[Synthesis of chlorophyll and of chloroplast structure in Chlorella without participation of chloroplast ribosomes].
The unicellular green alga Chlorella pyrenoidosa shows normal heterotrophic growth and pigment synthesis in the presence of inhibitors of chloroplast transcription and translation.Cells treated with 100 μg/ml of rifampin, 25 μg/ml of lincomycin or 25 μg/ml of spectinomycin for 48 h do not contain any chloroplast ribosomes, 16 S or 23 S RNA as shown with cell fractionation and gel electrophoresis. Labeling experiments with [5(-3) H]uridine indicate that rifampin blocks completely the formation of 16 S and 23 S RNA whilst cytoplasmic rRNA synthesis is unaffected.Production of dry matter and of cell nitrogen are unaffected by treatment of the cells with antibiotics. Chlorophyll production is almost normal as compared with the untreated control culture. The release of daughter cells is partially inhibited by rifampin treatment. In such cultures, giant cells can be observed among cells of normal size.The O2-production of rifampin-treated cells remains unaffected up to 24 h after application of the drug. Later on, the oxygen evolution declines and, after 72 h, oxygen is consumed even during illumination. The O2-consumption in the dark is markedly enhanced after rifampin treatment.Electron microscopy of rifampin-treated Chlorella shows that apparently normal chloroplast membranes are formed. The thylakoids are arranged in grana-like structures whereas in untreated cells they form only stacks of two or three thylakoids. In the chloroplasts of rifampin-treated Chlorella cells, no more ribosomes are found.The cellular location of synthesis of some chloroplast constituents is discussed.
Pflanzenphysiologisches Institut der Universität, D-3400, Göttingen, Federal Republic of Germany.
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G
Galling
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Salzmann
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Spieß