is well known that most of our important crops will decrease yield with temperature above 30°C, as they growth faster in high temperature they have less time to accumulate carbohydrates, proteins and oil. Increas‐ ing temperature will perhaps make some areas available for agriculture, but will it be

Recently, it was discussed the physical and economic consequences of climate changes con‐ sidering temperature rising in Europe over four different factors such as agriculture, river floods, coastal systems and tourism [3]. Considering four different temperature increases from 2.5 to 5.1°C and five Europe regions (Southern, Central South, Central North, British Isle and Northern). Yield change (%) would affect Southern Europe (Portugal, Spain, Italy, Greece and Bulgaria) more than any other region with temperature increase. Northern Eu‐ rope (Sweden, Finland, Estonia, Latvia, and Lithuania) instead would benefit from positive yield changes. River floods are natural disasters anywhere it happens, resulting in very large economic losses due to properties and agriculture damage. An increase on river flood is expected with global warming [4]. As a consequence of increasing temperature river floods would affect 250,000-400,000 additional people in Europe in the 2080s, specially West‐ ern Europe, British Isle and Central Europe regions. All the costal systems across Europe would suffer with people flooded. Tourism in Europe would be impacted as well. Accord‐ ing to bed night's percentage measures the effects will be a decrease in Southern Europe and an increase in all other areas such as Central and Northern Europe. But not only tempera‐ ture would have importance to agriculture, fluctuation in seasonal precipitation is also ex‐

The effects of climate change on rainfed and irrigated crops for developing and devel‐ oped countries were also discussed [2]. Percentage change in yield for irrigated and rainfed crops like maize, rice and wheat were analyzed using Decision Support System for Agrotechnology Transfer (DSSAT) crop-simulation model with and without CO2 fer‐ tilization in 2050 scenario. The observed effects on rainfed were attributed to changes in temperature and precipitation index, while for irrigated areas the effects were only relat‐ ed to temperature variation. In general, yields in developed countries were less affected than those in developing countries, where for most crops without CO2 fertilization the yield declines. The stress imposed by climate changes on agriculture will certainly inten‐

Nevertheless, prices for major grain crops like rice, wheat, maize and soybean will increase up to 60 to 70 %, over the next few years, even without climate changes. Bearing in mind the predicted weather changes an additional of 32 to 37% for rice, 52 to 55% for maize, 94 to

enough to replace the areas that will certainly be lost?

152 Responses of Organisms to Water Stress

tremely relevant and as well as increasing evaporation rates [3].

111% for wheat and 11 to 14% for soybean can be expected [2].

sify the disparities among regions.

It is well known that plant growth and development can be affected by abiotic agents such as salinity, high temperatures, radiation, flood and water deficit. Exacerbate action of those environmental conditions can led to great losses in productivity due to crop stress. When subjected to water deficit plants go through a cascade of metabolic alterations started with reduction in photosynthetic pigments concentration. Physiological mechanisms of plant re‐ sponse to water stress are summarized in Figure 1. Facing a water deficit situation plant re‐ sponses can be species/genotype specific, under rehydration after a mild water deficit almost every plant can return to normal growth, but if the stress intensity was moderated or severe some will not recover at all.

**Figure 1.** Physiological mechanisms induced by water stress.

#### **2.1. Photosynthetic responses**

One of the significant alterations responsible for reduction in crop productivity is low pho‐ tosynthetic ability. The water stress may cause decrease in CO2 assimilation in the leaves, the amount of ATP and the level of ribulose bisphosphate [5-8]. Stomatal closure limiting diffusion through stomata and mesophyll is one of the first events in plants response under water deficit situation with consequent increase of the Rubisco enzyme, responsible for CO2 fixation, e in order to overcome the low conductance [9-13]. However, some species (*Gos‐ sypium barbadense, Hypericum balearicum*) show, instead, a decrease in Rubisco activity [13-15]. Furthermore the decrease in CO2 concentration will induce a reduction in the dy‐ namic of the carboxylation process [8].

plays a role in controlling senescence [29, 30]. The high concentration of ABA possibly pre‐ vents excessive accumulation of ethylene (ET), thus indirectly maintaining the growth of

Water Stress and Agriculture http://dx.doi.org/10.5772/53877 155

ABA seems to be also involved in remobilize carbon to accelerate grains filling in rice and wheat [29, 30, 33]. The ABA increased level also induce ROS production and in order to pre‐ vent the oxidative stress, antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) are immediately activat‐ ed [34, 35]. The importance of regulating ABA contents as a stress signaling was also ob‐ served in rice leaves when, after a water stress period, plants were rehydrated; decreasing

Wheat and maize plants submitted to a moderate water deficit exhibit an increase in ET con‐ centration [27, 37] that would be partly responsible for decreasing growth rates. In contrast for beans, cotton and miniature rose it has been shown that the rate of ethylene production is not affected during progressive drought [27]. ET is also involved in ROS production and

Cytokinins are generally involved in root and shoot development, but it has been shown an increased cytokinin concentration in leaves, from roots translocation, in plants submitted to water deficit [24, 29, 38]. Bentgrass transgenic plants expressing the enzyme adenine isopen‐ tenyl phosphotransferase for Ck synthesis ligated to a senescence-activated promoter (*SAG12*), resulted in increases in Ck accumulation in the leaves and roots and in the overall

The gibberellins (GA), Ax and brassinosteroids (BR) do not seem to have a direct involve‐ ment with water stress, however, the accumulation of GA in some dicots has been reported and also the BR along with ABA regulate the development and function of stomata [27]. In contrast in monocots such as maize, there is a decrease in the levels of GA in leaves [25, 27]. The Ax content in plants seems to decrease in roots and leaves under stress, but the impor‐

The JA instead seems to play a role in the biosynthesis of ABA in water stress. In citrus plants, for example, drought causes an increase of JA concentration in roots with subsequent increase in the concentration of ABA. One can conclude that JA is possibly the precursor in the signal transduction cascade in case of drought stress, providing increased levels of ABA

All the known morphological changes that occur in plants under water deficit can be associ‐ ated to hormone actions. Plants develop more roots in order to access more water, increas‐ ing the ratio root/shoot, reduce leaf number and leaf area to lower transpiration rates what leads, unfortunately, to a decrease in photosynthetic rates and biomass production [20, 26, 42] and develop the epinasty/hyponasty effects [43]. The increase of apoplastic pH in the elongation of leaf area could be the responsible for the foliar reduction [44]. The number of

tance of auxin in water stress response remains inconclusive [24, 25, 27, 40].

lateral seedling roots [17] as well as the stem length can also be affected [20].

ABA content occurred a reduction on ROS, CAT and SOD [36].

roots and shoots [31, 32].

antioxidant enzymes synthesis [23].

plant tolerance to water stress [39].

which, in turn, induce later responses [41].

**2.4. Morphological and anatomical modifications**

The electron transport in thylakoids and the use of trioses phosphates are also reduced in the stress biochemical control therefore, the net photosynthetic rate tends to be lower. It has been proved that in plants subjected to water stress the photochemical efficiency of photo‐ system II (PSII) and quantum generation is reduced [6, 15-17]. Alterations in the level of photosynthetic pigment were also detected in water stressed plants; showing reduced or even no pigmentation. Both chlorophyll *a* and *b* declines in stressed plants and this directly affect plant biomass production. The reduction of photosynthetic pigments will drive a cut down in energy consumption and carbon demand for chlorophyll synthesis [8, 11, 17, 18]. Other pigments such as carotenoids, which play essential role in the antioxidant defense system under stress conditions, can function as an accessory pigment for photosynthesis al‐ though, their concentration can also be reduced as part of plant response [8, 17, 19, 20].

## **2.2. Sugar and Reactive Oxygen Species (ROS) protection**

Changes in the content of carbohydrates such as sucrose and raffinose, together with the un‐ balanced of plant hormones function as a signal that plant response to stress should be initi‐ ated [21]. Raffinose has been correlated to a plant tolerance to desiccation, possibly involved in the protection against ROS that are responsible for loss of membrane integrity and cellu‐ lar death [22, 23]. Moreover, induction of sugar accumulation, i. e, sucrose, fructose, maltose and inositol is relevant for the osmoprotection process and has been associated to plant tol‐ erance to water stress [22].

#### **2.3. Hormonal regulation**

It is well known that hormones play a special role in plant reaction to water stress condi‐ tions. The abscisic acid (ABA) is the main hormone correlated to water stress. Plants ex‐ posed to drought substantially increase the level of ABA in shoots and roots [24-26], and the ABA positive regulators induce plant response as G protein activation, ROS production, in‐ crease in cytosolic Ca2+, protein phosphorylation and dephosphorylation events and imme‐ diate stomatal closure [27, 28]. Actually the balance of positive and negative ABA regulators actions command the resistance or sensitivity to water scarcity situation. However, the regu‐ lation of stomatal closure occurs not only due the action of ABA, but by the integrated hor‐ monal balance between ABA, Auxin (Ax) and Cytokinin (Ck) [21]. Along with Ck, ABA plays a role in controlling senescence [29, 30]. The high concentration of ABA possibly pre‐ vents excessive accumulation of ethylene (ET), thus indirectly maintaining the growth of roots and shoots [31, 32].

ABA seems to be also involved in remobilize carbon to accelerate grains filling in rice and wheat [29, 30, 33]. The ABA increased level also induce ROS production and in order to pre‐ vent the oxidative stress, antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) are immediately activat‐ ed [34, 35]. The importance of regulating ABA contents as a stress signaling was also ob‐ served in rice leaves when, after a water stress period, plants were rehydrated; decreasing ABA content occurred a reduction on ROS, CAT and SOD [36].

Wheat and maize plants submitted to a moderate water deficit exhibit an increase in ET con‐ centration [27, 37] that would be partly responsible for decreasing growth rates. In contrast for beans, cotton and miniature rose it has been shown that the rate of ethylene production is not affected during progressive drought [27]. ET is also involved in ROS production and antioxidant enzymes synthesis [23].

Cytokinins are generally involved in root and shoot development, but it has been shown an increased cytokinin concentration in leaves, from roots translocation, in plants submitted to water deficit [24, 29, 38]. Bentgrass transgenic plants expressing the enzyme adenine isopen‐ tenyl phosphotransferase for Ck synthesis ligated to a senescence-activated promoter (*SAG12*), resulted in increases in Ck accumulation in the leaves and roots and in the overall plant tolerance to water stress [39].

The gibberellins (GA), Ax and brassinosteroids (BR) do not seem to have a direct involve‐ ment with water stress, however, the accumulation of GA in some dicots has been reported and also the BR along with ABA regulate the development and function of stomata [27]. In contrast in monocots such as maize, there is a decrease in the levels of GA in leaves [25, 27]. The Ax content in plants seems to decrease in roots and leaves under stress, but the impor‐ tance of auxin in water stress response remains inconclusive [24, 25, 27, 40].

The JA instead seems to play a role in the biosynthesis of ABA in water stress. In citrus plants, for example, drought causes an increase of JA concentration in roots with subsequent increase in the concentration of ABA. One can conclude that JA is possibly the precursor in the signal transduction cascade in case of drought stress, providing increased levels of ABA which, in turn, induce later responses [41].

#### **2.4. Morphological and anatomical modifications**

**2.1. Photosynthetic responses**

154 Responses of Organisms to Water Stress

namic of the carboxylation process [8].

erance to water stress [22].

**2.3. Hormonal regulation**

**2.2. Sugar and Reactive Oxygen Species (ROS) protection**

One of the significant alterations responsible for reduction in crop productivity is low pho‐ tosynthetic ability. The water stress may cause decrease in CO2 assimilation in the leaves, the amount of ATP and the level of ribulose bisphosphate [5-8]. Stomatal closure limiting diffusion through stomata and mesophyll is one of the first events in plants response under water deficit situation with consequent increase of the Rubisco enzyme, responsible for CO2 fixation, e in order to overcome the low conductance [9-13]. However, some species (*Gos‐ sypium barbadense, Hypericum balearicum*) show, instead, a decrease in Rubisco activity [13-15]. Furthermore the decrease in CO2 concentration will induce a reduction in the dy‐

The electron transport in thylakoids and the use of trioses phosphates are also reduced in the stress biochemical control therefore, the net photosynthetic rate tends to be lower. It has been proved that in plants subjected to water stress the photochemical efficiency of photo‐ system II (PSII) and quantum generation is reduced [6, 15-17]. Alterations in the level of photosynthetic pigment were also detected in water stressed plants; showing reduced or even no pigmentation. Both chlorophyll *a* and *b* declines in stressed plants and this directly affect plant biomass production. The reduction of photosynthetic pigments will drive a cut down in energy consumption and carbon demand for chlorophyll synthesis [8, 11, 17, 18]. Other pigments such as carotenoids, which play essential role in the antioxidant defense system under stress conditions, can function as an accessory pigment for photosynthesis al‐ though, their concentration can also be reduced as part of plant response [8, 17, 19, 20].

Changes in the content of carbohydrates such as sucrose and raffinose, together with the un‐ balanced of plant hormones function as a signal that plant response to stress should be initi‐ ated [21]. Raffinose has been correlated to a plant tolerance to desiccation, possibly involved in the protection against ROS that are responsible for loss of membrane integrity and cellu‐ lar death [22, 23]. Moreover, induction of sugar accumulation, i. e, sucrose, fructose, maltose and inositol is relevant for the osmoprotection process and has been associated to plant tol‐

It is well known that hormones play a special role in plant reaction to water stress condi‐ tions. The abscisic acid (ABA) is the main hormone correlated to water stress. Plants ex‐ posed to drought substantially increase the level of ABA in shoots and roots [24-26], and the ABA positive regulators induce plant response as G protein activation, ROS production, in‐ crease in cytosolic Ca2+, protein phosphorylation and dephosphorylation events and imme‐ diate stomatal closure [27, 28]. Actually the balance of positive and negative ABA regulators actions command the resistance or sensitivity to water scarcity situation. However, the regu‐ lation of stomatal closure occurs not only due the action of ABA, but by the integrated hor‐ monal balance between ABA, Auxin (Ax) and Cytokinin (Ck) [21]. Along with Ck, ABA

All the known morphological changes that occur in plants under water deficit can be associ‐ ated to hormone actions. Plants develop more roots in order to access more water, increas‐ ing the ratio root/shoot, reduce leaf number and leaf area to lower transpiration rates what leads, unfortunately, to a decrease in photosynthetic rates and biomass production [20, 26, 42] and develop the epinasty/hyponasty effects [43]. The increase of apoplastic pH in the elongation of leaf area could be the responsible for the foliar reduction [44]. The number of lateral seedling roots [17] as well as the stem length can also be affected [20].

The deformation of tracheids in the xylem due to the decrease in osmotic potential [45], the reduction of mitotic activity of mesophyll cells [46], the increase of starch granules in chloro‐ plasts [17, 47] and trichome production, as well as the decrease in cell size and number of stomata per leaf, the thickness of palisade parenchyma are anatomical changes resulting from water stress [7].

can play important role in protecting plant species against oxidative stress caused by wa‐ ter deficit. It is well known that terpenoids possess antioxidative properties. Volatile iso‐ prenoids accumulated in *Hevea brasiliensis* were thought to be involved in scavenging

Water Stress and Agriculture http://dx.doi.org/10.5772/53877 157

Similarly, drought stress markedly enhanced the total concentrations of monoterpenes and resin acids in the main stem wood of Scots Pine and Norway Spruce Seedlings [52]. Results of investigations conducted on the effect of water deficit imposed to potted *Prunella vulgaris* L. a Chinese plant of medicinal and industrial importance, demonstrated increased levels of the phenolic triterpenes rosmarinic acid, ursolic acid and oleanolic acid [53]. Drought also caused increased accumulation of phenolic compounds (ferulic acid) in the leaves of triticale seedlings [54] and enhancement of total phenolic contents of *Trachyspermum ammi* leaves [55]. Investigation conducted with water-stressed cucumber (*Cucumis sativus* L.) demonstrat‐ ed that adverse effects of water stress can be minimized by the application of melatonin which promotes activities of the ROS scavenging enzymes, i.e., superoxide dismutase, per‐ oxidase, and catalase; significantly reduced chlorophyll degradation and stimulates root

Polyamines (PAs) are low molecular weight polycations that have been implicated in a wide range of biological processes in plant growth and development, including environmental stress. The major PAs occurring in plant cells are the diamine putrescine (PUT), triamine spermidine (SPD) and tetramine spermine (SPM). Among the important roles attributed to those plant polyamines are: membrane stabilization and free radicals scavenger action. Poly‐ amine mediated regulation of the water deficit stress response of soybean seedlings was in‐ vestigated using exogenous applications of polyamines and their biosynthetic inhibitors. The exogenous supply of PUT, SPD and SPM to soybean seedlings resulted in reduction of the stress injury in roots which showed increased length and water content over non-treated stressed controls. Moreover, up to 40% increase of shoot growth was observed in seedlings supplemented PUT, SPD and SPM in comparison with controls. In contrast, in the presence of polyamines inhibitors the stress injury intensified, growth was severely inhibited, and water content of roots was significantly decreased. Overall results suggested that polya‐

mines are potentially useful to overcome the detrimental effects of drought [56].

secondary metabolite can be upgraded during drought stress *C. roseus* plants [60].

Water stress is also known to increase the secondary metabolite production in a variety of medicinal plants. Increase of hypericin and betulinic acid levels upon *Hypericum brasiliense* Choisy exposure to drought represents an antioxidant response to ROS production [57, 58]. *Artemisia annua* plants tolerate well water deficit treatments showing increased accumula‐ tion of artemisinin, a potent anti-parasitic drug, as proved in greenhouse experiments. The authors suggested that artemisinin could be part of *A. annua* chemical system of defense against water deficit [59]. Pharmacologically active terpene indole alkaloids production is stimulated in Apocynaceae species in response to water deficit. Comparing *Catharanthus roseus* drought stress plants with well watered controls it was observed significant enrich‐ ment in the antihypertensive drug ajmalicine suggesting that the production of this class of

ROS and potentially in protecting this species against oxidative stress [51].

generation and vitality [17].

## **2.5. C3 and C4 responses**

The response to water deficit may vary from species C3 i.e. *Triticum aestivum* and *Panicum bisulcatum* and C4 i.e. *Zuloagaea bulbosa* and *Zea mays*. Although in the oxidative stress the production of hydrogen peroxide seems to be higher in C3 plants, the C4 plants are much more sensitive to water stress mainly due to stomatal closure and non-stomatal factors such as decreased activity of photosynthesis enzymes, the induction of premature senescence and changes in leaf anatomy [48-50].

## **3. Plant biochemical mechanisms to face water stress**

Drought stress and its detrimental effects on plants in both natural and agricultural environ‐ ments are receiving increasing attention in order to discover alternative solutions to enhance plant vigor and high tolerance; to maintaining crop yields under adverse or extreme climate conditions overcoming economic losses.

#### **3.1. Drought effects: Two sides of the coin**

Contrasting with the negative environmental aspects caused by water stress, the adverse ef‐ fects on agriculture affecting plant growth and crop productivity can be mitigated by meta‐ bolic changes which invigorate the plant biosynthesis of natural products with widespread use by the pharmaceutical, energy and food industries.

#### **3.2. Protective role of secondary metabolites in the plant response and tolerance to water stress**

Plant defense response and tolerance to drought and salinity involves the perception of signal stress by receptors at the membrane level followed by signaling transduction in the cell, inducting a multiplicity of biochemical mechanisms involved in the protective role of secondary metabolites. Water stress reduces plant growth, so the carbon fixed during photosynthesis could be used to form secondary metabolites as established in several studies. Restrictions of water supply to plant bring about the production of a complex variety of secondary metabolites which level can be modulated through bio‐ chemical and genetic manipulation. Water stress induce the accumulation of reactive oxy‐ gen species (ROS), resulting in oxidative stress in the plant cells. Thus, antioxidant secondary metabolites, able to scavenger and detoxify ROS by the availability of –OH, – NH2, and –SH groupings, as well as aromatic nuclei and unsaturated aliphatic chains, can play important role in protecting plant species against oxidative stress caused by wa‐ ter deficit. It is well known that terpenoids possess antioxidative properties. Volatile iso‐ prenoids accumulated in *Hevea brasiliensis* were thought to be involved in scavenging ROS and potentially in protecting this species against oxidative stress [51].

The deformation of tracheids in the xylem due to the decrease in osmotic potential [45], the reduction of mitotic activity of mesophyll cells [46], the increase of starch granules in chloro‐ plasts [17, 47] and trichome production, as well as the decrease in cell size and number of stomata per leaf, the thickness of palisade parenchyma are anatomical changes resulting

The response to water deficit may vary from species C3 i.e. *Triticum aestivum* and *Panicum bisulcatum* and C4 i.e. *Zuloagaea bulbosa* and *Zea mays*. Although in the oxidative stress the production of hydrogen peroxide seems to be higher in C3 plants, the C4 plants are much more sensitive to water stress mainly due to stomatal closure and non-stomatal factors such as decreased activity of photosynthesis enzymes, the induction of premature senescence and

Drought stress and its detrimental effects on plants in both natural and agricultural environ‐ ments are receiving increasing attention in order to discover alternative solutions to enhance plant vigor and high tolerance; to maintaining crop yields under adverse or extreme climate

Contrasting with the negative environmental aspects caused by water stress, the adverse ef‐ fects on agriculture affecting plant growth and crop productivity can be mitigated by meta‐ bolic changes which invigorate the plant biosynthesis of natural products with widespread

**3.2. Protective role of secondary metabolites in the plant response and tolerance to water**

Plant defense response and tolerance to drought and salinity involves the perception of signal stress by receptors at the membrane level followed by signaling transduction in the cell, inducting a multiplicity of biochemical mechanisms involved in the protective role of secondary metabolites. Water stress reduces plant growth, so the carbon fixed during photosynthesis could be used to form secondary metabolites as established in several studies. Restrictions of water supply to plant bring about the production of a complex variety of secondary metabolites which level can be modulated through bio‐ chemical and genetic manipulation. Water stress induce the accumulation of reactive oxy‐ gen species (ROS), resulting in oxidative stress in the plant cells. Thus, antioxidant secondary metabolites, able to scavenger and detoxify ROS by the availability of –OH, – NH2, and –SH groupings, as well as aromatic nuclei and unsaturated aliphatic chains,

**3. Plant biochemical mechanisms to face water stress**

from water stress [7].

**2.5. C3 and C4 responses**

156 Responses of Organisms to Water Stress

changes in leaf anatomy [48-50].

conditions overcoming economic losses.

**stress**

**3.1. Drought effects: Two sides of the coin**

use by the pharmaceutical, energy and food industries.

Similarly, drought stress markedly enhanced the total concentrations of monoterpenes and resin acids in the main stem wood of Scots Pine and Norway Spruce Seedlings [52]. Results of investigations conducted on the effect of water deficit imposed to potted *Prunella vulgaris* L. a Chinese plant of medicinal and industrial importance, demonstrated increased levels of the phenolic triterpenes rosmarinic acid, ursolic acid and oleanolic acid [53]. Drought also caused increased accumulation of phenolic compounds (ferulic acid) in the leaves of triticale seedlings [54] and enhancement of total phenolic contents of *Trachyspermum ammi* leaves [55]. Investigation conducted with water-stressed cucumber (*Cucumis sativus* L.) demonstrat‐ ed that adverse effects of water stress can be minimized by the application of melatonin which promotes activities of the ROS scavenging enzymes, i.e., superoxide dismutase, per‐ oxidase, and catalase; significantly reduced chlorophyll degradation and stimulates root generation and vitality [17].

Polyamines (PAs) are low molecular weight polycations that have been implicated in a wide range of biological processes in plant growth and development, including environmental stress. The major PAs occurring in plant cells are the diamine putrescine (PUT), triamine spermidine (SPD) and tetramine spermine (SPM). Among the important roles attributed to those plant polyamines are: membrane stabilization and free radicals scavenger action. Poly‐ amine mediated regulation of the water deficit stress response of soybean seedlings was in‐ vestigated using exogenous applications of polyamines and their biosynthetic inhibitors. The exogenous supply of PUT, SPD and SPM to soybean seedlings resulted in reduction of the stress injury in roots which showed increased length and water content over non-treated stressed controls. Moreover, up to 40% increase of shoot growth was observed in seedlings supplemented PUT, SPD and SPM in comparison with controls. In contrast, in the presence of polyamines inhibitors the stress injury intensified, growth was severely inhibited, and water content of roots was significantly decreased. Overall results suggested that polya‐ mines are potentially useful to overcome the detrimental effects of drought [56].

Water stress is also known to increase the secondary metabolite production in a variety of medicinal plants. Increase of hypericin and betulinic acid levels upon *Hypericum brasiliense* Choisy exposure to drought represents an antioxidant response to ROS production [57, 58]. *Artemisia annua* plants tolerate well water deficit treatments showing increased accumula‐ tion of artemisinin, a potent anti-parasitic drug, as proved in greenhouse experiments. The authors suggested that artemisinin could be part of *A. annua* chemical system of defense against water deficit [59]. Pharmacologically active terpene indole alkaloids production is stimulated in Apocynaceae species in response to water deficit. Comparing *Catharanthus roseus* drought stress plants with well watered controls it was observed significant enrich‐ ment in the antihypertensive drug ajmalicine suggesting that the production of this class of secondary metabolite can be upgraded during drought stress *C. roseus* plants [60].

The main physiological and biochemical known mechanisms triggered by water stressed plants are illustrated in Figure 2.

Besides the oil production, Jatropha species are source of jatrophone and jatropholone, macrocyclic diterpenoids, secondary metabolites that display varied pharmacological ac‐

Water Stress and Agriculture http://dx.doi.org/10.5772/53877 159

Based on the high quality of the oil, and on the fact that some varieties show oil concentra‐ tions of up to 9.5%, quinoa could be considered as a potentially valuable new oil crop [66]. Quinoa is currently grown for its grain in the South American countries of Peru, Bolivia, Ecua‐ dor, Argentina, Chile and Colombia. Quinoa populations display a high degree of genetic dis‐ tancing, and variable tolerance to salinity. Cultivars of quinoa can be adapted to growth from sea level to an altitude of 4,000 m, from 40°S to 2°N latitude, and from the cold highland climate to subtropical conditions, i.e. quinoa plant is cold and drought tolerant. The plasticity of quinoa biochemical response to a wide range of environmental conditions makes it possible to select, adapt, and breed cultivars [67]. Studies have shown that quinoa is a very good source of antioxi‐ dants and it can be a substitute for common cereals [68, 69]. The content of total phenolic com‐ pounds and the correlated radical scavenging activity of quinoa varieties have been analyzed. There were significant differences between the varieties and the content of total polyphenols [70]. Moreover, the saponins obtained as a by-product in the processing of quinoa grain can be

Polyphenols and carotenoids compounds with reactive oxygen species (ROS)-scavenging ability biosynthesized in drought tolerance Cotton genotypes were correlated to the drought

In order to cope with the major environmental problems that affect crops such as drought, salinity, cold and heat shock, genetic engineering and breeding techniques have become fundamental tools, as they have been for decades regarding biotic stresses, pests and diseas‐ es resistance. It is well known that very often an adversity results in another unfavorable condition for the development of a crop, for example high temperatures provoke water defi‐

Biotechnological approaches focused on secondary metabolism pathways induction or re‐ pression at the transcriptional level are now being conducted to significantly improve plant

Considering all climate changes that the planet is going through it is vital the development of crops with high efficiency in water recovery and consequently tolerance to water stress,

cit reducing soil moisture resulting in salinity problems and desertification.

tolerance to water deficit, extreme temperatures and ion imbalance.

utilized by the cosmetics and pharmaceutical industries.

tolerance of this important crop [71].

**4. What have been done?**

**4.1. Breeding crops**

tivities [64, 65].

*3.3.2. Quinoa*

*3.3.3. Cotton*

**Figure 2.** Plant global response to cope with water deficit, high temperature and salinity.

#### **3.3. Sustainable exploitation of cultured drought-resistant plants**

#### *3.3.1. Oilseed crops: Biofuel production*

Recently, considerable attention has been given to biofuels as an alternative to fossil fuels and the challenge is to find oil bearing plants that produce non-edible oils as the feedstock for biodiesel production. Jatropha (*Jatropha curcas* L.) popularly known in Brazil as "pinhão manso" is a drought resistant perennial tree widespread in arid, semi-arid and tropical re‐ gions of the world and requires a minimum rainfall of 250 mm [61]. Native grown in mar‐ ginal and waste lands is one of the potential plant species to be exploited as a new source of oil for biodiesel production. Jatropha represents great promise to the energy economy of de‐ veloping, as well as developed countries. It has been reported that new and large markets for biodiesel demand are expected to emerge in China, India and Brazil [62]. In those coun‐ tries farmers have started to produce Jatropha for biodiesel production. The Jatropha seed is particularly suitable for biodiesel production because it can be harvested in the third year of plantation five or six times annually. Diesel consumption in Brazil is about 40 billion liters per year, providing huge opportunities for biodiesel production, and it is estimated that by 2013 the biodiesel market will be approximately 2 billion liters [63].

Besides the oil production, Jatropha species are source of jatrophone and jatropholone, macrocyclic diterpenoids, secondary metabolites that display varied pharmacological ac‐ tivities [64, 65].

## *3.3.2. Quinoa*

The main physiological and biochemical known mechanisms triggered by water stressed

**Figure 2.** Plant global response to cope with water deficit, high temperature and salinity.

Recently, considerable attention has been given to biofuels as an alternative to fossil fuels and the challenge is to find oil bearing plants that produce non-edible oils as the feedstock for biodiesel production. Jatropha (*Jatropha curcas* L.) popularly known in Brazil as "pinhão manso" is a drought resistant perennial tree widespread in arid, semi-arid and tropical re‐ gions of the world and requires a minimum rainfall of 250 mm [61]. Native grown in mar‐ ginal and waste lands is one of the potential plant species to be exploited as a new source of oil for biodiesel production. Jatropha represents great promise to the energy economy of de‐ veloping, as well as developed countries. It has been reported that new and large markets for biodiesel demand are expected to emerge in China, India and Brazil [62]. In those coun‐ tries farmers have started to produce Jatropha for biodiesel production. The Jatropha seed is particularly suitable for biodiesel production because it can be harvested in the third year of plantation five or six times annually. Diesel consumption in Brazil is about 40 billion liters per year, providing huge opportunities for biodiesel production, and it is estimated that by

**3.3. Sustainable exploitation of cultured drought-resistant plants**

2013 the biodiesel market will be approximately 2 billion liters [63].

*3.3.1. Oilseed crops: Biofuel production*

plants are illustrated in Figure 2.

158 Responses of Organisms to Water Stress

Based on the high quality of the oil, and on the fact that some varieties show oil concentra‐ tions of up to 9.5%, quinoa could be considered as a potentially valuable new oil crop [66].

Quinoa is currently grown for its grain in the South American countries of Peru, Bolivia, Ecua‐ dor, Argentina, Chile and Colombia. Quinoa populations display a high degree of genetic dis‐ tancing, and variable tolerance to salinity. Cultivars of quinoa can be adapted to growth from sea level to an altitude of 4,000 m, from 40°S to 2°N latitude, and from the cold highland climate to subtropical conditions, i.e. quinoa plant is cold and drought tolerant. The plasticity of quinoa biochemical response to a wide range of environmental conditions makes it possible to select, adapt, and breed cultivars [67]. Studies have shown that quinoa is a very good source of antioxi‐ dants and it can be a substitute for common cereals [68, 69]. The content of total phenolic com‐ pounds and the correlated radical scavenging activity of quinoa varieties have been analyzed. There were significant differences between the varieties and the content of total polyphenols [70]. Moreover, the saponins obtained as a by-product in the processing of quinoa grain can be utilized by the cosmetics and pharmaceutical industries.

## *3.3.3. Cotton*

Polyphenols and carotenoids compounds with reactive oxygen species (ROS)-scavenging ability biosynthesized in drought tolerance Cotton genotypes were correlated to the drought tolerance of this important crop [71].

## **4. What have been done?**

In order to cope with the major environmental problems that affect crops such as drought, salinity, cold and heat shock, genetic engineering and breeding techniques have become fundamental tools, as they have been for decades regarding biotic stresses, pests and diseas‐ es resistance. It is well known that very often an adversity results in another unfavorable condition for the development of a crop, for example high temperatures provoke water defi‐ cit reducing soil moisture resulting in salinity problems and desertification.

Biotechnological approaches focused on secondary metabolism pathways induction or re‐ pression at the transcriptional level are now being conducted to significantly improve plant tolerance to water deficit, extreme temperatures and ion imbalance.

#### **4.1. Breeding crops**

Considering all climate changes that the planet is going through it is vital the development of crops with high efficiency in water recovery and consequently tolerance to water stress, higher temperatures, salinity and desertification. Through conventional breeding methods and selection based in progeny tests it was possible to obtain stress resistant varieties [72], but it has to be considered that instability of genotypes in different environments may affect the cultivars agronomic performance.

sponded differently to stress. Morphological changes occurred, but some genes may repre‐ sent the difference between tolerance and sensitivity, as the S-adenosylmethionein decarboxylase (SAMDC) and induced cinnamoyl-CoA reductase (CCR) in resistant cultivars

Water Stress and Agriculture http://dx.doi.org/10.5772/53877 161

The expression of some sugarcane water-stress related genes and their association with su‐ crose accumulation was also investigated and a group of stress-induced genes that could be associated with sucrose accumulation were identified, showing that genes associated with the synthesis of proline are associated with stress and sucrose accumulation. Stress-related transcription factors and sugar transporter also play a role in sucrose accumulation [82].

For better understanding the processes and genes involved in water deficit tolerance it is re‐ quired a full knowledge of the molecular principles that regulate plant responses to stress conditions. Thus, studies with model plants stand for and will continue to represent a rele‐ vant strategy for the elucidation of signaling and transcription processes using molecular

Genes isolated from several cultured species have been the focus of researches using gene expression in model plants with the objective of elucidating their direct effect on abiotic stress tolerance. Genetic transformation of plants in order to increase resistance is often based on the manipulation of genes to preserve the function and structure of cellular com‐ ponents [84]. In this context, the genetic engineering techniques for pest and herbicide resist‐ ance differ from the procedures for abiotic stress tolerance, since the first is a monogenic trait, more easily manipulated. In contrast, tolerance to environmental stresses may asso‐

The expression of *SPCP2* that encodes the putative papain-like cysteine protease isolated from senescent leaves of sweet potato has been studied in transgenic Arabidopsis plants subjected to stress conditions and has shown very interesting results. Firstly, changes in phenotypic characteristics were noted, such as alterations in the development of seeds and silique resulting in greater incompatibility and lower production and seed germination. Fur‐ thermore, *SPCP2* gene expression caused early transition from vegetative to reproductive stage and foliar senescence, indicating that the gene is associated with senescence. Results also indicated that the gene expression was induced by darkness, ethephon, abiscisc acid (ABA) and jasmonic acid (JA). However, tolerance to salinity and drought stress was in‐

Many of these genes encode proteins involved in signaling pathways, including protein kin‐ ases mitogen-activated (MAPKs), histidine kinases, protein kinase Ca2+ dependent (CDPKs),

The association of three genes *SRK2D, SRK2E* and *SRK2I* in ABA signaling and in water stress tolerance, since their gene products were found to be involved in ABRE-protein phos‐ phorylation (ABA responsive element) and ABA signaling during germination and root de‐ velopment and at stomatal level was reported [88]. Genetic transformation and genetic

or lipid transfer protein that have been repressed, as well as other genes [81].

ciate more than one of the genes involved in different signaling pathways.

family SOS3 sensors Ca2+ as well as transcription factors [86, 87].

genetics techniques [79, 83].

creased [85].

*4.2.1. Signaling genes*

Researchers consider that genetic improvement for stress tolerance can be achieved in two ways: directly, through the evaluation of primary features in the target environment, i.e. as productivity (empirical breeding); or indirectly (analytical breeding), through secondary characteristics related to stress adaptation observed in crops growing in limiting environ‐ ment. Over the past 50 years genetic improvement have been carried out empirically, how‐ ever, this type of traditional selection has not presented significant efficiency in terms of productivity, requiring the support of indirect selection [73]. The selection of genotypes with promising agronomic characteristics and tolerant to abiotic stresses demands successive sea‐ sonal evaluations of field cultures conducted in different locations, and under influence of stress agents, requesting arduous and extensive work.

Furthermore, it is important to highlight that the low heritability of complex traits have lim‐ ited the development of tolerant cultivars due to significant G x E interaction and the QTLby-environment interaction (QTL x E), and the trivial understanding of the physiological parameters related to the genetic yield potential in dry environments [73]. Biotechnology plays an important role for managing abiotic stress, allowing the exploitation of large germ‐ plasm collections with no need of experimental procedures under unfavorable environmen‐ tal conditions [74].

## **4.2. Which genes are involved in plant responses?**

Lately, much has been done to identify and isolate drought-induced genes in order to inves‐ tigate the role those gene products play and the paths for induction of those genes [75, 76]. Gene expression in response to water stress can enhance the plant's ability to respond ap‐ propriately to the deleterious effect of drought, stimulating its aptitude to survive desertifi‐ cation [77]. In general, the stress-induced gene products can be classified in two ways: genes that directly protect the plant against stress and genes that regulate the expression of other genes [78, 79].

Through analysis of transcripts it was observed that the genes exhibit distinct expression profiles, being that stress-induced gene decrease mRNA levels when the plants are freed from stress conditions. However, the expression patterns of those genes are complex, with some genes responding very quickly to water deficit while others answer very slowly after the accumulation of ABA (abscisic acid) [80].

The differential gene expression analysis of two sugar cane cultivars, tolerant and sensitive to drought, showed that the number of genes expressed in the sensitive cultivar increased with the severity of the drought. Comparing the gene expression profiles 91 common genes were found among both cultivars, most of them drought-induced genes that are still un‐ known. Moreover, genes of important pathways related to drought stress were suppressed in sensitive plants. It was evidenced that plants submitted to the same water conditions re‐ sponded differently to stress. Morphological changes occurred, but some genes may repre‐ sent the difference between tolerance and sensitivity, as the S-adenosylmethionein decarboxylase (SAMDC) and induced cinnamoyl-CoA reductase (CCR) in resistant cultivars or lipid transfer protein that have been repressed, as well as other genes [81].

The expression of some sugarcane water-stress related genes and their association with su‐ crose accumulation was also investigated and a group of stress-induced genes that could be associated with sucrose accumulation were identified, showing that genes associated with the synthesis of proline are associated with stress and sucrose accumulation. Stress-related transcription factors and sugar transporter also play a role in sucrose accumulation [82].

For better understanding the processes and genes involved in water deficit tolerance it is re‐ quired a full knowledge of the molecular principles that regulate plant responses to stress conditions. Thus, studies with model plants stand for and will continue to represent a rele‐ vant strategy for the elucidation of signaling and transcription processes using molecular genetics techniques [79, 83].

Genes isolated from several cultured species have been the focus of researches using gene expression in model plants with the objective of elucidating their direct effect on abiotic stress tolerance. Genetic transformation of plants in order to increase resistance is often based on the manipulation of genes to preserve the function and structure of cellular com‐ ponents [84]. In this context, the genetic engineering techniques for pest and herbicide resist‐ ance differ from the procedures for abiotic stress tolerance, since the first is a monogenic trait, more easily manipulated. In contrast, tolerance to environmental stresses may asso‐ ciate more than one of the genes involved in different signaling pathways.

The expression of *SPCP2* that encodes the putative papain-like cysteine protease isolated from senescent leaves of sweet potato has been studied in transgenic Arabidopsis plants subjected to stress conditions and has shown very interesting results. Firstly, changes in phenotypic characteristics were noted, such as alterations in the development of seeds and silique resulting in greater incompatibility and lower production and seed germination. Fur‐ thermore, *SPCP2* gene expression caused early transition from vegetative to reproductive stage and foliar senescence, indicating that the gene is associated with senescence. Results also indicated that the gene expression was induced by darkness, ethephon, abiscisc acid (ABA) and jasmonic acid (JA). However, tolerance to salinity and drought stress was in‐ creased [85].

#### *4.2.1. Signaling genes*

higher temperatures, salinity and desertification. Through conventional breeding methods and selection based in progeny tests it was possible to obtain stress resistant varieties [72], but it has to be considered that instability of genotypes in different environments may affect

Researchers consider that genetic improvement for stress tolerance can be achieved in two ways: directly, through the evaluation of primary features in the target environment, i.e. as productivity (empirical breeding); or indirectly (analytical breeding), through secondary characteristics related to stress adaptation observed in crops growing in limiting environ‐ ment. Over the past 50 years genetic improvement have been carried out empirically, how‐ ever, this type of traditional selection has not presented significant efficiency in terms of productivity, requiring the support of indirect selection [73]. The selection of genotypes with promising agronomic characteristics and tolerant to abiotic stresses demands successive sea‐ sonal evaluations of field cultures conducted in different locations, and under influence of

Furthermore, it is important to highlight that the low heritability of complex traits have lim‐ ited the development of tolerant cultivars due to significant G x E interaction and the QTLby-environment interaction (QTL x E), and the trivial understanding of the physiological parameters related to the genetic yield potential in dry environments [73]. Biotechnology plays an important role for managing abiotic stress, allowing the exploitation of large germ‐ plasm collections with no need of experimental procedures under unfavorable environmen‐

Lately, much has been done to identify and isolate drought-induced genes in order to inves‐ tigate the role those gene products play and the paths for induction of those genes [75, 76]. Gene expression in response to water stress can enhance the plant's ability to respond ap‐ propriately to the deleterious effect of drought, stimulating its aptitude to survive desertifi‐ cation [77]. In general, the stress-induced gene products can be classified in two ways: genes that directly protect the plant against stress and genes that regulate the expression of other

Through analysis of transcripts it was observed that the genes exhibit distinct expression profiles, being that stress-induced gene decrease mRNA levels when the plants are freed from stress conditions. However, the expression patterns of those genes are complex, with some genes responding very quickly to water deficit while others answer very slowly after

The differential gene expression analysis of two sugar cane cultivars, tolerant and sensitive to drought, showed that the number of genes expressed in the sensitive cultivar increased with the severity of the drought. Comparing the gene expression profiles 91 common genes were found among both cultivars, most of them drought-induced genes that are still un‐ known. Moreover, genes of important pathways related to drought stress were suppressed in sensitive plants. It was evidenced that plants submitted to the same water conditions re‐

the cultivars agronomic performance.

160 Responses of Organisms to Water Stress

tal conditions [74].

genes [78, 79].

stress agents, requesting arduous and extensive work.

**4.2. Which genes are involved in plant responses?**

the accumulation of ABA (abscisic acid) [80].

Many of these genes encode proteins involved in signaling pathways, including protein kin‐ ases mitogen-activated (MAPKs), histidine kinases, protein kinase Ca2+ dependent (CDPKs), family SOS3 sensors Ca2+ as well as transcription factors [86, 87].

The association of three genes *SRK2D, SRK2E* and *SRK2I* in ABA signaling and in water stress tolerance, since their gene products were found to be involved in ABRE-protein phos‐ phorylation (ABA responsive element) and ABA signaling during germination and root de‐ velopment and at stomatal level was reported [88]. Genetic transformation and genetic crosses carried out to obtain double and triple mutants of Arabidopsis plants subsequently subjected to drought tolerance bioassay, showed that only the triple mutant plants (srk2d/e/i) died after seven days of water suppression, while all other mutants and wild type plants survived to maturity after rehydration. Obtained results suggest that the triple mutation completely blocks the ABA signaling and greatly affect the expression of various ABA/stress-responsive genes previously identified. Moreover, many osmotic stress marker genes (*KIN2, RD20,* and *COR15A RD29B*) are regulated by transcription factors that are con‐ trolled by protein kinases SRK2D/E/I that can act on ABA dependent and independent path‐ ways in response to water stress.

that *TSRF1* increased resistance to pathogens in tomato and tobacco plants, but reduced os‐

The *sodERF3* another sugarcane TF, was also characterized, after *in silico* analyses of sugar‐ cane cDNA sequence and the similarity of its 201 aa encoded proteins of the superfamily of ERF transcription factors was confirmed. A bioassay revealed that transgenic tobacco plants expressing the gene *sodERF3* showed to be tolerant to drought and osmotic stress. Further‐ more, it was observed the gene induction in response to salt stress injuries and treatment

Additionally, the soybean *GmERF3* TF from the *AP2/ERF* family was evaluated in transgenic tobacco plants and promoted tolerance to drought, salinity and disease. Furthermore, the gene expression was induced by salinity, desertification and treatments with salicylic acid (AS), ethylene (ET), JA and ABA. However, the cold stress did not affect gene expression. Thus, it is possible to assume that the *GmERF3* transcription factor plays a role in the re‐

It is evident the relevance of studying and elucidating the role of genes putatively related to water stress tolerance. In this context the molecular biology and the plant biotechnology comprise an efficient and helpful tool to achieve cultivars tolerant to environmental stresses

Currently private companies have invested heavily in biotechnological programs for libera‐ tion of cultivars tolerant to insects, herbicides and drought. GMOs have been commercially cultivated since the 90's, tolerance to herbicides and insects are the main features of GM crops, including maize, soybean, cotton, canola, rice, tomato, etc. Some crops that has been transformed using genetic engineering technology to receive genes which metabolic func‐ tion are related to water stress response are listed in Table 1. Genes involved in osmoprotec‐ tion, ABA responsive elements and Transcription factors have been used to generate more resistant plants. Soybean, maize, rice, cotton and tomato are the most denoted transgenic

**Gene Gene function Metabolic Functions Specie References**

under drought stress

Maintenance of osmotic potential

Salinity tolerance *Daucus carota*

*Adc* Polyamine synthesis Drought resistance *Oryza sativa* [97]

*Oryza sativa* [96]

*lycopersicum* [98]

[99]

Water Stress and Agriculture http://dx.doi.org/10.5772/53877 163

*Solanum*

that are gradually responsible for production losses all over the world.

motic tolerance in tobacco.

sponses to biotic and abiotic stresses [95].

*4.2.3. Genetic modified crops using genetic engineering*

*adc* Arginine decarboxylase Reduced chlorophyll loss

*badh-1* Betaine aldehyde

*badh-1* Betaine aldehyde

dehydrogenase

dehydrogenase

with ABA [94].

crops.

Transgenic sugarcane plants overexpressing heterologous *P5CS* genes, responsible for the production of proline a protein commonly induced under stress conditions, revealed toler‐ ance to severe water deficit, not as a mediator of osmotic adjustment, but as a component of the antioxidant defense system [89].

In the same way, after detecting the up-regulated expression of two maize putatives PIS in response to drought, one of them, the *ZmPIS* gene was over-expressed in tobacco plants showing to enhance drought tolerance, since it increased the membrane integrity and de‐ creased the solute loss. The PIS gene is involved on the synthesis of phosphatidylinositol, an important lipid that functions as a key membrane constituent [90].

Remarkable results were observed with the *Arabidopsis* vacuolar pyrophosphatase gene (*AVP1*) over-expressed in cotton, which improved drought and salt tolerance in greenhouse conditions, and also increased fiber yield in dry land field conditions. Moreover, it was ob‐ served larger root systems and enhanced shoot biomass compared to controls when cul‐ tured under saline or reduced irrigation conditions [91].

#### *4.2.2. Transcriptional factors genes*

Transcription factors (TFs) have been extensively studied and have shown to be important in the regulation of stress tolerance in plants. The TFs are proteins that play a role in physio‐ logical and biological processes such as growth, development and responses to environmen‐ tal stresses acting as key regulators involved in early stages of expression, gene regulation, signal transduction [92].

The TF *MYB15*, a member of the Arabidopsis *R2R3 MYB* family showed interesting results in studies carried out with Arabidopsis transgenic plants over-expressing the gene. It was found that the *MYB15* positively regulated tolerance to drought and salinity, inversely to what was observed in studies of freezing tolerance. Furthermore, the *MYB15* gene was found to be induced by treatment with ABA and salinity and drought conditions [83].

In *Oriza sativa* [93] reported that the gene *TSRF1* TF, a protein ERF (ethylene-responsive fac‐ tor), when overexpressed increased drought and osmotic tolerance of transgenic rice plants, without affecting plant development. It also increased the sensitivity to ABA treatment, in‐ creased the content of proline and soluble sugars and the expression of genes related to re‐ sponses to stress and photosynthesis. Curiously, in previous studies, the authors observed that *TSRF1* increased resistance to pathogens in tomato and tobacco plants, but reduced os‐ motic tolerance in tobacco.

The *sodERF3* another sugarcane TF, was also characterized, after *in silico* analyses of sugar‐ cane cDNA sequence and the similarity of its 201 aa encoded proteins of the superfamily of ERF transcription factors was confirmed. A bioassay revealed that transgenic tobacco plants expressing the gene *sodERF3* showed to be tolerant to drought and osmotic stress. Further‐ more, it was observed the gene induction in response to salt stress injuries and treatment with ABA [94].

Additionally, the soybean *GmERF3* TF from the *AP2/ERF* family was evaluated in transgenic tobacco plants and promoted tolerance to drought, salinity and disease. Furthermore, the gene expression was induced by salinity, desertification and treatments with salicylic acid (AS), ethylene (ET), JA and ABA. However, the cold stress did not affect gene expression. Thus, it is possible to assume that the *GmERF3* transcription factor plays a role in the re‐ sponses to biotic and abiotic stresses [95].

It is evident the relevance of studying and elucidating the role of genes putatively related to water stress tolerance. In this context the molecular biology and the plant biotechnology comprise an efficient and helpful tool to achieve cultivars tolerant to environmental stresses that are gradually responsible for production losses all over the world.

#### *4.2.3. Genetic modified crops using genetic engineering*

crosses carried out to obtain double and triple mutants of Arabidopsis plants subsequently subjected to drought tolerance bioassay, showed that only the triple mutant plants (srk2d/e/i) died after seven days of water suppression, while all other mutants and wild type plants survived to maturity after rehydration. Obtained results suggest that the triple mutation completely blocks the ABA signaling and greatly affect the expression of various ABA/stress-responsive genes previously identified. Moreover, many osmotic stress marker genes (*KIN2, RD20,* and *COR15A RD29B*) are regulated by transcription factors that are con‐ trolled by protein kinases SRK2D/E/I that can act on ABA dependent and independent path‐

Transgenic sugarcane plants overexpressing heterologous *P5CS* genes, responsible for the production of proline a protein commonly induced under stress conditions, revealed toler‐ ance to severe water deficit, not as a mediator of osmotic adjustment, but as a component of

In the same way, after detecting the up-regulated expression of two maize putatives PIS in response to drought, one of them, the *ZmPIS* gene was over-expressed in tobacco plants showing to enhance drought tolerance, since it increased the membrane integrity and de‐ creased the solute loss. The PIS gene is involved on the synthesis of phosphatidylinositol, an

Remarkable results were observed with the *Arabidopsis* vacuolar pyrophosphatase gene (*AVP1*) over-expressed in cotton, which improved drought and salt tolerance in greenhouse conditions, and also increased fiber yield in dry land field conditions. Moreover, it was ob‐ served larger root systems and enhanced shoot biomass compared to controls when cul‐

Transcription factors (TFs) have been extensively studied and have shown to be important in the regulation of stress tolerance in plants. The TFs are proteins that play a role in physio‐ logical and biological processes such as growth, development and responses to environmen‐ tal stresses acting as key regulators involved in early stages of expression, gene regulation,

The TF *MYB15*, a member of the Arabidopsis *R2R3 MYB* family showed interesting results in studies carried out with Arabidopsis transgenic plants over-expressing the gene. It was found that the *MYB15* positively regulated tolerance to drought and salinity, inversely to what was observed in studies of freezing tolerance. Furthermore, the *MYB15* gene was found to be induced by treatment with ABA and salinity and drought conditions [83].

In *Oriza sativa* [93] reported that the gene *TSRF1* TF, a protein ERF (ethylene-responsive fac‐ tor), when overexpressed increased drought and osmotic tolerance of transgenic rice plants, without affecting plant development. It also increased the sensitivity to ABA treatment, in‐ creased the content of proline and soluble sugars and the expression of genes related to re‐ sponses to stress and photosynthesis. Curiously, in previous studies, the authors observed

important lipid that functions as a key membrane constituent [90].

tured under saline or reduced irrigation conditions [91].

ways in response to water stress.

162 Responses of Organisms to Water Stress

the antioxidant defense system [89].

*4.2.2. Transcriptional factors genes*

signal transduction [92].

Currently private companies have invested heavily in biotechnological programs for libera‐ tion of cultivars tolerant to insects, herbicides and drought. GMOs have been commercially cultivated since the 90's, tolerance to herbicides and insects are the main features of GM crops, including maize, soybean, cotton, canola, rice, tomato, etc. Some crops that has been transformed using genetic engineering technology to receive genes which metabolic func‐ tion are related to water stress response are listed in Table 1. Genes involved in osmoprotec‐ tion, ABA responsive elements and Transcription factors have been used to generate more resistant plants. Soybean, maize, rice, cotton and tomato are the most denoted transgenic crops.



**Gene Gene function Metabolic Functions Specie References**

accumulation at low water status

tolerance

stress Tolerance

drought stress

plant

cell membrane Stability

tolerance

under stress

and yield under field drought conditions

the field

potential and transpiration under 10 h PEG stress

Salt tolerance in photosynthesis and yield

Salt tolerance, growth, fruit yield

Salt tolerance for grain yield in the field

improved K+/Na+ ratio

*abf3* Transcription factor Drought resistance *Oryza sativa* [128]

Polyamine accumulation and salt resistance in biomass accumulation

*Solanum tuberosum*

*Solanum*

*Avena sativa*

*Avena sativa*

*Triticum vulgare*

*Oryza sativa*

*Solanum*

*Oryza saitva*

*Oryza sativa* [114]

*lycopersicum* [115]

*Oryza saitva* [118]

*Oryza saitva* [119]

*Triticum vulgare* [120]

*Oryza sativa* [122]

*Gossypium hirsutum* [124]

*lycopersicum* [125]

*Triticum vulgare* [126]

*Triticum vulgare* [127]

[113]

Water Stress and Agriculture http://dx.doi.org/10.5772/53877 165

[116]

[117]

[121]

[123]

[129]

*sst/fft* Fructan accumulation Reduced proline

*tpsp* Trehalose synthesis Drought, salt and cold

*tps1* Trehalose synthesis Drought, salt and oxidative

*hva1* Group 3 LEA protein gene Delayed wilting under

*hva1* Group 3 LEA protein gene Salinity tolerance in yield/

*hva1* Group 3 LEA protein gene Dehydration avoidance and

*hva1* Group 3 LEA protein gene Increased biomass and WUE

*hva1* Group 3 LEA protein gene Improved plant water status

*OsLEA3-1* Lea protein Drought resistance for yield in

*rwc3* Aquaporin overexpression Maintenance of leaf water

*hkt1* Potassium transporter Salt tolerance in growth and

*atnhx1* Vacuolar Na+/H+

*atnhx1* Vacuolar Na+/H+

*atnhx1* Vacuolar Na+/H+

*adc* Arginine decarboxylase

antiporter

antiporter

antiporter

overexpression

*hva1* Group 3 LEA protein gene Drought and salinity


**Gene Gene function Metabolic Functions Specie References**

Drought resistance at seedling stage and high yield after drought

Tolerance to stress induced photo inhibition

Increased tolerance to salinity and cold

Recovery from a week long salt stress

Increased salinity resistance and chilling tolerance

High salt tolerance due to mannitol and glucitol accumulation

Drought and salinity tolerance of calli and plants

Osmotic adjustment and drought Resistance

Increased biomass production under drought and salinity stress

Reduced oxidative stress under osmotic stress

Drought resistance, high RWC, high proline

Drought resistance via antioxidant role of proline *Zea mays*

Salt and stress tolerance *Oryza sativa* [104]

*Pinus taeda*

*Triticum vulgare*

*Citrus*

*Oryza sativa*

*Oryza sativa*

*Glycine max*

*Saccharum spp.*

Salinity tolerance *Solanum tuberosum*

*Brassica juncea* [101]

*Oryza sativa* [102]

*Oryza sativa* [103]

*Oryza sativa* [105]

[100]

[106]

[107]

[108]

[109]

[110]

[111]

[112]

[89]

*betA* Choline dehydrogenase

164 Responses of Organisms to Water Stress

*codA* Choline oxidase (glycine

*codA* Choline oxidase (glycine

*codA* Choline oxidase (glycine

*cox* Choline oxidase (glycine

*gs2* Chloroplastic glutamine

*mt1D* Mannitol-1-phosphate

*p5cs* Pyrroline carboxylate

*p5cs* Pyrroline carboxylate

*p5cs* Pyrroline carboxylate

*p5cs* Pyrroline carboxylate

*p5cs* Pyrroline carboxylate

*p5cs* Pyrroline carboxylate

*mt1D and GutD*

(glycinebetaine synthesis)

betaine synthesis)

betaine synthesis)

betaine synthesis)

betaine synthesis)

synthetase

Mannitol-1-phosphate dehydrogenase & glucitol-6-phosphate dehydrogenase

dehydrogenase (mannitol synthesis)

> synthase (proline synthesis)

> synthase (proline synthesis)

> synthase (proline synthesis)

> synthase (proline synthesis)

> synthase (proline synthesis)

> synthase (proline synthesis)


**5. Concluding remarks**

high temperature.

**Acknowledgements**

The global warming is a reality that we have to face and in order to provide food to the growing population some actions have to be taken by government and researchers. The development of new cultivars more resistant to the environmental conditions, for every crop, must be a priority, in order to guarantee food demand security. To avoid yield re‐ ductions from floods, droughts and rising temperatures agribusiness will have to be re‐ considered, investments have to be done, researchers will have to focus on ways to improve food quality, nutritional composition and increase yield using less land for farming. Crops will have to grow under a different scenario including less water and

Water Stress and Agriculture http://dx.doi.org/10.5772/53877 167

As it was discussed in this chapter changes in climate conditions will require several plant adaptations in order to minimize decreases in crop yield and to maintain food ac‐ cessibility. Genetic breeding has been used over the last decades to improve yield and food quality. But how much can we still get from traditional plant breeding programs re‐ garding to improve plants to face water scarcity? It is time to adopt new technologies as genetic engineering to help breeders in generating more adapted plants to survive water stress. For several years researchers have been spending time to understand how plants adapt to different situations, understanding the physiological parameters and their role in plants response to water stress specially hormones and transcriptional factors can help the development of new cultivars more resistant to stress conditions. All this knowledge allied to molecular biology techniques and genetic engineering can promote the develop‐ ment of transgenic plants with higher product quality, better storage conditions, easer

Nowadays, transgenic crops are cultivated all over the world, but there are some re‐ mains questions: How much are farmers dependent on biotechnology companies? Which economic and cultural losses transgenic cultures will bring about? These subjects are still extensively debated and researchers do not know for sure what is ahead. In the specific case of drought tolerance, much has been discussed about genetic engineering and ex‐

The authors are grateful to: Fundação do Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq) and Universidade de Ribeirão Preto (UNAERP) for the constant financial support and also to

Ms Rosane Castro França for her precious help during this chapter organization.

processing, more efficient and more resistant to extreme conditions.

perts consider the biotechnology relevant in developing higher genotypes.

**Table 1.** Genes, gene function, metabolic function and transgenic.

## **5. Concluding remarks**

**Gene Gene function Metabolic Functions Specie References**

tolerance with reduced growth under non-stress

drought stress

transpiration and greater root hydraulic conductance

stress and exogenous ABA

expressed drought induced Senescence

related to protein degradation for nutrient remobilization during leaf senescence

> ABRE protein phosphorylation

ABA responses, salinity and drought conditions tolerance

ABA responses , accumulation of proline and soluble sugars content, induction of genes related to responses to stress and photosynthesis

Drought, osmotic stress, salt stress injuries and treatment with ABA

Responses against biotic and abiotic stresses

Membrane protection *Nicotiana tabacum*

Proton pump activity *Gossypium hirsutum* [91]

*Oryza sativa*

*Solanum*

*Solanum*

*Zea mays*

*Ipoema batatas*

*Triticum vulgare* [131]

*lycopersicum* [132]

*lycopersicum* [133]

*Arabidopsis thaliana* [88]

*Arabidopsis thaliana* [83]

*Oryza sativa*

*Nicotiana tabacum*

*Nicotiana tabacum*

[130]

[134]

[85]

[90]

[93]

[94]

[95]

Transcription factor Drought, salt and cold

*dreb1a* Transcription factor Delayed wilting under

*sp12 and sp5* ABA overproduction High water-use efficiency, low

*tos1* Increased ABA sensitivity Hypersensitive to osmotic

*ZmACS6* Ethylene synthesis Non-functional mutant

*spcp2* putative papain-like

*zmpis* Phosphatidylinositol

*myb15* Transcription factor (R2R3

*tsrf1* Protein ERF (ethylene-

*soderf3* Sugarcane ERF

*ap2/erf* Soybean transcription

LEA Later embryogenesis abundant proteins

*avp1* Vacuolar

cysteine protease

ABA signaling (ABA responsive element)

synthesis

pyrophosphatase gene

MYB family member)

responsive factor)

transcription factors

factor family

**Table 1.** Genes, gene function, metabolic function and transgenic.

*dreb1 or osdreb1*

166 Responses of Organisms to Water Stress

*srk2d, srk2e, srk2i*

The global warming is a reality that we have to face and in order to provide food to the growing population some actions have to be taken by government and researchers. The development of new cultivars more resistant to the environmental conditions, for every crop, must be a priority, in order to guarantee food demand security. To avoid yield re‐ ductions from floods, droughts and rising temperatures agribusiness will have to be re‐ considered, investments have to be done, researchers will have to focus on ways to improve food quality, nutritional composition and increase yield using less land for farming. Crops will have to grow under a different scenario including less water and high temperature.

As it was discussed in this chapter changes in climate conditions will require several plant adaptations in order to minimize decreases in crop yield and to maintain food ac‐ cessibility. Genetic breeding has been used over the last decades to improve yield and food quality. But how much can we still get from traditional plant breeding programs re‐ garding to improve plants to face water scarcity? It is time to adopt new technologies as genetic engineering to help breeders in generating more adapted plants to survive water stress. For several years researchers have been spending time to understand how plants adapt to different situations, understanding the physiological parameters and their role in plants response to water stress specially hormones and transcriptional factors can help the development of new cultivars more resistant to stress conditions. All this knowledge allied to molecular biology techniques and genetic engineering can promote the develop‐ ment of transgenic plants with higher product quality, better storage conditions, easer processing, more efficient and more resistant to extreme conditions.

Nowadays, transgenic crops are cultivated all over the world, but there are some re‐ mains questions: How much are farmers dependent on biotechnology companies? Which economic and cultural losses transgenic cultures will bring about? These subjects are still extensively debated and researchers do not know for sure what is ahead. In the specific case of drought tolerance, much has been discussed about genetic engineering and ex‐ perts consider the biotechnology relevant in developing higher genotypes.

## **Acknowledgements**

The authors are grateful to: Fundação do Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq) and Universidade de Ribeirão Preto (UNAERP) for the constant financial support and also to Ms Rosane Castro França for her precious help during this chapter organization.

## **Author details**

Sonia Marli Zingaretti1 , Marielle Cascaes Inácio2 , Lívia de Matos Pereira2 , Tiago Antunes Paz2 and Suzelei de Castro França1


## **References**

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Sonia Marli Zingaretti1

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1 Universidade de Ribeirão Preto, Brazil

2 Universidade Estadual Paulista, Brazil

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## *Edited by Şener Akıncı*

The same amount of water has been present on our planet for about 4 billion years, since shortly after the Earth was formed. Since then it has cycled through evaporation, condensation, precipitation and surface runoff multiple times. Water scarcity as an abiotic factor ranging from moderate to severe stress levels, accompanied by loss of moisture in the soil, is extremely hard for most organisms to cope with, particularly terrestrial plants and their food-chain dependents. Because of the potential for increasing temporary, or posssibly permanent, drought conditions in the future, there is intense focus on improving plant resistance to drought and increasing yield performance in water- limited environments through genotype selection in important crops. This book aims to contribute to understanding of how plants and other organisms respond to water stress conditions, and the various survival strategies adopted under differing moisture levels.

Responses of Organisms to Water Stress

Responses of Organisms to

Water Stress

*Edited by Şener Akıncı*

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