On Metastable States of Carotenoids in Primary Events of Photosynthesis

A repetitive ultra-short-flash photometer is described which can resolve absorption changes of 0,01% in the time range of 10-7 sec. With this instrument the following results have been obtained. Air-saturated suspensions of photosynthetic systems show light induced absorption changes with a decay time of τ1/2≅ 3·10-6 sec. The properties of absorption changes indicate that they are caused by a metastable state. The difference spectrum of the changes are characterized by peaks at 430, 460, 490 and 520 nm. No absorption changes are observed in the red region! Therefore the metastable state is formed by carotenoids. Excitation of chlorophyll sensitizes the formation of the metastable state of the carotenoid. Therefore a transfer of energy from chlorophyll to carotenoid has to be assumed. The desactivation of the metastable state represents probably an energy valve reaction.