Further evidence for carotenoids engaged in a metastable state in photosynthesis.

During photosynthesis a metastable state with a half life of ~ 3 jus has been observed which probably represents a valve for superfluous excitation energy 1. The difference spectrum caused by the formation of this state shows three pronounced negative peaks in the blue spectral range (at 430, 460 and 490 nm). Therefore probably a carotenoid is involved. Because of the negative peak at 430 nm the participation of chlorophyll-a could not be excluded. But in this case there must occur additionally absorption changes in the red spectral range between 660 and 705 nm where chlorophyll-a in vivo has its second absorption band but not the carotenoids. Measurement of fast and small absorption changes within microseconds can, however, not be carried out by the normal ultra-short-flash photometry apparatus1 in the red spectral range because of the ££ 104 times larger chlorophyll fluorescence at the same wavelengths. This fluorescence can, however, be eliminated from interference with absorption changes by a special apparatus allowing time resolution of about 1 jus2. With this apparatus we succeeded in extending the difference spectrum in question into the red region. No absorption changes of ~ 3 jus life time take place in the red. Therefore only carotenoids are responsible for the observed metastable state. This has already been reported in1 . The experimental documents and details on these measurements in the red region are presented in this paper.