Copper toxicity in Ceratophyllum demersum L. (Coontail), a free floating macrophyte: Response of antioxidant enzymes and antioxidants

Copper-induced oxidative stress, response of antioxidative enzymes and subs tances were investigated in Ceratophyllum demersum L. (Coontail), a free fl oating macrophyte to understand the mechanisms of Cu resistance. Bioconcent ration of Cu in plants treated with 2 and 4 mu M Cu for 24 h was dependent on external Cu concentration. Cu uptake decreased the chlorophyll content a nd increased both lipid peroxidation and leakage of ions which were attribu ted to Cu-induced oxidative stress. Plants responded to Cu-induced oxidativ e stress by modulating antioxidative enzymes and antioxidants. Cu (2 and 4 mu M) considerably increased the activities of ascorbate peroxidase, catala se and superoxide dismutase. The extent of increase with 4 mu M Cu was lowe r compared to 2 mu M Cu for catalase and superoxide dismutase, while for as corbate peroxidase the activity remained virtually identical. Cu also alter ed the antioxidants level such as GSH and other non-protein thiols. At 2 mu M Cu, both GSH and other non-protein thiols were increased and the extent of increase varied among them. However, 4 mu M Cu decreased their levels, p ossibly due to the greater oxidation in the presence of Cu compared to the rate of synthesis. This decrease could also partly due to limited activity of antioxidant enzymes fostering oxidation. The results suggest that Cu acc umulation in C. demersum induces oxidative stress and the level of toleranc e depends on the antioxidative capacity of the plants. (C) 1998 Elsevier Sc ience ireland Ltd. All rights reserved.