THE CHROMOPHORES AS ENDOGENOUS SENSITIZERS INVOLVED IN THE PHOTOGENERATION OF SINGLET OXYGEN IN SPINACH THYLAKOIDS

Abstract— The photogeneration of singlet oxygen (1O2) from thylakoids and the chromophores involved as endogenous sensitizers were investigated using chloroplasts and thylakoids isolated from spinach. The blue light‐induced inhibition kinetics of photosynthetic electron transport and that of CTvCF, ATPase were also studied. The spectral dependence of the generation of 1O2 from thylakoid membranes, measured by the imidazole plus RNO method, clearly demonstrated that the Fe‐S centers play an important role in 1O2 generation, acting as sensitizers in thylakoids. The photoinhibition of the electron transport in isolated chloroplasts was strikingly depressed by a lipid‐soluble '02 quencher and enhanced by deuterium oxide substitution, indicating that the inhibition processes are mainly mediated by 1O2 which is produced via photodynamic activation. The involvement of chloroplast cytochromes in the production of 1O2 was deduced from the action spectrum for the photodynamic inhibition of the electron carrier chain. The results obtained from the kinetic studies appear consistent with the involvement of some components such as the Fe‐S centers and cytochrome chromophores of the carrier chain in the generation of 1O2. Copyright © 1990, Wiley Blackwell. All rights reserved