**7. Final considerations**

The progressive increase in ABA concentration in the plants of the stress treatment is related to the stomatal mechanism because this hormone, under these conditions, provokes stomatal closing [62], consequently reducing the water losses during the gas exchanges in essential

Based in study carried out by Costa et al. [5] on impact of water deficit and rehydration on nitrogen compounds and ABA in *V. unguiculata* leaves (Figure 4), the research detected that

**Figure 4.** (a) Abscisic acid concentration and (b) proline in *Vigna unguiculata* plants cv. Vita 7 subjected to 4 days of water restriction and 2 days of rehydration. Means followed by the same letter are not significantly different by Tu‐ key's test at 5% of probability. The bars represent the mean standard error, and the arrow indicates the rehydration

Therefore, the relative water content acts as a signal, and the ABA works during the signal transduction due to the easy and fast movement of this compound into plant tissue, and as a response, the stomatal closing occurs in *V. unguiculata* plants subjected to water deficit.

point [5].

physiological processes such as transpiration and photosynthesis [59].

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

leaf relative water content influences ABA concentration present in the leaf.

This chapter reports that the performance in leguminous is affected by water deficiency, which can cause lower growth and development, with progressive reduction in leaf dry matter, moreover to promote abortion of flowers during drought periods, and to affect the yield significantly, with consequent repercussion on production parameters, such as number of grains and pods per plant. In relation to morphological parameters, negative alterations related to height of plants, shoot dry matter, number of leaves, root dry matter, and paraheliotropic leaf movement were described. For gas exchange, leaf relative water content, stomatal conductance, and transpiration rate suffered decrease when cultivated under water deficit. Biochemical compounds, such as soluble amino acids, soluble proteins, proline, and ABA, are intensively modified after a period under water restriction. The results prove that ABA mediates actively and significantly the proline accumulation and consequent osmotic adjust‐ ment in *V. unguiculata* leaves that were induced to water deficit and rehydration.
