**3. Interference of water deficit on growth and development**

As in other crops, performance in leguminous is affected by water deficiency, which can cause lower growth and development, with progressive reduction in leaf dry matter [5], moreover, to promote the abortion of flowers during drought periods and to affect the yield significantly [6], with consequent repercussion on production parameters, such as number of grains and

The deficit water is characterized by water losses that exceed the absorption rate and by this way acts directly in the plant–water relations [7–8], depending on intense and exposure period, in addition to promote changes in the cell and molecular pathways [9], whereby accumulation of organic solutes with the carbohydrates and proline [10], differential gene expression of DNA [11], and quantity variation in the photosynthetic pigments, mainly chlorophylls and carote‐

The osmotic adjustment is considered one of the important mechanisms developed by the plants to tolerate the water deficiency [14], which promotes the protection of the plant cell structures with membranes and chloroplasts [15], as well as avoid the cell toxicity provoked by the free radicals and maximize the water retention in cell inside [16]; besides it has the

Drought is directly related to the overproduction of reactive oxygen species (ROS) [17], such

ROS promote the oxidation of membranes and damage essential organelles such as chloro‐

Ascorbate (ASC) and glutathione (GSH) have essential functions in antioxidant metabolism [23,24] because ASC is used as a substrate [25–27]. In addition, GSH produces ASC and glutathione disulfide (GSSG), which is used to regenerate GSH via glutathione reductase (GR)

The soybean is considered a species sensitive to several abiotic stresses [30], when compared with other tropical legumes, such as *Vigna unguiculata* and *Phaseolus vulgaris* [31,32], as well as other species such as *Gossypium hirsutum* and *Sorghum bicolor* [33,34], in which the sensitivity at water deficit can be emphasized, mainly during the growth and development period, which might cause strong reduction in the yield [35]. However, *V. unguiculata* (L.) Walp. is a species tolerant to drought due to rusticity, and it presents large protein content in grain. This crop is frequently found in agricultural areas in Brazil that are under the influence of abiotic stresses. These areas present small rain index and high temperature. In addition, the soil is susceptible

The aim of this chapter is (i) to define what is water deficit and the consequences on growth and development of higher plants; (ii) to present the interferences induced on metabolism, including gas exchange, biochemical compounds, and osmotic substances; and (iii) to explain

−

) [18], which are highly toxic compounds.

noids [12], in which the stomata enclosed interfere in photosynthetic rates occur [13].

advantage of using carbohydrates as energy source under severe stress [6].

plasts [19] and mitochondria [20], which result in cell damage or death [21,22].

as hydrogen peroxide (H2O2) and superoxide (O2

280 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

pods per plant.

[28,29].

to salinity or to fertility loss [36].

**2. Objectives**

Lizana et al. [37] while working with two varieties of *P. vulgaris* under water deficit observed paraheliotropic leaf movement, which was previously described by Pastenes et al. [38]. Leaf movements in Arroz and Orfeo subjected to drought were shown and compared. Figure 1B presents the evolution of the movement of leaves after increasing periods of drought, being determined that the variety Arroz is more sensitive than Orfeo [37].

**Figure 1.** Leaf movement in different drought times. (A) Plants before (left) and after (right) drought-induced leaf movement. Leaf rotation was measured on flanking leaves (arrows) of the first mature trifoliate leaves. (B) Relation‐ ship between period of drought and leaf rotation angle (h) in Arroz (closed symbols) and Orfeo (open symbols) [37].

Lobato et al. [39] while studying morphological alterations in *Glycine max* under progressive water stress found variations in the following parameters: (A) evaluated height of plants, (B) shoot dry matter, (C) number of leaves, and (D) root dry matter.

The lower height and shoot dry matter in the plants under water deficiency occurred, probably due to the abscisic acid (ABA) action, in which case it is produced in the cells under abnormal conditions and this way inhibited the cell division and/or DNA synthesis [39].

The smaller number of leaves showed in the plants under water stress occurred with conse‐ quence a lower or void extension rate of the leaf area existent in the plant, moreover probably increase in the ABA levels in roots, in which it will be transported from roots to shoot and act in the apical region of the plant with antagonist of the auxin and cytokinin, responsible for growth and cell division, respectively [40]; through these hormonal mechanisms, the buds remain dormant and develop not the leaf news. In the period between 0 and 2 days of water stress (Figure 2D), the weight higher of the root dry matter. According to Kerbauy [41], studies with gene-modified plants describe a decrease in the ethylene levels and increase in the ABA in plant roots under water stress, when compared with plants normally irrigated; hence, it proves the different behavior of these hormones, besides it are attributes at ABA the capacity of the remain ethylene normal levels produced in root of plants under normal conditions.

**Figure 2.** (A) Height of plants, (B) shoot dry matter, (C) number of leaves, and (D) root dry matter in plants of *Glycine max* cultivar sambaiba under 0, 2, 4, and 6 days of water stress. Averages followed by the same letter do not differ among themselves by the Tukey's test at 5% of probability, and the bars represent the mean standard error [39].

#### **4. Modifications on gas exchange**

Barbosa et al. [42] evaluated the root contribution to water relations and shoot in two con‐ trasting *V. unguiculata* cultivars and showed that water deficit promoted significant decrease in leaf relative water content (Figure 3A) in tolerant and sensitive cultivars. Inoculated plants of control treatment presented higher values of leaf relative water content, when compared with same treatments of non-inoculated plants.

The tolerant cultivar showed better performance in this parameter, when compared with that of same treatments the cultivar that is sensitive to water stress. In both tolerant and sensitive cultivars, stomatal conductance had a significant reduction in plants exposed to water deficiency (Figure 3B). Plants that were inoculated presented non-significant difference, when compared with that of non-inoculated plants.

Water restriction produced a significant decrease in transpiration rates in both cultivars (Figure 3C). The inoculation provoked non-significant changes in tolerant and sensitive plants. When the tolerant cultivar was submitted to water deficit, the values were higher than those found in the sensitive cultivar, this behavior being similar in inoculated and non-inoculated plants.

increase in the ABA levels in roots, in which it will be transported from roots to shoot and act in the apical region of the plant with antagonist of the auxin and cytokinin, responsible for growth and cell division, respectively [40]; through these hormonal mechanisms, the buds remain dormant and develop not the leaf news. In the period between 0 and 2 days of water stress (Figure 2D), the weight higher of the root dry matter. According to Kerbauy [41], studies with gene-modified plants describe a decrease in the ethylene levels and increase in the ABA in plant roots under water stress, when compared with plants normally irrigated; hence, it proves the different behavior of these hormones, besides it are attributes at ABA the capacity of the remain ethylene normal levels produced in root of plants under normal conditions.

282 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

**A**

**B**

**D**

**C**

**4. Modifications on gas exchange**

with same treatments of non-inoculated plants.

compared with that of non-inoculated plants.

**Figure 2.** (A) Height of plants, (B) shoot dry matter, (C) number of leaves, and (D) root dry matter in plants of *Glycine max* cultivar sambaiba under 0, 2, 4, and 6 days of water stress. Averages followed by the same letter do not differ among themselves by the Tukey's test at 5% of probability, and the bars represent the mean standard error [39].

Barbosa et al. [42] evaluated the root contribution to water relations and shoot in two con‐ trasting *V. unguiculata* cultivars and showed that water deficit promoted significant decrease in leaf relative water content (Figure 3A) in tolerant and sensitive cultivars. Inoculated plants of control treatment presented higher values of leaf relative water content, when compared

The tolerant cultivar showed better performance in this parameter, when compared with that of same treatments the cultivar that is sensitive to water stress. In both tolerant and sensitive cultivars, stomatal conductance had a significant reduction in plants exposed to water deficiency (Figure 3B). Plants that were inoculated presented non-significant difference, when

**Figure 3.** (A) LRWC, (B) *g*s, and (C) *E* in two contrasting *Vigna unguiculata* cultivars under water deficit and subjected to inoculation. Means followed by the same letter are not significantly different by the Scott–Knott test at 5% of proba‐ bility. The bars represent the mean standard error [42].

The reduction in relative water content in leaf is because of lower absorption rate of water by plant via roots and water loss occasioned by gas exchanges through stomata [43]. Similar results were reported by Maia et al. [44] when working with *Zea mays*.

Water deficit promoted a significant fall in stomatal conductance of the two cultivars, but tolerant plants presented higher values of this variable, probably by maintaining better plant water condition. This study revealed that root dry matter exercises influence on stomatal conductance in *V. unguiculata* plants submitted to 5 days of water deficiency, and this fact is based on the indirect effect produced by root on stomatal mechanisms. In other words, an insufficient root system developed during water deficiency will supply lower amount of water to shoot and, consequently, will promote reduction in stomatal conductance.

Decrease in stomatal conductance is explained by reduction in water availability in substrate, and it produces a reduction in leaf water potential, with consequent stomatal closing. The results described by Santos and Carlesso [4] reported that on conditions of water deficit, there is an increase in ABA concentration in xylem sap, promoting stomata closing.

Gholz et al. [45] reported that stomatal closing reduces the CO2 influx to leaf, affecting production, transport, and utilization of photo-assimilates, and hence the yield. Results similar to those found in this study were found by Santos et al. [46], who studied five *P. vulgaris* genotypes subjected to water deficiency.

Decrease in transpiration rate of *V. unguiculata* plants can be attributed to stomatal behavior, because under water deficit, stomata are kept partially closed, contributing to change in transpiration behavior of plant [47]. Leite and Filho [48] reported that reduction of transpira‐ tion is an important mechanism of tolerance to drought. Values of transpiration demonstrated direct relation with stomatal conductance and also with leaf relative water content. Similar results were shown by Nogueira et al. [49] in a study oftwo *Arachis hypogeae* cultivars exposed to water deficiency.
