Comparison of light induced and cell cycle dependent changes in the photosynthetic apparatus: A fluorescence induction study on the green alga Scenedesmus obliquus

Changes in the photosynthetic apparatus occurring during the synchronous ce ll cycle of the green alga Scenedesmus obliquus are compared to the adaptat ional response induced by light intensity variations. To investigate and co mpare these two phenomena, we analyze the polyphasic rise of the chlorophyl l fluorescence yield exhibited by plants and cyanobacteria when exposed to high intensity actinic light. Four fluorescence parameters are calculated w hich are closely related to Photosystem II (PS II) structure and function: ABS/RC, the antenna size of PS II; phi(P0), the quantum yield for reduction of the primary PS II quinone acceptor; q(PQ), related to the size of the p lastoquinone pool; q(Emax), the capacity for pH dependent non-photochemical quenching. The capacity for non-photochemical quenching changes in respons e to light intensity variations, but it is not affected by the developmenta l changes occurring during the cell cycle. In contrast, for ABS/RC, phi(P0) and q(PQ), we observe light induced as well as cell cycle dependent variat ions. We discuss the relations of the four fluorescence parameters to the m olecular organization of the photosynthetic apparatus and its cell cycle an d light dependent changes.