[Specific role of carotenoid-absorption in photosynthetic oxygen evolution]

The photosynthetic oxygen evolution rate of the unicellular green algae Ankistrodesmus braunii slowly decreased in the course of time when the algae were illuminated only by interrupted or continuous red light. Illumination with blue-green light (493 nm and 2 min duration) instead of one red light exposure induced oxygen uptake and produced a higher efficiency of oxygen evolution in the following illuminations with red light.This effect has been observed with red light absorbed by chlorophyll a1 (wave-length longer than 680 nm) as well as with light of 647 nm which is mainly absorbed by chlorophyll b. For this reason and because of the long-lasting enhancement of the O2-evolution after a short blue-green illumination and the absence of the effect under anaerobic conditions, it is not possible to interpret this phenomenon as an Emerson-enhancement-effect.