Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones

*Haifa Abdulaziz S. Alhaithloul, Abdelghafar M. Abu-Elsaoud and Mona H. Soliman*

#### **Abstract**

Crop plants are encountered by various abiotic pressures which limit their growth and development. Stresses such as drought, heat, pathogen attack, heavy metal, salinity, and radiations impose negative effect on crop plants. The reduction in crop productivity in the current era of climate change is compromising the efforts/strategies used for sustainable agricultural practices. Therefore, plant stress physiologists are engineering plants with suitable exogenous signaling elicitors to engineer tolerance to various stresses. In the present chapter, an appraisal has been made in the "Introduction" section to first assess the damages caused by various abiotic stresses in crop plants. In the second section, we attempt to summarize the role of various plant hormones, namely, salicylic acid (SA), brassinosteroids (BRs), ethylene (ET), and methyl jasmonate (MJ) in enhancing abiotic stress tolerance. The current concept may lead to the development of strategies for unraveling the underlying mechanisms of plant hormone-mediated abiotic stress tolerance in crop plants.

**Keywords:** abiotic stress, plant hormones, crop plants, stress tolerance

#### **1. Introduction**

Due to overexploitation of natural resources for catering to basic human needs coupled with hunger, the aim of Food and Agricultural Organization's [1] of making world agriculture for enhancing 70% food production by 2050 for 2.3 billion newborn individual is facing a lot of challenges. As a result of changing climate and global warming, these threats are now called as "global warning" due to their effects on plant productivity [2]. According to a report published by IPCC [3], global climate change will increase the mean temperature of the Earth by 2–4°C. Due to increased anthropogenic activities, the change in climate will further increase and will definitely affect the agriculture sector as this is being more prone to climate changes [4]. A change in climate scenarios is the main reason of biotic and abiotic pressures of a particular region. Various abiotic stresses all over the world have now been adjudged as the most potential threat for sustainable agricultural productivity [5, 6]. Myriads of anthropogenic emissions in the developmental era have further intensified the abiotic stress-induced negative impacts on agricultural productivity. The major abiotic stresses such as metals/metalloids (hereafter termed as "metal/s"), salt, ozone, UV-B radiation, temperature extremes, nutrient (deficiency and excess), flooding, and water deficit are jeopardizing the agriculture system

worldwide [7–19]. These abiotic stresses can modulate almost all plant physiological, biochemical, and molecular processes starting from the seedling to maturity stage and can ultimately cause severe negative impacts on economic yield of various crop plants. Nevertheless, abiotic stresses have been reported to adversely affect 70% yield of crops [20]. The stress of metal/s is known to affect the photosynthetic process to a great extent [19, 21]. According to an estimate of U.S. Environmental Action Group, various metals pose negative effects on health in more than 10 million of human population in eight countries (such as China, India, Russia, Dominican Republic, Kyrgyzstan, Peru, Ukraine, and Zambia) and the effect imposed by them is regarded as one of the major threats to the agriculture [22]. Wang et al. [23] have reports to show that the salinization of arable land could accelerate to a land loss of 30% by the year end of 2028 and up to 50% by 2050.In current times, an increase in atmospheric CO2 concentration has been reported to reach by 407.4 ppm, and its levels today are more than at any point recorded for at least the past 800,000 years [24]. In addition, the data accessed on NOAA website [25] show that the average global temperature in June 2020 was found to be 1.66 °F (0.92 of a °C) above the twentieth century's average of 59.9 °F (15.5 °C) and the average temperature of June across the U.S. was found to be 70.3 °F (which is 1.8° above average), which ranks it the warmest third month in the history of the 126-year record. Hence, all these abiotic stress factors under the effect of climate change could be expected to significantly pose a potential threat to agriculture [11, 26–30]. Therefore, the knowledge of crop productivity improvement techniques under various abiotic stresses is one of the biggest challenges encountered by the scientific community across the world. Despite much and extensive efforts being utilized in the current field, the underlying quest for obtaining abiotic stress-resistant crops is very low and receives little attention. Various efforts are being utilized to decipher the potential mechanisms behind plant responses to abiotic stress conditions. Plants are sessile and are exposed to various environmental regimes and have to tolerate these abiotic stress-induced adverse impacts for performing their growth and development in an optimal manner. As a result of an exponential increase in the global human population, the demand for enhanced food is also accelerating and in order to meet these challenges under a challenging environment, it has become necessary to increase crop productivity. Nevertheless, the exogenous use of phytohormones in these adaptive mechanisms for engineering abiotic stress tolerance in diverse crop plants can yield better results.

Phytohormones are small chemicals messengers that play important roles in regulating the promotion of growth, development, and metabolism of the plants in a wide range of biotic and abiotic stresses. These are biodegradable and highly promote the growth and crop yield under optimal as well as stressed conditions. The knowledge of engineering in plants could be exploited to impart tolerance against a wide range of abiotic stresses. Thus, the present chapter focuses on the potent role of various phytohormones in enhancing the morphological and physiological properties of crop plants and also sheds light on the alleviative role in providing plant tolerance to various environmental stresses.

#### **2. Regulatory role played by various phytohormones in abiotic stress tolerance in crop plants**

In the following sections, we will be discussing the potential role of different phytohormones like SA-, BRs-, ET- and MJ-mediated mechanisms in countering diverse abiotic pressures like salinity, drought, heat, and metal/s stress in diverse crop species. The role of these phytohormones in eliciting various responses in different crop plants has also been represented in **Table 1**.

**235**

**Name of plant**

*Mentha arvensis* L.

*Mentha piperita*

*Glycine max* L.

*Linum usitatissimum*

*Brassica juncea* *Brassica juncea* L.

*Phaseolus coccineus*

Metal stress Cu (50 μM)

Methyl jasmonate 10 μM

As 50 and 200 μM

Methyl jasmonate 0.1 and

1.00 μM

Cr 1.2 mM

200 μL/L ethephon

application

Salt 150 mM

24-epibrassinolide 10−8 M

NaCl decreased methylation of CCGG sequences. EBL application

Amraee

et al. [34].

Asgher

et al. [35]

Farooq et al. [36]

induced the total methylation under salinity stress conditions

ET was found to be involved in reversal of Cr-inhibited growth and

photosynthesis by increasing PSII efficiency and enhanced N and S

MJ application effectively mitigated the adverse effects of As stress by

increasing the biomass, chlorophyll fluorescence, and the biosynthesis

of secondary metabolites, reducing the oxidative stress biomarkers and

The enzymatic activities SOD, CAT, APX, POX, as well as MDA, GSH,

Hanaka et al. [37]

and proline increased under Cu stress. MJ also elevated the activities

CAT, APX, and POX activities in the roots. Final results showed that

MJ was partially effective in modulating the anti-oxidative enzymes'

activities and accumulation of metabolites, in both normal and

Cu-stressed plants

maintaining antioxidant system

assimilation

Salt 100 mM

24-epibrassinolide 10−7 M

EBL application decreased Na+ accumulation and promoted the uptake of the mineral nutrients, modulated osmolytes, activities of key antioxidant enzymes, and the levels of nonenzymatic antioxidants thus improves growth and photosynthesis

Cd 30, 60, and 120 mg/kg

Salicylic acid 10−4 M

**Abiotic stress, type, and doses**

Metal stress Cd (150 mg/Kg)

**Phytohormone doses**

Methyl jasmonate 1 μM

**Consequent response**

A significant decrease in length of root and shoot, fresh and dry masses of shoot and leaf area; decreased chlorophyll and leaf gas exchange traits, and leaf N, P, and K content; increase in the activities of APX, GR, SOD, CAT, ROS production, osmolytes; and closure in stomatal movement under Cd. Improvement in these traits and alleviation of stress by MJ application

Decreased growth and photosynthetic traits and enzymes like NR and CA activities; increased phenolics, activities of SOD, POX, and proline content under Cd. SA improved photosynthesis; activity of RuBisCo, CA, and GSH pool, EO content; and yield of peppermint plants

Alam et al. [33].

**Reference** Zaid and Mohammad [31]

*Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones*

*DOI: http://dx.doi.org/10.5772/intechopen.93710*

Ahmad et al. [32]


#### *Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones DOI: http://dx.doi.org/10.5772/intechopen.93710*

*Abiotic Stress in Plants*

worldwide [7–19]. These abiotic stresses can modulate almost all plant physiological, biochemical, and molecular processes starting from the seedling to maturity stage and can ultimately cause severe negative impacts on economic yield of various crop plants. Nevertheless, abiotic stresses have been reported to adversely affect 70% yield of crops [20]. The stress of metal/s is known to affect the photosynthetic process to a great extent [19, 21]. According to an estimate of U.S. Environmental Action Group, various metals pose negative effects on health in more than 10 million of human population in eight countries (such as China, India, Russia, Dominican Republic, Kyrgyzstan, Peru, Ukraine, and Zambia) and the effect imposed by them is regarded as one of the major threats to the agriculture [22]. Wang et al. [23] have reports to show that the salinization of arable land could accelerate to a land loss of 30% by the year end of 2028 and up to 50% by 2050.In current times, an increase in atmospheric CO2 concentration has been reported to reach by 407.4 ppm, and its levels today are more than at any point recorded for at least the past 800,000 years [24]. In addition, the data accessed on NOAA website [25] show that the average global temperature in June 2020 was found to be 1.66 °F (0.92 of a °C) above the twentieth century's average of 59.9 °F (15.5 °C) and the average temperature of June across the U.S. was found to be 70.3 °F (which is 1.8° above average), which ranks it the warmest third month in the history of the 126-year record. Hence, all these abiotic stress factors under the effect of climate change could be expected to significantly pose a potential threat to agriculture [11, 26–30]. Therefore, the knowledge of crop productivity improvement techniques under various abiotic stresses is one of the biggest challenges encountered by the scientific community across the world. Despite much and extensive efforts being utilized in the current field, the underlying quest for obtaining abiotic stress-resistant crops is very low and receives little attention. Various efforts are being utilized to decipher the potential mechanisms behind plant responses to abiotic stress conditions. Plants are sessile and are exposed to various environmental regimes and have to tolerate these abiotic stress-induced adverse impacts for performing their growth and development in an optimal manner. As a result of an exponential increase in the global human population, the demand for enhanced food is also accelerating and in order to meet these challenges under a challenging environment, it has become necessary to increase crop productivity. Nevertheless, the exogenous use of phytohormones in these adaptive mechanisms for engineering abiotic stress tolerance in diverse crop plants can yield better results. Phytohormones are small chemicals messengers that play important roles in regulating the promotion of growth, development, and metabolism of the plants in a wide range of biotic and abiotic stresses. These are biodegradable and highly promote the growth and crop yield under optimal as well as stressed conditions. The knowledge of engineering in plants could be exploited to impart tolerance against a wide range of abiotic stresses. Thus, the present chapter focuses on the potent role of various phytohormones in enhancing the morphological and physiological properties of crop plants and also sheds light on the alleviative role in providing

**234**

plant tolerance to various environmental stresses.

different crop plants has also been represented in **Table 1**.

**tolerance in crop plants**

**2. Regulatory role played by various phytohormones in abiotic stress** 

In the following sections, we will be discussing the potential role of different phytohormones like SA-, BRs-, ET- and MJ-mediated mechanisms in countering diverse abiotic pressures like salinity, drought, heat, and metal/s stress in diverse crop species. The role of these phytohormones in eliciting various responses in


*Various studies in diverse crop plants under different abiotic stresses conditions and the consequent response shown by these plants under various phytohormone application.*

**237**

*Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones*

The name of "salicylic acid SA" is known to be derived from the Latin word *Salix*

2) to induce enhanced flavonoid biosynthesis in tea plants. The results advocated the cross talk of SA for enhanced biosynthesis of secondary metabolites in tea plants under the era of climate change. In watermelon plants, resistance against root-knot nematode by red light is regulated by the coordination of SA with jasmonate signal

ing. This shows the potentiality of SA in enhancing tolerance against biotic stress. In Indian mustard plants, SA (10−5 M) alleviated the toxicity of Ni (50, 100 and 150 μM) by upregulating the activities of enzymes associated with antioxidant defense and glyoxalase systems [44]. In yet a recent study, Zaid et al. [45] tested the efficacy of foliar supplementation of SA (10−6 M) in two menthol mint cultivars, namely, Kosi and Kushal grown under Cd (50 μM) stress conditions. A reduction in growth, photosynthesis, and mineral nutrients with a concomitant increase in electrolyte leakage (EL), malondialdehyde (MDA), and hydrogen peroxide (H

contents was observed under Cd stress in both cultivars. Nevertheless, a differential upregulation of proline content and the activities of antioxidant enzymes under Cd stress were also noticed in both cultivars. In contrast, out of three foliar-applied PGRs, the application of SA at three different growth stages proved best in alleviat

ing Cd toxicity that too in both the cultivars but the effect of SA in Kushal was much more pronounced and better than Kosi. Application of SA (10−6 and 10−5 M) was also found to restrain As toxicity in two varieties of Artemisia annua L., namely, "CIM-Arogya" and "Jeevan Raksha" at 90 and 120 days after plantation [46]. The results suggested that the minimum reduction in growth and yield occurs with enhanced artemisinin production in "CIM Arogya" compared to "Jeevan Raksha" under As toxicity (45 mg kg−1 of soil). The application of SA via leaf significantly increased the content and yield of artemisinin in both varieties. El Dakak and Hassan [47] in a study evaluated the underlying physiological and biochemical mechanisms through which SA (1.0 mM) applied as a soil drench treatment allevi

ated the toxicity of Cd (5 and 10 μM) in maize plants. The results showed that exposure of maize plants to Cd reduced the chlorophyll content, chlorophyll fluores

lis L. grown under Cu contamination (40 mM)

cence traits, photosynthesis, and catalase (CAT) activity, but, however, enhanced non-photochemical quenching (NPQ ), MDA content and activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and guaiacol peroxidase (GPOX). Application of SA through soil drenching had an additive effect on the activities of antioxidant enzymes, but an inverse effect was found in case of MDA content. Es-sbihi et al. [48] studied the effects of SA (0.5 and 1 mM) on physiological traits, distribution of glandular hairs and essential oil (EO) composition in Salvia officina

of stem and root, Ca, P and K content in leaves as well as in roots. Interestingly, Cu increased EO yield. SA spray more prominently at 0.5 mM significantly improved stem and root growth, Ca, P, K and EO content and increased the density of peltate glands in presence of Cu stress. The study concluded with the observation that foliar

7 H 6 O 3) and


2 O 2)





*.* The Cu stress decreased the growth

(willow tree). A German scientist, namely, Johann Andreas Buchner in 1828, isolated a quantity of glucoside of salicylic alcohol "salicin." Later on it was found that salicin, an important salicylate, is present in 36 other plants in addition to

consists of an aromatic ring to which one carboxylic and a hydroxyl group are attached. SA participates in several important plant processes either in stress-free or stressful environmental cues. It is now regarded as an important protector and growth regulating molecules in plants [42]. SA has an evidenced role in improving abiotic stress tolerance in various crop plants. Nonetheless, a report by Li et al. [43] suggested that SA acts upstream of NO under high concentration of carbon dioxide

willow tree [41]. Chemically, SA is a simple phenolic compound (C

*DOI: http://dx.doi.org/10.5772/intechopen.93710*

**3. Role of salicylic acid**

(CO

#### *Abiotic Stress in Plants*

## **3. Role of salicylic acid**

*Abiotic Stress in Plants*

**236**

**Name of plant**

*Mentha piperita*

*Brassica juncea* *Artemisia annua*

**Table 1.**

Metalloid stress (Boron) 1.00

Methyl jasmonate 300 μM

and 2.00 mM

Ni 200 mg/kg

Ethylene 200 μL/L

**Abiotic stress, type, and doses**

Salt (0, 50, 100, or 150 mM

NaCl)

**Phytohormone doses**

Salicylic acid, gibberellic

acid, and triacontanol,

each with 10−6 M

**Consequent response**

The salinity stress decreased growth, photosynthesis, activity of

CA, contents of N, P, K, peltate glandular trichome density, EO and

menthol content, and herbage yield but increased CAT, POX, and SOD

activities and proline. The foliar spray of SA surpassed the other two

phytohormones and maximally improved all parameters under both

The results showed that Ni decreased growth and photosynthesis

Khan et al. [39]

but increased oxidative stress. Supply of ET ameliorated the stress by

increasing the proline synthesis, antioxidant defense, and glyoxalase

systems to promote the photosynthetic effectiveness under Ni stress

B decreased the stem height, fresh and dry masses of the plant, the net

Aftab et al. [40]

photosynthetic rate, stomatal conductance, internal CO2 concentration,

and total chlorophyll content. MJ supply alleviates changes in growth

and photosynthetic efficiency by increasing the activities of antioxidant

enzymes and yield of secondary metabolites

*Various studies in diverse crop plants under different abiotic stresses conditions and the consequent response shown by these plants under various phytohormone application.*

salt stress and salt free conditions

**Reference**

Khanam and

Mohammad [38]

The name of "salicylic acid SA" is known to be derived from the Latin word *Salix* (willow tree). A German scientist, namely, Johann Andreas Buchner in 1828, isolated a quantity of glucoside of salicylic alcohol "salicin." Later on it was found that salicin, an important salicylate, is present in 36 other plants in addition to willow tree [41]. Chemically, SA is a simple phenolic compound (C7H6O3) and consists of an aromatic ring to which one carboxylic and a hydroxyl group are attached. SA participates in several important plant processes either in stress-free or stressful environmental cues. It is now regarded as an important protector and growth regulating molecules in plants [42]. SA has an evidenced role in improving abiotic stress tolerance in various crop plants. Nonetheless, a report by Li et al. [43] suggested that SA acts upstream of NO under high concentration of carbon dioxide (CO2) to induce enhanced flavonoid biosynthesis in tea plants. The results advocated the cross talk of SA for enhanced biosynthesis of secondary metabolites in tea plants under the era of climate change. In watermelon plants, resistance against root-knot nematode by red light is regulated by the coordination of SA with jasmonate signaling. This shows the potentiality of SA in enhancing tolerance against biotic stress. In Indian mustard plants, SA (10−5 M) alleviated the toxicity of Ni (50, 100 and 150 μM) by upregulating the activities of enzymes associated with antioxidant defense and glyoxalase systems [44]. In yet a recent study, Zaid et al. [45] tested the efficacy of foliar supplementation of SA (10−6 M) in two menthol mint cultivars, namely, Kosi and Kushal grown under Cd (50 μM) stress conditions. A reduction in growth, photosynthesis, and mineral nutrients with a concomitant increase in electrolyte leakage (EL), malondialdehyde (MDA), and hydrogen peroxide (H2O2) contents was observed under Cd stress in both cultivars. Nevertheless, a differential upregulation of proline content and the activities of antioxidant enzymes under Cd stress were also noticed in both cultivars. In contrast, out of three foliar-applied PGRs, the application of SA at three different growth stages proved best in alleviating Cd toxicity that too in both the cultivars but the effect of SA in Kushal was much more pronounced and better than Kosi. Application of SA (10−6 and 10−5 M) was also found to restrain As toxicity in two varieties of Artemisia annua L., namely, "CIM-Arogya" and "Jeevan Raksha" at 90 and 120 days after plantation [46]. The results suggested that the minimum reduction in growth and yield occurs with enhanced artemisinin production in "CIM Arogya" compared to "Jeevan Raksha" under As toxicity (45 mg kg−1 of soil). The application of SA via leaf significantly increased the content and yield of artemisinin in both varieties. El Dakak and Hassan [47] in a study evaluated the underlying physiological and biochemical mechanisms through which SA (1.0 mM) applied as a soil drench treatment alleviated the toxicity of Cd (5 and 10 μM) in maize plants. The results showed that exposure of maize plants to Cd reduced the chlorophyll content, chlorophyll fluorescence traits, photosynthesis, and catalase (CAT) activity, but, however, enhanced non-photochemical quenching (NPQ ), MDA content and activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and guaiacol peroxidase (GPOX). Application of SA through soil drenching had an additive effect on the activities of antioxidant enzymes, but an inverse effect was found in case of MDA content. Es-sbihi et al. [48] studied the effects of SA (0.5 and 1 mM) on physiological traits, distribution of glandular hairs and essential oil (EO) composition in Salvia officinalis L. grown under Cu contamination (40 mM)*.* The Cu stress decreased the growth of stem and root, Ca, P and K content in leaves as well as in roots. Interestingly, Cu increased EO yield. SA spray more prominently at 0.5 mM significantly improved stem and root growth, Ca, P, K and EO content and increased the density of peltate glands in presence of Cu stress. The study concluded with the observation that foliar

spray of SA showed the remediating effect on growth traits, biosynthesis, and composition of EO of S. officinalis plants grown under Cu-challenged environment. This shows the key role of SA in enhancing tolerance to metal stress. In case of salt stress, SA also plays a mitigating role in minimizing the salt-induced damages in diverse crop plants. Miao et al. [49] in a hydroponic study applied exogenous SA (0.3 mM) in alleviating salt stress (50 mM NaCl) in cucumber seedlings. The results showed that 50 mM NaCl toxicity reduced relative growth rate and leaf photosynthetic traits like Fv/Fm, ΦII, and Pn. However, plants receiving NaCl + SA treatment showed a significant increment in relative growth rate, leaf photosynthetic traits (mentioned above) and an increase in case of total root length, root surface area, number and total lengths of primary and secondary roots. Both NaCl and SA downregulated and upregulated the expression of *GL2* and *RHD2* gene expression, while the application of SA treatment to NaCl-treated plants showed a notable upregulation in the expression of *NAC1*, *NAC2*, *GL2*, *EXP*, and downregulation of *RHD2* gene expression. Taken together the exogenous application of SA alleviated the NaCl toxicity by enhancing photosynthesis and architecture of root system in cucumber seedlings. Hussain et al. [50, 51] worked out the mechanistic elucidation of SA (0.5 mM) interplay with S (2.0 mM) under salt stress (50 mM NaCl) in mung bean plants. Salt-exposed plants showed an elevation in reactive oxygen species (ROS) content, lipid peroxidation, glucose and enzymatic activities like APX, GR, SOD, and reduced glutathione (GSH) and proline but marked inhibitions in the nitrate reductase (NR) and nitrite reductase (NiR) activities, N content, photosynthesis, photosynthetic N-use-efficiency (NUE), and growth traits. The supplementation of SA and S strengthened the antioxidant machinery, improved NR and NiR activities, N content, GSH, APX, GR and also decrease in ROS, MDA and glucose (a photosynthesis repressor) accumulation. These observations suggested that finetuning of SA with S diminished the NaCl-mediated changes in tested plants. Fahad and Bano [52] investigated the effect of foliar spray of SA (10−5 M) on maize (Zea mays L.) hybrid cv. 3025 grown in saline environments (pH 8.4 and EC 4.2 ds/m). The salinity treatment was found to significantly increased sugar contents, protein, proline, and activities of SOD, POD, CAT, and APX but decreased the pigment contents like chlorophyll and carotenoid and osmotic potential and membrane stability index. The application of SA to plants grown under salt-stressed plants further incremented the osmolytes, antioxidant enzymes, contents of endogenous abscisic acid (ABA), indole acetic acid (IAA), root length, and fresh and dry weights of roots. The results indicated that foliar application of SA proved to be effective in ameliorating the ill effects of salinity stress on maize plants. Pan et al. [53] worked out the involvement of hydrogen sulfide (H2S) in SA-induced chilling stress tolerance in cucumber seedlings by using specific scavenger and inhibitor of H2S. They found that under optimal conditions, the donor of H2S or removing of endogenous H2S by its scavenger (hypotaurine) or inhibitor (DL-propargylglycine) showed no impact on the level of endogenous SA, but SA induced H2S endogenously and triggered the activities and mRNA transcript levels of L−/D-cysteine desulfhydrase (L−/D-CD). In addition, inhibiting endogenous SA with paclobutrazol or 2-aminoindan-2-phosphonic acid inhibited the effects of SA on H2S. Nevertheless, both SA and H2S donor NaHS minimized chilling-induced injury by lowering EL, MDA content, and ROS accumulation, improving the activities and mRNA levels of SOD, POD, CAT, APX, and GR, contents of ascorbate (AsA) and GSH contents and enhanced the expression of the chilling responsive genes (*ICE*, *CBF1*, and *COR*). It was postulated from this study that SA acts as an up-streaming signaling molecule under chilling tolerance of cucumber plants via increasing antioxidant defense system and modulating the expression of chilling stress-responsive genes. In a comparative study involving three deficit irrigation regimes, viz., 100, 80, and 60%

**239**

abiotic stress in diverse crop plants.

**4. Role of brassinosteroids**

*Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones*

of crop evapo-transpiration and four levels of salinity, that is, 2, 4, 8, and 12 dS m−1, the effect of SA in pearl millet and wheat plants was studied [54, 55]. Water and salinity stress caused significant reductions in grain yields, plant height, water and

Supply of SA caused a significant enhancement in plant height and grain yield and significantly improved all physiological, biochemical traits and consequently grain yield in both crop plants. In order to evaluate the participation of NR in SA-mediated improvements in water deficit tolerance in pepper plants, Kaya [56] applied 0.5 mM SA as a foliar spray. The results revealed that water stress caused decrement in total plant dry weight, Fv/Fm, contents of chlorophyll *a* and *b*, relative water content, leaf water potential but increment in MDA, H2O2, EL, methylglyoxal (MG), proline, and (nitric oxide) NO, NR and antioxidant enzymes' activities. The supply of SA reduced oxidative stress biomarkers, but triggered a marked increment in antioxidant defense system, enzymes of ascorbate-glutathione (AsA-GSH) cycle and glyoxalase system-glyoxalase I (Gly I) and glyoxalase II (Gly II), growth and photosynthetic traits, activities of NO, NR and proline content. In a recent study, the effect of foliar SA (0, 0.5, and 1 mM) under drought stress (90, 60, and 30% field capacity) in Portulaca oleracea L. was studied [57]. Imposition of drought stress showed a decrement in the contents of photosynthetic pigments, gas exchanges attributes, growth, and biomass production, soluble sugars, total phenolic, flavonoids and unsaturated fatty acids (FA) like oleic, linoleic and linolenic acid, and stearic and behenic acid but increased the contents of H2O2, MDA, and palmitic and arachidonic acid, respectively. Application of SA improved the growth, photosynthetic pigment contents, gas exchanges traits, FA contents, compatible solutes, and secondary metabolites, while simultaneously decreasing drought-induced oxidative stress biomarkers. With regard to heat stress, SA is effective in alleviating the damages on plants' physiology. Karpets et al. [58] studied the interplay of hydrogen sulfide (H2S) in SA-mediated induction of heat resistance via the performance of antioxidant system in wheat plantlets. The data showed that H2S actively participates under the protective influence of SA application in wheat heat stress tolerance. Khan et al. [59] exposed wheat plants to heat stress (40°C for 6 h) and studied the potential of 0.5 mM SA in alleviating the negative effects of heat stress on photosynthesis. The net photosynthesis (Pn) and activity of ribulose 1,5-bisphosphate carboxylase (RuBisCo) and photosynthetic nitrogen use efficiency (NUE) decreased under heat stress, but metabolism of proline was found to be increased. The application of SA alleviated heat stress by further increasing proline metabolism via the enhancement in the activity of γ-glutamyl kinase (GK) and decrement in proline oxidase (PROX), which maintained optimum osmotic and water potential for optimally maintaining the photosynthesis. Nonetheless, SA restricted the production of stress ethylene under heat-stressed plants to optimal range. The results suggested that SA supplementation alleviates heat stress effects by interacting with proline metabolism and ethylene formation to improve photosynthesis in wheat plants. In yet another related work, Kumar et al. [60] by using MALDI-TOF–TOF/MS analysis showed that spraying 100 mM SA alleviates the heat-induced (38°C) oxidative stress damage in wheat plants via modulation of the expression of heat-stable genes and proteins. Thus, SA application plays a pivotal role in alleviation the damages of myriads of

Brassinosteroids (BRs) are an important class of plant steroid-based phytohor-

mone that plays multiple roles in regulating plant growth, development, and

ratios in both pearl millet and wheat plants.

*DOI: http://dx.doi.org/10.5772/intechopen.93710*

proline content, and Fv/Fm and Na/K+

*Abiotic Stress in Plants*

spray of SA showed the remediating effect on growth traits, biosynthesis, and composition of EO of S. officinalis plants grown under Cu-challenged environment. This shows the key role of SA in enhancing tolerance to metal stress. In case of salt stress, SA also plays a mitigating role in minimizing the salt-induced damages in diverse crop plants. Miao et al. [49] in a hydroponic study applied exogenous SA (0.3 mM) in alleviating salt stress (50 mM NaCl) in cucumber seedlings. The results showed that 50 mM NaCl toxicity reduced relative growth rate and leaf photosynthetic traits like Fv/Fm, ΦII, and Pn. However, plants receiving NaCl + SA treatment showed a significant increment in relative growth rate, leaf photosynthetic traits (mentioned above) and an increase in case of total root length, root surface area, number and total lengths of primary and secondary roots. Both NaCl and SA downregulated and upregulated the expression of *GL2* and *RHD2* gene expression, while the application of SA treatment to NaCl-treated plants showed a notable upregulation in the expression of *NAC1*, *NAC2*, *GL2*, *EXP*, and downregulation of *RHD2* gene expression. Taken together the exogenous application of SA alleviated the NaCl toxicity by enhancing photosynthesis and architecture of root system in cucumber seedlings. Hussain et al. [50, 51] worked out the mechanistic elucidation of SA (0.5 mM) interplay with S (2.0 mM) under salt stress (50 mM NaCl) in mung bean plants. Salt-exposed plants showed an elevation in reactive oxygen species (ROS) content, lipid peroxidation, glucose and enzymatic activities like APX, GR, SOD, and reduced glutathione (GSH) and proline but marked inhibitions in the nitrate reductase (NR) and nitrite reductase (NiR) activities, N content, photosynthesis, photosynthetic N-use-efficiency (NUE), and growth traits. The supplementation of SA and S strengthened the antioxidant machinery, improved NR and NiR activities, N content, GSH, APX, GR and also decrease in ROS, MDA and glucose (a photosynthesis repressor) accumulation. These observations suggested that finetuning of SA with S diminished the NaCl-mediated changes in tested plants. Fahad and Bano [52] investigated the effect of foliar spray of SA (10−5 M) on maize (Zea mays L.) hybrid cv. 3025 grown in saline environments (pH 8.4 and EC 4.2 ds/m). The salinity treatment was found to significantly increased sugar contents, protein, proline, and activities of SOD, POD, CAT, and APX but decreased the pigment contents like chlorophyll and carotenoid and osmotic potential and membrane stability index. The application of SA to plants grown under salt-stressed plants further incremented the osmolytes, antioxidant enzymes, contents of endogenous abscisic acid (ABA), indole acetic acid (IAA), root length, and fresh and dry weights of roots. The results indicated that foliar application of SA proved to be effective in ameliorating the ill effects of salinity stress on maize plants. Pan et al. [53] worked out the involvement of hydrogen sulfide (H2S) in SA-induced chilling stress tolerance in cucumber seedlings by using specific scavenger and inhibitor of H2S. They found that under optimal conditions, the donor of H2S or removing of endogenous H2S by its scavenger (hypotaurine) or inhibitor (DL-propargylglycine) showed no impact on the level of endogenous SA, but SA induced H2S endogenously and triggered the activities and mRNA transcript levels of L−/D-cysteine desulfhydrase (L−/D-CD). In addition, inhibiting endogenous SA with paclobutrazol or 2-aminoindan-2-phosphonic acid inhibited the effects of SA on H2S. Nevertheless, both SA and H2S donor NaHS minimized chilling-induced injury by lowering EL, MDA content, and ROS accumulation, improving the activities and mRNA levels of SOD, POD, CAT, APX, and GR, contents of ascorbate (AsA) and GSH contents and enhanced the expression of the chilling responsive genes (*ICE*, *CBF1*, and *COR*). It was postulated from this study that SA acts as an up-streaming signaling molecule under chilling tolerance of cucumber plants via increasing antioxidant defense system and modulating the expression of chilling stress-responsive genes. In a comparative study involving three deficit irrigation regimes, viz., 100, 80, and 60%

**238**

of crop evapo-transpiration and four levels of salinity, that is, 2, 4, 8, and 12 dS m−1, the effect of SA in pearl millet and wheat plants was studied [54, 55]. Water and salinity stress caused significant reductions in grain yields, plant height, water and proline content, and Fv/Fm and Na/K+ ratios in both pearl millet and wheat plants. Supply of SA caused a significant enhancement in plant height and grain yield and significantly improved all physiological, biochemical traits and consequently grain yield in both crop plants. In order to evaluate the participation of NR in SA-mediated improvements in water deficit tolerance in pepper plants, Kaya [56] applied 0.5 mM SA as a foliar spray. The results revealed that water stress caused decrement in total plant dry weight, Fv/Fm, contents of chlorophyll *a* and *b*, relative water content, leaf water potential but increment in MDA, H2O2, EL, methylglyoxal (MG), proline, and (nitric oxide) NO, NR and antioxidant enzymes' activities. The supply of SA reduced oxidative stress biomarkers, but triggered a marked increment in antioxidant defense system, enzymes of ascorbate-glutathione (AsA-GSH) cycle and glyoxalase system-glyoxalase I (Gly I) and glyoxalase II (Gly II), growth and photosynthetic traits, activities of NO, NR and proline content. In a recent study, the effect of foliar SA (0, 0.5, and 1 mM) under drought stress (90, 60, and 30% field capacity) in Portulaca oleracea L. was studied [57]. Imposition of drought stress showed a decrement in the contents of photosynthetic pigments, gas exchanges attributes, growth, and biomass production, soluble sugars, total phenolic, flavonoids and unsaturated fatty acids (FA) like oleic, linoleic and linolenic acid, and stearic and behenic acid but increased the contents of H2O2, MDA, and palmitic and arachidonic acid, respectively. Application of SA improved the growth, photosynthetic pigment contents, gas exchanges traits, FA contents, compatible solutes, and secondary metabolites, while simultaneously decreasing drought-induced oxidative stress biomarkers. With regard to heat stress, SA is effective in alleviating the damages on plants' physiology. Karpets et al. [58] studied the interplay of hydrogen sulfide (H2S) in SA-mediated induction of heat resistance via the performance of antioxidant system in wheat plantlets. The data showed that H2S actively participates under the protective influence of SA application in wheat heat stress tolerance. Khan et al. [59] exposed wheat plants to heat stress (40°C for 6 h) and studied the potential of 0.5 mM SA in alleviating the negative effects of heat stress on photosynthesis. The net photosynthesis (Pn) and activity of ribulose 1,5-bisphosphate carboxylase (RuBisCo) and photosynthetic nitrogen use efficiency (NUE) decreased under heat stress, but metabolism of proline was found to be increased. The application of SA alleviated heat stress by further increasing proline metabolism via the enhancement in the activity of γ-glutamyl kinase (GK) and decrement in proline oxidase (PROX), which maintained optimum osmotic and water potential for optimally maintaining the photosynthesis. Nonetheless, SA restricted the production of stress ethylene under heat-stressed plants to optimal range. The results suggested that SA supplementation alleviates heat stress effects by interacting with proline metabolism and ethylene formation to improve photosynthesis in wheat plants. In yet another related work, Kumar et al. [60] by using MALDI-TOF–TOF/MS analysis showed that spraying 100 mM SA alleviates the heat-induced (38°C) oxidative stress damage in wheat plants via modulation of the expression of heat-stable genes and proteins. Thus, SA application plays a pivotal role in alleviation the damages of myriads of abiotic stress in diverse crop plants.

#### **4. Role of brassinosteroids**

Brassinosteroids (BRs) are an important class of plant steroid-based phytohormone that plays multiple roles in regulating plant growth, development, and

responses to environmental stresses [7, 8, 50, 51, 61–64]. 28-homobrassinolide (HBL) and 24-epibrassinolide (EBL) are the two isomers of BRs which regulate an array of plant physiological processes [65, 66]. BRs have structural resemblance with androgens, estrogens, corticoids, and ecdysteroids. The discovery of brassinolide (BL) dates back to 1979, and now about 70 compounds which are naturally occurring have been reported as free molecules or form conjugates with glucose and FA [67]. The isomers of BRs play a significant role in imparting abiotic stress tolerance in crop plants. In potato plants, Kolomeichuk et al. [68] studied the EBL-mediated (10−10 M) alleviation of NaCl toxicity (root application 100 mM) on photosynthetic processes. Salinity inhibited the contents of photosynthetic pigments, photosynthetic electron transport and photosystem II (PSII) maximal and effective quantum yields, oxidation of the plastoquinone (PQ ). The treatment with 24-EBL under salinity stress maintained the efficiency of PSII photochemistry, PQ pool oxidation, and decrease in leaf osmotic potential. Amraee et al. [34] reported the 24-EBL-mediated (10−8 M) alteration on the extent and pattern of DNA cytosine methylation in Linum usitatissimum L. plants under salinity stress (150 mM) by using methylation-sensitive amplified polymorphisms (MSAP) technique. In conclusion, they found that the seed priming with 24-EBL play an important regulatory role via the epigenetic modification and induction of methylation in response to salinity toxicity. 24-EBL (10−8 mM) also confers tolerance against NaCl (100 mM) stress in soybean plants [33]. Exposure of soybean plants to 100 mM salt stress decreased growth, biomass yield, gas exchange traits, photosynthetic pigment contents, and chlorophyll fluorescence but increased H2O2, MDA, EL, and the antioxidant activities like SOD, CAT, accumulation of proline, and glycinebetaine (GB), total phenols, and total flavonoids. Application of 24-EBL (10−8 mM) to salt-stressed plants' upregulated the growth, biomass, yield, gas exchange and photosynthetic pigment contents, and chlorophyll fluorescence parameters but concomitantly reduced the accumulation of oxidative stress biomarkers. In a factorial experiment, Kaya et al. [69] studied the effect of 24-EBL (1.5 and 2.0 μM) application in regulating key physio-biochemical traits and oxidative defense system in two cultivars of maize, namely, PR32T83 and PR34N24 under two salinity levels (1.1 and 8.0 dS/m). Salinity levels decreased the fresh and dry weights of plant, yield of PS-II, chlorophyll contents, leaf water potential, and leaf K and Ca levels, but triggered an increase in membrane permeability, lipid peroxidation, H2O2, SOD, POD, CAT enzymes' activities, leaf Na and Cl, proline and GB, and leaf sap osmotic pressure. However, 24-EBL supply via both seed treatment and foliar application to the maize cultivars alleviated the detrimental effects of salt stress. In Cucumis sativus L. cv. Jinyan No. 4, plants grown under vermiculite and in hydroponic culture, Ahammed et al. [70] tested the efficacy of 24-EBL in alleviating organic pollutants (OPs), namely, 2,4,6-trichlorophenol, chlorpyrifos and oxytetracycline-retarded root elongation by unraveling the redox homeostasis and secondary metabolism-mediated underlying mechanisms. The results revealed that all the three tested OPs retarded elongation of roots, increased MDA, H2O2 and NO, while exogenous 24-EBL markedly decreased the accumulations of H2O2, NO and MDA *vis-a-vis* upregulating the expression of genes associated with antioxidant and detoxification systems. In case of pesticide stress, 24-EBL maintained the optimum synthesis of proteins and amino acids in Brassica juncea L. plants [71]. They applied 24-EBL (100 nM) via the seed presoaking treatment to study the changes in the synthesis of protein and amino acid contents grown under im-idacloprid (IMI) challenged environment. Plants grown under IMI stress (300 mg/kg soil) showed a decrease in protein and 21 amino acid contents. However, application of 24-EBL restored the total protein as well as amino acid contents which was decreased under IMI amended soils. In a recent study laid out in a randomized block design under

**241**

**5. Role of ethylene**

*Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones*

H2O2 and the response of plants was dose-dependent.

Phytohormone "ethylene" (ET) is a small gaseous plant growth regulator which is responsible for ripening of fruits and is known for inducing triple response in plants [77]. The growth-regulating effects of ET were first observed

greenhouse, Jan et al. [72] applied 24-EBL (10−7 M) for 8 h as seed priming method to alleviate the toxic effects of Cr (10 mg/kg soil) in tomato plants. The results suggested that that 24-EBL application effectively stimulate growth of tomato plants exposed to Cr stress via the remodulation of the physiological, metabolic, and defense mechanisms and by maintained accumulation of Cr. Alam et al. [33] applied 24-EBL (10−7 M) in countering NaCl (100 mM) stress in soybean plants. Salinity decreased growth, gas exchange parameters, pigment contents, and

MG content, the activities of SOD and CAT, accumulation of proline, GB, total

 uptake in root and shoot, and total flavonoids were found to be increased. Overall, 24-EBL supplementation provided tolerance to soybean plants by upregulating the antioxidant system, AsA-GSH cycle, and glyoxalase system. Yusuf et al. [73] under completely randomized block design studied the BRsmediated protection of growth and N metabolism and the potentiality of antioxidant system under Ni stress (0, 50, 100, or 150 mg/kg) in two cultivars of Vigna radiata, namely, PDM-139 and T-44. The role of two doses (10−8 or 10−6 M) of HBL in alleviating the Ni-induced damages via the ability of antioxidant enzymes and proline content was investigated. It was found that the Ni imposes toxic impact on the plants in a concentration dependent manner. The supply of HBL was effective in countering Ni stress as its application conferred tolerance up to 100 mg/kg in improving growth, nodulation, photosynthesis and yield attributes consequently. Fariduddin et al. [74] exposed Cucumis sativus L. plants to chilling stress to study the ameliorative role of HBL through studying the growth, photosynthesis, enzymes, and biochemical parameters. Cucumber seedlings were exposed to two chilling regimes, that is, 10/8 and 5/3°C for 18 h. The spray treatment consisted 10−8 or 10−6 M of HBL applied at 30-day stage to plants. Chilling stress imposes marked reductions in growth, chlorophyll, net photosynthesis, efficiency of photosystem II and alterations in NR and carbonic anhydrase (CA) activities. In contrast, the activities of antioxidant enzymes viz-CAT, POD, and SOD along with the proline content increased in response to chilling stress. HBL supply exerted a protective role via the maintained higher values of antioxidant enzymes and proline content under chilling stress. In order to assess the role of HBL (10−8 M) under two Cd doses (3 and 9 mg/kg sand) in Solanum lycopersicum plants, Singh and Prasad [75] designed an experiment in plant growth chamber. Treatment of plants to Cd stress resulted in a significant decrease in enzymes associate with N metabolism. The application of exogenous HBL supply ameliorated the ill effects of Cd stress by triggering an increase in growth, photosynthesis, protein and carbohydrate content and inorganic N and N assimilating enzymes. Kaur et al. [76] proposed the model of HBL-mediated regulation of antioxidant enzyme activities and gene expression in Brassica juncea plants to counteract the combined salt-and temperature-induced oxidative stress. HBL treatments (0, 10−6, 10−9, and 10−12 M) was applied as seed priming on plants exposed to the low (4°C) or high (44°C) temperature and salinity (180 mM) stresses. The combined treatments of salt and temperature significantly reduced length but increased H2O2 content and the activities of SOD, CAT, APX, GR, DHAR, and MDHAR. Application of HBL improved growth traits, reduced

, and P and biomass yield but H2O2, MDA, EL,

*DOI: http://dx.doi.org/10.5772/intechopen.93710*

chlorophyll fluorescence, Ca2+, K+

phenols, Na<sup>+</sup>

*Abiotic Stress in Plants*

responses to environmental stresses [7, 8, 50, 51, 61–64]. 28-homobrassinolide (HBL) and 24-epibrassinolide (EBL) are the two isomers of BRs which regulate an array of plant physiological processes [65, 66]. BRs have structural resemblance with androgens, estrogens, corticoids, and ecdysteroids. The discovery of brassinolide (BL) dates back to 1979, and now about 70 compounds which are naturally occurring have been reported as free molecules or form conjugates with glucose and FA [67]. The isomers of BRs play a significant role in imparting abiotic stress tolerance in crop plants. In potato plants, Kolomeichuk et al. [68] studied the EBL-mediated (10−10 M) alleviation of NaCl toxicity (root application 100 mM) on photosynthetic processes. Salinity inhibited the contents of photosynthetic pigments, photosynthetic electron transport and photosystem II (PSII) maximal and effective quantum yields, oxidation of the plastoquinone (PQ ). The treatment with 24-EBL under salinity stress maintained the efficiency of PSII photochemistry, PQ pool oxidation, and decrease in leaf osmotic potential. Amraee et al. [34] reported the 24-EBL-mediated (10−8 M) alteration on the extent and pattern of DNA cytosine methylation in Linum usitatissimum L. plants under salinity stress (150 mM) by using methylation-sensitive amplified polymorphisms (MSAP) technique. In conclusion, they found that the seed priming with 24-EBL play an important regulatory role via the epigenetic modification and induction of methylation in response to salinity toxicity. 24-EBL (10−8 mM) also confers tolerance against NaCl (100 mM) stress in soybean plants [33]. Exposure of soybean plants to 100 mM salt stress decreased growth, biomass yield, gas exchange traits, photosynthetic pigment contents, and chlorophyll fluorescence but increased H2O2, MDA, EL, and the antioxidant activities like SOD, CAT, accumulation of proline, and glycinebetaine (GB), total phenols, and total flavonoids. Application of 24-EBL (10−8 mM) to salt-stressed plants' upregulated the growth, biomass, yield, gas exchange and photosynthetic pigment contents, and chlorophyll fluorescence parameters but concomitantly reduced the accumulation of oxidative stress biomarkers. In a factorial experiment, Kaya et al. [69] studied the effect of 24-EBL (1.5 and 2.0 μM) application in regulating key physio-biochemical traits and oxidative defense system in two cultivars of maize, namely, PR32T83 and PR34N24 under two salinity levels (1.1 and 8.0 dS/m). Salinity levels decreased the fresh and dry weights of plant, yield of PS-II, chlorophyll contents, leaf water potential, and leaf K and Ca levels, but triggered an increase in membrane permeability, lipid peroxidation, H2O2, SOD, POD, CAT enzymes' activities, leaf Na and Cl, proline and GB, and leaf sap osmotic pressure. However, 24-EBL supply via both seed treatment and foliar application to the maize cultivars alleviated the detrimental effects of salt stress. In Cucumis sativus L. cv. Jinyan No. 4, plants grown under vermiculite and in hydroponic culture, Ahammed et al. [70] tested the efficacy of 24-EBL in alleviating organic pollutants (OPs), namely, 2,4,6-trichlorophenol, chlorpyrifos and oxytetracycline-retarded root elongation by unraveling the redox homeostasis and secondary metabolism-mediated underlying mechanisms. The results revealed that all the three tested OPs retarded elongation of roots, increased MDA, H2O2 and NO, while exogenous 24-EBL markedly decreased the accumulations of H2O2, NO and MDA *vis-a-vis* upregulating the expression of genes associated with antioxidant and detoxification systems. In case of pesticide stress, 24-EBL maintained the optimum synthesis of proteins and amino acids in Brassica juncea L. plants [71]. They applied 24-EBL (100 nM) via the seed presoaking treatment to study the changes in the synthesis of protein and amino acid contents grown under im-idacloprid (IMI) challenged environment. Plants grown under IMI stress (300 mg/kg soil) showed a decrease in protein and 21 amino acid contents. However, application of 24-EBL restored the total protein as well as amino acid contents which was decreased under IMI amended soils. In a recent study laid out in a randomized block design under

**240**

greenhouse, Jan et al. [72] applied 24-EBL (10−7 M) for 8 h as seed priming method to alleviate the toxic effects of Cr (10 mg/kg soil) in tomato plants. The results suggested that that 24-EBL application effectively stimulate growth of tomato plants exposed to Cr stress via the remodulation of the physiological, metabolic, and defense mechanisms and by maintained accumulation of Cr. Alam et al. [33] applied 24-EBL (10−7 M) in countering NaCl (100 mM) stress in soybean plants. Salinity decreased growth, gas exchange parameters, pigment contents, and chlorophyll fluorescence, Ca2+, K+ , and P and biomass yield but H2O2, MDA, EL, MG content, the activities of SOD and CAT, accumulation of proline, GB, total phenols, Na<sup>+</sup> uptake in root and shoot, and total flavonoids were found to be increased. Overall, 24-EBL supplementation provided tolerance to soybean plants by upregulating the antioxidant system, AsA-GSH cycle, and glyoxalase system. Yusuf et al. [73] under completely randomized block design studied the BRsmediated protection of growth and N metabolism and the potentiality of antioxidant system under Ni stress (0, 50, 100, or 150 mg/kg) in two cultivars of Vigna radiata, namely, PDM-139 and T-44. The role of two doses (10−8 or 10−6 M) of HBL in alleviating the Ni-induced damages via the ability of antioxidant enzymes and proline content was investigated. It was found that the Ni imposes toxic impact on the plants in a concentration dependent manner. The supply of HBL was effective in countering Ni stress as its application conferred tolerance up to 100 mg/kg in improving growth, nodulation, photosynthesis and yield attributes consequently. Fariduddin et al. [74] exposed Cucumis sativus L. plants to chilling stress to study the ameliorative role of HBL through studying the growth, photosynthesis, enzymes, and biochemical parameters. Cucumber seedlings were exposed to two chilling regimes, that is, 10/8 and 5/3°C for 18 h. The spray treatment consisted 10−8 or 10−6 M of HBL applied at 30-day stage to plants. Chilling stress imposes marked reductions in growth, chlorophyll, net photosynthesis, efficiency of photosystem II and alterations in NR and carbonic anhydrase (CA) activities. In contrast, the activities of antioxidant enzymes viz-CAT, POD, and SOD along with the proline content increased in response to chilling stress. HBL supply exerted a protective role via the maintained higher values of antioxidant enzymes and proline content under chilling stress. In order to assess the role of HBL (10−8 M) under two Cd doses (3 and 9 mg/kg sand) in Solanum lycopersicum plants, Singh and Prasad [75] designed an experiment in plant growth chamber. Treatment of plants to Cd stress resulted in a significant decrease in enzymes associate with N metabolism. The application of exogenous HBL supply ameliorated the ill effects of Cd stress by triggering an increase in growth, photosynthesis, protein and carbohydrate content and inorganic N and N assimilating enzymes. Kaur et al. [76] proposed the model of HBL-mediated regulation of antioxidant enzyme activities and gene expression in Brassica juncea plants to counteract the combined salt-and temperature-induced oxidative stress. HBL treatments (0, 10−6, 10−9, and 10−12 M) was applied as seed priming on plants exposed to the low (4°C) or high (44°C) temperature and salinity (180 mM) stresses. The combined treatments of salt and temperature significantly reduced length but increased H2O2 content and the activities of SOD, CAT, APX, GR, DHAR, and MDHAR. Application of HBL improved growth traits, reduced H2O2 and the response of plants was dose-dependent.

#### **5. Role of ethylene**

Phytohormone "ethylene" (ET) is a small gaseous plant growth regulator which is responsible for ripening of fruits and is known for inducing triple response in plants [77]. The growth-regulating effects of ET were first observed by a Russian physiologist Dimitry K. Neljubov in 1901, however almost 60 years later in 1965 ET was established as a plant hormone [78]. Plant growth and senescence are chiefly regulated by the signaling mechanisms of ET [79–81]. However, it exerts its multifunctional role as one of the diversified signaling molecules to confer acclimatization to crop plants under various abiotic stresses. The signal perception of ET takes place at the membrane of endoplasmic reticulum and is bacterial two-component type which initiates a cascade signaling events through transcriptional regulation in the nucleus, thus eventually controlling a myriad of plant developmental events. Meanwhile, the interplay of ET with other signaling molecules provides adaptation to plants under various abiotic pressures [7, 8, 82–88]. Now, we will focus our attention on various reports on the functions of ET on tolerance toward major abiotic stresses in crop plants. Indian mustard plants were grown under 200 mg Zn/kg soil and the effects of 200 μL/L spray of ethephon at 20 days after sowing (DAS) was tested to alleviate the Zn toxicity. The results after 30 DAS revealed that exposure to Zn stress causes toxicity by inhibiting photosynthesis and growth, while increasing the oxidative stress biomarkers. ET application (as ethephon) to Zn-stressed plants restored photosynthesis and growth of mustard plants by decreasing oxidative stress via augmenting antioxidant activity, the metabolism of proline, glyoxalase system, and optimum nutrient homoeostasis [89]. In tomato plants, Alves et al. [90] provided new insights into the interactive role of ET on selenium-mediated antioxidant enzymes under Cd stress. Overall, the results suggested that cross talk of ET with Se manipulated the ET regulated expression of genes to induce Cd tolerance. The effect of Cr toxicity at 1.2 mM concentration given as K2Cr2O7 after 10 DAS through nutrient solution on four cultivars of Brassica juncea, namely, Varuna, Pusa Bold, Rohini and SS2 were studied under ET supplementation [35]. Plants grown under Cr stress showed an enhanced accumulation of H2O2, MDA content, and superoxide production and a marked reduction in photosynthesis and growth traits. Ethylene (2-chloroethyl phosphonic acid, 200 μL/L) boosted the activities of enzymes associated with S assimilation, proline accumulation, anti-oxidant defense system, ATP-sulfurylase and serine acetyl transferase, and GSH level and resulted in inhibition of stress ET levels to the optimal range under Cr stress, thus increasing the photosynthesis and growth. The key role of ET was further substantiated by using ET action inhibitor, silver nitrate (AgNO3) in the reversal of Cr-induced changes. In Brassica juncea plants, alleviatory role of ET (200 μL/L as ethephon) in the presence of 200 mg/kg soil each of Ni and Zn stress was investigated [91]. Application of ET reverses photosynthetic inhibition and promotes growth by inducing changes in PS II photochemistry, photosynthetic NUE, and modulation of antioxidant enzymes. The study got further confirmation by using ET action inhibitor-norbornadiene which reversed ET-induced changes. In Arabidopsis thaliana, Hartman et al. [92] studied the changes in NO and oxygen in controlling the stability of TFs in regulating of N-degron pathway and adaptation to flooding-induced hypoxia. They concluded that ET-mediated decrease in NO conferred tolerance to plants against hypoxia stress. The pretreatment of rice plants with the ET precursor under submergence stress plays a key role in the survival of rice plants [93]. ET signaling helped in the survival of rice seedlings under submergence stress by affecting intracellular redox homeostasis and antioxidant systems. Jegadeesan et al. [94] unraveled the proteomics involved in pollen of Solanum lycopersicum thermotolerance mechanisms mediated by ET. The quantitative analysis showed that heat stress-affected protein homeostasis and metabolism of carbohydrate and energy. ET (ethephon) increased pollen quality prior to heat stress exposure. According to gel LC-MS fractionation a total of 1355 proteins were identified. ET application shifted pollen proteome exposed to the heat stress closer to the proteome under non-stressful conditions and caused an upregulation into

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*Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones*

salt tolerance in Arabidopsis thaliana by maintaining K<sup>+</sup>

Arabidopsis thaliana has also been reported [101].

**6. Role of methyl jasmonate**

soluble sugars, protein, and K<sup>+</sup>

increase in proline, Na+

the protective mechanisms against the heat-induced oxidative stress by causing a significant higher abundance of glutathione-disulfide reductase, glutaredoxin, and protein disulfide isomerase. Iqbal et al. [95] studied the potential of exogenously sourced ET (200 μL/L) under nutrient deficiency (40 mg N/kg soil) at 40 DAS. ET supply increased the stomatal conductance, photosynthesis, and promotes growth under low nutrient availability in mustard plants. Application ET also alleviated salt stress response in various crop plants. In fact, the alteration of ET signaling mechanism significantly affects the response of plants to salt stress [96]. Freitas et al. [97] worked out the capacity of ET in triggering salinity stress tolerance in maize plants. During NaCl exposure, a biphasic ET production (at 5.5 and 12.5 h) and decrease in total polyamine content was noticed in salt-sensitive plants. In the salttolerant genotype, there was lack of stress ET biosynthesis and this was attributed to the 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) and *ZmACO5b* gene downregulation activity and expression. The ET was involved in promoting salt stress tolerance by activating pathways of signaling by H2O2 that is dependent upon enzymes of polyamine catabolism. Application of ET also improved the tolerance to

to an appreciable extent [98]. Gharbi et al. [99] showed that inhibition of ET biosynthesis minimizes salt (125 mM) tolerance in Solanum chilense. The involvement of ET was also ascertained in the alleviation of salt-induced photosynthesis and growth reductions in Vigna radiata L. [100]. A central role of ET in BRs-induced alternative respiratory pathway which played an important role in abiotic stress tolerance in Cucumis sativus L. has also been reported [88]. A critical role of ET for the maintenance of root growth and mineral homeostasis under excess Fe stress in

Methyl jasmonate (MJ) is one of the conjugates of jasmonic acids (JAs) and are important as well as ubiquitous phytohormone distributed in plants [102]. MJ is implicated in plant responses to salt, drought, metal/s, and heat stresses. MJ exert its alleviatory role under abiotic stresses by modulating plant morphology and physiology to a great extent. Taheri et al. [103] studied the effects of exogenous MJ-mediated (0, 60, and 120 mM) improvements in physiological and biochemical traits of *Anchusa italic* plants under salinity (5, 10, and 15 dS m−1). Salinity stress significantly decreased growth characters, RWC, chlorophyll a, total chlorophyll,

aforementioned traits in plants grown under salt stress. In salt-tolerant rice genotypes, a higher concentration of MJ has been reported [104]. In wheat plants, application of 2.0 mM MJ ameliorated salt induced changes by boosting the expression of antioxidant enzymes, such as CAT, SOD and APX, and enhancing the GSH, chlorophyll b, and carotenoids contents [105]. In Hordeum vulgare, MJ-mediated (12 μM) regulation of genes of enzymes such as arginine decarboxylase, apoplastic invertase, and RuBisCo activase were found to be involved in imparting salt stress resistance [106]. The signaling of JAs promotes salt stress tolerance via the wheat allene oxide cyclase gene [107]. The wheat plants were exposed to saline stress conditions (12 dS m−1) and the results showed that height of plant, leaf number per plant, tiller number, fresh and dry weight per plant, spike length, grain number per spike, grain weight per spike, and yield were reduced. MJ application mitigated the ill effects of salt stress by increasing the abovementioned traits in wheat plants [108]. In a polyethylene applied pot study, Tavallali and Karimi [109] studied the

contents but at the same time induced a marked

, and Ca2+ contents. The application of MJ increases the

content in shoots and roots

*DOI: http://dx.doi.org/10.5772/intechopen.93710*

*Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones DOI: http://dx.doi.org/10.5772/intechopen.93710*

*Abiotic Stress in Plants*

by a Russian physiologist Dimitry K. Neljubov in 1901, however almost 60 years later in 1965 ET was established as a plant hormone [78]. Plant growth and senescence are chiefly regulated by the signaling mechanisms of ET [79–81]. However, it exerts its multifunctional role as one of the diversified signaling molecules to confer acclimatization to crop plants under various abiotic stresses. The signal perception of ET takes place at the membrane of endoplasmic reticulum and is bacterial two-component type which initiates a cascade signaling events through transcriptional regulation in the nucleus, thus eventually controlling a myriad of plant developmental events. Meanwhile, the interplay of ET with other signaling molecules provides adaptation to plants under various abiotic pressures [7, 8, 82–88]. Now, we will focus our attention on various reports on the functions of ET on tolerance toward major abiotic stresses in crop plants. Indian mustard plants were grown under 200 mg Zn/kg soil and the effects of 200 μL/L spray of ethephon at 20 days after sowing (DAS) was tested to alleviate the Zn toxicity. The results after 30 DAS revealed that exposure to Zn stress causes toxicity by inhibiting photosynthesis and growth, while increasing the oxidative stress biomarkers. ET application (as ethephon) to Zn-stressed plants restored photosynthesis and growth of mustard plants by decreasing oxidative stress via augmenting antioxidant activity, the metabolism of proline, glyoxalase system, and optimum nutrient homoeostasis [89]. In tomato plants, Alves et al. [90] provided new insights into the interactive role of ET on selenium-mediated antioxidant enzymes under Cd stress. Overall, the results suggested that cross talk of ET with Se manipulated the ET regulated expression of genes to induce Cd tolerance. The effect of Cr toxicity at 1.2 mM concentration given as K2Cr2O7 after 10 DAS through nutrient solution on four cultivars of Brassica juncea, namely, Varuna, Pusa Bold, Rohini and SS2 were studied under ET supplementation [35]. Plants grown under Cr stress showed an enhanced accumulation of H2O2, MDA content, and superoxide production and a marked reduction in photosynthesis and growth traits. Ethylene (2-chloroethyl phosphonic acid, 200 μL/L) boosted the activities of enzymes associated with S assimilation, proline accumulation, anti-oxidant defense system, ATP-sulfurylase and serine acetyl transferase, and GSH level and resulted in inhibition of stress ET levels to the optimal range under Cr stress, thus increasing the photosynthesis and growth. The key role of ET was further substantiated by using ET action inhibitor, silver nitrate (AgNO3) in the reversal of Cr-induced changes. In Brassica juncea plants, alleviatory role of ET (200 μL/L as ethephon) in the presence of 200 mg/kg soil each of Ni and Zn stress was investigated [91]. Application of ET reverses photosynthetic inhibition and promotes growth by inducing changes in PS II photochemistry, photosynthetic NUE, and modulation of antioxidant enzymes. The study got further confirmation by using ET action inhibitor-norbornadiene which reversed ET-induced changes. In Arabidopsis thaliana, Hartman et al. [92] studied the changes in NO and oxygen in controlling the stability of TFs in regulating of N-degron pathway and adaptation to flooding-induced hypoxia. They concluded that ET-mediated decrease in NO conferred tolerance to plants against hypoxia stress. The pretreatment of rice plants with the ET precursor under submergence stress plays a key role in the survival of rice plants [93]. ET signaling helped in the survival of rice seedlings under submergence stress by affecting intracellular redox homeostasis and antioxidant systems. Jegadeesan et al. [94] unraveled the proteomics involved in pollen of Solanum lycopersicum thermotolerance mechanisms mediated by ET. The quantitative analysis showed that heat stress-affected protein homeostasis and metabolism of carbohydrate and energy. ET (ethephon) increased pollen quality prior to heat stress exposure. According to gel LC-MS fractionation a total of 1355 proteins were identified. ET application shifted pollen proteome exposed to the heat stress closer to the proteome under non-stressful conditions and caused an upregulation into

**242**

the protective mechanisms against the heat-induced oxidative stress by causing a significant higher abundance of glutathione-disulfide reductase, glutaredoxin, and protein disulfide isomerase. Iqbal et al. [95] studied the potential of exogenously sourced ET (200 μL/L) under nutrient deficiency (40 mg N/kg soil) at 40 DAS. ET supply increased the stomatal conductance, photosynthesis, and promotes growth under low nutrient availability in mustard plants. Application ET also alleviated salt stress response in various crop plants. In fact, the alteration of ET signaling mechanism significantly affects the response of plants to salt stress [96]. Freitas et al. [97] worked out the capacity of ET in triggering salinity stress tolerance in maize plants. During NaCl exposure, a biphasic ET production (at 5.5 and 12.5 h) and decrease in total polyamine content was noticed in salt-sensitive plants. In the salttolerant genotype, there was lack of stress ET biosynthesis and this was attributed to the 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) and *ZmACO5b* gene downregulation activity and expression. The ET was involved in promoting salt stress tolerance by activating pathways of signaling by H2O2 that is dependent upon enzymes of polyamine catabolism. Application of ET also improved the tolerance to salt tolerance in Arabidopsis thaliana by maintaining K<sup>+</sup> content in shoots and roots to an appreciable extent [98]. Gharbi et al. [99] showed that inhibition of ET biosynthesis minimizes salt (125 mM) tolerance in Solanum chilense. The involvement of ET was also ascertained in the alleviation of salt-induced photosynthesis and growth reductions in Vigna radiata L. [100]. A central role of ET in BRs-induced alternative respiratory pathway which played an important role in abiotic stress tolerance in Cucumis sativus L. has also been reported [88]. A critical role of ET for the maintenance of root growth and mineral homeostasis under excess Fe stress in Arabidopsis thaliana has also been reported [101].

#### **6. Role of methyl jasmonate**

Methyl jasmonate (MJ) is one of the conjugates of jasmonic acids (JAs) and are important as well as ubiquitous phytohormone distributed in plants [102]. MJ is implicated in plant responses to salt, drought, metal/s, and heat stresses. MJ exert its alleviatory role under abiotic stresses by modulating plant morphology and physiology to a great extent. Taheri et al. [103] studied the effects of exogenous MJ-mediated (0, 60, and 120 mM) improvements in physiological and biochemical traits of *Anchusa italic* plants under salinity (5, 10, and 15 dS m−1). Salinity stress significantly decreased growth characters, RWC, chlorophyll a, total chlorophyll, soluble sugars, protein, and K<sup>+</sup> contents but at the same time induced a marked increase in proline, Na+ , and Ca2+ contents. The application of MJ increases the aforementioned traits in plants grown under salt stress. In salt-tolerant rice genotypes, a higher concentration of MJ has been reported [104]. In wheat plants, application of 2.0 mM MJ ameliorated salt induced changes by boosting the expression of antioxidant enzymes, such as CAT, SOD and APX, and enhancing the GSH, chlorophyll b, and carotenoids contents [105]. In Hordeum vulgare, MJ-mediated (12 μM) regulation of genes of enzymes such as arginine decarboxylase, apoplastic invertase, and RuBisCo activase were found to be involved in imparting salt stress resistance [106]. The signaling of JAs promotes salt stress tolerance via the wheat allene oxide cyclase gene [107]. The wheat plants were exposed to saline stress conditions (12 dS m−1) and the results showed that height of plant, leaf number per plant, tiller number, fresh and dry weight per plant, spike length, grain number per spike, grain weight per spike, and yield were reduced. MJ application mitigated the ill effects of salt stress by increasing the abovementioned traits in wheat plants [108]. In a polyethylene applied pot study, Tavallali and Karimi [109] studied the

effect of foliar application of MJ (0, 0.025, 0.050, and 0.075 mM) in enhancing salinity stress (0, 50, 100, and 150 mM) mitigation of almond root stocks. The MJ-mediated improvement in salt stress tolerance was attributed to the restriction of gene expression and activity of cytokinin oxidase which results in the inhibition of cytokinin decrease. MJ imparted salt tolerance by regulating the endogenous biosynthesis of phytohormones, expression of antioxidant activity, and gas-exchange traits of almond rootstocks. The possible role of MJ (0.25 mM) on the physiological responses and growth of *Fragaria* × *ananassa* cv. "camarosa" under salinity stress (0, 30, and, 60 mM NaCl) was investigated. Application of 0.25 mM MJ boosted the activities of antioxidant enzymes that ameliorated the salt-induced salinity stress effects [110]. Priming rice plants with MJ was reported to ameliorate the polyethylene glycol-induced osmotic stress [111]. In a recent study involving wheat plants, Allagulova et al. [112] applied MJ (0.1 μM) to unravel its alleviatory role under water-induced stress by investigating the potential participation of dehydrins. The stress was imposed by increasing the concentration of mannitol from 3 to 5% in the growth medium. Wheat seedlings pretreated with 0.1 μM MJ found to reduce the level of drought-induced retardations and enhanced the accumulation of the transcripts of *TADHN* dehydrin and proteins as well. In order to evaluate the effects of drought under exogenously applied MJ in wheat cultivars (Yu-Mai-1, Lu-Nong-116, HuaiMai-19, Yan-Nong-19, Bai-Maizi), a simple randomized complete design experiment was executed [113]. The drought was imposed at three stages: jointing, heading, or grain filling. The application of MJ was accomplished one week after the exposure of plants to the imposition of drought stress. The results showed that drought stress substantially decreased the growth and yield of all wheat cultivars reflected in the form of plant height, peduncle length, dry biomass of different plant parts, and also in yield. The application of MJ improved the drought resistance mainly by maintaining growth and yield traits of wheat plants. A pot-culture experiment in order to investigate the role of MJ presoaking (50 μM) for 8 h treatment on maize plants under water stress in the form of water field capacity (WFC) 65, 55, and 45% was setup. MJ application lead to an increase in plant height, fresh and dry weight, the pigment levels total carbohydrates, total soluble sugar, polysaccharides, free amino acids, proline, total protein, activities of CAT, POX and SOD and contents of N, P, and K and endogenous IAA but a decrease in ABA levels of wheat plants under stress condition [114]. In Solanum lycopersicum*,* the role of JA accumulation in the modification of water deficit-induced stomatal closure was studied. The drought stress-induced the closure of stomata that was correlated with the accumulation of JA, but in grafts of WT and *def-1* mutant which does not accumulate JA, the stomata was found to be insensitive [115]. Improvement of drought stress tolerance by the application of MJ has also been reported in soybean genotypes (Giza 22 and 35) [116], pear [117], sunflower seedlings [118], and *Cistus albidus* L. [119] plants. Nonetheless, application of MJ (10 μM) has been found to reduce chilling injury in cucumber by inhibiting the production of H2O2 [120]. MJ-mediated improvements in chilling stress tolerance in cold-stored lemon fruits has also been reported [121]. In case of metal/s stress, MJ application played a significant role in ameliorating the damages in physiology and morphology of diverse crop plants. The effect of exogenous MJ in two Brassica napus L. cultivars (ZS 758—a black seed type, and Zheda 622—a yellow seed type) was investigated against exposure to arsenic toxicity. MJ alleviates As-induced oxidative damages by significantly increasing chlorophyll fluorescence, biomass production and concomitant reduction in MDA and ROS contents. MJ application also maintained the high pools of GSH and AsA along with enhanced transcript expression SOD, APX, CAT, POD, and secondary metabolites (*PAL, PPO, CAD*) and reduction in As uptake [36]. Zaid and Mohammad [31] applied 1 μM MJ to test its alleviating capacity

**245**

**Figure 1.**

*Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones*

against Cd (150 mg/kg) stress in Mentha arvensis plants. Cd applied through soil imposes restrictions in growth, physio-biochemical traits. The enhanced ROS accumulation and stomatal closure were also observed in plants grown under Cd stress. Application of MJ alleviated the Cd stress by reducing the damages in physiobiochemical traits along with reduced ROS detoxification. Pre-incubating Phaseolus coccineus plants with 10−5 M MJ has been found to minimize the Cu toxicity [122]. The identification of differentially expressed protein spots suggested the putative role of MJ in diverse physiological processes including oxidative tolerance and defense-related metabolism [123]. Thus, the above discussion clearly suggests that MJ alleviates the metal/s-induced oxidative stress by modulating the key physio-

Crop plants are exposed to myriads of abiotic stress conditions and undergo a significant retardation in growth and development, thus reducing crop productivity. Stresses are perceived, and modulation in the expression of genes encoding diverse proteins are induced in the signal transduction pathways in plants. Application of discussed phytohormones in the present chapter showed that the cross talk of phytohormones with various signaling agents under different stress conditions in diverse crop plants impart stress tolerance under stress pressures. A schematic representation on phytohormones-mediated abiotic stress tolerance in given in

morphological traits in diverse crop plant to impart stress tolerance.

*Abiotic stress and phytohormones' signal transduction pathway in plants.*

*DOI: http://dx.doi.org/10.5772/intechopen.93710*

**7. Conclusion and future outlook**

**Figure 1**.

*Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones DOI: http://dx.doi.org/10.5772/intechopen.93710*

*Abiotic Stress in Plants*

effect of foliar application of MJ (0, 0.025, 0.050, and 0.075 mM) in enhancing salinity stress (0, 50, 100, and 150 mM) mitigation of almond root stocks. The MJ-mediated improvement in salt stress tolerance was attributed to the restriction of gene expression and activity of cytokinin oxidase which results in the inhibition of cytokinin decrease. MJ imparted salt tolerance by regulating the endogenous biosynthesis of phytohormones, expression of antioxidant activity, and gas-exchange traits of almond rootstocks. The possible role of MJ (0.25 mM) on the physiological responses and growth of *Fragaria* × *ananassa* cv. "camarosa" under salinity stress (0, 30, and, 60 mM NaCl) was investigated. Application of 0.25 mM MJ boosted the activities of antioxidant enzymes that ameliorated the salt-induced salinity stress effects [110]. Priming rice plants with MJ was reported to ameliorate the polyethylene glycol-induced osmotic stress [111]. In a recent study involving wheat plants, Allagulova et al. [112] applied MJ (0.1 μM) to unravel its alleviatory role under water-induced stress by investigating the potential participation of dehydrins. The stress was imposed by increasing the concentration of mannitol from 3 to 5% in the growth medium. Wheat seedlings pretreated with 0.1 μM MJ found to reduce the level of drought-induced retardations and enhanced the accumulation of the transcripts of *TADHN* dehydrin and proteins as well. In order to evaluate the effects of drought under exogenously applied MJ in wheat cultivars (Yu-Mai-1, Lu-Nong-116, HuaiMai-19, Yan-Nong-19, Bai-Maizi), a simple randomized complete design experiment was executed [113]. The drought was imposed at three stages: jointing, heading, or grain filling. The application of MJ was accomplished one week after the exposure of plants to the imposition of drought stress. The results showed that drought stress substantially decreased the growth and yield of all wheat cultivars reflected in the form of plant height, peduncle length, dry biomass of different plant parts, and also in yield. The application of MJ improved the drought resistance mainly by maintaining growth and yield traits of wheat plants. A pot-culture experiment in order to investigate the role of MJ presoaking (50 μM) for 8 h treatment on maize plants under water stress in the form of water field capacity (WFC) 65, 55, and 45% was setup. MJ application lead to an increase in plant height, fresh and dry weight, the pigment levels total carbohydrates, total soluble sugar, polysaccharides, free amino acids, proline, total protein, activities of CAT, POX and SOD and contents of N, P, and K and endogenous IAA but a decrease in ABA levels of wheat plants under stress condition [114]. In Solanum lycopersicum*,* the role of JA accumulation in the modification of water deficit-induced stomatal closure was studied. The drought stress-induced the closure of stomata that was correlated with the accumulation of JA, but in grafts of WT and *def-1* mutant which does not accumulate JA, the stomata was found to be insensitive [115]. Improvement

of drought stress tolerance by the application of MJ has also been reported in soybean genotypes (Giza 22 and 35) [116], pear [117], sunflower seedlings [118], and *Cistus albidus* L. [119] plants. Nonetheless, application of MJ (10 μM) has been found to reduce chilling injury in cucumber by inhibiting the production of H2O2 [120]. MJ-mediated improvements in chilling stress tolerance in cold-stored lemon fruits has also been reported [121]. In case of metal/s stress, MJ application played a significant role in ameliorating the damages in physiology and morphology of diverse crop plants. The effect of exogenous MJ in two Brassica napus L. cultivars (ZS 758—a black seed type, and Zheda 622—a yellow seed type) was investigated against exposure to arsenic toxicity. MJ alleviates As-induced oxidative damages by significantly increasing chlorophyll fluorescence, biomass production and concomitant reduction in MDA and ROS contents. MJ application also maintained the high pools of GSH and AsA along with enhanced transcript expression SOD, APX, CAT, POD, and secondary metabolites (*PAL, PPO, CAD*) and reduction in As uptake [36]. Zaid and Mohammad [31] applied 1 μM MJ to test its alleviating capacity

**244**

against Cd (150 mg/kg) stress in Mentha arvensis plants. Cd applied through soil imposes restrictions in growth, physio-biochemical traits. The enhanced ROS accumulation and stomatal closure were also observed in plants grown under Cd stress. Application of MJ alleviated the Cd stress by reducing the damages in physiobiochemical traits along with reduced ROS detoxification. Pre-incubating Phaseolus coccineus plants with 10−5 M MJ has been found to minimize the Cu toxicity [122]. The identification of differentially expressed protein spots suggested the putative role of MJ in diverse physiological processes including oxidative tolerance and defense-related metabolism [123]. Thus, the above discussion clearly suggests that MJ alleviates the metal/s-induced oxidative stress by modulating the key physiomorphological traits in diverse crop plant to impart stress tolerance.

#### **7. Conclusion and future outlook**

Crop plants are exposed to myriads of abiotic stress conditions and undergo a significant retardation in growth and development, thus reducing crop productivity. Stresses are perceived, and modulation in the expression of genes encoding diverse proteins are induced in the signal transduction pathways in plants. Application of discussed phytohormones in the present chapter showed that the cross talk of phytohormones with various signaling agents under different stress conditions in diverse crop plants impart stress tolerance under stress pressures. A schematic representation on phytohormones-mediated abiotic stress tolerance in given in **Figure 1**.

*Abiotic stress and phytohormones' signal transduction pathway in plants.*

*Abiotic Stress in Plants*

#### **Author details**

Haifa Abdulaziz S. Alhaithloul1 , Abdelghafar M. Abu-Elsaoud2 and Mona H. Soliman3 \*

1 Biology Department, College of Science, Jouf University, Sakaka, Kingdom of Saudi Arabia

2 Botany Department, Faculty of Science, Suez Canal University, Ismailia, Egypt

3 Botany and Microbiology Department, Faculty of Science, Cairo University, Giza, Egypt

\*Address all correspondence to: monahsh1@gmail.com

© 2020 The Author(s). Licensee IntechOpen. This chapter is 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.

**247**

*Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones*

[8] Ahammed GJ, Gantait S, Mitra M, Yang Y, Li X. Role of ethylene crosstalk

[9] Ahmad B, Zaid A, Sadiq Y, Bashir S, Wani SH. Role of selective exogenous elicitors in plant responses to abiotic stress tolerance. In: Plant Abiotic Stress Tolerance. Cham: Springer; 2019. pp.

in seed germination and early seedling development: A review. Plant Physiology and Biochemistry. 2020b;**151**:124-131. DOI: 10.1016/j.

[10] Anjum NA, Gill SS, Gill R. Plant Adaptation to Environmental Change: Significance of Amino Acids and their Derivatives. 1st ed. Wallingford: CABI; 2014. DOI: 10.1079/9781780642734.0000

[11] Fahad S, Bajwa AA, Nazir U, Anjum SA, Farooq A, Zohaib A, et al. Crop production under drought and heat stress: Plant responses and management options. Frontiers in Plant Science. 2017;**8**:1147. DOI: 10.3389/

[12] Fahad S, Chen Y, Saud S, Wang K, Xiong D, Chen C, et al. Ultraviolet radiation effect on photosynthetic pigments, biochemical attributes, antioxidant enzyme activity and hormonal contents of wheat. Journal of Food, Agriculture and Environment.

[13] Fahad S, Hussain S, Bano A, Saud S, Hassan S, Shan D, et al. Potential role of phytohormones and plant growthpromoting rhizobacteria in abiotic stresses: Consequences for changing environment. Environmental Science and Pollution Research. 2014a;**22**(7):4907-4921. DOI: 10.1007/

[14] Fahad S, Hussain S, Matloob A, Khan FA, Khaliq A, Saud S, et al.

plaphy.2020.03.016

273-290

fpls.2017.01147

2013;**11**(3&4):1635-1641

s11356-014-3754-2

*DOI: http://dx.doi.org/10.5772/intechopen.93710*

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[2] Sadiq Y, Zaid A, Khan MMA. Adaptive physiological responses of plants under abiotic stresses: Role of phytohormones. In: Plant Ecophysiology and Adaptation under Climate Change: Mechanisms and Perspectives I. Singapore: Springer;

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#### **References**

*Abiotic Stress in Plants*

**246**

Egypt

**Author details**

and Mona H. Soliman3

Kingdom of Saudi Arabia

Haifa Abdulaziz S. Alhaithloul1

\*

\*Address all correspondence to: monahsh1@gmail.com

provided the original work is properly cited.

1 Biology Department, College of Science, Jouf University, Sakaka,

2 Botany Department, Faculty of Science, Suez Canal University, Ismailia, Egypt

3 Botany and Microbiology Department, Faculty of Science, Cairo University, Giza,

© 2020 The Author(s). Licensee IntechOpen. This chapter is 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,

, Abdelghafar M. Abu-Elsaoud2

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[89] Khan MIR, Jahan B, Alajmi MF, Rehman MT, Khan NA. Exogenouslysourced ethylene modulates defense mechanisms and promotes tolerance to zinc stress in mustard (*Brassica juncea*

[90] Alves LR, dos Reis AR, Prado ER, Lavres J, Pompeu GB, Azevedo RA, et al. New insights into cadmium stressful-conditions: Role of ethylene on selenium-mediated antioxidant enzymes. Ecotoxicology and

Environmental Safety. 2019;**186**:109747

antioxidant metabolism. Protoplasma.

[92] Hartman S, Liu Z, Van Veen H, Vicente J, Reinen E, Martopawiro S, et al. Ethylene-mediated nitric oxide depletion pre-adapts plants to hypoxia stress. Nature Communications.

[93] Huang YC, Yeh TH, Yang CY. Ethylene signaling involves in seeds germination upon submergence and antioxidant response elicited confers submergence tolerance to rice seedlings.

[94] Jegadeesan S, Chaturvedi P, Ghatak A, Pressman E, Meir S, Faigenboim A, et al. Proteomics of heat-stress and ethylene-mediated thermotolerance mechanisms in tomato pollen grains. Frontiers in Plant Science.

[95] Iqbal N, Nazar R, Syeed S,

Masood A, Khan NA.

[91] Khan MIR, Khan NA. Ethylene reverses photosynthetic inhibition by nickel and zinc in mustard through changes in PS II activity, photosynthetic

nitrogen use efficiency, and

2014;**251**(5):1007-1019

2019;**10**(1):1-9

Rice. 2019;**12**(1):1-8

2018;**9**:1558

Science. 2015a;**6**:982

L.). Plants. 2019;**8**(12):540

*DOI: http://dx.doi.org/10.5772/intechopen.93710*

Interaction with other phytohormones. Frontiers in Plant Science. 2017;**8**:475

[81] Qin H, He L, Huang R. The coordination of ethylene and other hormones in primary root development. Frontiers in Plant Science. 2019;**10**:874

[82] Husain T, Fatima A, Suhel M, Singh S, Sharma A, Prasad SM, et al. A brief appraisal of ethylene signaling under abiotic stress in plants. Plant Signaling & Behavior.

[83] Khan MIR, Trivellini A, Chhillar H, Chopra P, Ferrante A, Khan NA, et al. The significance and functions of ethylene in flooding stress tolerance in plants. Environmental and

Experimental Botany. 2020;**179**:104-188. DOI: 10.1016/j.envexpbot.2020.104188

[84] Kolbert Z, Feigl G, Freschi L, Poór P. Gasotransmitters in action: Nitric oxide-

ethylene crosstalk during plant growth and abiotic stress responses.

[85] Sharma A, Kumar V, Sidhu GPS, Kumar R, Kohli SK, Yadav P, et al. Abiotic stress management in plants: Role of ethylene. In: Molecular Plant Abiotic Stress. USA: John Wiley & Sons, Ltd; 2019. pp. 185-208. DOI: 10.1002/9781119463665.ch10.

[86] Sun X, Li X, Zhu J, Huang N, Bian X, Li H, et al. Polyamines and ethylene metabolism during cold acclimation in zoysia grass (*Zoysia Japonica* Steud.). Acta Physiologiae Plantarum. 2020;**42**(8):1-10

[87] Valluru R, Davies WJ, Reynolds MP,

[88] Wei L, Deng XG, Zhu T, Zheng T, Li PX, Wu JQ, et al. Ethylene is involved

Dodd IC. Foliar abscisic acid-toethylene accumulation and response regulate shoot growth sensitivity to mild drought in wheat. Frontiers in Plant

Science. 2016;**7**:461

Antioxidants. 2019;**8**(6):167

2020;**15**(9):e1782051-1-7

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[84] Kolbert Z, Feigl G, Freschi L, Poór P. Gasotransmitters in action: Nitric oxideethylene crosstalk during plant growth and abiotic stress responses. Antioxidants. 2019;**8**(6):167

[85] Sharma A, Kumar V, Sidhu GPS, Kumar R, Kohli SK, Yadav P, et al. Abiotic stress management in plants: Role of ethylene. In: Molecular Plant Abiotic Stress. USA: John Wiley & Sons, Ltd; 2019. pp. 185-208. DOI: 10.1002/9781119463665.ch10.

[86] Sun X, Li X, Zhu J, Huang N, Bian X, Li H, et al. Polyamines and ethylene metabolism during cold acclimation in zoysia grass (*Zoysia Japonica* Steud.). Acta Physiologiae Plantarum. 2020;**42**(8):1-10

[87] Valluru R, Davies WJ, Reynolds MP, Dodd IC. Foliar abscisic acid-toethylene accumulation and response regulate shoot growth sensitivity to mild drought in wheat. Frontiers in Plant Science. 2016;**7**:461

[88] Wei L, Deng XG, Zhu T, Zheng T, Li PX, Wu JQ, et al. Ethylene is involved in brassinosteroids induced alternative respiratory pathway in cucumber (*Cucumis sativus* L.) seedlings response to abiotic stress. Frontiers in Plant Science. 2015a;**6**:982

[89] Khan MIR, Jahan B, Alajmi MF, Rehman MT, Khan NA. Exogenouslysourced ethylene modulates defense mechanisms and promotes tolerance to zinc stress in mustard (*Brassica juncea* L.). Plants. 2019;**8**(12):540

[90] Alves LR, dos Reis AR, Prado ER, Lavres J, Pompeu GB, Azevedo RA, et al. New insights into cadmium stressful-conditions: Role of ethylene on selenium-mediated antioxidant enzymes. Ecotoxicology and Environmental Safety. 2019;**186**:109747

[91] Khan MIR, Khan NA. Ethylene reverses photosynthetic inhibition by nickel and zinc in mustard through changes in PS II activity, photosynthetic nitrogen use efficiency, and antioxidant metabolism. Protoplasma. 2014;**251**(5):1007-1019

[92] Hartman S, Liu Z, Van Veen H, Vicente J, Reinen E, Martopawiro S, et al. Ethylene-mediated nitric oxide depletion pre-adapts plants to hypoxia stress. Nature Communications. 2019;**10**(1):1-9

[93] Huang YC, Yeh TH, Yang CY. Ethylene signaling involves in seeds germination upon submergence and antioxidant response elicited confers submergence tolerance to rice seedlings. Rice. 2019;**12**(1):1-8

[94] Jegadeesan S, Chaturvedi P, Ghatak A, Pressman E, Meir S, Faigenboim A, et al. Proteomics of heat-stress and ethylene-mediated thermotolerance mechanisms in tomato pollen grains. Frontiers in Plant Science. 2018;**9**:1558

[95] Iqbal N, Nazar R, Syeed S, Masood A, Khan NA.

Exogenously-sourced ethylene increases stomatal conductance, photosynthesis, and growth under optimal and deficient nitrogen fertilization in mustard. Journal of Experimental Botany. 2011;**62**(14):4955-4963

[96] Cao WH, Liu J, He XJ, Mu RL, Zhou HL, Chen SY, et al. Modulation of ethylene responses affects plant salt-stress responses. Plant Physiology. 2007;**143**(2):707-719

[97] Freitas VS, de Souza Miranda R, Costa JH, de Oliveira DF, de Oliveira Paula S, de Castro Miguel E, et al. Ethylene triggers salt tolerance in maize genotypes by modulating polyamine catabolism enzymes associated with H2O2 production. Environmental and Experimental Botany. 2018;**145**:75-86

[98] Yang L, Zu YG, Tang ZH. Ethylene improves *Arabidopsis* salt tolerance mainly via retaining K+ in shoots and roots rather than decreasing tissue Na+ content. Environmental and Experimental Botany. 2013;**86**:60-69

[99] Gharbi E, Martínez JP, Benahmed H, Lepoint G, Vanpee B, Quinet M, et al. Inhibition of ethylene synthesis reduces salt-tolerance in tomato wild relative species *Solanum chilense*. Journal of Plant Physiology. 2017;**210**:24-37

[100] Khan MIR, Asgher M, Khan NA. Alleviation of salt-induced photosynthesis and growth inhibition by salicylic acid involves glycinebetaine and ethylene in mungbean (*Vigna radiata* L.). Plant Physiology and Biochemistry. 2014;**80**:67-74

[101] Li G, Xu W, Kronzucker HJ, Shi W. Ethylene is critical to the maintenance of primary root growth and Fe homeostasis under Fe stress in *Arabidopsis*. Journal of Experimental Botany. 2015;**66**(7):2041-2054

[102] Ghasemi Pirbalouti A, Sajjadi SE, Parang K. A review (research and

patents) on jasmonic acid and its derivatives. Archiv der Pharmazie. 2014;**347**:229-239

[103] Taheri Z, Vatankhah E, Jafarian V. Methyl jasmonate improves physiological and biochemical responses of *Anchusa italica* under salinity stress. South African Journal of Botany. 2020;**130**:375-382

[104] Kang DJ, Seo YJ, Lee JD, Ishii R, Kim KU, Shin DH, et al. Jasmonic acid differentially affects growth, ion uptake and abscisic acid concentration in salttolerant and salt-sensitive rice cultivars. Journal of Agronomy and Crop Science. 2005;**191**:273-282

[105] Qiu Z, Guo J, Zhu A, Zhang L, Zhang M. Exogenous jasmonic acid can enhance tolerance of wheat seedlings to salt stress. Ecotoxicology and Environmental Safety. 2014;**104**:202-208

[106] Walia H, Wilson C, Condamine P, Liu X, Ismail AM, Close TJ. Large-scale expression profiling and physiological characterization of jasmonic acidmediated adaptation of barley to salinity stress. Plant, Cell & Environment. 2007;**30**(4):410-421

[107] Zhao Y, Dong W, Zhang N, Ai X, Wang M, Huang Z, et al. A wheat allene oxide cyclase gene enhances salinity tolerance via jasmonate signaling. Plant Physiology. 2014;**164**(2):1068-1076

[108] Islam MM, Islam S, Parvin S, Haque MA. Mitigation of salt stress by foliar application of Jasmonic acid in wheat. American Journal of Plant Biology. 2019;**4**(1):18-34

[109] Tavallali V, Karimi S. Methyl jasmonate enhances salt tolerance of almond rootstocks by regulating endogenous phytohormones, antioxidant activity and gasexchange. Journal of Plant Physiology. 2019;**234**:98-105

**255**

*Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones*

Jasmonic acid is involved in the waterstress-induced betaine accumulation in pear leaves. Plant, Cell & Environment.

2004;**27**(4):497-507

2017;**83**(3):501-511

[118] Andrade A, Escalante M, Vigliocco A, del Carmen Tordable M, Alemano S. Involvement of jasmonates in responses of sunflower (*Helianthus annuus*) seedlings to moderate water stress. Plant Growth Regulation.

[119] Jubany-Marí T, Prinsen E,

Botany. 2010;**69**(1):47-55

2014;**171**(18):1722-1731

2011;**168**(10):995-1008

[122] Hanaka A, Maksymiec W, Bednarek W. The effect of methyl jasmonate on selected physiological parameters of copper-treated *Phaseolus* 

*coccineus* plants. Plant Growth Regulation. 2015;**77**(2):167-177

[123] Chen Y, Pang Q, Dai S, Wang Y, Chen S, Yan X. Proteomic identification of differentially expressed proteins in *Arabidopsis* in response to methyl jasmonate. Journal of Plant Physiology.

[120] Liu Y, Yang X, Zhu S, Wang Y. Postharvest application of MeJA and NO reduced chilling injury in cucumber (*Cucumis sativus*) through inhibition of H2O2 accumulation. Postharvest Biology and Technology. 2016;**119**:77-83

[121] Siboza XI, Bertling I, Odindo AO. Salicylic acid and methyl jasmonate improve chilling tolerance in cold-stored lemon fruit (*Citrus limon*). Journal of Plant Physiology.

Munné-Bosch S, Alegre L. The timing of methyl jasmonate, hydrogen peroxide and ascorbate accumulation during water deficit and subsequent recovery in the Mediterranean shrub *Cistus albidus* L. Environmental and Experimental

*DOI: http://dx.doi.org/10.5772/intechopen.93710*

Zarei A. Response of strawberry plant cv.'Camarosa'to salicylic acid and methyl jasmonate application under salt stress condition. Journal of Plant Growth Regulation. 2017;**36**(3):651-659

[111] Sheteiwy MS, Gong D, Gao Y, Pan R, Hu J, Guan Y. Priming with methyl jasmonate alleviates

polyethylene glycol-induced osmotic stress in rice seeds by regulating the seed metabolic profile. Environmental and Experimental Botany. 2018;**153**:236-248

dehydrins accumulation in wheat plants. Plant Physiology and Biochemistry. 2020;**155**:676-682. DOI: 10.1016/j.

[113] Anjum SA, Tanveer M, Hussain S, Tung SA, Samad RA, Wang L, et al. Exogenously applied methyl jasmonate improves the drought tolerance in wheat imposed at early and late developmental stages. Acta Physiologiae Plantarum.

[114] Abdelgawad ZA, Khalafaallah AA, Abdallah MM. Impact of methyl jasmonate on antioxidant activity and some biochemical aspects of maize plant grown under water stress condition. Agricultural Sciences. 2014;**5**(12):1077

Attenuated accumulation of jasmonates modifies stomatal responses to water deficit. Journal of Experimental Botany.

[115] De Ollas C, Arbona V, Gómez-Cadenas A, Dodd IC.

2018;**69**(8):2103-2116

[116] Mohamed HI, Latif HH. Improvement of drought tolerance of soybean plants by using methyl jasmonate. Physiology and Molecular Biology of Plants. 2017;**23**(3):545-556

[117] Gao XP, Wang XF, Lu YF, Zhang LY, Shen YY, Liang Z, et al.

[112] Allagulova C, Avalbaev A, Fedorova K, Shakirova F. Methyl jasmonate alleviates water stress induced damages by promoting

plaphy.2020.07.012

2016;**38**(1):25

[110] Faghih S, Ghobadi C,

*Abiotic Stress Tolerance in Crop Plants: Role of Phytohormones DOI: http://dx.doi.org/10.5772/intechopen.93710*

[110] Faghih S, Ghobadi C, Zarei A. Response of strawberry plant cv.'Camarosa'to salicylic acid and methyl jasmonate application under salt stress condition. Journal of Plant Growth Regulation. 2017;**36**(3):651-659

*Abiotic Stress in Plants*

2011;**62**(14):4955-4963

2007;**143**(2):707-719

[96] Cao WH, Liu J, He XJ, Mu RL, Zhou HL, Chen SY, et al. Modulation of ethylene responses affects plant salt-stress responses. Plant Physiology.

[97] Freitas VS, de Souza Miranda R, Costa JH, de Oliveira DF, de Oliveira Paula S, de Castro Miguel E, et al. Ethylene triggers salt tolerance in maize genotypes by modulating polyamine catabolism enzymes associated with H2O2 production. Environmental and Experimental Botany. 2018;**145**:75-86

[98] Yang L, Zu YG, Tang ZH. Ethylene improves *Arabidopsis* salt tolerance mainly via retaining K+ in shoots and roots rather than decreasing tissue Na+ content. Environmental and Experimental Botany. 2013;**86**:60-69

[99] Gharbi E, Martínez JP,

[100] Khan MIR, Asgher M,

2017;**210**:24-37

Benahmed H, Lepoint G, Vanpee B, Quinet M, et al. Inhibition of ethylene synthesis reduces salt-tolerance in tomato wild relative species *Solanum chilense*. Journal of Plant Physiology.

Khan NA. Alleviation of salt-induced photosynthesis and growth inhibition by salicylic acid involves glycinebetaine and ethylene in mungbean (*Vigna radiata* L.). Plant Physiology and Biochemistry. 2014;**80**:67-74

[101] Li G, Xu W, Kronzucker HJ, Shi W. Ethylene is critical to the maintenance

[102] Ghasemi Pirbalouti A, Sajjadi SE, Parang K. A review (research and

of primary root growth and Fe homeostasis under Fe stress in *Arabidopsis*. Journal of Experimental Botany. 2015;**66**(7):2041-2054

Exogenously-sourced ethylene increases stomatal conductance, photosynthesis, and growth under optimal and deficient nitrogen fertilization in mustard. Journal of Experimental Botany.

patents) on jasmonic acid and its derivatives. Archiv der Pharmazie.

Jafarian V. Methyl jasmonate improves physiological and biochemical responses of *Anchusa italica* under salinity stress. South African Journal of Botany.

[104] Kang DJ, Seo YJ, Lee JD, Ishii R, Kim KU, Shin DH, et al. Jasmonic acid differentially affects growth, ion uptake and abscisic acid concentration in salttolerant and salt-sensitive rice cultivars. Journal of Agronomy and Crop Science.

[105] Qiu Z, Guo J, Zhu A, Zhang L, Zhang M. Exogenous jasmonic acid can enhance tolerance of wheat seedlings to salt stress. Ecotoxicology and

Environmental Safety. 2014;**104**:202-208

[106] Walia H, Wilson C, Condamine P, Liu X, Ismail AM, Close TJ. Large-scale expression profiling and physiological characterization of jasmonic acidmediated adaptation of barley to salinity stress. Plant, Cell & Environment.

[107] Zhao Y, Dong W, Zhang N, Ai X, Wang M, Huang Z, et al. A wheat allene oxide cyclase gene enhances salinity tolerance via jasmonate signaling. Plant Physiology. 2014;**164**(2):1068-1076

[108] Islam MM, Islam S, Parvin S, Haque MA. Mitigation of salt stress by foliar application of Jasmonic acid in wheat. American Journal of Plant

[109] Tavallali V, Karimi S. Methyl jasmonate enhances salt tolerance of almond rootstocks by regulating endogenous phytohormones, antioxidant activity and gas-

exchange. Journal of Plant Physiology.

Biology. 2019;**4**(1):18-34

2019;**234**:98-105

[103] Taheri Z, Vatankhah E,

2014;**347**:229-239

2020;**130**:375-382

2005;**191**:273-282

2007;**30**(4):410-421

**254**

[111] Sheteiwy MS, Gong D, Gao Y, Pan R, Hu J, Guan Y. Priming with methyl jasmonate alleviates polyethylene glycol-induced osmotic stress in rice seeds by regulating the seed metabolic profile. Environmental and Experimental Botany. 2018;**153**:236-248

[112] Allagulova C, Avalbaev A, Fedorova K, Shakirova F. Methyl jasmonate alleviates water stress induced damages by promoting dehydrins accumulation in wheat plants. Plant Physiology and Biochemistry. 2020;**155**:676-682. DOI: 10.1016/j. plaphy.2020.07.012

[113] Anjum SA, Tanveer M, Hussain S, Tung SA, Samad RA, Wang L, et al. Exogenously applied methyl jasmonate improves the drought tolerance in wheat imposed at early and late developmental stages. Acta Physiologiae Plantarum. 2016;**38**(1):25

[114] Abdelgawad ZA, Khalafaallah AA, Abdallah MM. Impact of methyl jasmonate on antioxidant activity and some biochemical aspects of maize plant grown under water stress condition. Agricultural Sciences. 2014;**5**(12):1077

[115] De Ollas C, Arbona V, Gómez-Cadenas A, Dodd IC. Attenuated accumulation of jasmonates modifies stomatal responses to water deficit. Journal of Experimental Botany. 2018;**69**(8):2103-2116

[116] Mohamed HI, Latif HH. Improvement of drought tolerance of soybean plants by using methyl jasmonate. Physiology and Molecular Biology of Plants. 2017;**23**(3):545-556

[117] Gao XP, Wang XF, Lu YF, Zhang LY, Shen YY, Liang Z, et al. Jasmonic acid is involved in the waterstress-induced betaine accumulation in pear leaves. Plant, Cell & Environment. 2004;**27**(4):497-507

[118] Andrade A, Escalante M, Vigliocco A, del Carmen Tordable M, Alemano S. Involvement of jasmonates in responses of sunflower (*Helianthus annuus*) seedlings to moderate water stress. Plant Growth Regulation. 2017;**83**(3):501-511

[119] Jubany-Marí T, Prinsen E, Munné-Bosch S, Alegre L. The timing of methyl jasmonate, hydrogen peroxide and ascorbate accumulation during water deficit and subsequent recovery in the Mediterranean shrub *Cistus albidus* L. Environmental and Experimental Botany. 2010;**69**(1):47-55

[120] Liu Y, Yang X, Zhu S, Wang Y. Postharvest application of MeJA and NO reduced chilling injury in cucumber (*Cucumis sativus*) through inhibition of H2O2 accumulation. Postharvest Biology and Technology. 2016;**119**:77-83

[121] Siboza XI, Bertling I, Odindo AO. Salicylic acid and methyl jasmonate improve chilling tolerance in cold-stored lemon fruit (*Citrus limon*). Journal of Plant Physiology. 2014;**171**(18):1722-1731

[122] Hanaka A, Maksymiec W, Bednarek W. The effect of methyl jasmonate on selected physiological parameters of copper-treated *Phaseolus coccineus* plants. Plant Growth Regulation. 2015;**77**(2):167-177

[123] Chen Y, Pang Q, Dai S, Wang Y, Chen S, Yan X. Proteomic identification of differentially expressed proteins in *Arabidopsis* in response to methyl jasmonate. Journal of Plant Physiology. 2011;**168**(10):995-1008

**257**

**Chapter 13**

N Uptake

N losses, NUE and WUE

**1. Introduction**

**Abstract**

*Nawab Ali and Mohammad Akmal*

Morphophysiological Traits,

Productivity of Wheat under

Biochemical Characteristic and

Water and Nitrogen-Colimitation:

Pathways to Improve Water and

Drought stress is the most prominent limiting factor and abiotic stress that manipulates the physiological pathway, biochemical traits and hence negatively affects wheat crop productivity. The global nitrogen (N) recovery indicated that about twofifths of N inputs are lost in the ecosystems through emission, denitrification, gaseous loss, leaching, surface runoff and volatilization etc. Farmers are using higher rates of N to harvest maximum yield but about 50–60% of applied N to crop field is not utilized by the plants and are lost to environment causing environmental pollution. These deleterious environmental consequences need to be reduced by efficient management of N and/or water. N-availability is often regulated by soil water; hence crop is experiencing N- and water-limitation simultaneously. There is great impetus to optimize their uptake through interconnectedness of water and N for yield determination of wheat because of the water scarcity and N losses. It is further advocate that there is need to investigate the intricate role of economizing N rate and water simultaneously for wheat crop growth, yield and backing quality may be beneficial to be investigate.

**Keywords:** drought, water-N co-limitation, physio biochemical traits of wheat,

Wheat is one of the most important staple food crops supporting the world population. It ranks the second most important cereal crop of the world grown on about 220 million hectares (mha) area with 716 million tons food grain production and 3.2 tons per hectare productivity globally [1]. The current wheat production meets the demand for the existing population, but we will have to increase the production with time keeping in view to achieve the target of 858 million tons by 2050 against the current production globally [2]. Hence about 1.5% annual increase in next three decades should be kept under consideration to feed the overwhelming population. Similarly, about 37% of the wheat is cultivated as rainfed where drought

#### **Chapter 13**

Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water and Nitrogen-Colimitation: Pathways to Improve Water and N Uptake

*Nawab Ali and Mohammad Akmal*

## **Abstract**

Drought stress is the most prominent limiting factor and abiotic stress that manipulates the physiological pathway, biochemical traits and hence negatively affects wheat crop productivity. The global nitrogen (N) recovery indicated that about twofifths of N inputs are lost in the ecosystems through emission, denitrification, gaseous loss, leaching, surface runoff and volatilization etc. Farmers are using higher rates of N to harvest maximum yield but about 50–60% of applied N to crop field is not utilized by the plants and are lost to environment causing environmental pollution. These deleterious environmental consequences need to be reduced by efficient management of N and/or water. N-availability is often regulated by soil water; hence crop is experiencing N- and water-limitation simultaneously. There is great impetus to optimize their uptake through interconnectedness of water and N for yield determination of wheat because of the water scarcity and N losses. It is further advocate that there is need to investigate the intricate role of economizing N rate and water simultaneously for wheat crop growth, yield and backing quality may be beneficial to be investigate.

**Keywords:** drought, water-N co-limitation, physio biochemical traits of wheat, N losses, NUE and WUE

#### **1. Introduction**

Wheat is one of the most important staple food crops supporting the world population. It ranks the second most important cereal crop of the world grown on about 220 million hectares (mha) area with 716 million tons food grain production and 3.2 tons per hectare productivity globally [1]. The current wheat production meets the demand for the existing population, but we will have to increase the production with time keeping in view to achieve the target of 858 million tons by 2050 against the current production globally [2]. Hence about 1.5% annual increase in next three decades should be kept under consideration to feed the overwhelming population. Similarly, about 37% of the wheat is cultivated as rainfed where drought is the most dominant constraint to limit wheat production [3]. Wheat is extensively grown in Asia, where Pakistan ranks eight in term of production (25 million tons) in the world [4]. The productivity of wheat is less than the 2.89 million tons per hectare for population with annual increment of 1.8% [5]. Wheat production affected by various biotic and abiotic stresses. Among the abiotic stress, water stress is affecting the vegetative growth and ultimately affecting yield of the wheat crop [6] (**Figure 1**).

Drought stress is the most prominent factor in crop production that affects the yield stability in the world [6]. Likewise, in rainfed areas the erratic rainfall is also the prime factor that limits crop productivity in in semiarid areas [7]. The occurrence of insufficient rainfall which does not meet the water requirement of the crop life cycle in certain areas occasionally cause the total crop failure [8]. The use of ground water is practice for crop production, and this ground water is declining with time with significant adverse effect on the water table due to the non-judicious use of the ground water resources [9]. Therefore, certain water conservation measures and water saving strategies and techniques should be adopted to cope with this adverse condition thereby conserving the precipitation water in the rhizosphere for the optimum crop production [10, 11].

As an essential macronutrient of plants, N is necessary for the vegetative growth, biomass, protein synthesis and the photosynthetic machinery of the crops [12]. This N is available in various forms in the rhizosphere, i.e. organic, such as in the form of amino acid and proteins, and inorganic forms, urea, nitrate ions (NO3− ), ammonium ions (NH4+) and is also found in the form of other nitrogenous compounds [13]. Of them, only NO3- and NH4+ are the forms of soil N that are easily taken by the plants through roots from the rhizosphere [14]. The aforesaid two forms need enough soil moisture for efficient absorption through the plant roots because of their high mobility in water [15]. The soil water is extracted by the plants through its roots and thereby using it for various physiological processes, maintaining internal temperature and for the process of transpiration [16]. Plant uptake various nutrients from soil solution including N for the optimum growth and development. In drought prone areas or areas where there is less and/or no eater availability because of the shortage of water or undependable nature of the

**259**

**Figure 2.**

*Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water…*

rainfall, plants are with lower N uptake and hence the overall physiological process and activity of N assimilation enzyme is also retarded [17, 18]. Therefore, the plants ability to uptake N from the soil is not only the function of N concentration and

Soil water and Nitrogen (N) are considered as the key limiting factors for maximizing plant growth, yield and quality [20]. The effect of these limiting factors is most prominent in the growing area where water stress is prevalent [21]. All the metabolic processes, biomass assimilation, growth functions and nutrients allocation in the plants are controlled by the interaction of N and water [22]. It is therefore kept in mind that wheat yield might be increased when crop ins not restricted with both N and water supply. For the availability of N optimum moisture in soil is needed. Contrary to this, enough amount of N needs to be in soil to make use of water available. In most areas, wheat yield is affected by the drought induced N deficit. Wheat morphology, physiology and biochemical character is also affected

**2. Morphophysiological, biochemicals and yield of wheat under water** 

Water and N availability, the most limiting crop growth factors affecting adversely the morphological traits, physiology of the crop, alter the biochemical changes in the grains and shoots and final yield of the crop [23]. The resource use efficiency of N and water for the crop is the need of the day. Water stress adversely affects the vegetative growth, physiological processes, biochemical properties of the grains and shoots [24] (**Figure 2**). The amount of N applied to the crop is determined by the soil moisture status, amount and frequency and frequency of precipitation during the crop growth season [25]. The higher photosynthesis, water use efficiency (NUE) and water uptake could be achieved with optimum N supply under optimum water supply [26]. Leaf anatomy, leaf rolling, leaf hairs, stomatal positions and opening/closing, are the traits of wheat crop to withstand with under various environmental stresses especially water

*Morphological, physiological and biochemical dynamics of plants affected by water stress.*

availability in soil but also the soil moisture in the root zone [19].

by water stress and nitrogen dynamics in the rhizosphere.

**and N-colimitation**

*DOI: http://dx.doi.org/10.5772/intechopen.94355*

**Figure 1.**

*Schematic representation of the drought effect on physiological processes, growth and yield.*

*Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water… DOI: http://dx.doi.org/10.5772/intechopen.94355*

rainfall, plants are with lower N uptake and hence the overall physiological process and activity of N assimilation enzyme is also retarded [17, 18]. Therefore, the plants ability to uptake N from the soil is not only the function of N concentration and availability in soil but also the soil moisture in the root zone [19].

Soil water and Nitrogen (N) are considered as the key limiting factors for maximizing plant growth, yield and quality [20]. The effect of these limiting factors is most prominent in the growing area where water stress is prevalent [21]. All the metabolic processes, biomass assimilation, growth functions and nutrients allocation in the plants are controlled by the interaction of N and water [22]. It is therefore kept in mind that wheat yield might be increased when crop ins not restricted with both N and water supply. For the availability of N optimum moisture in soil is needed. Contrary to this, enough amount of N needs to be in soil to make use of water available. In most areas, wheat yield is affected by the drought induced N deficit. Wheat morphology, physiology and biochemical character is also affected by water stress and nitrogen dynamics in the rhizosphere.

#### **2. Morphophysiological, biochemicals and yield of wheat under water and N-colimitation**

Water and N availability, the most limiting crop growth factors affecting adversely the morphological traits, physiology of the crop, alter the biochemical changes in the grains and shoots and final yield of the crop [23]. The resource use efficiency of N and water for the crop is the need of the day. Water stress adversely affects the vegetative growth, physiological processes, biochemical properties of the grains and shoots [24] (**Figure 2**). The amount of N applied to the crop is determined by the soil moisture status, amount and frequency and frequency of precipitation during the crop growth season [25]. The higher photosynthesis, water use efficiency (NUE) and water uptake could be achieved with optimum N supply under optimum water supply [26]. Leaf anatomy, leaf rolling, leaf hairs, stomatal positions and opening/closing, are the traits of wheat crop to withstand with under various environmental stresses especially water

#### **Figure 2.**

*Morphological, physiological and biochemical dynamics of plants affected by water stress.*

*Abiotic Stress in Plants*

(NO3−

for the optimum crop production [10, 11].

is the most dominant constraint to limit wheat production [3]. Wheat is extensively grown in Asia, where Pakistan ranks eight in term of production (25 million tons) in the world [4]. The productivity of wheat is less than the 2.89 million tons per hectare for population with annual increment of 1.8% [5]. Wheat production affected by various biotic and abiotic stresses. Among the abiotic stress, water stress is affecting the vegetative growth and ultimately affecting yield of the wheat crop [6] (**Figure 1**). Drought stress is the most prominent factor in crop production that affects the yield stability in the world [6]. Likewise, in rainfed areas the erratic rainfall is also the prime factor that limits crop productivity in in semiarid areas [7]. The occurrence of insufficient rainfall which does not meet the water requirement of the crop life cycle in certain areas occasionally cause the total crop failure [8]. The use of ground water is practice for crop production, and this ground water is declining with time with significant adverse effect on the water table due to the non-judicious use of the ground water resources [9]. Therefore, certain water conservation measures and water saving strategies and techniques should be adopted to cope with this adverse condition thereby conserving the precipitation water in the rhizosphere

As an essential macronutrient of plants, N is necessary for the vegetative growth, biomass, protein synthesis and the photosynthetic machinery of the crops [12]. This N is available in various forms in the rhizosphere, i.e. organic, such as in the form of amino acid and proteins, and inorganic forms, urea, nitrate ions

compounds [13]. Of them, only NO3- and NH4+ are the forms of soil N that are easily taken by the plants through roots from the rhizosphere [14]. The aforesaid two forms need enough soil moisture for efficient absorption through the plant roots because of their high mobility in water [15]. The soil water is extracted by the plants through its roots and thereby using it for various physiological processes, maintaining internal temperature and for the process of transpiration [16]. Plant uptake various nutrients from soil solution including N for the optimum growth and development. In drought prone areas or areas where there is less and/or no eater availability because of the shortage of water or undependable nature of the

*Schematic representation of the drought effect on physiological processes, growth and yield.*

), ammonium ions (NH4+) and is also found in the form of other nitrogenous

**258**

**Figure 1.**

deficit [27]. Likewise, the photosynthesis rate, transpiration, osmotic potential, relative water contents, stomatal conductance are also affected by water and N depletion [28]. Rubisco efficiency, photochemical efficiency, reactive oxygen species, antioxidants defense system, abscisic acid generation, proline accumulation, polyamines generation, increase in antioxidative enzymes, carbohydrate and protein dynamics, amylose and amylopectin contents are affected by under water and N colimitation [29].

#### **2.1 Morphological traits of wheat under water and N colimitation**

The strong association of WUE and NUE are observed commonly in different agriculture systems including crop husbandry [29]. Certain management practices which are in the way to enhance N and/or WUE at the same time are considered beneficial in term of production cost for the crops especially cereals thereby economizing water and N inputs separately [30]. The morphological attributes of the wheat crop especially the leaf traits i.e. leaf shape, size, expansion, leaf area, senescence, waxiness, leaf hairs and pubescence and the cuticle tolerance of the wheat is affected under water limited conditions [31, 32]. Similarly, the root characteristics i.e. dry weight, density and root length are adversely affected by soil moisture limitation in the rhizosphere [33]. Despite this, the vegetative and reproductive stages of the wheat crop are also affected by water deficit and limited N supply [34]. The better strategies adopted by the plants by modifying its life cycles to theses abiotic stresses (i.e. water and N deficit) are early maturation, small plant size and reduced leaf area for the drought tolerance [35]. It is observed that under water limitation, the flag leaf length is increased, and no significant change was observed in leaf width [36]. Hence, leaf expansion is the function of water extracted from the rhizosphere through rood and its abundance in plant tissues [37]. A decrease in leaf number, size and longevity may be observed under water and N limitation subsequently and their non availability alone as well [37]. In wheat crop, the leaf development is significantly affected by soil moisture depletion thereby decreasing overall biomass [38]. Similarly, N is considered as the integral part of the plant and plays a key role in increasing the leaf area, plant height and finally biomass of the plant under optimum supply [39]. Therefore, both water and N are equally important, their distribution and prevalence should keep in mind as there is a strong linkage between water and N limited supply [40]. Better morphological attributes with less production cost could be achieved under N and water colimitation.

#### **2.2 Physiological response of wheat under water and N colimitation**

In regulating plant growth, N plays vital role with a prominent impact on the crop physiology under drought induced N deficit [41]. The biomass of the wheat crop is not only affected under low N availability, but does significantly increased under optimum water supply, mainly because of the higher N content in the rhizosphere which clarifies that with the optimum N supply the presence of adequate availability of soil moisture is therefore essential for biomass, yield and physiological attributes of the wheat crop [42]. The N deficiency the sensitivity of the stomata under water deficit condition in drought prone areas [43]. The leaf photosynthesis rate is significantly affected by the optimum supply of both N and water to the crop [44]. Increase in the photosynthetic activity and biomass accumulation is observed under optimum water and limited N supply [45]. Water use efficiency (WUE) is enhanced through photosynthesis, stomatal conductance and mesophyll conductance in wheat crop and thus ultimately increasing N uptake and nitrogen use efficiency (NUE) [46].

**261**

*Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water…*

Non availability of soil moisture will not only affect N supply but also have bad effect on N cycling [47]. Thus, water plays vital role in the availability of N in the soil solution to crop and thereby enhancing the photosynthesis process, translocation of

**2.3 Biochemical traits of wheat crop under water stress and N limitation**

Certain different compounds and metabolites that are accumulated in the crop under water deficit conditions to cope with the drought stress imposition [49]. These metabolites are of key importance because of their peculiar biochemical routes and thereby enhancing the tolerance mechanism in crop plants [50]. A cross talk between various biochemical substances and metabolites are initiated through drought signaling [51]. Various substances are accumulated in the plants body under abiotic stresses especially water stress. Under water limited conditions, proline a key metabolite, that is accumulated in higher concentration under dehydration [52]. The antioxidation enzymes that scavenge the ROS (reactive oxygen species) through various osmo-protection processes that includes stability of the membrane, osmotic adjustment and gene signaling are strongly associated [52]. The vital role in drought tolerance and strong defensive antioxidant mechanism in wheat genotypes are strongly correlated with high proline concentration [53]. The genotypes grown in rainfed areas having high proline concentration compared with the ones grown in irrigated and/or humid areas [54]. Various internal physiological processes are taking place under the crop plants to cope with the drought stress [55]. Plant growth is inhibited, water loss and stomatal closure are regulated, guard cell ion translocation is alternated under water stress through the translocation of ABA from roots to leaves [56]. The wheat crop having less ABA accumulation in leaves are considered to be susceptible to drought stress compared to those which accumulate high proline contents in leaves are drought tolerant [57]. Similarly, the wheat genotypes with high proline concentration in the leaves exhibited better water use efficiency [58]. In wheat crop auxin is considered as negative regulator for drought stress. Similarly, the indole acetic acid (IAA) contents also decreasing under water limitation [59]. The antioxidant enzymes (POD), H2O2, glutathionse (GSH), proline, and malondialdehyde (MDA) concentrations are measured maximum in the wheat plants

Most of the yield traits that are associated with the improved productivity in water limited areas are complex and polygenic in nature [61]. Drought stress significantly affected the yield and yield attributes of wheat compared with well water conditions [62]. Thousand kernel weight decreased by 16% under water limited condition thereby affecting overall grain production of wheat crop under drought prone environments [63]. Similarly, the most important yield contributing trait i.e. grain number were also affected by the water stress with less grain number in the crop under drought stress imposition [64]. All the yield components are affected by the drought stress, but the effect was more prominent on grain weight and grain number that contribute to the economic yield of the crop [65]. Water stress causes reduction in grain number to a greater degree that size of the grain, hence grain number exhibiting more plasticity that rest of the components [66]. The narrow variability and low plasticity of the grain size under water stress environments resulting in efficient transport of the pre anthesis assimilates to sink [67]. The reproduction process in the plants is severely affected by water stress, cereal crops exhibits a strong adaptive mechanism up to some extent through the accumulation

assimilates, metabolism and conversion efficiency of the crop [48].

*DOI: http://dx.doi.org/10.5772/intechopen.94355*

subjected to water stress [60].

**2.4 Yield and yield contributing traits**

*Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water… DOI: http://dx.doi.org/10.5772/intechopen.94355*

Non availability of soil moisture will not only affect N supply but also have bad effect on N cycling [47]. Thus, water plays vital role in the availability of N in the soil solution to crop and thereby enhancing the photosynthesis process, translocation of assimilates, metabolism and conversion efficiency of the crop [48].

#### **2.3 Biochemical traits of wheat crop under water stress and N limitation**

Certain different compounds and metabolites that are accumulated in the crop under water deficit conditions to cope with the drought stress imposition [49]. These metabolites are of key importance because of their peculiar biochemical routes and thereby enhancing the tolerance mechanism in crop plants [50]. A cross talk between various biochemical substances and metabolites are initiated through drought signaling [51]. Various substances are accumulated in the plants body under abiotic stresses especially water stress. Under water limited conditions, proline a key metabolite, that is accumulated in higher concentration under dehydration [52]. The antioxidation enzymes that scavenge the ROS (reactive oxygen species) through various osmo-protection processes that includes stability of the membrane, osmotic adjustment and gene signaling are strongly associated [52]. The vital role in drought tolerance and strong defensive antioxidant mechanism in wheat genotypes are strongly correlated with high proline concentration [53]. The genotypes grown in rainfed areas having high proline concentration compared with the ones grown in irrigated and/or humid areas [54]. Various internal physiological processes are taking place under the crop plants to cope with the drought stress [55]. Plant growth is inhibited, water loss and stomatal closure are regulated, guard cell ion translocation is alternated under water stress through the translocation of ABA from roots to leaves [56]. The wheat crop having less ABA accumulation in leaves are considered to be susceptible to drought stress compared to those which accumulate high proline contents in leaves are drought tolerant [57]. Similarly, the wheat genotypes with high proline concentration in the leaves exhibited better water use efficiency [58]. In wheat crop auxin is considered as negative regulator for drought stress. Similarly, the indole acetic acid (IAA) contents also decreasing under water limitation [59]. The antioxidant enzymes (POD), H2O2, glutathionse (GSH), proline, and malondialdehyde (MDA) concentrations are measured maximum in the wheat plants subjected to water stress [60].

#### **2.4 Yield and yield contributing traits**

Most of the yield traits that are associated with the improved productivity in water limited areas are complex and polygenic in nature [61]. Drought stress significantly affected the yield and yield attributes of wheat compared with well water conditions [62]. Thousand kernel weight decreased by 16% under water limited condition thereby affecting overall grain production of wheat crop under drought prone environments [63]. Similarly, the most important yield contributing trait i.e. grain number were also affected by the water stress with less grain number in the crop under drought stress imposition [64]. All the yield components are affected by the drought stress, but the effect was more prominent on grain weight and grain number that contribute to the economic yield of the crop [65]. Water stress causes reduction in grain number to a greater degree that size of the grain, hence grain number exhibiting more plasticity that rest of the components [66]. The narrow variability and low plasticity of the grain size under water stress environments resulting in efficient transport of the pre anthesis assimilates to sink [67]. The reproduction process in the plants is severely affected by water stress, cereal crops exhibits a strong adaptive mechanism up to some extent through the accumulation

*Abiotic Stress in Plants*

and N colimitation [29].

N and water colimitation.

deficit [27]. Likewise, the photosynthesis rate, transpiration, osmotic potential, relative water contents, stomatal conductance are also affected by water and N depletion [28]. Rubisco efficiency, photochemical efficiency, reactive oxygen species, antioxidants defense system, abscisic acid generation, proline accumulation, polyamines generation, increase in antioxidative enzymes, carbohydrate and protein dynamics, amylose and amylopectin contents are affected by under water

The strong association of WUE and NUE are observed commonly in different agriculture systems including crop husbandry [29]. Certain management practices which are in the way to enhance N and/or WUE at the same time are considered beneficial in term of production cost for the crops especially cereals thereby economizing water and N inputs separately [30]. The morphological attributes of the wheat crop especially the leaf traits i.e. leaf shape, size, expansion, leaf area, senescence, waxiness, leaf hairs and pubescence and the cuticle tolerance of the wheat is affected under water limited conditions [31, 32]. Similarly, the root characteristics i.e. dry weight, density and root length are adversely affected by soil moisture limitation in the rhizosphere [33]. Despite this, the vegetative and reproductive stages of the wheat crop are also affected by water deficit and limited N supply [34]. The better strategies adopted by the plants by modifying its life cycles to theses abiotic stresses (i.e. water and N deficit) are early maturation, small plant size and reduced leaf area for the drought tolerance [35]. It is observed that under water limitation, the flag leaf length is increased, and no significant change was observed in leaf width [36]. Hence, leaf expansion is the function of water extracted from the rhizosphere through rood and its abundance in plant tissues [37]. A decrease in leaf number, size and longevity may be observed under water and N limitation subsequently and their non availability alone as well [37]. In wheat crop, the leaf development is significantly affected by soil moisture depletion thereby decreasing overall biomass [38]. Similarly, N is considered as the integral part of the plant and plays a key role in increasing the leaf area, plant height and finally biomass of the plant under optimum supply [39]. Therefore, both water and N are equally important, their distribution and prevalence should keep in mind as there is a strong linkage between water and N limited supply [40]. Better morphological attributes with less production cost could be achieved under

**2.1 Morphological traits of wheat under water and N colimitation**

**2.2 Physiological response of wheat under water and N colimitation**

In regulating plant growth, N plays vital role with a prominent impact on the crop physiology under drought induced N deficit [41]. The biomass of the wheat crop is not only affected under low N availability, but does significantly increased under optimum water supply, mainly because of the higher N content in the rhizosphere which clarifies that with the optimum N supply the presence of adequate availability of soil moisture is therefore essential for biomass, yield and physiological attributes of the wheat crop [42]. The N deficiency the sensitivity of the stomata under water deficit condition in drought prone areas [43]. The leaf photosynthesis rate is significantly affected by the optimum supply of both N and water to the crop [44]. Increase in the photosynthetic activity and biomass accumulation is observed under optimum water and limited N supply [45]. Water use efficiency (WUE) is enhanced through photosynthesis, stomatal conductance and mesophyll conductance in wheat crop and thus ultimately increasing N uptake and nitrogen use efficiency (NUE) [46].

**260**

of the photosynthates in various parts i.e. stem and roots in early growth phase and having the ability to reallocate the assimilates to the sink in reproductive phase of development [68]. The efficient use of the resources like limited water and N rates are the better strategy for wheat production [69]. For primary productivity photosynthetic capacity of the crop plants is the key to higher yield [70]. Water use efficiency provides a simplest mean of assessing whether yield is limited by water supply or other factors and is considered an important component of adaptation to water deficit conditions [71]. As the amount of water used is strongly affected by crop management, a good understanding of crop management effects on WUE may provide researchers opportunities to identify and select appropriate crop management practices for improved water use efficiency [72]. Limited supplemental irrigation and fertilization during the growth season can significantly increase WUE and wheat yield [73].

#### **3. Pathways to improve water and N use efficiency**

#### **3.1 Approaches for enhancing water use efficiency (WUE)**

Certain agronomic, soil management strategies that may improve the WUE are discussed as under.

#### *3.1.1 Agronomic perspectives*

The water use efficiency is the function of the agronomic practices that includes tillage practices, drought resistant and adaptive cultivars, soil fertility and pest management [74]. The crop growth and yield tends to increase under no till system or incorporation of the crop residues which directly influences the availability of soil moisture [75]. Similarly, WUE of the wheat crop enhanced under optimum sowing window, row spacing and seed rate which ultimately increments in wheat production [76]. Decreasing row spacing and increasing seed rate could enhance water soil moisture and thereby increasing water use efficiency [77]. Under optimum row spacing weeds growth is discouraged and hence crop may uptake nutrients and water efficiently [78]. Adjustment in the crop growth season through alteration of the sowing dates keeping in view the seasonal transpiration demand [79]. Early sown crop under conservation agriculture could also increase WUE of grain crops. Drought resistant cultivars resulting in high WUE than the cultivars which are drought susceptible [80]. A well-prepared sowing beds and leveled fields are the prerequisites for water saving and greater yield harvesting. The laser leveling is considered as the effective method responsible for various benefits i.e. germination uniformity, irrigation time reduction, decrease in pest and decreasing production cost [80]. The exogeneous application of certain compounds like silicon, selenium, potassium, hydrogel etc. increase the water use efficiency of the wheat crop under stressful environments, decreasing the adverse effects of biotic and abiotic stresses, enhance bioavailability of nutrients, photosynthetic efficiency and better light harvesting [81].

#### *3.1.2 Soil management perspective*

The crop yield and WUE could be significantly increased under better soil management practices through increasing water holding capacity (WHC), ease in soil moisture extraction and by decreasing the water losses through leaching [82]. Increment in WUE could be observed under good soil management practices,

**263**

*Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water…*

that causes soil moisture dynamics by evaporation and infiltration to soil that tends to increase soil water retention capacity and organic matter contents [83]. It is observed over various types and classes of soils, increment in water content at field capacity (FC) is greater than that at permanent wilting point (PWP) when soil organic matter contents are increased [84]. There is also a chance to conserve soil moisture through albedo under high plant density and narrow row spacing [85]. Compared to no tillage, disturbance taken place through tillage practices are more prominent in moisture loss through evaporation. The soil evaporation could be reduced up to 50% by crop residue incorporation [86]. This shows the gaps related to soil management that are responsible and having potential to improve WUE.

High stomatal conductance in needs more water to fix per unit leaf area for increasing the soil and water use during transpiration [87]. For increasing WUE, during peak hours of the day when transpiration is high by preventing the loss of water from the leaves through prevention by sensitivity of the stomata. Through the process of transpiration water is lost in the form vapor which facilitates CO2 uptake [88]. Thus stomata plays a vital role in increasing WUE, thereby controlling the water loss in the form of vapor and CO2 gain [89]. The opening and closing of stomata is also regulated by the environment determinants [90]. Stomatal moment is controlled by the transport and osmotically active solute accumulation and the guard cells lateral moments [91]. In most of the plant leaves, stomata are separated through an epidermal cell creating space for opening and closing [92]. In certain plant species, the clustering of stomata is also considered a better strategy for lowering evaporation demand and this phenomenon in the crop plants is considered

*3.1.3.2 Crop environment, root architecture and harvest index enhancement*

Growing of the crops in environments where there is less transpiration will result in higher WUE. The identification and allocation of such areas having less transpiration could be identified through spatial and temporal scale [94]. Enhancement in harvest index increases the water use efficiency, this provides a new research window for increasing WUE in drought prone environments [95]. The harvest index is decreased by the water stress imposition at reproductive stage of the wheat crop, hence certain strategies need to be defined to conserve the soil moisture for the future use in reproductive stage of plant growth and development [96]. Similarly, root canopy and architecture are playing important role in extracting soil moisture [96]. Rood density, root angle, root hairs, root type and root length are the characteristics that determines the water uptake from various depths of the rhizosphere [97]. In wheat crop stele and xylem number are considered to be more responsive in wheat crop in water stress conditions because of the more xylem developmental plasticity in wheat crop [98]. In cereal crops, the metaxylem diam-

The grain production per unit of soil available N is termed as nitrogen use efficiency. Certain approaches that should be kept in mind while enhancing the NUE of

*DOI: http://dx.doi.org/10.5772/intechopen.94355*

*3.1.3 Physiological and anatomical perspective*

better adaptation in drought prone areas [93].

eter and density are responsible for high WUE [99].

grain crop are described as under.

**3.2 Approaches for enhancing nitrogen use efficiency (NUE)**

*3.1.3.1 Stomatal physiology and biochemistry dynamics*

*Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water… DOI: http://dx.doi.org/10.5772/intechopen.94355*

that causes soil moisture dynamics by evaporation and infiltration to soil that tends to increase soil water retention capacity and organic matter contents [83]. It is observed over various types and classes of soils, increment in water content at field capacity (FC) is greater than that at permanent wilting point (PWP) when soil organic matter contents are increased [84]. There is also a chance to conserve soil moisture through albedo under high plant density and narrow row spacing [85]. Compared to no tillage, disturbance taken place through tillage practices are more prominent in moisture loss through evaporation. The soil evaporation could be reduced up to 50% by crop residue incorporation [86]. This shows the gaps related to soil management that are responsible and having potential to improve WUE.

#### *3.1.3 Physiological and anatomical perspective*

*Abiotic Stress in Plants*

wheat yield [73].

discussed as under.

*3.1.1 Agronomic perspectives*

better light harvesting [81].

*3.1.2 Soil management perspective*

of the photosynthates in various parts i.e. stem and roots in early growth phase and having the ability to reallocate the assimilates to the sink in reproductive phase of development [68]. The efficient use of the resources like limited water and N rates are the better strategy for wheat production [69]. For primary productivity photosynthetic capacity of the crop plants is the key to higher yield [70]. Water use efficiency provides a simplest mean of assessing whether yield is limited by water supply or other factors and is considered an important component of adaptation to water deficit conditions [71]. As the amount of water used is strongly affected by crop management, a good understanding of crop management effects on WUE may provide researchers opportunities to identify and select appropriate crop management practices for improved water use efficiency [72]. Limited supplemental irrigation and fertilization during the growth season can significantly increase WUE and

**3. Pathways to improve water and N use efficiency**

**3.1 Approaches for enhancing water use efficiency (WUE)**

Certain agronomic, soil management strategies that may improve the WUE are

The water use efficiency is the function of the agronomic practices that includes

tillage practices, drought resistant and adaptive cultivars, soil fertility and pest management [74]. The crop growth and yield tends to increase under no till system or incorporation of the crop residues which directly influences the availability of soil moisture [75]. Similarly, WUE of the wheat crop enhanced under optimum sowing window, row spacing and seed rate which ultimately increments in wheat production [76]. Decreasing row spacing and increasing seed rate could enhance water soil moisture and thereby increasing water use efficiency [77]. Under optimum row spacing weeds growth is discouraged and hence crop may uptake nutrients and water efficiently [78]. Adjustment in the crop growth season through alteration of the sowing dates keeping in view the seasonal transpiration demand [79]. Early sown crop under conservation agriculture could also increase WUE of grain crops. Drought resistant cultivars resulting in high WUE than the cultivars which are drought susceptible [80]. A well-prepared sowing beds and leveled fields are the prerequisites for water saving and greater yield harvesting. The laser leveling is considered as the effective method responsible for various benefits i.e. germination uniformity, irrigation time reduction, decrease in pest and decreasing production cost [80]. The exogeneous application of certain compounds like silicon, selenium, potassium, hydrogel etc. increase the water use efficiency of the wheat crop under stressful environments, decreasing the adverse effects of biotic and abiotic stresses, enhance bioavailability of nutrients, photosynthetic efficiency and

The crop yield and WUE could be significantly increased under better soil management practices through increasing water holding capacity (WHC), ease in soil moisture extraction and by decreasing the water losses through leaching [82]. Increment in WUE could be observed under good soil management practices,

**262**

#### *3.1.3.1 Stomatal physiology and biochemistry dynamics*

High stomatal conductance in needs more water to fix per unit leaf area for increasing the soil and water use during transpiration [87]. For increasing WUE, during peak hours of the day when transpiration is high by preventing the loss of water from the leaves through prevention by sensitivity of the stomata. Through the process of transpiration water is lost in the form vapor which facilitates CO2 uptake [88]. Thus stomata plays a vital role in increasing WUE, thereby controlling the water loss in the form of vapor and CO2 gain [89]. The opening and closing of stomata is also regulated by the environment determinants [90]. Stomatal moment is controlled by the transport and osmotically active solute accumulation and the guard cells lateral moments [91]. In most of the plant leaves, stomata are separated through an epidermal cell creating space for opening and closing [92]. In certain plant species, the clustering of stomata is also considered a better strategy for lowering evaporation demand and this phenomenon in the crop plants is considered better adaptation in drought prone areas [93].

#### *3.1.3.2 Crop environment, root architecture and harvest index enhancement*

Growing of the crops in environments where there is less transpiration will result in higher WUE. The identification and allocation of such areas having less transpiration could be identified through spatial and temporal scale [94]. Enhancement in harvest index increases the water use efficiency, this provides a new research window for increasing WUE in drought prone environments [95]. The harvest index is decreased by the water stress imposition at reproductive stage of the wheat crop, hence certain strategies need to be defined to conserve the soil moisture for the future use in reproductive stage of plant growth and development [96]. Similarly, root canopy and architecture are playing important role in extracting soil moisture [96]. Rood density, root angle, root hairs, root type and root length are the characteristics that determines the water uptake from various depths of the rhizosphere [97]. In wheat crop stele and xylem number are considered to be more responsive in wheat crop in water stress conditions because of the more xylem developmental plasticity in wheat crop [98]. In cereal crops, the metaxylem diameter and density are responsible for high WUE [99].

#### **3.2 Approaches for enhancing nitrogen use efficiency (NUE)**

The grain production per unit of soil available N is termed as nitrogen use efficiency. Certain approaches that should be kept in mind while enhancing the NUE of grain crop are described as under.

#### *3.2.1 Agronomic perspective*

Nitrogen is accepted universally as an essential component of crop production. The climatic condition is different for every crop. There are some of the main factors i.e. rainfall, solar radiation and temperature that significantly influence the demand for nitrogen, influence nitrogen use efficiency (NUE) and crop growth [100]. The demand of N to plant increases as plant grows showing a sigmoid curve (**Figure 3**). It has generally observed that nitrogen element significantly enhanced the biomass of the plant/crop if it absorbed by plant properly because maximum biomass and plant growth totally determined by the uptake and loss of nitrogen [101]. Yet, due to leaching and volatilization of nitrogen the crop cannot uptake nitrogen easily from the soil because the due to leaching the nitrogen moves down from the below root zone. Thus, efficient nitrogen management could significantly improve the nitrogen use efficiency [102].

Water availability is the essential factor that affected the NUE under limited water availability which is crucial from an environmental and economic standpoint [103]. Maximum nitrogen use efficiency (NUE) in drought tolerant varieties of winter wheat as compared with drought sensitive lines of winter wheat. Drought resistant varieties of wheat crop consistently produced higher yield as compare with drought sensitive varieties [104]. Higher nitrogen use efficiency (NUE) and water use efficiency (WUE) in drought resistant wheat varieties. Nitrogen rate parabolically increased with rainfall, while WUE and NUE were linearly related [105]. Simultaneous enhancement of NUE and WUE were more beneficial than optimization of nitrogen and water individually. It is also stated that low nitrogen application could enhanced the nitrogen use efficiency when supplied it from organic sources rather than commercial. Excess application of nitrogen to the crop could significantly reduce the crop yield and drastically decreased the nitrogen use efficiency. It is therefore, important to obtain the higher nitrogen use efficiency through adaptation of nitrogen management strategies and agronomic practices under deficit irrigation or water stress condition.

#### *3.2.2 Rotation of crops*

It is an effective strategy to enhance the nitrogen use efficiency. Effective use of soil resources i.e. nutrient and water and appropriate crop sequences could

**Figure 3.** *Graphical representation of N needed for plant growth/N uptake pattern during life cycle the plant.*

**265**

*Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water…*

maximize the crop yield. Increase in crop yield is associated with crop rotation is known as rotation effect while monoculture practice significantly decreased the crop yield [106]. There is an effective management practice of legumes and nonleguminous crop which linearly enhanced the crop yield and other yield components. Monoculture practice in field significantly declined the cop yield and degrade the soil fertility, while crop rotation is an effective strategy to obtain the higher crop yield [107]. Leguminous crops should be included to enhance the crop yield and also suppress the weeds and decreased the risk of disease infestation. There are the following benefits of crop rotation which enhanced the nutrient use efficiency, water use efficiency, reduced allelopathy and improved soil quality [108]. Cereals are the largest consumers of nitrogen use efficiency as compared with leguminous crop. Crop rotation could reduce the immobilization and residual soil nitrate available for leaching. Leguminous crops increased the soil fertility, enhanced the soil microbial activity and improve the soil structure. Leguminous crop also add nitrogen to the soil from the atmosphere due to presence of nodules in the roots [109]. Rotation practices also enhance the nitrogen use efficiency (NUE). As compare to cereals crop, leguminous crops enhanced the soil fertility, improve soil texture and structure and enhance microbial activity. Rotation practice enhance the nitrogen use efficiency (NUE), However, they also stated from their study that nitrogen supplied to the crop following a legume have been inconsistent [110]. Several studies have been documented that NUE could enhance the crop yield when supplied it from organic sources as compared with inorganic sources. Crop rotation practice significantly

increased the nitrogen use efficiency (NUE) and other components.

Irrigation management is an appropriate strategy to improve the water use efficiency and fertilizer use efficiency. Border and furrow irrigation are traditional method used for vegetable and field crops [111]. These two practices are generally associated with higher percolation losses which resulted in low nitrogen use efficiency (NUE) and water use efficiency (WUE). These traditional methods are increasingly becoming difficult in the changing climate scenario. Adoption of water efficient irrigation and other modern irrigation techniques are the best strategies to obtain the higher NUE and WUE. Many researchers confirmed that deficit irrigation strategy enhance the WUE and NUE (water use and nitrogen use efficiency) [112]. According the several authors, maximum recovery efficiency, of nitrogen applied is due to high irrigation of overhead sprinklers. Strategy of water management is linked with the nitrogen nutrition and significantly affects the NUE and WUE [113]. Water application and their adjustment is to match the actual crop demand which is

an effective management technique for obtaining higher NUE and WUE.

The uptake efficiency of most of the crops is dependent on the N source and application method. Nitrogen is lost (**Figure 4**) through urease hydrolysis to atmosphere when applied to the soil surface from urea based N source, this is because of the increased soil pH resulting its volatilization [114]. Farmers are increasing the application rate to their field for optimum productivity but in vain because this have a deleterious effect on soil, atmosphere and aquatic bodies as well [115]. Certain slow N release fertilizers are manufactured with the aim to reduce the losses [116]. The NUE could be maximized and losses are reduced under proper N application strategies [117]. Side dressing or band application, mixing in soil, injecting to soil sub surface of N fertilizers are the different strategies that could enhance the N

*3.2.4 Nitrogen source and placement method*

*DOI: http://dx.doi.org/10.5772/intechopen.94355*

*3.2.3 Irrigation management*

*Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water… DOI: http://dx.doi.org/10.5772/intechopen.94355*

maximize the crop yield. Increase in crop yield is associated with crop rotation is known as rotation effect while monoculture practice significantly decreased the crop yield [106]. There is an effective management practice of legumes and nonleguminous crop which linearly enhanced the crop yield and other yield components. Monoculture practice in field significantly declined the cop yield and degrade the soil fertility, while crop rotation is an effective strategy to obtain the higher crop yield [107]. Leguminous crops should be included to enhance the crop yield and also suppress the weeds and decreased the risk of disease infestation. There are the following benefits of crop rotation which enhanced the nutrient use efficiency, water use efficiency, reduced allelopathy and improved soil quality [108]. Cereals are the largest consumers of nitrogen use efficiency as compared with leguminous crop. Crop rotation could reduce the immobilization and residual soil nitrate available for leaching. Leguminous crops increased the soil fertility, enhanced the soil microbial activity and improve the soil structure. Leguminous crop also add nitrogen to the soil from the atmosphere due to presence of nodules in the roots [109]. Rotation practices also enhance the nitrogen use efficiency (NUE). As compare to cereals crop, leguminous crops enhanced the soil fertility, improve soil texture and structure and enhance microbial activity. Rotation practice enhance the nitrogen use efficiency (NUE), However, they also stated from their study that nitrogen supplied to the crop following a legume have been inconsistent [110]. Several studies have been documented that NUE could enhance the crop yield when supplied it from organic sources as compared with inorganic sources. Crop rotation practice significantly increased the nitrogen use efficiency (NUE) and other components.

#### *3.2.3 Irrigation management*

*Abiotic Stress in Plants*

*3.2.1 Agronomic perspective*

improve the nitrogen use efficiency [102].

irrigation or water stress condition.

*3.2.2 Rotation of crops*

Nitrogen is accepted universally as an essential component of crop production.

Water availability is the essential factor that affected the NUE under limited water availability which is crucial from an environmental and economic standpoint [103]. Maximum nitrogen use efficiency (NUE) in drought tolerant varieties of winter wheat as compared with drought sensitive lines of winter wheat. Drought resistant varieties of wheat crop consistently produced higher yield as compare with drought sensitive varieties [104]. Higher nitrogen use efficiency (NUE) and water use efficiency (WUE) in drought resistant wheat varieties. Nitrogen rate parabolically increased with rainfall, while WUE and NUE were linearly related [105]. Simultaneous enhancement of NUE and WUE were more beneficial than optimization of nitrogen and water individually. It is also stated that low nitrogen application could enhanced the nitrogen use efficiency when supplied it from organic sources rather than commercial. Excess application of nitrogen to the crop could significantly reduce the crop yield and drastically decreased the nitrogen use efficiency. It is therefore, important to obtain the higher nitrogen use efficiency through adaptation of nitrogen management strategies and agronomic practices under deficit

It is an effective strategy to enhance the nitrogen use efficiency. Effective use of soil resources i.e. nutrient and water and appropriate crop sequences could

*Graphical representation of N needed for plant growth/N uptake pattern during life cycle the plant.*

The climatic condition is different for every crop. There are some of the main factors i.e. rainfall, solar radiation and temperature that significantly influence the demand for nitrogen, influence nitrogen use efficiency (NUE) and crop growth [100]. The demand of N to plant increases as plant grows showing a sigmoid curve (**Figure 3**). It has generally observed that nitrogen element significantly enhanced the biomass of the plant/crop if it absorbed by plant properly because maximum biomass and plant growth totally determined by the uptake and loss of nitrogen [101]. Yet, due to leaching and volatilization of nitrogen the crop cannot uptake nitrogen easily from the soil because the due to leaching the nitrogen moves down from the below root zone. Thus, efficient nitrogen management could significantly

**264**

**Figure 3.**

Irrigation management is an appropriate strategy to improve the water use efficiency and fertilizer use efficiency. Border and furrow irrigation are traditional method used for vegetable and field crops [111]. These two practices are generally associated with higher percolation losses which resulted in low nitrogen use efficiency (NUE) and water use efficiency (WUE). These traditional methods are increasingly becoming difficult in the changing climate scenario. Adoption of water efficient irrigation and other modern irrigation techniques are the best strategies to obtain the higher NUE and WUE. Many researchers confirmed that deficit irrigation strategy enhance the WUE and NUE (water use and nitrogen use efficiency) [112]. According the several authors, maximum recovery efficiency, of nitrogen applied is due to high irrigation of overhead sprinklers. Strategy of water management is linked with the nitrogen nutrition and significantly affects the NUE and WUE [113]. Water application and their adjustment is to match the actual crop demand which is an effective management technique for obtaining higher NUE and WUE.

#### *3.2.4 Nitrogen source and placement method*

The uptake efficiency of most of the crops is dependent on the N source and application method. Nitrogen is lost (**Figure 4**) through urease hydrolysis to atmosphere when applied to the soil surface from urea based N source, this is because of the increased soil pH resulting its volatilization [114]. Farmers are increasing the application rate to their field for optimum productivity but in vain because this have a deleterious effect on soil, atmosphere and aquatic bodies as well [115]. Certain slow N release fertilizers are manufactured with the aim to reduce the losses [116]. The NUE could be maximized and losses are reduced under proper N application strategies [117]. Side dressing or band application, mixing in soil, injecting to soil sub surface of N fertilizers are the different strategies that could enhance the N

**Figure 4.** *Schematic diagram showing various processes of N cycle in soil plant atmosphere system.*

efficiency than the broadcast application. Surface broadcast N application resulting in greater loss as ammonia-N to atmosphere, this could be minimized if banded, side dressed, placed with or below seed, or injected to soil [118].

#### *3.2.5 Physiological perspective*

The vital factor which is responsible for growth and development of the crop is nitrogen, increases various traits of the crop thereby improving final yield [119]. The N availability affects the carbon and N partitioning between roots and shoots of the crop [120]. Under high N availability, the root shoot ratio decreases because of the prominent growth of shoots [121], this varies among varieties and cultivars. The timing of N availability is of utmost importance in wheat crop where it affects all the yield parameters especially tiller density, spike compactness, grain number, kernel weight and grain N ad protein concentration [122]. Wheat crop store and sequester the N in vegetative stage, this stored N is re allocated to the grains during reproductive stage, of them some become the part of cell wall. In grain crops, about 50–70% of the N is translocated and accumulated at maturity [123]. The N harvest index could be improved by the sequestration of N in shoots and grains. Alteration in leaf area index and specific leaf N can enhance the NUE. Understanding these physiological characteristics that regulate plant N uptake, grain N uptake, root N uptake, assimilatory process, redistribution of N within the cell, and leaf structure and architecture can help improve NUE physiologically [124]. N uptake and LAI were found directly proportional for NUE and wheat productivity [125]. Under N- and water-limited conditions the overexpressing a downstream N assimilation gene called alanine amino transferase has increased N uptake and use efficiency [126]. Another way of increasing N uptake in plants is enhancing larger and deeper roots that can capture more available N in the soil profile. Vigorous root and shoot growth are necessary for higher N recovery [127].

#### **4. The intricate relationship between nitrogen and water colimitation**

Various literatures are present and research work has been done on the nitrogen and water stress individually but there is need to explore the intricate effect of both

**267**

*Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water…*

N and/or water (**Figure 5**) thereby decreasing cost of production of wheat crop and to enhance the grain and biomass yield [128]. Both the water and N rates need to be economized for optimum wheat production under high WUE and NUE simultaneously [129]. The effect of N and water on the process of photosynthesis is present in literature, claims the positive effect of N rate on photosynthesis. Similarly, with increase in soil moisture the physiological processes are positively influenced and results in optimum wheat production [130]. In fact, there are diminishing return that with the increase of N and water, the photosynthesis rate increases, but the rate of photosynthesis tends to saturate with further increment of water and N resulting in less WUE and NUE for the wheat crop and increasing cost of production [131]. Under certain environments, it is reported that NUE may increase under maximum supply of water and contrary to this N increment may also increase WUE [132]. Therefore, the interaction of N and water is the interplay of management, environment and cultivar collectively [133]. Application of irrigation water at higher rate may cause N losses through leaching resulting in N shortage in the rhizosphere [134], this condition also leads to stomatal closure thereby affecting the crop physiological processes. Under low N availability, photosynthesis process will be less leading to reduction in wheat productivity with less WUE [135]. On the other hand, the crop susceptibility to drought, temperature stress and may increase under high N application. Plant species differs in demand for N and water that affects the photosynthesis process. The studies also suggest that increasing both N and water has positive effect on yield rather than increment in either factor. This increment in both N and water leads to higher production cost, water loss, affecting water quality, aquatic flora and fauna and ultimately causes pollution of water and air as well [136]. It is thought that N input effect will be more efficient at low water input that the higher water supply. Similarly, the NUE decreases with higher N rate and increment in water input may increase NUE at lower N rate.

*The intricate relationship of water and N for optimum N uptake affecting plant physiological processes.*

**5. Nitrogen (N)-climate interaction; fix N to fix climate change**

The wide spread use of synthetic fertilizers in agriculture [137, 138], fossil fuel use from the industry, leguminous crops cultivation on large scale has therefore increased the reactive nitrogen in the atmosphere in the last five decades [139–141]. Globally, a great threat is there to impair the water and air quality [142], biodiversity and human health due to unpredictable alteration in biogeochemical cycle especially N [143]. The considerable amount of N is lost through leaching in the form of NO3-N [144, 145]. This NO3-N leaching varies due to the N status of the soil and greatly depends on soil properties [146–149]. Thus, the shallow ground water and aquifers are contaminated through the soluble nature of the NO3 in soil water [150, 151].

*DOI: http://dx.doi.org/10.5772/intechopen.94355*

**Figure 5.**

*Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water… DOI: http://dx.doi.org/10.5772/intechopen.94355*

**Figure 5.**

*Abiotic Stress in Plants*

*3.2.5 Physiological perspective*

**Figure 4.**

efficiency than the broadcast application. Surface broadcast N application resulting in greater loss as ammonia-N to atmosphere, this could be minimized if banded,

The vital factor which is responsible for growth and development of the crop is nitrogen, increases various traits of the crop thereby improving final yield [119]. The N availability affects the carbon and N partitioning between roots and shoots of the crop [120]. Under high N availability, the root shoot ratio decreases because of the prominent growth of shoots [121], this varies among varieties and cultivars. The timing of N availability is of utmost importance in wheat crop where it affects all the yield parameters especially tiller density, spike compactness, grain number, kernel weight and grain N ad protein concentration [122]. Wheat crop store and sequester the N in vegetative stage, this stored N is re allocated to the grains during reproductive stage, of them some become the part of cell wall. In grain crops, about 50–70% of the N is translocated and accumulated at maturity [123]. The N harvest index could be improved by the sequestration of N in shoots and grains. Alteration in leaf area index and specific leaf N can enhance the NUE. Understanding these physiological characteristics that regulate plant N uptake, grain N uptake, root N uptake, assimilatory process, redistribution of N within the cell, and leaf structure and architecture can help improve NUE physiologically [124]. N uptake and LAI were found directly proportional for NUE and wheat productivity [125]. Under N- and water-limited conditions the overexpressing a downstream N assimilation gene called alanine amino transferase has increased N uptake and use efficiency [126]. Another way of increasing N uptake in plants is enhancing larger and deeper roots that can capture more available N in the soil profile. Vigorous root and shoot

**4. The intricate relationship between nitrogen and water colimitation**

Various literatures are present and research work has been done on the nitrogen and water stress individually but there is need to explore the intricate effect of both

side dressed, placed with or below seed, or injected to soil [118].

*Schematic diagram showing various processes of N cycle in soil plant atmosphere system.*

growth are necessary for higher N recovery [127].

**266**

*The intricate relationship of water and N for optimum N uptake affecting plant physiological processes.*

N and/or water (**Figure 5**) thereby decreasing cost of production of wheat crop and to enhance the grain and biomass yield [128]. Both the water and N rates need to be economized for optimum wheat production under high WUE and NUE simultaneously [129]. The effect of N and water on the process of photosynthesis is present in literature, claims the positive effect of N rate on photosynthesis. Similarly, with increase in soil moisture the physiological processes are positively influenced and results in optimum wheat production [130]. In fact, there are diminishing return that with the increase of N and water, the photosynthesis rate increases, but the rate of photosynthesis tends to saturate with further increment of water and N resulting in less WUE and NUE for the wheat crop and increasing cost of production [131]. Under certain environments, it is reported that NUE may increase under maximum supply of water and contrary to this N increment may also increase WUE [132]. Therefore, the interaction of N and water is the interplay of management, environment and cultivar collectively [133]. Application of irrigation water at higher rate may cause N losses through leaching resulting in N shortage in the rhizosphere [134], this condition also leads to stomatal closure thereby affecting the crop physiological processes. Under low N availability, photosynthesis process will be less leading to reduction in wheat productivity with less WUE [135]. On the other hand, the crop susceptibility to drought, temperature stress and may increase under high N application. Plant species differs in demand for N and water that affects the photosynthesis process. The studies also suggest that increasing both N and water has positive effect on yield rather than increment in either factor. This increment in both N and water leads to higher production cost, water loss, affecting water quality, aquatic flora and fauna and ultimately causes pollution of water and air as well [136]. It is thought that N input effect will be more efficient at low water input that the higher water supply. Similarly, the NUE decreases with higher N rate and increment in water input may increase NUE at lower N rate.

#### **5. Nitrogen (N)-climate interaction; fix N to fix climate change**

The wide spread use of synthetic fertilizers in agriculture [137, 138], fossil fuel use from the industry, leguminous crops cultivation on large scale has therefore increased the reactive nitrogen in the atmosphere in the last five decades [139–141]. Globally, a great threat is there to impair the water and air quality [142], biodiversity and human health due to unpredictable alteration in biogeochemical cycle especially N [143]. The considerable amount of N is lost through leaching in the form of NO3-N [144, 145]. This NO3-N leaching varies due to the N status of the soil and greatly depends on soil properties [146–149]. Thus, the shallow ground water and aquifers are contaminated through the soluble nature of the NO3 in soil water [150, 151].

Worldwide, NO3-N is considered as the major concern as it deteriorates the ground water and surface water quality since few decades [152–154]. Increment in the NO3-N contents in drinking water have bad effect on human and animals health as well [155, 156], also the aquatic bodies are contaminated through its higher concentration accumulation [157–160] thereby favoring the aquatic plants to grow and nourish well [161, 162] by making a surface layer thereby impeding the solar radiation to reach the aquatic fauna [163–166] and ultimately causing the death of the aquatic fauna [167] which creates eutrophication [168]. Besides this, blue baby syndrome in infants (methemoglobinemia) and human birth defects [169] are the major serious problems linked with NO3 contamination [170–171]. Therefore, it is of prime importance to estimate the NO3 leaching from cropland [172] and to evaluate the environmentally compatible and economically suitable agronomic practices [173] that could maintain and/or decrease this phenomenon [174].

The increment in the NO3 leaching loss is strongly correlated with the rainfall occurrence, intensity and irrigation volume and methods [175]. The excessive fertilization increases the risk of N loss through leaching in agriculture system [176, 177]. To feed the overwhelming population of the world, higher fertilizer application to crop field [178] is under practice have rapidly raised the NO2 emission of the atmosphere [179, 180] and is expected to increase linearly in coming decades [188], aggravating the environmental quality [181]. Through the anthropogenic rise in NO2 emission from agriculture sector to atmosphere thereby offset the efforts to decrease the CO2 sully from other sectors [182].

Global warming is directly affected by NO2 emission [183] which is considered as a major greenhouse gas [192], having 300 times more potent than CO2 because of its greater resident time in the atmosphere usually greater than 100 years [184]. The unregulated and increasing trend of the NO2 defines the global warming [185]. This increment in N availability in atmosphere affects the sinks and sources of NO2, CH4 and CO2 thereby potential increase in CO2 sequestration [186].

Climate change will certainly increase the N emission, which in turn will affect the agriculture system, aquatic water bodies, humans and animals' health [187]. Thus, climate N cross talk will expose the crops to elevated O3 [188]. Greater emission of the N will be observed from livestock and agriculture production systems as well [189]. Drought spell, erratic and unpredictable rainfall, temperature events taken place because of climate change will ultimately affects the farmers decisions and practices thereby enhancing C and N release from agriculture ecosystem [190] when higher N rates are practiced keeping in mind leaching losses [191]. N availability to crops impedes and its losses will increase under drought induction, irregularity in rainfall, high temperature events and flooding [192].

Nitrogen, the essential macronutrient responsible for plant growth and development is fundamental for farming [191]. Climate change impact may be taken under consideration for minimizing N losses [193, 194] and to manage N in better way [195–197]. Perturbation to both N and climate needs to be fixed to reduce its adverse effects environmentally compatible and economically suitable agronomic practices [198]. Firstly, irrigation water availability to field crops is a great question and this the situation become worsen in each passing day. Then the application volume to field crops in higher rates decreasing the WUE on one way and depleting the available nutrients in the soil on other hand because farmers are applying higher fertilizers to harvest maximum yield thereby ultimately increasing their cost of production. Therefore, a gate way for future research is to economize the N rates/levels for the crop growth, yield and quality by monitoring the rhizosphere moisture for irrigation water optimization till moisture allowable depletion (MAD) of the respective crops that may not affect its growth and development but also enhance the availability and utilization of the nutrients in soil solution.

**269**

*Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water…*

This chapter provides the information regarding water and N rates on wheat physiological, morphological, biochemical, qualitative changes and yield traits of wheat crop focusing on the NUE and WUE. Drought stress is the most prominent limiting factor that manipulates the physiological pathway, biochemical traits and hence negatively affects wheat crop productivity. The global nitrogen (N) recovery indicated that about two-fifths of N inputs are lost in the ecosystems through leaching, gaseous emission, denitrification, surface runoff and volatilization. About 50–60% of the applied N fertilizer to the field are lost to environment and thus not available to the plants. These deleterious environmental consequences need to be reduced by efficient management of N and/or water focusing on their intricate relationship. N-availability is often regulated by soil water; hence crop is experiencing N- and water-limitation simultaneously. There is great impetus to optimize their uptake through interconnectedness of water and N for yield determination of wheat because of the water scarcity and N losses for enhancing wheat productivity and thereby reducing the production cost. There is need to optimize the N and water colimitation simultaneously to determine the minimum N and water to harvest optimum yield with better baking quality and hence safeguarding the environment,

Therefore, a gate way for future research is to economize the N rates/levels for the crop growth, yield and quality by monitoring the rhizosphere moisture for irrigation water optimization till moisture allowable depletion (MAD) of the respective crops that may not affect its growth and development but also enhance

Department of Agronomy, Faculty of Crop Production Sciences, The University of

© 2020 The Author(s). Licensee IntechOpen. This chapter is 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,

the availability and utilization of the nutrients in soil solution.

The authors declare no conflict of interest.

*DOI: http://dx.doi.org/10.5772/intechopen.94355*

soil micro fauna and water bodies.

**Conflict of interest**

**Author details**

Nawab Ali\* and Mohammad Akmal

Agriculture Peshawar, Khyber Pakhtunkhwa, Pakistan

\*Address all correspondence to: nawab@aup.edu.pk

provided the original work is properly cited.

**6. Conclusion**

*Morphophysiological Traits, Biochemical Characteristic and Productivity of Wheat under Water… DOI: http://dx.doi.org/10.5772/intechopen.94355*

#### **6. Conclusion**

*Abiotic Stress in Plants*

and/or decrease this phenomenon [174].

decrease the CO2 sully from other sectors [182].

and CO2 thereby potential increase in CO2 sequestration [186].

irregularity in rainfall, high temperature events and flooding [192].

enhance the availability and utilization of the nutrients in soil solution.

Worldwide, NO3-N is considered as the major concern as it deteriorates the ground water and surface water quality since few decades [152–154]. Increment in the NO3-N contents in drinking water have bad effect on human and animals health as well [155, 156], also the aquatic bodies are contaminated through its higher concentration accumulation [157–160] thereby favoring the aquatic plants to grow and nourish well [161, 162] by making a surface layer thereby impeding the solar radiation to reach the aquatic fauna [163–166] and ultimately causing the death of the aquatic fauna [167] which creates eutrophication [168]. Besides this, blue baby syndrome in infants (methemoglobinemia) and human birth defects [169] are the major serious problems linked with NO3 contamination [170–171]. Therefore, it is of prime importance to estimate the NO3 leaching from cropland [172] and to evaluate the environmentally compatible and economically suitable agronomic practices [173] that could maintain

The increment in the NO3 leaching loss is strongly correlated with the rainfall occurrence, intensity and irrigation volume and methods [175]. The excessive fertilization increases the risk of N loss through leaching in agriculture system [176, 177]. To feed the overwhelming population of the world, higher fertilizer application to crop field [178] is under practice have rapidly raised the NO2 emission of the atmosphere [179, 180] and is expected to increase linearly in coming decades [188], aggravating the environmental quality [181]. Through the anthropogenic rise in NO2 emission from agriculture sector to atmosphere thereby offset the efforts to

Global warming is directly affected by NO2 emission [183] which is considered as a major greenhouse gas [192], having 300 times more potent than CO2 because of its greater resident time in the atmosphere usually greater than 100 years [184]. The unregulated and increasing trend of the NO2 defines the global warming [185]. This increment in N availability in atmosphere affects the sinks and sources of NO2, CH4

Climate change will certainly increase the N emission, which in turn will affect the agriculture system, aquatic water bodies, humans and animals' health [187]. Thus, climate N cross talk will expose the crops to elevated O3 [188]. Greater emission of the N will be observed from livestock and agriculture production systems as well [189]. Drought spell, erratic and unpredictable rainfall, temperature events taken place because of climate change will ultimately affects the farmers decisions and practices thereby enhancing C and N release from agriculture ecosystem [190] when higher N rates are practiced keeping in mind leaching losses [191]. N availability to crops impedes and its losses will increase under drought induction,

Nitrogen, the essential macronutrient responsible for plant growth and development is fundamental for farming [191]. Climate change impact may be taken under consideration for minimizing N losses [193, 194] and to manage N in better way [195–197]. Perturbation to both N and climate needs to be fixed to reduce its adverse effects environmentally compatible and economically suitable agronomic practices [198]. Firstly, irrigation water availability to field crops is a great question and this the situation become worsen in each passing day. Then the application volume to field crops in higher rates decreasing the WUE on one way and depleting the available nutrients in the soil on other hand because farmers are applying higher fertilizers to harvest maximum yield thereby ultimately increasing their cost of production. Therefore, a gate way for future research is to economize the N rates/levels for the crop growth, yield and quality by monitoring the rhizosphere moisture for irrigation water optimization till moisture allowable depletion (MAD) of the respective crops that may not affect its growth and development but also

**268**

This chapter provides the information regarding water and N rates on wheat physiological, morphological, biochemical, qualitative changes and yield traits of wheat crop focusing on the NUE and WUE. Drought stress is the most prominent limiting factor that manipulates the physiological pathway, biochemical traits and hence negatively affects wheat crop productivity. The global nitrogen (N) recovery indicated that about two-fifths of N inputs are lost in the ecosystems through leaching, gaseous emission, denitrification, surface runoff and volatilization. About 50–60% of the applied N fertilizer to the field are lost to environment and thus not available to the plants. These deleterious environmental consequences need to be reduced by efficient management of N and/or water focusing on their intricate relationship. N-availability is often regulated by soil water; hence crop is experiencing N- and water-limitation simultaneously. There is great impetus to optimize their uptake through interconnectedness of water and N for yield determination of wheat because of the water scarcity and N losses for enhancing wheat productivity and thereby reducing the production cost. There is need to optimize the N and water colimitation simultaneously to determine the minimum N and water to harvest optimum yield with better baking quality and hence safeguarding the environment, soil micro fauna and water bodies.

Therefore, a gate way for future research is to economize the N rates/levels for the crop growth, yield and quality by monitoring the rhizosphere moisture for irrigation water optimization till moisture allowable depletion (MAD) of the respective crops that may not affect its growth and development but also enhance the availability and utilization of the nutrients in soil solution.

#### **Conflict of interest**

The authors declare no conflict of interest.

#### **Author details**

Nawab Ali\* and Mohammad Akmal Department of Agronomy, Faculty of Crop Production Sciences, The University of Agriculture Peshawar, Khyber Pakhtunkhwa, Pakistan

\*Address all correspondence to: nawab@aup.edu.pk

© 2020 The Author(s). Licensee IntechOpen. This chapter is 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.

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[4] Younis H, Abbas G, Naz S, Fatima Z, Ali MA, Ahmed M, Khan MA, Ahmad S. Advanced production technologies of wheat. InAgronomic Crops 2019 (pp. 223-236). Springer, Singapore.

[5] Shiferaw B, Smale M, Braun HJ, Duveiller E, Reynolds M, Muricho G. Crops that feed the world 10. Past successes and future challenges to the role played by wheat in global food security. Food Security. 2013 Jun 1;5(3):291-317.

[6] Fahad S, Bajwa AA, Nazir U, Anjum SA, Farooq A, Zohaib A, Sadia S, Nasim W, Adkins S, Saud S, Ihsan MZ. Crop production under drought and heat stress: plant responses and management options. Frontiers in plant science. 2017 Jun 29;8:1147.

[7] Singh HP. Unit-1 Definition and Concept of Rain Fed Farming. IGNOU.

[8] Van Loon AF. Hydrological drought explained. Wiley Interdisciplinary Reviews: Water. 2015 Jul;2(4):359-92.

[9] Sahrawat KL, Wani SP, Pathak P, Rego TJ. Managing natural resources of watersheds in the semi-arid tropics for improved soil and water

quality: A review. Agricultural Water Management. 2010 Mar 1;97(3):375-81.

[10] Ullah H, Santiago-Arenas R, Ferdous Z, Attia A, Datta A. Improving water use efficiency, nitrogen use efficiency, and radiation use efficiency in field crops under drought stress: A review. InAdvances in Agronomy 2019 Jan 1 (Vol. 156, pp. 109-157). Academic Press.

[11] Kumar A, Nayak AK, Das BS, Panigrahi N, Dasgupta P, Mohanty S, Kumar U, Panneerselvam P, Pathak H. Effects of water deficit stress on agronomic and physiological responses of rice and greenhouse gas emission from rice soil under elevated atmospheric CO2. Science of the Total Environment. 2019 Feb 10;650:2032-50.

[12] Nowicka B, Ciura J, Szymańska R, Kruk J. Improving photosynthesis, plant productivity and abiotic stress tolerance–current trends and future perspectives. Journal of plant physiology. 2018 Dec 1;231:415-33.

[13] Manikandan A, Subramanian KS. Ability of Urea Impregnated Biochar Fertilizers For Securing the Slow Release of Nitrogen in Soils–Preliminary Study. International Journal of Agriculture Sciences, ISSN. 2015:0975-3710.

[14] Hill PW, Jones DL. Plant-microbe competition: does injection of isotopes of C and N into the rhizosphere effectively characterise plant use of soil N. New Phytol. 2019 Jan 1;221:796-806.

[15] Tardieu F, Simonneau T, Muller B. The physiological basis of drought tolerance in crop plants: a scenariodependent probabilistic approach. Annual review of plant biology. 2018 Apr 29;69:733-59.

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[20] Jaleel CA, Manivannan PA, Wahid A, Farooq M, Al-Juburi HJ, Somasundaram RA, Panneerselvam R. Drought stress in plants: a review on morphological characteristics and pigments composition. Int. J. Agric.

Biol. 2009 Jan 1;11(1):100-5.

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[22] Hussain M, Farooq S, Hasan W, Ul-Allah S, Tanveer M, Farooq M, Nawaz A. Drought stress in sunflower:

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[17] Kitonyo OM, Sadras VO, Zhou Y, Denton MD. Nitrogen supply and sink demand modulate the patterns of leaf senescence in maize. Field Crops Research. 2018 Aug 1;225:92-103.

[18] Antoniadis V, Levizou E, Shaheen SM, Ok YS, Sebastian A, Baum C, Prasad MN, Wenzel WW, Rinklebe J. Trace elements in the soil-plant interface: Phytoavailability, translocation, and phytoremediation–A review. Earth-Science Reviews. 2017 Aug 1;171:621-45.

[19] Leghari SJ, Wahocho NA, Laghari GM, HafeezLaghari A, MustafaBhabhan G, HussainTalpur K, Bhutto TA, Wahocho SA, Lashari AA. Role of nitrogen for plant growth and development: A review. Advances in Environmental Biology. 2016 Sep 1; 10(9):209-19.

[20] Jaleel CA, Manivannan PA, Wahid A, Farooq M, Al-Juburi HJ, Somasundaram RA, Panneerselvam R. Drought stress in plants: a review on morphological characteristics and pigments composition. Int. J. Agric. Biol. 2009 Jan 1;11(1):100-5.

[21] Hermans C, Hammond JP, White PJ, Verbruggen N. How do plants respond to nutrient shortage by biomass allocation?. Trends in plant science. 2006 Dec 1;11(12):610-7.

[22] Hussain M, Farooq S, Hasan W, Ul-Allah S, Tanveer M, Farooq M, Nawaz A. Drought stress in sunflower: Physiological effects and its management through breeding and agronomic alternatives. Agricultural water management. 2018 Mar 31;201:152-66.

[23] Prasad PV, Staggenborg SA, Ristic Z. Impacts of drought and/or heat stress on physiological, developmental,

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[24] Chakraborty D, Nagarajan S, Aggarwal P, Gupta VK, Tomar RK, Garg RN, Sahoo RN, Sarkar A, Chopra UK, Sarma KS, Kalra N. Effect of mulching on soil and plant water status, and the growth and yield of wheat (*Triticum aestivum* L.) in a semi-arid environment. Agricultural water management. 2008 Dec 1;95(12):1323-34.

[25] Noor MA. Nitrogen management and regulation for optimum NUE in maize–A mini review. Cogent Food & Agriculture. 2017 Jan 1;3(1):1348214.

[26] Tripathi DK, Singh VP, Chauhan DK, Sharma S, Prasad SM, Dubey NK, Ramawat N, editors. Plant Life under Changing Environment: Responses and Management. Academic Press; 2020 Apr 21.

[27] Santander C, Aroca R, Ruiz-Lozano JM, Olave J, Cartes P, Borie F, Cornejo P. Arbuscular mycorrhiza effects on plant performance under osmotic stress. Mycorrhiza. 2017 Oct 1; 27(7):639-57.

[28] Abid M, Tian Z, Zahoor R, Ata-Ul-Karim ST, Daryl C, Snider JL, Dai T. Pre-Drought Priming: A Key Drought Tolerance Engine in Support of Grain Development in Wheat. InAdvances in agronomy 2018 Jan 1 (Vol. 152, pp. 51-85). Academic Press.

[29] Spiertz JH. Nitrogen, sustainable agriculture and food security: a review. InSustainable agriculture 2009 (pp. 635-651). Springer, Dordrecht.

[30] Ahmad Z, Waraich EA, Akhtar S, Anjum S, Ahmad T, Mahboob W, Hafeez OB, Tapera T, Labuschagne M, Rizwan M. Physiological responses

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1;40(4):80.

of wheat to drought stress and its mitigation approaches. Acta Physiologiae Plantarum. 2018 Apr [38] Freschet GT, Swart EM, Cornelissen JH. Integrated plant phenotypic responses to contrasting above-and below-ground resources: Key roles of specific leaf area and root mass fraction. New Phytologist. 2015

[39] Li SX, Wang ZH, Hu TT, Gao YJ, Stewart BA. Nitrogen in dryland soils of China and its management. Advances in Agronomy. 2009 Jan 1;101:123-81.

[40] Kamran M, Shahbaz M, Ashraf M, Akram NA. Alleviation of droughtinduced adverse effects in spring wheat (*Triticum aestivum* L.) using proline as a pre-sowing seed treatment. Pak. J. Bot.

Jun;206(4):1247-60.

2009 Apr 1;41(2):621-32.

2014 May 1;59(3):276-83.

Biology. 2017 Mar 1;38(2):179.

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2006 Apr;440(7086):922-5.

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photosynthetic nitrogen-use efficiency:

30;7:981.

[41] Hawkesford MJ. Reducing the reliance on nitrogen fertilizer for wheat production. Journal of cereal science.

[42] Husen A, Iqbal M, Aref IM. Plant growth and foliar characteristics of faba bean (*Vicia faba* L.) as affected by indole-acetic acid under water-sufficient and water-deficient conditions. Journal of Environmental

[43] Abid M, Tian Z, Ata-Ul-Karim ST, Cui Y, Liu Y, Zahoor R, Jiang D, Dai T. Nitrogen nutrition improves the potential of wheat (*Triticum aestivum* L.) to alleviate the effects of drought stress during vegetative growth periods. Frontiers in plant science. 2016 Jun

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Ecological Monographs. 2004

2007 Sep 1;39(9):2264-74.

Feb;74(1):25-44.

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Apr;177(2):168-77.

1;31(5):1103-12.

2019 Feb;5(2):153-9.

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[50] Reddy AR, Chaitanya KV, Vivekanandan M. Drought-induced responses of photosynthesis and antioxidant metabolism in higher plants. Journal of plant physiology. 2004 Nov 18;161(11):1189-202.

[51] Chen H, Jiang JG. Osmotic adjustment and plant adaptation to environmental changes related to drought and salinity. Environmental Reviews. 2010 Dec;18(NA):309-19.

[52] Hayat S, Hayat Q, Alyemeni MN, Wani AS, Pichtel J, Ahmad A. Role of proline under changing environments: a review. Plant signaling & behavior. 2012 Nov 1;7(11):1456-66.

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61(4):291-304.

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Andralojc PJ, Raines CA, Parry MA. Natural variation in photosynthetic capacity, growth, and yield in 64 field-grown wheat genotypes. Journal of Experimental Botany. 2014 Sep

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they compatible, dissonant, or

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[62] Mwadzingeni L, Shimelis H, Tesfay S, Tsilo TJ. Screening of bread wheat genotypes for drought tolerance using phenotypic and proline analyses. Frontiers in plant science. 2016 Aug

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[65] Suneja Y, Gupta AK, Bains NS. Stress adaptive plasticity: *Aegilops tauschii* and *Triticum dicoccoides* as potential donors of drought associated morpho-physiological traits in wheat. Frontiers in Plant Science. 2019 Feb

[66] Wang JY, Xiong YC, Li FM, Siddique KH, Turner NC. Effects of drought stress on morphophysiological traits, biochemical characteristics, yield, and yield components in

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[76] Hatfield JL, Sauer TJ, Prueger JH. Managing soils to achieve greater water use efficiency: a review. Agronomy journal. 2001 Mar;93(2):271-80.

[77] Chauhan BS. Weed ecology and weed management strategies for dryseeded rice in Asia. Weed Technology. 2012 Jan;26(1):1-3.

[78] Debaeke P, Aboudrare A. Adaptation of crop management to water-limited environments. European Journal of Agronomy. 2004 Dec 1;21(4):433-46.

[79] Li Y, Li H, Li Y, Zhang S. Improving water-use efficiency by decreasing stomatal conductance and transpiration rate to maintain higher ear photosynthetic rate in drought-resistant wheat. The Crop Journal. 2017 Jun 1; 5(3):231-9.

[80] Timmusk S, Abd El-Daim IA, Copolovici L, Tanilas T, Kännaste A, Behers L, Nevo E, Seisenbaeva G, Stenström E, Niinemets Ü. Droughttolerance of wheat improved by rhizosphere bacteria from harsh environments: enhanced biomass production and reduced emissions of stress volatiles. PloS one. 2014 May 8;9(5):e96086.

[81] Abd El-Mageed TA,

El-Samnoudi IM, Ibrahim AE, Abd El Tawwab AR. Compost and mulching modulates morphological, physiological responses and water use efficiency in sorghum (bicolor L. Moench) under low moisture regime. Agricultural Water Management. 2018 Sep 30;208:431-9.

[82] Ogle SM, Alsaker C, Baldock J, Bernoux M, Breidt FJ, McConkey B, Regina K, Vazquez-Amabile GG. Climate and soil characteristics determine where no-till management can store carbon in soils and mitigate greenhouse gas emissions. Scientific reports. 2019 Aug 12;9(1):1-8.

[83] Mohanty M, Sinha NK, Painuli DK, Bandyopadhyay KK, Hati KM, Reddy KS, Chaudhary RS. Modelling soil water contents at field capacity and permanent wilting point using artificial neural network for Indian soils. National Academy Science Letters. 2015 Oct 1;38(5):373-7.

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[86] Patanè C. Leaf area index, leaf transpiration and stomatal conductance as affected by soil water deficit and VPD in processing tomato in semi arid Mediterranean climate. Journal of Agronomy and Crop Science. 2011 Jun;197(3):165-76.

[87] Papanatsiou M, Petersen J, Henderson L, Wang Y, Christie JM, Blatt MR. Optogenetic manipulation of stomatal kinetics improves carbon assimilation, water use, and growth. Science. 2019 Mar 29;363(6434):1456-9.

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[184] Wahid F, Fahad S, Danish S, Adnan M, Yue Z, Saud S, Siddiqui MH, Brtnicky M, Hammerschmiedt T, Datta R. Sustainable Management with Mycorrhizae and Phosphate Solubilizing Bacteria for Enhanced Phosphorus Uptake in Calcareous Soils. Agriculture. 2020 Aug;10(8):334.

[185] Saud SH, Chen Y, Long B, Fahad SH, Sadiq AR. The different impact on the growth of cool season turf grass under the various conditions on salinity and draught stress. Int J Agric Sci Res. 2013;3(4):77-84.

[186] Watanabe S, Iimori M, Chan DV, Hara E, Kitao H, Maehara Y. MDC1 methylation mediated by lysine methyltransferases EHMT1 and EHMT2 regulates active ATM accumulation flanking DNA damage sites. Scientific reports. 2018 Jul 18;8(1):1-0.

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[188] Saud S, Li X, Chen Y, Zhang L, Fahad S, Hussain S, Sadiq A, Chen Y. Silicon application increases drought tolerance of Kentucky bluegrass by improving plant water relations and morphophysiological functions. The Scientific World Journal. 2014 Oct;2014.

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[190] Danish S, Zafar-ul-Hye M, Fahad S, Saud S, Brtnicky M, Hammerschmiedt T, Datta R. Drought Stress Alleviation by ACC Deaminase Producing Achromobacter xylosoxidans and *Enterobacter cloacae*, with and without Timber Waste Biochar in Maize. Sustainability. 2020 Jan;12(15):6286.

[191] Tariq M, Ahmad S, Fahad S, Abbas G, Hussain S, Fatima Z, Nasim W, Mubeen M, ur Rehman MH, Khan MA, Adnan M. The impact of climate warming and crop management on phenology of sunflower-based cropping systems in Punjab, Pakistan. Agricultural and Forest Meteorology. 2018 Jun 15;256:270-82.

[192] Wajid N, Ashfaq A, Asad A. Muhammad Habib ur R, Veysel T, Fahad S, Suad S, Aziz K, Shahzad A (2017) Radiation efficiency and nitrogen fertilizer impacts on sunflower crop in contrasting environments of Punjab. Pakistan Environ Sci Pollut Res 25: 1822-1836.

[193] Wu C, Tang S, Li G, Wang S, Fahad S, Ding Y. Roles of phytohormone changes in the grain yield of rice plants exposed to heat: a review. PeerJ. 2019 Nov 19;7:e7792.

[194] Yang Z, Zhang Z, Zhang T, Fahad S, Cui K, Nie L, Peng S, Huang J. The effect of season-long temperature increases on rice cultivars grown in the central and southern regions of China. Frontiers in plant science. 2017 Nov 6;8:1908.

[195] Zafar-ul-Hye M, Naeem M, Danish S, Fahad S, Datta R, Abbas M, Rahi AA, Brtnicky M, Holátko J, Tarar ZH, Nasir M. Alleviation

of Cadmium Adverse Effects by Improving Nutrients Uptake in Bitter Gourd through Cadmium Tolerant Rhizobacteria. Environments. 2020 Aug;7(8):54.

[196] Zafar-ul-Hye M, Tahzeebul-Hassan M, Abid M, Fahad S, Brtnicky M, Dokulilova T, Datta R, Danish S. Potential role of compost mixed biochar with rhizobacteria in mitigating lead toxicity in spinach. Scientific reports. 2020 Jul 22;10(1):1-2.

[197] Zia Z, Bakhat HF, Saqib ZA, Shah GM, Fahad S, Ashraf MR, Hammad HM, Naseem W, Shahid M. Effect of water management and silicon on germination, growth, phosphorus and arsenic uptake in rice. Ecotoxicology and environmental safety. 2017 Oct 1;144:11-8.

[198] Cousins OH, Garnett TP, Rasmussen A, Mooney SJ, Smernik RJ, Brien CJ, Cavagnaro TR. Variable water cycles have a greater impact on wheat growth and soil nitrogen response than constant watering. Plant Science. 2020 Jan 1;290:110146.

**285**

**1. Introduction**

**Chapter 14**

**Abstract**

Adapting Cereal Grain Crops to

*Tinashe Zenda, Songtao Liu and Huijun Duan*

adaptation to future climate change exacerbated drought stress.

is particularly relevant for cereal grain crops.

**Keywords:** drought stress, drought tolerance, cereal crops, omics approaches, phenotyping, genetic engineering, climate change, conservation agriculture

Drought stress is the primary environmental factor influencing the growth, development and productivity of crops and its significance is expected to increase in the wake of global climate change [1–4]. This presents a serious challenge to the food and nutrition security of an ever-rising world human population. Moreover, the current transition from carbon/fossil intensive fuel driven economies to modern climate-smart low-carbon economies further strains our crop production systems [5]. Adapting field crops to drought stress therefore becomes critical for sustainable agricultural production under such climate change scenario [6]. To achieve that goal, breeding drought resilient crop cultivars that maintain yield stability under such conditions befits the most economical, effective and sustainable strategy. This

Cereal grain crops, chiefly rice (*Oryza sativa* L.), wheat (*Triticum aestivum* L.), maize (*Zea mays* L.), sorghum [*Sorghum bicolor* (L.) Moench], barley (*Hordeum* 

Drought Stress: 2020 and Beyond

Among other environmental instabilities, drought stress is the primary limitation to cereal crops growth, development and productivity. In the context of continuing global climate change, breeding of drought resistant crop cultivars is the most economical, effective and sustainable strategy for adapting the crop production system and ensuring food security for the growing human population. Additionally, there is need for improving management practices. Whereas conventional breeding has sustained crop productivity gains in the past century, modern technological advancements have revolutionized our identification of important drought tolerance genes and underlying mechanisms, and accelerated new cultivar development. Large-scale high throughput sequencing, phenotyping, 'omics' and systems biology, as well as marker assisted and quantitative trait loci mapping based breeding approaches have offered significant insights into crop drought stress tolerance and provided some new tools for crop improvement. Despite this significant progress in elucidating the mechanisms underlying drought tolerance, considerable challenges remain and our understanding of the crop drought tolerance mechanisms is still abstract. In this chapter, therefore, we highlight current progress in the identification of drought tolerance genes and underlying mechanisms, as well as their practical applications. We then offer a holistic approach for cereal crops

#### **Chapter 14**

*Abiotic Stress in Plants*

Aug;7(8):54.

of Cadmium Adverse Effects by Improving Nutrients Uptake in Bitter Gourd through Cadmium Tolerant Rhizobacteria. Environments. 2020

[196] Zafar-ul-Hye M, Tahzeebul-Hassan M, Abid M, Fahad S, Brtnicky M, Dokulilova T, Datta R, Danish S. Potential role of compost mixed biochar with rhizobacteria in mitigating lead toxicity in spinach. Scientific reports. 2020 Jul 22;10(1):1-2.

[197] Zia Z, Bakhat HF, Saqib ZA, Shah GM, Fahad S, Ashraf MR, Hammad HM, Naseem W, Shahid M. Effect of water management and silicon on germination, growth, phosphorus and arsenic uptake in rice. Ecotoxicology and environmental safety. 2017 Oct 1;144:11-8.

[198] Cousins OH, Garnett TP,

Jan 1;290:110146.

Rasmussen A, Mooney SJ, Smernik RJ, Brien CJ, Cavagnaro TR. Variable water cycles have a greater impact on wheat growth and soil nitrogen response than constant watering. Plant Science. 2020

**284**
