Drought Stress Tolerance in Wheat: Omics Approaches in Understanding and Enhancing Antioxidant Defense

Abstract

Plants face various kinds of stresses in the changing environment. Among the environmental stresses, drought is one of the most devastating stressors due to its diverse negative effects on crop plants. Drought stress in plants is very complex as it occurs due to varying environmental conditions such as soil water scarcity, soil salinity, and high temperature. The latter ones are termed as physiological drought. Bread wheat (Triticum aestivum L.) ranks first in the world’s grain production and is consumed as staple food by more than 36% of the world population. Wheat plant is highly sensitive to drought, especially at flowering and grain filling stages. Growth, photosynthesis, metabolic processes, nutrient assimilation, and yield of wheat plants remarkably decrease under drought. The responses of wheat to drought are varied at morphological, physiological, molecular, and biochemical levels. One of the most common consequences of drought is the disturbance of the balance between production of reactive oxygen species (ROS) and antioxidant defense causing overaccumulation of ROS which induces oxidative stress. This happens due to closure of the stomata, CO2 influx, and decrease of leaf internal CO2 which direct more electrons to form ROS and enhance photorespiration. These ROS can incur direct damage to protein, lipid, and nucleic acid which can ultimately cause plant cell death. Enhancing the antioxidant defense system to mitigate the oxidative stress is one of the effective strategies to make the wheat plants tolerant to drought. It appears that plants synthesize or activate several molecules like osmoprotectants, phytohormones, signaling molecules, and antioxidants to protect themselves from drought-induced oxidative damages. Novel approaches for enhancing the antioxidant defense system to minimize the impacts of drought-induced damage in plants are prime targets of plant biologists. Several genes and their overexpression were found to confer drought tolerance in plants. Application of plant probiotic bacteria also enhances tolerance of wheat plants to drought. Recent advances in genomic, transcriptomic, proteomic, and metabolomic studies on wheat under varying levels of drought generate useful information for designing drought-tolerant wheat. This chapter comprehensively reviews and updates our understanding on molecular mechanisms of adaptation of wheat plants to drought stress with special emphasis to antioxidant defense systems.