INTENSITY OF THERMOINDUCED DELAYED LUMINESCENCE OF PSI CHLOROPHYLL INWHOLE CELLS OF THERMOPHILIC CYANOBACTERIA DEPENDS ON THE PRESENCE OF OXYGEN AND DEGREE OF REDUCTION OF P700

We investigated factors determining the low quantum yield of the milli second component of delayed luminescence (DL) of PSI chlorophyll in wh ole cells of the thermophilic cyanobacterium Synechococcus elongatus. Intensity of PSI DL is shown to increase with removal of oxygen from t he medium and as a result of osmotic shock to the cells. This effect i s probably based on the ability of molecules of oxygen and other endog enous compounds-chloride ions in particular-to quench triplet states o f chlorophyll. Formation of the latter in the reaction center is direc tly associated with generation of the singlet excited state of chlorop hyll in the process of charge recombination in PSI at high temperature s. The cell yield of DL also increases sharply in the presence of dich lorophenolindophenol and sodium ascorbate, which reduce P700+. Registr ation of PSI DL under conditions ensuring its fairly high intensity ca n be used to investigate the influence of various factors on PSI in wh ole cells of thermophilic cyanobacteria.