Cyclic Electron Flow Around Photosystem II as Examined by Photosynthetic Oxygen Evolution Induced by Short Light Flashes

W. I. Gruszecki3 K. Strzałkab, A. Radunzc and G. H. Schmidc a Department o f Biophysics, Institute of Physics, Maria Curie-Sklodowska University, 20-031 Lublin, Poland h Department o f Plant Physiology and Biochemistry, Jan Zurzycki Institute of Molecular Biology, Jagiellonian University, 31-120 Krakow, Poland c Fakultät für Biologie, Lehrstuhl Zellphysiologie, Universität Bielefeld. Postfach 100131, D-33501 Bielefeld, Germany Z. Naturforsch. 52c, 175-179 (1997); received November 24, 1996/January 24, 1997 Cyclic Electron Transport, Photosystem II. Oxygen Evolution, Light Flashes, Carotenoids Photosynthetic oxygen evolution from photosystem II particles was analyzed as conse­ quence of a train of short (5 îs) flashes of different light quality and different intensities to study cyclic electron flow around photosystem II. Damped oscillations of the amplitudes of 0 2-evolution corresponding to a flash sequence were fitted numerically and analyzed in terms of a nonhomogeneous distribution of misses, represented by the probability parameter ctj. Application of red light, known to promote cyclic electron flow around photosystem II (Grus­ zecki et al., 1995) results in a considerable increase of all a{, indicating that at the molecular level the misses may be interpreted as resulting from a competition for the reduction of oxidized P680 between cyclic electron flow and the electron flow coming from the water splitting enzyme. In accordance with previous findings, application of light flashes of the spectrum covering the absorption region of carotenoids resulted in an inhibition of cyclic electron flow and a pronounced decrease of the level of the miss parameter. Possible molecu­ lar mechanisms for the activity control of this cyclic electron transport around photosystem II by carotenoids are discussed.