Control of excitation transfer in photosynthesis. III. Light-induced decrease of chlorophyll a fluorescence related to photophosphorylation system in spinach chloroplasts

Abstract

1. 1. A light-induced reversible decrease in fluorescence yield of chlorophyll a, designated as “fluorescence lowering”, was discovered in isolated spinach chloroplasts on illumination at high light intensities in the presence of N-methylphenazonium methosulfate and 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea. The decrease in fluorescence yield amounted to 20–30%. 2. 2. The “fluorescence lowering” was markedly lessened by addition of uncouplers of photophosphorylation. The concentrations for 50% suppression of the light-induced effect were 2.0 μM atebrin, 2.5 μM carbonylcyanide m-chlorophenylhydrazone and 1 mM methylamine. These findings indicate the involvement of the photophosphorylation system in the “fluorescence lowering”. 3. 3. Kinetic analyses showed that the ‘fluorescence lowering’ commenced at about 0.2 sec and reached an half-level of the “fluorescence lowering” about 2 sec after onset of illumination. The half-decay time of the recovery after cessation of illumination was approx. 5 sec. 4. 4. The time response of the “fluorescence lowering” differed from that of the light-scattering change in the chloroplasts, thus indicating that the “fluorescence lowering” was not caused by the conformational change corresponding to the light-scattering change of the chloroplasts. 5. 5. In experiments at liquid-nitrogen temperature, preillumination before cooling decreased the yields of the three emissions of chlorophyll a at 684 nm, 695 nm and 735 nm.