RELATIONSHIP BETWEEN LIGHT-INDUCED STATE I/II-TRANSITIONS and Mg2+-EFFECT ON FLUORESCENCE, TESTED IN SYNCHRONOUS CULTURES OF Scenedesmus obliquus

Abstract— Light induced transition of the photosynthetic apparatus from state II to state I by preillumination with PS I light in vivo and the addition of cations to chloroplasts or chloroplast particles prepared in low-salt buffer have rather similar effects on the fluorescence properties at room temperature and at 77 K. Using synchronous cultures of Scenedesmus obliquus, we were able to study both phenomena in parallel in different developmental stages under well defined conditions. Both phenomena show an inverse course during ontogenetic development of S. obliquus. This result suggests that Mg²⁺ ions and PS I light don't necessarily act in the same way. Hence, changes in the ionic environment cannot be the unique basis of light induced state changes within the photosynthetic apparatus in vivo.