Abstract:A hydroponic experiment was conducted to investigate the role of the antioxidative defense system in cadmium (Cd) tolerance of a new Cd-hyperaccumulator Picris divaricata V. The results showed that low and moderate levels of Cd (1-10 μmol?L-1) in solution did not affect the growth of P. divaricata, whereas high levels of Cd addition (50-100 μmol?L-1) inhibited the growth, with 72% and 86% biomass reduction compared to the control. Cd concentration in shoots reached 270 mg?kg-1 at 10 μmol?L-1 Cd with a translocation factor of 1.41, in accordance with the characteristics of Cd hyperaccumulation. The maximum shoot concentration of Cd reached 3919 mg?kg-1 and about 64%-87% of total Cd was allocated in the shoots. Addition of 1-10 μmol?L-1 Cd did not affect the amounts of malondialdehyde (MDA), H2O2, superoxide (O?－2) and the activities of antioxidative enzymes. However, 50-100 μmol?L-1 Cd induced the accumulation of MDA, H2O2 and O?－2 both in the shoots and roots, which were increased by 5-17 and 1-5 folds, 1.6-6 and 1.4 folds, 2.9-7.2 and 9.5-11 folds than those of the control, respectively. Meanwhile, high levels of Cd significantly enhanced the activities of superoxide dismutase (SOD) and peroxidase (POD) in shoots and roots as well as the shoot glutathione (GSH) concentration, but had no obvious effects on the activities of glutathione reducatse (GR) and catalase (CAT). We concluded here that P. divaricata has a strong capability in Cd accumulation and translocation. Low and moderate addition of Cd did not induce any obvious oxidative stress; high Cd treatments induced the lipid peroxidation and accumulation of reactive oxygen species (ROS), which might be removed by different mechanisms in shoots and roots.