Photosynthetic Activity and Peroxidation of Thylakoid Lipids during Photoinhibition and High Temperature Treatment of Isolated Wheat Chloroplasts

Abstract

Summary Interactive effects of strong visible light and high temperature on isolated wheat ( Triticum aestivum ) chloroplasts were investigated by imposing them one after another and simultaneously. Both of the stresses were observed to impair photosystem II mediated electron transport activity. A concomitant reduction in chlorophyll fluorescence parameters and increase in thylakoid lipid peroxidation were also observed. Peroxidation of thylakoid lipids suggests the involvement of active oxygen species, which could be generated during photoinhibition. Our results demonstrate that the extent of damage to chloroplasts varied quantitatively upon reversing the order of imposition of strong light and high temperature stresses. Loss of electron transport activity, variable chlorophyll fluorescence (F v ) and increase in thylakoid lipid peroxidation were greater when photoinhibition treatment was given before heat stress. The reason for this differential damage upon changing the order of the two stresses is discussed on the basis of the, primary target site and the amount of potentially damaging active oxygen species generated under stress conditions.