Arbuscular mycorrhizas alter root system architecture of Citrus tangerine through regulating metabolism of endogenous polyamines

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.