ANTIOXIDANT DEFENSE MECHANISM IN PIGEON PEA UNDER COBALT STRESS

Influence of excess cobalt (Co; 10 to 400 μM Co) on growth, biomass, Co accumulation, photosynthetic pigments, lipid peroxidation, proline, non-protein thiols and cysteine contents as well as activities of anti-oxidative enzymes was studied in pigeon pea (Cajanus cajan Mill). In pigeon pea leaves decreased concentrations of chlorophyll and carotenoids on exposure to excess Co was associated with decrease activity of catalase and super oxide dismutase and suggest antiperoxidative nature of excess Co. However, a marked increase in the activities of ascorbate peroxidase and peroxidase and enhanced levels of cysteine, non-protein thiols, and proline are suggestive of induction of antioxidants in excess Co. The threshold of toxicity (10% growth reduction) and toxicity (33% growth reduction) values of Co in pigeon pea were 75 and 160 μg g^?1in leaves, 42 and 180 μg g^?1in stem and 50 and 340 μg g^?1Co in roots, respectively.