**7. Other biotic and abiotic stress effects**

Plants are normally adapted to grow in complex and diverse environments. The success in growth establishment, reproduction and productivity of plant species rely upon a set of environmental conditions, natural resources and the interactions (beneficial or harmful) that exist among plants and other organisms. However, certain types of interactions, especially those including biological factors such as insects, parasites, viruses and bacterial pathogens have detrimental effects on plants. In addition, the non-living physical or chemical factors such as light, temperature, salinity, water, nutrient and other variables that can be found in the aquatic or terrestrial ecosystem also have major impacts on plant life. All above-mentioned factors may induce plant stress, defined by Taiz et al. [17] as a condition that prevent a given plant from achieving its maximum growth and reproductive potential as measured by vegetative growth, flowering, seed formation and yield quantity. Gerhardson [45] gave further information by providing more insights on disease symptoms caused by pathogenic strains of *Fusarium*, *Cylindrocarpon*, *Phoma* and *Pythium* mostly on legume crops. Strains of the genera *Pythium* have also been found to cause seedling mortality in cowpea [46]. These soil-borne legume pathogens, including other wide spread disease causing fungi; induce root, stem and leaf rots in pea, beans and alfalfa [45]. Abiotic environmental stress dramatically affects growth and productivity of many cereals, oilseeds, vegetables and fruit crops.

many regions worldwide have led to tremendous adversities on agriculture, biodiversity, wildlife and subsequently, the well-beings of many people. Plants normally evolve in order to adapt and adjust to the low water conditions or any other biotic and abiotic constraint. These adaptive measures are an important event of evolution in the history of life, with far reaching consequences as described by Kenrick and Crane [55]. However, this is a very slow process in nature, even if it may result in greater diversity of plants, making changes in plants at their physiological, biochemical and molecular levels. These changes show a wide range of adaptations, at different levels in which plants attempt to deal with drought stress [56]. Plants manage water stress in various ways. They regulate stomatal closure to reduce water loss, especially through transpiration. The stomatal opening and closing is very essential for gaseous exchange as reported by Osakabe et al. [57]. They are controlled by complex regulatory events mediated by abscisic acid (ABA) signalling and ion transport induced by abiotic stress. Nonetheless, stomata closure negatively affects the rates of photosynthetic metabolism by lowering the

. Plants also alter metabolic functions in order to inhibit the production of reac-

¯), and H2

photorespiration from the Calvin cycle. However, some succulent plants use Crassulaceae acid

dependent process) and in the specialised cell around the leaf veins called the bundle sheath

produce oxaloacetate which is converted into malate, transported into the bundle sheath for

water use. In addition to all of the metabolic strategies mentioned above, modern genetic engineering technology can be used. This technology is focused on breeding biotic/ abiotic stress tolerant plants. The biotechnological approaches such as *Agrobacterium*-mediated genetic transformation allow manipulation of the host plant's genome for the expression of foreign genes required in the plant stress response. This technique was initially used to isolate genes used for stress tolerance in *Arabidopsis*. This plant was only used as a model plant and has played an important role in elucidating the basic processes constituting the expression of regulatory genes for stress tolerance [61]. The insights from research on *Arabidopsis* have been used in attempts of unravelling biotic/ abiotic stress effects in plants, subsequently resulting in the development of transgenic plants tolerant to drought, salinity and chilling stress. Montero-Tavera et al. [62] reported upregulation of a number of genes in two common bean varieties with different susceptibility to drought stress. Variety Pinto Villa was relatively susceptible than cultivar Carioca. The reports indicated that drought tolerant variety displayed a more developed root vascular tissue system under stress conditions, when compared to the other non-transgenic cultivars. Differential root phenotype showing variations in root lengths, surface area and fineness of the root system was also reported by Abenavoli et al. [63]. In soybean, stress tolerant genes were introduced and DREB or ARED genes expressed to show improved tolerance to water stress under greenhouse conditions [11, 64]. The genetic

O2

Water Stress: Morphological and Anatomical Changes in Soybean (*Glycine max* L.) Plants

with minimum loss of water. For example; many C3

is fixed in the mesophyll spongy cells (a light-

and CAM plants are well adapted to hot, dry envi-

plants lack strategies to efficiently and effectively manage

minimising photorespiration thus, saving water.

plants like peanut (*Arachis hypogaea*), potato (*Solanum tuberosum*) and

[52, 58]. Other changes involve

http://dx.doi.org/10.5772/intechopen.72899

molecules by separating

plants and they

plants

25

amount of CO2

tive oxygen species (ROS) such as superoxide (O2

In monocots such as maize and wheat, CO2

use in Calvin cycle [17, 59, 60]. Both C4

soybean (*Glycine max* L.). These C3

ronments than the C3

do not have photosynthetic adaptations to reduce the loss of CO2

(light-independent). These monocotyledonous plants are referred to as C4

development of strategies to fix CO<sup>2</sup>

metabolism (CAM) to salvage CO2

Oilseeds such as soybeans have suffered major losses from the short and prolonged occurrence of abiotic stress, especially drought, extreme temperatures, flooding and waterlogging [47]. Plants experiencing drought stress may also endure other stress effects simultaneously, like salinity and heat stress. Multiple stress effects and symptoms may be concomitantly induced by the occurrence of a single stress as described by Miransari [48] leading to combinational abiotic stress. In soybean, drought stress has many negative consequences ranging from reduced production of signalling and communication metabolites, decreased photosynthetic assimilates, nutrient deficiency, accumulation of reactive oxygen species (ROS) and reduction in nitrogen (N) fixation by affecting symbiotic relationship with *Rhizobium* species [49–52]. Soybean is an important crop for the production of oils and proteins used for feed and human consumption. It is a potential source for biodiesel and has been used to manufacture a number of pharmaceutical products [53]. But, the high sensitivity to water deficit stress shown in this study by this crop encourage the development of stress tolerant soybean varieties. Drought and other growth constraints are inevitable consequences of climate change. Therefore, investigation on the physiological, anatomical and morphological response of soybean to these biotic and abiotic constraints is highly recommended.

#### **8. Water stress management and crop improvement**

As previously discussed, drought stress is the most widely known and devastating stress factor that limit plant growth, development and productivity. Khaine and Woo [54] reported that, frequent drought effects recently and currently experienced, are largely induced by the changes in climatic conditions. The continuously fluctuating meteorological conditions in many regions worldwide have led to tremendous adversities on agriculture, biodiversity, wildlife and subsequently, the well-beings of many people. Plants normally evolve in order to adapt and adjust to the low water conditions or any other biotic and abiotic constraint. These adaptive measures are an important event of evolution in the history of life, with far reaching consequences as described by Kenrick and Crane [55]. However, this is a very slow process in nature, even if it may result in greater diversity of plants, making changes in plants at their physiological, biochemical and molecular levels. These changes show a wide range of adaptations, at different levels in which plants attempt to deal with drought stress [56]. Plants manage water stress in various ways. They regulate stomatal closure to reduce water loss, especially through transpiration. The stomatal opening and closing is very essential for gaseous exchange as reported by Osakabe et al. [57]. They are controlled by complex regulatory events mediated by abscisic acid (ABA) signalling and ion transport induced by abiotic stress. Nonetheless, stomata closure negatively affects the rates of photosynthetic metabolism by lowering the amount of CO2 . Plants also alter metabolic functions in order to inhibit the production of reactive oxygen species (ROS) such as superoxide (O2 ¯), and H2 O2 [52, 58]. Other changes involve development of strategies to fix CO<sup>2</sup> with minimum loss of water. For example; many C3 plants do not have photosynthetic adaptations to reduce the loss of CO2 molecules by separating photorespiration from the Calvin cycle. However, some succulent plants use Crassulaceae acid metabolism (CAM) to salvage CO2 minimising photorespiration thus, saving water.

**7. Other biotic and abiotic stress effects**

24 Plant, Abiotic Stress and Responses to Climate Change

Plants are normally adapted to grow in complex and diverse environments. The success in growth establishment, reproduction and productivity of plant species rely upon a set of environmental conditions, natural resources and the interactions (beneficial or harmful) that exist among plants and other organisms. However, certain types of interactions, especially those including biological factors such as insects, parasites, viruses and bacterial pathogens have detrimental effects on plants. In addition, the non-living physical or chemical factors such as light, temperature, salinity, water, nutrient and other variables that can be found in the aquatic or terrestrial ecosystem also have major impacts on plant life. All above-mentioned factors may induce plant stress, defined by Taiz et al. [17] as a condition that prevent a given plant from achieving its maximum growth and reproductive potential as measured by vegetative growth, flowering, seed formation and yield quantity. Gerhardson [45] gave further information by providing more insights on disease symptoms caused by pathogenic strains of *Fusarium*, *Cylindrocarpon*, *Phoma* and *Pythium* mostly on legume crops. Strains of the genera *Pythium* have also been found to cause seedling mortality in cowpea [46]. These soil-borne legume pathogens, including other wide spread disease causing fungi; induce root, stem and leaf rots in pea, beans and alfalfa [45]. Abiotic environmental stress dramatically affects

growth and productivity of many cereals, oilseeds, vegetables and fruit crops.

soybean to these biotic and abiotic constraints is highly recommended.

**8. Water stress management and crop improvement**

Oilseeds such as soybeans have suffered major losses from the short and prolonged occurrence of abiotic stress, especially drought, extreme temperatures, flooding and waterlogging [47]. Plants experiencing drought stress may also endure other stress effects simultaneously, like salinity and heat stress. Multiple stress effects and symptoms may be concomitantly induced by the occurrence of a single stress as described by Miransari [48] leading to combinational abiotic stress. In soybean, drought stress has many negative consequences ranging from reduced production of signalling and communication metabolites, decreased photosynthetic assimilates, nutrient deficiency, accumulation of reactive oxygen species (ROS) and reduction in nitrogen (N) fixation by affecting symbiotic relationship with *Rhizobium* species [49–52]. Soybean is an important crop for the production of oils and proteins used for feed and human consumption. It is a potential source for biodiesel and has been used to manufacture a number of pharmaceutical products [53]. But, the high sensitivity to water deficit stress shown in this study by this crop encourage the development of stress tolerant soybean varieties. Drought and other growth constraints are inevitable consequences of climate change. Therefore, investigation on the physiological, anatomical and morphological response of

As previously discussed, drought stress is the most widely known and devastating stress factor that limit plant growth, development and productivity. Khaine and Woo [54] reported that, frequent drought effects recently and currently experienced, are largely induced by the changes in climatic conditions. The continuously fluctuating meteorological conditions in In monocots such as maize and wheat, CO2 is fixed in the mesophyll spongy cells (a lightdependent process) and in the specialised cell around the leaf veins called the bundle sheath (light-independent). These monocotyledonous plants are referred to as C4 plants and they produce oxaloacetate which is converted into malate, transported into the bundle sheath for use in Calvin cycle [17, 59, 60]. Both C4 and CAM plants are well adapted to hot, dry environments than the C3 plants like peanut (*Arachis hypogaea*), potato (*Solanum tuberosum*) and soybean (*Glycine max* L.). These C3 plants lack strategies to efficiently and effectively manage water use. In addition to all of the metabolic strategies mentioned above, modern genetic engineering technology can be used. This technology is focused on breeding biotic/ abiotic stress tolerant plants. The biotechnological approaches such as *Agrobacterium*-mediated genetic transformation allow manipulation of the host plant's genome for the expression of foreign genes required in the plant stress response. This technique was initially used to isolate genes used for stress tolerance in *Arabidopsis*. This plant was only used as a model plant and has played an important role in elucidating the basic processes constituting the expression of regulatory genes for stress tolerance [61]. The insights from research on *Arabidopsis* have been used in attempts of unravelling biotic/ abiotic stress effects in plants, subsequently resulting in the development of transgenic plants tolerant to drought, salinity and chilling stress. Montero-Tavera et al. [62] reported upregulation of a number of genes in two common bean varieties with different susceptibility to drought stress. Variety Pinto Villa was relatively susceptible than cultivar Carioca. The reports indicated that drought tolerant variety displayed a more developed root vascular tissue system under stress conditions, when compared to the other non-transgenic cultivars. Differential root phenotype showing variations in root lengths, surface area and fineness of the root system was also reported by Abenavoli et al. [63]. In soybean, stress tolerant genes were introduced and DREB or ARED genes expressed to show improved tolerance to water stress under greenhouse conditions [11, 64]. The genetic transformation of many crops, including soybean via *in vitro* or *in vivo* transformation techniques is still very difficult to achieve, despite the aforementioned successes. Several drought tolerant cultivars have been reported in rice (*Oryza sativa*), maize (*Zea mays* L.) and kidney bean (*Phaseolus vulgaris* L.) by Liu et al. [65], Saijo et al. [66] and Shou et al. [67]. The methods used for genetic transformation of these crops are continuously optimised to establish efficient and reproducible protocols using *Agrobacterium tumefaciens*. Lastly, agronomic practices such as reduction of water loss from irrigation systems, minimising water inputs and increasing crop water use efficiency can also be employed to manage water stress [68].

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Water Stress: Morphological and Anatomical Changes in Soybean (*Glycine max* L.) Plants

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