Light-induced shifts in pigment absorption in green, red and blue-green algae

Abstract

1. 1. Light-induced absorption changes in the region 640–730 nm which were not associated with the oxidation of the primary electron donor of system 1, P700, were observed in green, red and blue-green algae. The shape of the difference spectra, showing alternating negative and positive bands, suggested shifts in the absorption bands of chlorophyll a types and of chlorophyll b. 2. 2. The chlorophyll absorption changes were correlated with changes in the blue spectral region, due to carotenoids. Absorption shifts of phycobilins were not observed. The uncoupler carbonylcyanide- p-trifluoromethoxyphenylhydrazone (FCCP) at low concentration stimulated the carotenoid and chlorophyll changes and inhibited at higher concentration. 3. 3. Difference spectra of the changes brought about by Photosystems 1 and 2 in Scenedesmus obliquus were approximately proportional to each other, indicating that shifts of chlorophyll a and b and carotenoid occur in the same relative proportion, independent of the activating photosystem. 4. 4. The results, together with older evidence, indicate that shifts in absorption spectra of photosynthetic pigments are universal phenomena, probably correlated with an energized state of the photosynthetic membrane. Evidence that the well-known change at 515 nm in green algae and higher plants is due to a carotenoid rather than to chlorophyll b is discussed.