Analyses of light-induced bacteriochlorophyll absorbance change and fluorescence emission in purple bacteria

Abstract

Abstract 1. 1. The light-induced absorbance change of Rhodopseudomonas palustris chromatophores in the far-red to near-infrared range of the spectrum was studied. The amount of bacteriochlorophyll changed was more than 1/80 of the total bacteriochlorophyll. The quantum efficiency of the change was about 0.4 and 0.24 when the primary light-absorbing pigment was bacteriochlorophyll and carotenoid, respectively. The absorption spectrum change induced by ferricyanide oxidation is different from the light-induced change. The gas-phase composition of the reaction system had little effect on the light-induced change. High concentrations of glycol moderately suppressed the light-induced change. 2. 2. The relative efficiencies of bacteriochlorophyll and carotenoids for the fluorescence emission of bacteriochlorophyll were compared in R. palustris and normal and carotenoid-poor green cells of Chromatium sp. strain D. In R. palustris , the efficiency of energy transfer from carotenoid to bacteriochlorophyll was about 0.6 of that of the light absorbed by bacteriochlorophyll. In the normal Chromatium cells, this relative efficiency was 0.3; in the green Chromatium cells, about 0.6. 3. 3. Additivity was observed in connection with the intensities of bacteriochlorophyll fluorescence when R. palustris or Chromatium cells were illuminated simultaneously with lights of two different wavelengths at varied intensities.