Impact of seasonal stress on reactive oxygen species and scavenging enzymes of two crop plants growing under tropical Indian conditions

Nearly all metabolic changes and responses in the plant life cycle are influenced by seasonal environmental conditions which profoundly affect their growth, yield and metabolism. This work was carried out under tropical environmental conditions of Kolkata, West Bengal, India in three seasons -summer, rainy and winter in two stages - preflowering and postflowering to study the effect of seasonal variations (if any) on some select antioxidants and scavenging enzyme activities in Okra ( Abelmoschus esculentus L. Moench) and Tomato ( Lycopersicon esculentum Mill.) to determine the favourable/unfavourable seasons for growth and yield and thus correlate with the yield quality. Favourable seasons (summer for Abelmoschus; winter for Lycopersicon ) recorded low reactive oxygen species production accompanied by elevated activities of scavenging enzymes while the unfavourable seasons (winter for Abelmoschus; rainy for Lycopersicon ) showed the opposite trend. These periods were marked by abundant production of free radicals (meaured as MDA and total peroxide contents), accompanied by poor scavenging and reduced detoxification of these active oxygen species by the antioxidants ( ascorbic acid) and scavenging enzymes (SOD, catalase, peroxidase, ascorbate peroxidase, glutathione reductase, ascorbic acid oxidase). These results could be well correlated with yield and yield quality of these two crop plants. The parameters under study served as useful bioassay indices of environmental stress, while the two plants acting as a measure of the prevailing environmental conditions, can serve as efficient bio indicator species . Thus, plant response to environment indicates the enormous impact of environmental stress on agricultural productivity.