Response of antioxidant enzymes in coontail (Ceratophylium demersum L.) plants under cadmium stress

Cadmium (Cd) contamination of aquatic systems is of major concern since it is a nonessential element and hampers plant growth upon accumulation. The aim of this study was to investigate the Cd accumulation behavior of coontail plant, Ceratophyllum demersum L., toxicity induced and response of the antioxidant system. Plants were exposed to various concentrations of Cd (0-10 mu M) for a period of 1-7 days. Accumulation of Cd was found to be a concentration duration dependent phenomenon. The maximum accumulation of Cd, 1293 mu g g(-1) dw, was observed after 7 days at 10 mu M. Plants showed significant stimulation of the activities of various antioxidant enzymes viz., superoxide dismutase (EC 1.15.1.1), ascorbate peroxiclase (EC 1.11.1.11), guaiacol peroxiclase (EC 1.11.1.7), catalase (EC 1.11.1.6), and glutathione reductase (EC 1.6.4.2) and tolerated toxicity of Cd up to moderate concentration of 5 mu M. At 10 mu M exposure, enzyme activities declined and plants experienced toxicity, which was evident by the significant decrease in the photosynthetic pigments and by increase in the levels of H2O2, lipid peroxidation and ion leakage. In conclusion, modulation of antioxidant system in a coordinated manner in response to Cd accumulation appears to help plants tolerate toxicity of Cd Up to 5 mu M. (C) 2008 Wiley Periodicals, Inc.