CONTROL OF EXCITATION TRANSFER IN PHOTOSYNTHESIS .I. LIGHT-INDUCED CHANGE OF CHLOROPHYLL A FLUORESCENCE IN PORPHYRIDIUM CRUENTUM

The emission spectra of chlorophyll a in Porphyridium cruentum at liquid nitrogen temperature change on illumination of the sample before cooling. Preillumination of phycoerythrin decreases the yields of F684 and F695 and increases that of F-1. Pre-illumination of chlorophyll a does not significantly change the fluorescence yield. These facts indicate that the pre-illumination of pigment system II changes the efficiency of excitation transfer between chlorophyll a molecules. The effects of additional actinic illumination on the yield of F684 at room temperature are also examined. The actinic illumination of chlorophyll a has two opposing effects on the fluoresence yield, i.e., decrease and increase of fluorescence yield. The two effects can be distinguished by the difference in times of response towards the onset and end of actinic illumination. The former (fast, decreasing) effect can be explained in connection with the cooperation of the two pigment systems through the photosynthetic electron transport. The latter (slow, increasing) effect is thought to reflect the change in efficiency of excitation transfer, as mentioned above concerning the fluorescence yields at liquid nitrogen temperature. The presence of a light-induced control for the efficient utilization of the absorbed light energy in photosynthesis is suggested. © 1960.