Light-induced proton translocation through thylakoid and cytoplasmic membranes of Plectonema boryanum

Abstract

Light-induced fluorescence changes of 9-aminoacridine, an indicator of proton gradient in energy-transducing membranes, were studied in Plectonema boryanum and other cyanobacteria. The fluorescence changes observed in cell suspensions resulted from a superposition of fluorescence quenching and enhancement as the analysis of the kinetic data shows. Both components of the fluorescence changes are abolished by 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) and m-chlorocarbonylcyanide phenylhydrazone. The inhibitory effect of DCMU is removed by 2,3,5,6- or N,N,N′,N′-tetramethyl-p-phenylenediamine. The fluorescence quenching sensitive to substrates and uncouplers of the photophosphorylation is only observed in membrane vesicles obtained by osmotic shock of P. boryanum spheroplasts. Presumably, light-induced quenching of the dye fluorescence in the cells of cyanobacteria is due to the proton transport from the cytoplasm in the inner space of thylakoids while fluorescence enhancement is due to the proton efflux from the cytoplasm into the incubation medium.