TWO PHOTOREACTIONS IN PHOTOSYNTHESIS: EVIDENCE FROM THE DELAYED LIGHT EMISSION OF CHLORELLA

Abstract

The time course of delayed light emission from living Chlorella depended on the wavelength of exciting light. Two distinct decay curves resulted when wavelengths were used that selectively excited the 2 photo-synthetic pigment systems. The decay curves intersected, and the time of intersection depended on temperature. At extremely low intensity, effects of the 2 exciting wavelengths were additive. At high intensity, simultaneous irradiation resulted in a decay curve intermediate between that obtained at each wavelength. Chromatic transients of delayed light were observed upon shifting from 1 wavelength to the other. These transients were of the same sign and similar in shape to oxygen chromatic transients. These results imply that delayed light is emitted by functionally active chlorophyll, and provide direct evidence that different photosynthetic pigment systems are absorbing the 2 wavelengths. The additivity results are interpreted as evidence that the individual photosynthetic units contain 2 pigment systems linked by an enzyme chain.