Physiological and Biochemical Mechanisms of Drought Tolerance in Plants: A Review

One major environmental factor limiting plant productivity is water scarcity. Drought stress affects plant water relations at the cellular, tissue, and organ levels, eliciting both specific and nonspecific responses, as well as causing damage and triggering adaptive mechanisms. Tolerant plants initiate multiple defense mechanisms against water deficit in order to cope with drought. i.e. biochemical and physiological processes. The main morpho-physiological mechanisms include smaller, succulent leaves to lessen transpirational loss, improved water uptake with profuse and deep root systems and its efficient use, and reduced water loss through increased diffusive resistance. Osmotic adjustment enhances the gradient for water influx and supports turgor maintenance by lowering the cell’s osmotic potential. Low-molecular-weight osmolytes, including glycine betaine, proline, other amino acids, organic acids, and polyols, play a crucial role in sustaining cellular functions under drought conditions. Other essential mechanisms of drought tolerance include the expression of stress proteins, cell membrane stability, and the enzymatic and non-enzymatic antioxidants. Enzymatic antioxidants—such as superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, and glutathione reductase—play a pivotal role in the detoxification of reactive oxygen species (ROS). Non-enzymatic antioxidants such as ascorbic acid, reduced glutathione, cysteine, and carotenoids also contribute to ROS scavenging and protection of cellular structures. Phytohormones and plant growth regulators are also integral in modulating plant physiological responses to drought stress.