NATURE OF PH-INDUCED HETEROGENEITY OF TEMPERATURE DEPENDENCIES OBTAINED FOR DELAYED LUMINESCENCE OF PSII IN MEMBRANES OF THERMOPHILIC CYANOBACTERIA

Lowering of pH in the inter,al from 7.5 to 4.7 increases the intensity and causes splitting of the band in the thermogram of the steady-stat e level of delayed luminescence (DL) of PSII chlorophyll in membranes of the thermophilic cyanobacterium Synechococcus elongatus. Diuron inc reases intensity of the high-temperature component of DL (with a maxim um at 50-55-degrees-C) and quenches the low-temperature component (the ''shoulder'' at 27-30-degrees-C), which makes it possible to classify them as deactivation luminescence and leakage luminescence, respectiv ely. Addition of ferricyanide (100 muM) sharply lowers the yield of de activation luminescence and increases the intensity of leakage lumines cence at temperatures of 15-20-degrees-C, which is quenched by high (> 1 mM) concentrations of ferricyanide. Coincidence of temperature of t he ''shoulder'' of afterglow with that of the phase transition of lipi ds of membranes from S. elongatus (30-degrees-C), together with the hi gh sensitivity of luminescence to ferricyanide, enables us to hypothes ize that the break in the temperature curves of DL is determined by sh arp increase in the rate of electron outflow from the PSII reaction ce nter. This apparently occurs as a result of a precipitate increase of membrane fluidity with transition to the mesomororphic state. Reductio n of the growth temperature of S. elongatus cells, isolation of PSII p articles with elevated content of saturated fatty acids, and treatment of membranes with a detergent lead to changes in parameters of the lo w-temperature component of luminescence, which supports the stated hyp othesis.