Nickel-induced inhibition of wheat root growth is related to H2O2 production, but not to lipid peroxidation

Effects of exogenous nickel (Ni: 10 and 200 mu M) on growth, mitotic activity, Ni accumulation, H2O2 content and lipid peroxidation as well as the activities of various antioxidative enzymes, such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GSH-Px) were investigated in wheat roots. A considerable Ni accumulation in the roots occurred at both the concentrations. Although Ni at 10 mu M did not have any significant effect on root growth, it strongly inhibited the root growth at 200 mu M. Mitotic activity in the root tips was not significantly affected by exposure of the seedlings to 10 mu M Ni; however, it was almost completely inhibited at 200 mu M treatment. Ni stress did not result in any significant changes in CAT and APX activities as well as lipid peroxidation. However, H2O2 concentration increased up to 82% over the control in the roots of seedlings exposed to 200 mu M Ni. There was a significant decline in both SOD (50%) and GSH-Px (20-30%) activities in the roots when the seedlings were treated with 200 mu M Ni. The results indicated that a strong inhibition of wheat root growth caused by Ni stress was not due to enhanced lipid peroxidation, but might be related to the accumulation of H2O2 in root tissue.