Exposure of plants to stressful environments can cause disruption of cellular homeostasis and uncoupling of major metabolic processes, such as photosynthesis and photorespiration, leading to enhanced production of reactive oxygen species, ultimately leading to drastic reduction in growth, yield and yield quality. The increased production of toxic oxygen species is a feature commonly observed under certain stress conditions, when the equilibrium of formation and detoxification of active oxygen species can no longer be maintained. To counter the hazardous effects of oxygen radicals, all aerobic organisms have evolved a complex antioxidative defense system composed of both enzymatic constituents and free radical scavengers, such as ascorbate and glutathione. The scavenging enzymes consist of superoxide dismutase (SOD), catalase, peroxidase, glutathione reductase, dehydroascorbate reductase, monodehydroascorbate radical reductase and ascorbate peroxidase. A positive correlation exists between increased antioxidant activity and different abiotic tolerance. Total peroxide and MDA content are highest in the unfavourable conditions indicating environmental stress. The antioxidant enzymes showed maximum activity in the stressful seasons for crops. Ascorbate peroxidase and Glutathione reductase enzyme activities and higher carotenoid, total phenols, Ascorbic acid and sulfhydryl content under optimum seasonal conditions provide the plants strong defense against ROS ensuring higher and quality yield.
