No abstract

The unicellular green alga Scenedesmus obliquus adapts to different irradiances and wavelengths of light by altering the molecular organization of the photosynthetic apparatus. Regulation occurs on the level of pigment-accumulation, assembly of pigmentprotein complexes and gene-expression. Action spectroscopy revealed the involvement of at least two photoreceptor-systems regulating adaptation antagonistically with markedly different thresholds (Thielmann et ai., 1991;. One of them was a BL-(flavin-type-) receptor, which mediates weak-light adaptation, resulting in increased Chi, LHC II (Humbeck et ai., 1988;Senger and Bauer, 1987) and accumulation of cab-mRNA (Hermsmeier et ai., 1991); the other one was a VL/RL-receptor with action peaks at 404 and 650 nm, inducing high-irradiance responses indicated by decreased amounts of Chi, LHC II, LHCP and cab-mRNA (Hermsmeier et ai., 1991).