Drought Stress and Their Adaptations in Plants

Abstract

Drought is one of the most important environmental constraints limiting plant growth, development and productivity. It occurs when water availability in the soil and atmosphere becomes insufficient to meet the water requirements of plants, resulting in a negative water balance and progressive tissue dehydration. The effects of drought are expressed at morphological, physiological, biochemical and molecular levels and depend on the intensity, duration and timing of stress as well as on plant species and genotype. Plants have evolved several adaptive mechanisms to withstand drought, broadly classified as drought escape, drought avoidance and drought tolerance. Drought escape involves completion of the life cycle before severe water deficit develops, whereas drought avoidance maintains plant water status through improved water uptake and reduced water loss. Drought tolerance enables plants to survive cellular dehydration through osmotic adjustment, maintenance of membrane integrity, accumulation of compatible solutes, antioxidant defense and stress-responsive gene expression. Drought commonly reduces root and shoot growth, biomass accumulation, leaf area, chlorophyll content, photosynthesis, stomatal conductance and transpiration. In contrast, tolerant plants may maintain higher relative water content, photosynthetic activity, water-use efficiency, osmolyte accumulation and antioxidant enzyme activities under stress. Understanding these mechanisms is essential for identifying physiological and biochemical traits that can be used in breeding drought-resilient crops.