Cadmium toxicity and translocation in rice seedlings are reduced by hydrogen peroxide pretreatment

A hydroponic experiment was carried out to study the role of hydrogen peroxide (H2O2) in enhancing tolerance and reducing translocation of cadmium (Cd) in rice seedlings. Plant growth (length and biomass of shoot and root) was significantly repressed by Cd exposure. However, pretreatment with 100 mu M H2O2 for 1d mitigated Cd stress by inducing enzyme activities for antioxidation (e.g., superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX)) and detoxification (e.g., glutathione S-transferase (GST)) as well as by elevating contents of reduced glutathione (GSH) and ascorbic acid (AsA). As a result, H2O2 and malondialdehyde (MDA) content decreased in plants and the seedling growth was less inhibited. On the other hand, H2O2 pretreatment decreased Cd concentration in shoots, thus lowered the ratio of Cd concentration in shoots and roots (S/R), indicating that H2O2 may affect Cd distribution in rice seedlings. The improved Cd tolerance is partly due to an enhanced antioxidative system that efficiently prevents the accumulation of H2O2 during Cd stress. Increased Cd sequestration in rice roots may contribute to the decline of Cd translocation.