Enhanced peroxidase activity in rice leaves in response to excess iron, copper and zinc

The effect of excess Fe2+ on the peroxidase (POD) activity in detached rice leaves was investigated. FeSO4 was effective in stimulating POD activity in detached rice leaves under both light and dark conditions. FeSO4 but not K2SO4 induced POD activity, indicating that POD activity is induced by Fe2+. FeSO4-induced POD activity is not. specific for the rice cultivar used in this study. CuSO4 and ZnSO4 were also observed to induce POD activity in detached rice leaves. Cycloheximide blocked the enhanced activity of POD by Fe2+, Cu2+ or Zn2+, indicating de novo biosynthesis of the enzyme. Paraquat treatment resulted in a decrease in POD activity. H2O2 had no effect on POD activity in detached rice leaves. It seems that Fe2+-, Cu2+- or Zn2+ -induced POD may not be mediated by free radicals. Using isoelectric focusing to separate POD, it was found that excess Fe2+, Cu2+ or Zn2+ induced both quantitative and qualitative metal-specific changes in POD isozyme pattern in detached rice leaves. A new POD isozyme with a pI of 4.81 can be induced by Fe2+, Cu2+ and Zn2+ in detached rice leaves. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.