Photosystem II fluorescence quenching in the cyanobacterium Synechocystis PCC 6803: involvement of two different mechanisms

The structural changes associated to non-photochemical quenching in cyanoba cteria is still a matter of discussion. The role of phycobilisome and/or ph otosystem mobility in this mechanism is a point of interest to be elucidate d. Changes in photosystem II fluorescence induced by different quality of i llumination (state transitions) or by strong light were characterized at di fferent temperatures in wild-type and mutant cells, that lacked polyunsatur ated fatty acids, of the cyanobacterium Synechocystis PCC 6803. The amplitu de and the rate of state transitions decreased by lowering temperature in b oth strains. Our results support the hypothesis that a movement of membrane complexes and/or changes in the oligomerization state of these complexes a re involved in the mechanism of state transitions. The quenching induced by strong blue light which was not associated to D1 damage and photoinhibitio n, did not depend on temperature or on the membrane state. Thus, the mechan ism involved in the formation of this type of quenching seems to be unrelat ed to the movement of membrane complexes. Our results strongly support the idea that the mechanism involved in the fluorescence quenching induced by l ight 2 is different from that involved in strong blue light induced quenchi ng. (C) 2000 Elsevier Science B.V. All rights reserved.