The role of hydrogen peroxide in cadmium-inhibited root growth of rice seedlings

Cadmium (Cd) is readily taken up by the roots of rice seedlings, leading to growth reduction. H(2)O(2) is a constituent of oxidative metabolism and is itself a reactive oxygen species. In this study, the participation of H(2)O(2) in CdCl(2)-inhibited growth of rice roots was investigated. CdCl(2) treatment increased H(2)O(2) production in rice roots. CdCl(2) treatment had no effect on the activities of superoxide dismutase, ascorbate peroxidase, and glutathione reductase, but inhibited the activity of catalase (CAT) in rice roots. CdCl(2)-inhibited root growth and -increased H(2)O(2) content were lessened in the presence of diphenyleneiodonium chloride, an inhibitor of H(2)O(2) generating NADPH oxidase. However, this stimulation of root growth in CdCl(2)-treated seedlings is small (about 5%). Calcium (Ca) is important in many physiological processes in plants. Attempts were also made to determine whether the action of Ca on CdCl(2)-inhibited growth of rice roots is associated with H(2)O(2). CaCl(2) application reduced the production of H(2)O(2), the decrease in CAT activity, and the inhibition of root growth caused by CdCl(2). The effects of CaCl(2) application could be reversed by exogenous H(2)O(2). Our results indicate that the Cd causes a decline in CAT and to a lower extent a stimulation of NADPH oxidase in rice roots, with the subsequent generation of H(2)O(2), an agent responsible for growth inhibition.