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

Abstract

Cadmium (Cd) is readily taken up by the roots of rice seedlings, leading to growth reduction. H2O2 is a constituent of oxidative metabolism and is itself a reactive oxygen species. In this study, the participation of H2O2 in CdCl2-inhibited growth of rice roots was investigated. CdCl2 treatment increased H2O2 production in rice roots. CdCl2 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. CdCl2-inhibited root growth and -increased H2O2 content were lessened in the presence of diphenyleneiodonium chloride, an inhibitor of H2O2 generating NADPH oxidase. However, this stimulation of root growth in CdCl2-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 CdCl2-inhibited growth of rice roots is associated with H2O2. CaCl2 application reduced the production of H2O2, the decrease in CAT activity, and the inhibition of root growth caused by CdCl2. The effects of CaCl2 application could be reversed by exogenous H2O2. 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 H2O2, an agent responsible for growth inhibition.