The development of structure and function in chloroplasts of greening mutants of Scenedesmus IV. Blue light-dependent carbohydrate and protein metabolism

Pigment mutant C-2A' of Scenedesmus obliquus forms only tracesof chlorophyll when grown heterotrophically in the dark. Thechloroplast shows pre-thylakoid structures and a high Contentof starch grains. Illumination causes a sequence of reactionsleading, finally, to chloroplasts with normal thylakoids andan efficiently functioning photosynthetic apparatus. Upon illumination the respiration of the cells is enhanced,starch is degraded and protein is synthesized. The newly-formedprotein in turn is used for formation of enzyme(s) leading tothe synthesis of -aminolevulinic acid, of structural proteinsin the thylakoid membranes and finally to the chlorophyll holochrome.Most of the newly-synthesized protein becomes part of the thylakoidmembranes. All these processes are strictly blue light-dependent. The blue light phenomena can be separated into two groups onthe basis of small wavelength shifts and of their energy requirement.Enhancement of respiration and starch degradation are saturatedat low energy (0.4 w/m² whereas the subsequent protein synthesisand following processes are saturated at high energy (100 w/m²) From the wavelength dependence of the reactions we conclude,in accordance with other authors, that flavoproteins are theprimary photoreceptors. The possibility that the primary lowenergy process might excite a flavoprotein which in turn causesa conformational change in its apoprotein, and that the highenergy process might present a direct energy transduction viaa flavoprotein is discussed. (Received May 10, 1978; )