FLUORESCENCE YIELD OF CHLOROPHYLL A AND PHOTOCHEMICAL ACTIVITIES OF ISOLATED CHLOROPLASTS

Abstract

Effect of various treatments on the fluorescence yield of chlorophyll o in isolated chloroplasts was studied in relation to the activities of the HILL reaction and the ascorbate photooxidation. CMU and o-phenanthroline showed no appreciable effect on thefluorescence yield at the concentration which completely inhibited the HILL reaction. 0.01% SDS was sufficient to inactivate the HILL reaction completely and caused a 40% decrease in the fluorescence yield, although no shift of the absorption and fluorescence bands could be observed. At higher concentrations of SDS, the fluorescence yield increased by more than three times the original value and the absorption and fluorescence bands shifted by 5 rap toward the shorter wavelength side. Ultraviolet irradiation, incubation at pH 9.2, heating at 40° and digestion with trypsin resulted in loss of the HILL activity and decrease of the fluorescence yield. The DPIP-mediated photooxidation of ascorbate was enhanced by heating broken chloroplasts at 55° for 5 min, and inactivated at 70°. The photooxidation of ascorbate in the absence of the dye was inhibited by 60% on heating at 55°. The o-phenanthroline-sensitive photooxidation of ascorbate was inactivated at 55°. The o-phenanthroline-resistant photooxidation of ascorbate was rather thermostable. The fluorescence yield was reduced by 40–50% at 55°.