Involvement of Reactive Oxygen Radicals in Photoinhibition of Primary Photosynthetic Reactions—Effect of Temperature and Oxygen Radical Scavengers

Abstract

ABSTRACTExposure of leaves or chloroplasts to high light intensity leads to inactivation of photosynthesis. Two processes are observed—inhibition of photochemical activity of both photosystems and photobleaching of pigments. Oxygen evolving complex, located at the oxidizing side of Photosystem II, is the most sensitive component of photosynthetic apparatus to environmental stress factors. In the present work the effect of high light treatment at room and low temperatures on kinetic parameters of flash oxygen yields and oxygen evolution were studied. Isolated thylakoid membranes were subjected to high light illumination for different periods of time at room (22°C) and low (4°C) temperature. Flash oxygen yields were determined using fast oxygen rate electrode. Photochemical activity of photosystem II was measured by Clark oxygen electrode using artificial electron acceptor. Data presented show that the damaging effect of high light treatment on oxygen evolution is lower at 4°C than at 22°C. When high light treatment was carried out in the presence of histidine and DMSO—scavengers of oxygen radicals, the inhibition process was retarded. Data are discussed in terms of different production rate and mobility of oxygen radicals at room and low temperature.