Drought Stress Induced Reactive Oxygen Species and Anti-oxidants in Plants

Abstract

Aerobic metabolism in plants results in the generation of reactive oxygen species (ROS). ROS are produced constantly in plants under physiological steady state condition, and plants have evolved to efficiently scavenge and maintain the levels of ROS at non-damaging levels. However, plants when exposed to either abiotic or biotic stress conditions, the production of ROS exceeds their scavenging capacity, leading to an outburst of highly reactive oxidative species capable of inflicting significant damage to the membranes, DNA, and proteins. On the other hand, these reactive molecules when maintained under non-damaging levels are useful signalling molecules involved in relaying stress signal to activate acclimation and defence mechanism. Drought or water deficit stress is one of the major abiotic stresses which induces the production of different kinds of ROS including both free radicals such as superoxide (O-2(-)), hydroxyl radicals (center dot OH), per-hydroxy radical (HO2 center dot) and alkoxy radicals (RO) and non-radical (molecular) forms, that is, singlet oxygen (O-1(2)), and hydrogen peroxide (H2O2,). (.OH) is the most reactive chemical species among the known ROS. Generally ROS are produced in cell organelles that are involved in active electron transport like, chloroplast, mitochondria, peroxisomes, apoplast, and their membranes. These organelles also harbour various anti-oxidative enzymes like superoxide dismutase (SOD), catalase (CAT), ascorbate per-oxidase (APX), glutathione peroxidase (GPX), etc., having the potential to quench the highly reactive oxidative species to maintain overall plant homeostasis. Additionally the plants are also equipped with the known non-enzymatic scavengers like ascorbate, glutathione, carotenoids, tocopherols. flavonoids, and alkaloids. Crop varieties having an efficient antioxidant quenching mechanism aided by increased production of enzymatic and non-enzymatic scavengers have developed the ability to withstand adverse conditions including drought stress.