Effect of cadmium on lipid peroxidation, superoxide anion generation and activities of antioxidant enzymes in growing rice seedlings

When seedlings of two rice cvs Ratna and Jaya were grown in sand cultures for a period of 5–20 days in the presence of 100 and 500 μM Cd(NO3)2 in the medium, elevated levels of lipid peroxides, increase in superoxide anion generation and a concomitant increase in the activities of guaiacol peroxidase and superoxide dismutase were noticed in Cd-grown seedlings compared to controls. Cd was freely absorbed by the rice plants and its level in rice shoots increased in parallel with its concentration in the growth medium. Under 500 μM Cd treatment about 1.4–1.6 times increase in malondialdehyde (MDA) levels indicating enhanced lipid peroxidation was noted in shoots of 20 days grown seedlings whereas under similar conditions nearly 0.8–1.7 times increase in superoxide anion (O2−) generation was observed in the seedling. With increase in Cd level in situ a marked elevation in superoxide dismutase (SOD) and peroxidase activities were observed. The increase in peroxidase activity was greater than SOD under Cd treatment. About 8–17 times higher level of peroxidase activity was recorded in the shoot of seedlings grown for 10 days under 500 μM Cd(NO3)2 compared to control grown seedlings. Higher level of peroxidase activity was observed in shoots than roots whereas higher SOD activity was noted in roots than shoots under both controls and Cd treatments. The activity of catalase increased in seedlings grown at moderately toxic Cd (100 μM) level whereas a highly toxic Cd (500 μM) level led to a marked inhibition in catalase activity. Results suggest that Cd induces oxidation stress in growing rice plants and that SOD and peroxidase could serve as important components of antioxidant defense mechanisms in rice to combat metal induced oxidative injury.