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

**Water Stress: Morphological and Anatomical Changes** 

DOI: 10.5772/intechopen.72899

#### Phetole Mangena Phetole Mangena Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

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

#### **Abstract**

Water stress is one of the most important physiological stress factors that adversely affect soybeans in many critical aspects of their growth and metabolism. Soybean's growth, development and productivity are severely diminished, when soil or cell water potential becomes inadequate to sustain metabolic functioning. However, little has been done to gather comprehensive information regarding the specific changes that occur in waterstressed plants at the anatomical and morphological level. In this study, deviations in root growth, shoot growth, stomatal conductance, yield components and anatomical features are reported. Treatments with two levels of water stress imposed by reducing irrigation (once in 7 days or once in 15 days) revealed that, all cultivars (Dundee, LS 677, LS 678, TGx 1740- 2F, TGx 1835-10E and Peking) were highly susceptible to prolonged water stress, exhibiting severe dehydration and death. A 15.0 and 30.0% survival frequency was obtained in plants irrigated once in 7 days; LS 677 and Peking, respectively. Unlike many other stresses, water deficit did not only affect the density of stomata, but, photosynthesis was affected by the lower levels of tissue CO2 . These results suggest that, balanced biochemical, physiological, anatomical and morphological regulations are necessary for increased growth and yields in soybean.

**Keywords:** anatomy, growth, morphology, soybean, water stress

#### **1. Introduction**

Water stress is one of the most important constraints in the growth and development of plants. Water deficit stress, in particular, is a major problem in agriculture and most crop plants show high sensitivity to this kind of stress than any kind of abiotic constraint conditions. Crop plant growth and yields are severely impacted by inadequate supply of water, which result in decreased carbon assimilates contents. In addition, plants exposed to prolonged shortage

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© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

in ground, surface or atmospheric water, known as drought are highly susceptible to pests and diseases. Mattson and Haack [1] provided evidence on the occurrence of fungi and insect induced stalk rots, wilts and foliar diseases in plants caused by drought stress. The prevalence in disease outbreak occurred in water-stressed plants compared to the normal water stressfree plants. Estimations of yield losses in soybeans compiled by Wrather and Koenning in the United States from 1996 until 2007 indicated that, the role of pathogens such as soybean cyst nematode, phytophthora root and stem rot, as well as charcoal rot that affected seedling development was exacerbated by the physical environmental stress conditions [2]. Drought is, and continues to be an insidious hazard to plants, animals and human lives. Drought conditions in many regions worldwide are worsening due to various factors, some of which are caused by climate change. The increase in atmospheric CO2 level, currently estimated at about 380–400 ppm, and alterations in hydrological cycles make drought a recurring natural hazard world-wide [3, 4]. In this regard, plants undergo permanent or temporary damage to their morphological architecture, and their anatomical and physiological processes when exposed to dry and hot conditions. According to Shao et al. [5], water stress effects can be extended in plants to alter gene expression, change cellular metabolism, cause reduction in mitotic cell division activities in mesophyll tissues and other organs, as well as to cause the decrease in stomatal conductance [6]. Scientific research showed that; drought stress causes imbalances in the natural status of the environment and drastically disrupts crop cultivation thus, threatening food security [7, 8]. Many regions have experienced the detrimental and severe effects of drought, particularly, populations in the developing countries. In the Southern African Development Community (SADC) region; poor rainfall conditions were recorded for the 2016/2017 agricultural season as a result of El Niño induced drought [9]. FAO's global information and early warning system in 2015 reported significant drought dating back to 1984 [10]. The area data covered regions such as the United States, Semi-Arido of Brazil, Eastern Europe and African countries where, severe drought causing food crisis across Ethiopia, Kenya and Somalia resulted into the deaths of over 1 million people. Therefore, the continuing drop into below-normal annual rainfalls and increasing temperatures create the relevance to study and understand the morphological/anatomical changes that plants undergo to cope with environmental stresses. In cultivated crops such as soybean (*Glycine max* L.), this would minimise limitations that adversely affect plant growth, and the improvement of this crop for yield purposes [11], as well as counteracting against factors that negatively influence the nutritional content and essential secondary metabolites synthesised in this plant.

in 15 days (WT 2). Plants used for the control were watered daily, depending on soil moisture content in the plastic pots. For the growth of soybean plants, plastic containers filled with a mixture of 4:1 (v/v) fertile sandy-loam soil with vermiculite was used. Seeds of soybean cultivar Dundee, LS 678, LS 677, TGx 1740-2F, TGx 1835-10E and Peking were inoculated into the pots for germination and seedling emergence. At least one soybean plant was grown per pot with 20 replicates per cultivar, and allowed to grow up to V3 stage before imposing water stress. The morphological and physiological data were then recorded, which included plant height, number of leaves plant-1, number of braches plant-1, yield and yield components, average leaf area, root length and the micro-morphological characteristics of the stomata and trichomes were evaluated. Assessment of these characteristics was guided by the methods according to Cornelissen et al. [12] with modifications. To study stomatal and trichomes characteristics the microscopic slides were prepared by a protocol modified from Yeung's [13] guide to study plant structures. Leaves of soybean plants from both the control and waterstressed plants (WT 1 and WT 2) were collected a week before the experiment was terminated. The experiment was terminated when the plants reached reproductive stage 4 (R4) of fruiting, involving maturity and seed filling. The free hand sectioning method by Yeung was used to study structural organisation of the root and stems, with section staining done using Toluidine blue O stain. Quantifying the chlorophyll content and leaf area is an important measurement for comparing plant growth, treated with different growth conditions. For leaf area assessment, leaf samples were randomly detached from the different cultivars, and their leaf area estimated as described by Richter et al. [14]. Leaves were randomly sampled for estimation of chlorophyll content using a CCM 200 plus Chlorophyll Meter, Opti-Sciences.

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

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

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**3. Description of soybean morphology and anatomy**

Plants are responsible for a number of essential ecological services. Plants are the main primary source of foods for humans and animals, supply oxygen, timber, medicine and also have ornamental value. The multiple and complex processes involving genetic, morphological, anatomical, physiological and biochemical mechanisms are responsible for the goods and services that plants provide. These functions are made possible by the architecture of the plant's internal and external structures. Soybeans like other legumes and non-leguminous plants display different types of internal and external growth forms that functions together to provide these services. The external form include indeterminate, determinate and semideterminate morphological growth habits, which typically take place in both the early and late maturity groups of varieties grown for commercial and subsistence farming [15]. Soybean plants with determinate growth terminate their vegetative growth stage during the onset of the reproductive stage. In contrast, indeterminate varieties continue growing even during flower setting and anthesis. Anthesis is the period in which flowers developed during the reproductive stage of the plant's life cycle begin to open. According to the NDSU [15] the semi-determinate growth habit lies between the polarity and growth of the other two growth habits (determinate and indeterminate form). The vegetative parts of soybean include the stem, leaves and the soil submerged roots. A few types of leaves can be found in soybean.

#### **2. Analyses of soybean responses to water deficit stress**

Plants experience water deficit stress when the amount of water in the cells and surrounding becomes limiting to growth and development. To investigate these effects, a study was conducted to primarily assess the influence of water stress on the growth of soybean; morphologically and anatomically, under greenhouse conditions. According to Lisar et al. [8] water deficit is caused by prolonged water shortage. In order to examine this stress, reduction in the frequency of irrigation was performed by limiting watering to once a week (WT 1) and once in 15 days (WT 2). Plants used for the control were watered daily, depending on soil moisture content in the plastic pots. For the growth of soybean plants, plastic containers filled with a mixture of 4:1 (v/v) fertile sandy-loam soil with vermiculite was used. Seeds of soybean cultivar Dundee, LS 678, LS 677, TGx 1740-2F, TGx 1835-10E and Peking were inoculated into the pots for germination and seedling emergence. At least one soybean plant was grown per pot with 20 replicates per cultivar, and allowed to grow up to V3 stage before imposing water stress. The morphological and physiological data were then recorded, which included plant height, number of leaves plant-1, number of braches plant-1, yield and yield components, average leaf area, root length and the micro-morphological characteristics of the stomata and trichomes were evaluated. Assessment of these characteristics was guided by the methods according to Cornelissen et al. [12] with modifications. To study stomatal and trichomes characteristics the microscopic slides were prepared by a protocol modified from Yeung's [13] guide to study plant structures. Leaves of soybean plants from both the control and waterstressed plants (WT 1 and WT 2) were collected a week before the experiment was terminated. The experiment was terminated when the plants reached reproductive stage 4 (R4) of fruiting, involving maturity and seed filling. The free hand sectioning method by Yeung was used to study structural organisation of the root and stems, with section staining done using Toluidine blue O stain. Quantifying the chlorophyll content and leaf area is an important measurement for comparing plant growth, treated with different growth conditions. For leaf area assessment, leaf samples were randomly detached from the different cultivars, and their leaf area estimated as described by Richter et al. [14]. Leaves were randomly sampled for estimation of chlorophyll content using a CCM 200 plus Chlorophyll Meter, Opti-Sciences.
