Role of two photosynthetic pigment systems in cytochrome oxidation, pyridine nucleotide reduction, and fluorescence

Abstract

The investigations of two light reactions in photosynthesis driven by different pigment systems started with Emerson’s discovery that in the green alga Chlorella pyrenoidosa the rate of photosynthesis in light beams of 700 and 650 applied simultaneously, was higher than the sum of the rates in each beam separately (Emerson, Chalmers & Cederstrand 1957). This effect has been called ‘Emerson effect’ or ‘enhancement effect’. Since the quantum efficiency of light of 700 mp, compared with that of 650 mpwas rather low, the increase in rate in the two beams was attributed to an enhancement of the photosynthetic efficiency of light of 700 nip, by light of 650 mp. In this paper we will present evidence that the rate of photosynthesis at both wavelengths is enhanced. Action spectra for the Emerson effect were determined by measuring the extra increase in photosynthesis obtained by adding light of various wavelengths to constant illumination of 700 mp. The action spectrum for the Emerson effect in Chlorella showed maxima at 650 and 480 mp, which indicated that light absorbed by chlorophyll b was particularly effective in the enhancement. In the red alga Porphyridium cruentum photosynthesis brought about by light absorbed in the region around 680 mp was ‘enhanced’ by light absorbed by the phycobilins phycocyanin and phycoerythrin (Brody & Emerson 1959). It was concluded that efficient photosynthesis was only possible, if at least one of the accessory pigments was excited (Emerson et al. 1957; Brody & Emerson 1959).