The Antenna Size Changes of Photosystem 2 Complexes Differing in QB Reduction

Abstract

The light is important environmental factor that affects the photosynthesis. The acclimation of plants to the low irradiances involves changes in the size of light harvesting antennae of photosystem 2 (PS2) (1). It is well known that thylakoid membranes contain two types of PS2 complexes which differ in their ability to reduce the secondary quinone acceptor QB (QB-reducing and QB-non-reducing PS2 complexes) (2). The investigation of sensitivity of both PS2 populations to the decrease of irradiance may be useful for understanding the physiological significance of the acceptor side heterogeneity. It was established that the antenna size of PS2 complexes located in non-appressed regions of thylakoid membranes does not change at low light acclimation (3). Since the QB-non-reducing PS2 complexes dominate in stroma-exposed thylakoids (2, 4), it may be suggested that these complexes do not take part in adaptation to low light conditions. In the paper (3) authors used the electrophoresis technique for the analysis of pigment-protein composition of particles obtained by thylakoids fragmentation. However, this method provides no information about the efficiency of the energy transfer between light harvesting antennae and reaction center. In addition, the accuracy of the determination of the Qs-non-reducing PS2 antenna size may be decreased because of QB-reducing PS2 complexes presence in non-appressed membranes (2, 5).