THERMALLY-INDUCED DELAYED LUMINESCENCE FROM PS-I IN MEMBRANES OF THERMOPHILIC CYANOBACTERIA

In our previous investigation on thermophilic cyanobacteria temperatur e was found to stimulate delayed luminescence (DL) from PS I associate d with charge recombination (Biol. Membr. 5 (1988) 1289-1296 (in Russi an)). In the following paper the half-time of luminescence decay (tau 1/2) is shown to be 6 ms at 66-78-degrees-C. This value coincides in o rder of magnitude with the tau 1/2 values for higher plants, suggestiv e of a similar mechanism behind. PS I luminescence is inhomogeneous in thermophiles. In the presence of DCIP-H-2 the amplitude of the main b and at 78-degrees-C shows a sharp rise and an additional more thermola bile band appears at 66-78-degrees-C. The splitting of the PS I peak i s probably caused by a charge in the steady-state distribution of char ges between the secondary acceptors. The abstraction of oxygen leads t o marked changes in the profiles of the temperature dependence curves and to a rise in the DL intensity. Along with these changes the photod ynamic destruction of chlorophyll decreases, electron transport become s more stable and degree of reversibility of thermally-activated delay ed luminescence increases. Besides oxygen, delayed luminescence is que nched with high efficiency by halogen ions (Cl-, Br-, I-) and NO3- ion s. The findings suggest at least two processes behind the thermal stim ulation effect: the temperature-induced increase in the charge recombi nation rate and the heat-induced impairment of the mechanism responsib le for the quenching of excited states of chlorophyll of the PS I reac tion center. The latter process is presumably dominant.