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

Abstract

The effect of excess Fe 2+ on the peroxidase (POD) activity in detached rice leaves was investigated. FeSO 4 was effective in stimulating POD activity in detached rice leaves under both light and dark conditions. FeSO 4 but not K 2SO 4 induced POD activity, indicating that POD activity is induced by Fe 2+. FeSO 4-induced POD activity is not specific for the rice cultivar used in this study. CuSO 4 and ZnSO 4 were also observed to induce POD activity in detached rice leaves. Cycloheximide blocked the enhanced activity of POD by Fe 2+, Cu 2+ or Zn 2+, indicating de novo biosynthesis of the enzyme. Paraquat treatment resulted in a decrease in POD activity. H 2O 2 had no effect on POD activity in detached rice leaves. It seems that Fe 2+-, Cu 2+- or Zn 2+-induced POD may not be mediated by free radicals. Using isoelectric focusing to separate POD, it was found that excess Fe 2+, Cu 2+ or Zn 2+ induced both quantitative and qualitative metal-specific changes in POD isozyme pattern in detached rice leaves. A new POD isozyme with a p I of 4.81 can be induced by Fe 2+, Cu 2+ and Zn 2+ in detached rice leaves.