OXIDATIVE DAMAGE AND ANTIOXIDANTS INDUCED BY HEAVY METAL STRESS IN TWO CULTIVARS OF MUSTARD (Brassica juncea L.) PLANTS

The present study evaluated the physiological and biochemical changes in two mustard cultivars (Brassica juncea L.), Varuna and local Rolioni, under individual and combined effects of Cd and Pb stress. Cd and Pb affected most of the considered parameters, e.g. reduction in shoot and root length, dry weight of shoot and root which ultimately leads to decreased biomass content. Cd and Pb stress induced oxidative stress leading to increase in peroxidation of membrane lipids and electrolyte leakage. The interaction of Cd+Pb was found to be more harmful for the plant growth. Under high Cd+Pb (300 mg/kg soil each) levels, a decrease in catalase (CAT, EC 1.11.1.6), accompanied with increases in superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (OR, EC 1.6.4.2), was observed detoxifying the negative effects of active oxygen species (AOS). The proline content was also increased in both the cultivars but the increase was more in Varuna than Rohini. At lower concentrations of Cd and Pb, protein content increased but decreased at higher levels. Maximum decrease in chlorophyll content was observed in Rohini as compared to Varuna cultivar.