Varietal differences in the growth of rice seedlings exposed to perchlorate and their antioxidative defense mechanisms.

A hydroponic experiment was conducted to investigate perchlorate (ClO4 (-) ) phytotoxicity in different rice varieties. Considerable variations were observed when 24 rice varieties were treated with ClO4 (-) . The shoot height, root length, and biomass of most varieties were significantly reduced by ClO4 (-) . The roots were more sensitive than the shoots. Hierarchical clustering analysis demonstrated primarily 4 groups: ClO4 (-) -sensitive, medium ClO4 (-) -sensitive, medium ClO4 (-) tolerant, and ClO4 (-) -tolerant. Gannuoxiang (a ClO4 (-) -tolerant variety) and IR65598-112-2 (a ClO4 (-) -sensitive variety) were chosen to explore their antioxidant response when exposed to 0.2 mmol/L, 2.0 mmol/L, and 4.0 mmol/L ClO4 (-) . The results showed that the activities of superoxide dismutase and catalase increased in the shoots and roots of gannuoxiang with increasing doses of ClO4 (-) , but both of them decreased at higher concentrations of ClO4 (-) in IR65598-112-2. The addition of ClO4 (-) led to a significant increase in peroxidase activities for both of the varieties, whereas the increase was more pronounced in gannuoxiang than in IR65598-112-2. No significant difference was found in malondialdehyde (MDA) contents in gannuoxiang, whereas the addition of ClO4 (-) increased the MDA level significantly in IR65598-112-2. The results indicated that gannuoxiang has higher activities of antioxidant enzymes than IR65598-112-2 to cope with oxidative damage caused by ClO4 (-) stress, which may be the main cause of its high tolerance.