Transcription and translation for carotenoid synthesis in Chlamydomonas reinhardtii

The sites of transcription and translation of carotenoid pigments were studied in synchronously grown cells of Chlamydomonas reinhardtii Dang. Rifampicin, cycloheximide and spectinomycin were used to distinguish between the nuclear-cytoplasmic genetic system and the genetic system of the chloroplast. Since rifampicin is without effect, chloroplast DNA appears not to possess information required for the synthesis of carotenoids. Carotenoid synthesis parallels chlorophyll synthesis in these cells. Carotenoid synthesis is dependent on de novo protein synthesis both on cytoplasmic and chloroplast ribosomes, for both cycloheximide and spectinomycin are effective inhibitors. However, the cells are able to form about 40% of the expected increase in carotenoids when cytoplasmic and chloroplast ribosomes are simultaneously inhibited. Of the major carotenoids in C. reinhardtii, lutein appears the least dependent on de novo protein synthesis. The synthesis of β-carotene and trollein appears to be completely dependent on the function of cytoplasmic ribosomes.