Effect of nickel on ROS content and antioxidative enzyme activities in wheat leaves

Influence of 100 μM Ni on growth, Ni accumulation, $\ \hbox{O}_{2}^{\cdot-}$ , H₂O₂ and lipid peroxides contents as well as the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (POD) and glutathione peroxidase (GSH-Px) were studied in the leaves of wheat plants on the 3rd, 6th and 9th days after treatment. Exposure of the plants to Ni for only 3 days led to almost 200-fold increase in this metal concentration in the leaf tissue but later the rate of Ni accumulation was much slower. Length and fresh weight of the leaves were substantially reduced, up to 25% and 39%, respectively at the end of experiment. Visible symptoms of Ni toxicity: chlorosis and necrosis were observed following the 3rd day. Treatment with Ni resulted in the increase in $ \ \hbox{O}_{2}^{\cdot -}$ and H₂O₂ contents in the leaves. Both showed their highest values, approximately 250% of those of the control, on the 3rd day and then their levels decreased but still markedly exceeded the control values. SOD and CAT activities decreased significantly in response to Ni treatment, however a several-fold increase in APX and POD activities was found. No significant changes in lipid peroxides content were observed in the leaves after Ni application. The activity of GSH-Px showed a 29% induction on the 3rd day. Our results indicated that despite prolonged increases in $ \ \hbox{O}_{2}^{\cdot-}$ and H₂O₂ levels, oxidative damage, measured as the level of lipid peroxidation, did not occur in the leaves of Ni-treated wheat.