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 substances were investigated in Ceratophyllum demersum L. (Coontail), a free floating macrophyte to understand the mechanisms of Cu resistance. Bioconcentration 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 and increased both lipid peroxidation and leakage of ions which were attributed to Cu-induced oxidative stress. Plants responded to Cu-induced oxidative stress by modulating antioxidative enzymes and antioxidants. Cu (2 and 4 mu M) considerably increased the activities of ascorbate peroxidase, catalase and superoxide dismutase. The extent of increase with 4 mu M Cu was lower compared to 2 mu M Cu for catalase and superoxide dismutase, while for ascorbate peroxidase the activity remained virtually identical. Cu also altered 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, possibly 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 accumulation in C. demersum induces oxidative stress and the level of tolerance depends on the antioxidative capacity of the plants. (C) 1998 Elsevier Science ireland Ltd. All rights reserved.