Copper Toxicity in Rice Seedlings: Changes in Antioxidative Enzyme Activities, H2O2 Level, and Cell Wall Peroxidase Activity in Roots

The changes in lipid peroxidation, antioxidative enzyme activity, H2O2 level, and cell wall peroxidase activity in Cu-stressed roots of rice seedlings and their relation with root growth inhibition were investigated. CuSO4 was effective in inhibiting root growth but not shoot growth. Treatment with CuSO4 resulted in an increase in lipid peroxidation and modulated antioxidative enzyme activities in rice roots. CuSO4 increased the activities of superoxide dismutase, ascorbate peroxidase, glutathione reductase, and peroxidase, but had no effect on catalase. CuSO4 also increased H2O2 level and cell wall peroxidase in roots of rice seedlings. Exogenous application of H2O2 resulted in an inhibition of root growth. It appears that growth inhibition of root caused by Cu is associated with H2O2 dependent peroxidase-catalyzed formation of cross-linking among cell wall polymers.