Early signs of oxidative stress in wheat plants subjected to zinc deficiency

Anti-oxidative defense systems in wheat plants were Studied as a function of zinc deficiency in Solution culture under glasshouse conditions. Zinc (Zn) deficiency enhanced cyanide-insensitive superoxide dismutase activity significantly, and decreased the activity of cyanide-sensitive superoxide dismutase before the appearance of visible effects of Zn deficiency. The plants with incipient deficiency of Zn also had significantly higher activities of nonspecific peroxidase, ascorbate peroxidase, and glutathione reductase. There was an increase in the concentrations of malondialdehyde, H2O2, dehydroascorbate, glutathione-sulfhydryl, and glutathione-disulphide, and the ratios carotenoids/chlorophyll, dehydroascorbate/ascorbate, and glutathione-sulfhydryl/glutathione-disulphide. As the effects of Zn deficiency became more severe, there was greater accumulation of malondialdehyde and H2O2, and the activities superoxide dismutase, peroxidase, ascorbate peroxidase, and glutathione reductase declined, particularly that of cyanide-sensitive superoxide dismutase. Restoration of Zn supply significantly increased activities of cyanide-sensitive and total superoxide dismutase and ascorbate peroxidase, and concentration of H2O2, and decreased malondialdehyde significantly within 24 h. Induction of anti-oxidative responses to Zn deficiency occurred rapidly and before symptoms of severe Zn deficiency. There was a depression of anti-oxidative responses as Zn deficiency become more severe, suggesting a break down of these defense systems at the onset of visible effects of Zn deficiency.