LEAF AGE AND SEASONALITY DETERMINES THE EXTENT OF OXIDATIVE STRESS AND INDUCTION OF ANTIOXIDANTS IN LEMONGRASS

Oxidative stress with the enhanced production of reactive oxygen species (ROS) due to climatic perturbations is a critical factor in the plant survival and biomass yield. Various plant parts may have differential response to the environmental perturbations in various seasons and adopting strategies to scavenge the ROS. In the current work, penultimate, middle and bottom leaves of a population of lemongrass [Cymbopogon citratus (D.C.) Stapf] were investigated over monthly intervals for changes in the production of hydrogen peroxide (H2O2) and malondialdehyde (MDA) and the induction of enzymatic antioxidants including super oxide dismutase (SOD), catalase (CAT) and peroxidase (POD). Moreover, correlations of these parameters with monthly changes in maximum and minimum temperature, relative humidity, evapotranspiration and average rainfall were drawn. The results revealed that production of MDA and H2O2 was significantly greater in the bottom leaf (15- 26 and 79-107 nmol g^-1 fresh weight MDA and H2O2, respectively) compared to penultimate (5-9 and 14-26 nmol g^-1 fresh weight MDA and H2O2, respectively) and middle (6-11 and 59-77 nmol g^-1 fresh weight MDA and H2O2, respectively) leaves. Results suggested that a higher induction of enzymatic antioxidants system in the scavenging of H2O2 and reduced production of MDA helped the penultimate and middle leaves to withstand adverse climatic conditions.