Gottfried Galling

Bevorzugter Einbau markierten Uridins in die Vorläufer von Chloroplasten-Ribosomen in Algenzellen

SummaryAfter short time pulses with 5-[3H]uridine have been given to Chlorella cells, most of the radioactivity of the ribosome fractions is neither in the polysomes nor in the cytoplasmic ribosomes. Peaks with sedimentation of about 50 S and 30 S are found which are comparable in sedimentation to ribosomal subunits of Escherichia coli. During chase treatment with the one-hundred-fold amount of unlabelled uridine, the radioactivity shifts into the 70 S region. The RNA of the rapidly labelled 50 S and 30 S particles is shown to have 23 S, 14 S and 5 S, respectively.In contrast to this, radioactive inorganic phosphate and amino acids are mainly incorporated into the cytoplasmic ribosomes with 80 S and into, their polysomes.The chloroplast-damaged mutant of Chlorella, Nr.125 of Schwarze, shows no uridine incorporation into particles of 50 S and of 30 S, but some very weak labelling of the 80 S cytoplasmic monosomes.Nitrogen deficient Chlorella cells also incorporate uridine mainly into the 50 S and 30 S particles. When chase treatment with unlabelled uridine is performed under recovering conditions, the label shifts into the 70 S particles as well as into the 80 S cytoplasmic ribosomes.The results indicate that in Chlorella, uridine is incorporated into chloroplast ribosome precursors rather than into particles of nuclear origin.After short time pulses with 5-[3H]uridine have been given to Chlorella cells, most of the radioactivity of the ribosome fractions is neither in the polysomes nor in the cytoplasmic ribosomes. Peaks with sedimentation of about 50 S and 30 S are found which are comparable in sedimentation to ribosomal subunits of Escherichia coli. During chase treatment with the one-hundred-fold amount of unlabelled uridine, the radioactivity shifts into the 70 S region. The RNA of the rapidly labelled 50 S and 30 S particles is shown to have 23 S, 14 S and 5 S, respectively.In contrast to this, radioactive inorganic phosphate and amino acids are mainly incorporated into the cytoplasmic ribosomes with 80 S and into, their polysomes.The chloroplast-damaged mutant of Chlorella, Nr.125 of Schwarze, shows no uridine incorporation into particles of 50 S and of 30 S, but some very weak labelling of the 80 S cytoplasmic monosomes.Nitrogen deficient Chlorella cells also incorporate uridine mainly into the 50 S and 30 S particles. When chase treatment with unlabelled uridine is performed under recovering conditions, the label shifts into the 70 S particles as well as into the 80 S cytoplasmic ribosomes.The results indicate that in Chlorella, uridine is incorporated into chloroplast ribosome precursors rather than into particles of nuclear origin.

Synthese von Chlorophyll und Strukturelementen des Plastiden in Chlorella ohne Beteiligung der Chloroplasten-Ribosomen

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.SummaryThe 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.

Einbau von Uridin und Orotsäure in plastidäre ribosomale RNA von Chlorella nach Antibiotica-Behandlung

SummaryNormal grown cells of Chlorella pyrenoidosa incorporate uridine exclusively into chloroplast ribosomal RNA after short time labeling. With sucrose gradient separation, labeled ribosomal particles of 70 S, 50 S and 30 S can be shown. This labeling is prevented by rifampin in low concentrations after a few minutes. At the same concentration of the antibiotic and also with 10-fold higher concentration, no effect on heterotrophic cell growth is observed. This indicates clearly that mitochondria cannot be influenced by rifampin. Chloramphenicol also inhibits the formation of uridine labeled ribosomal particles of 70 S, 50 S and 30 S. In the presence of this antibiotic, some labeled ribosomal RNA is formed. Also the effect of chloramphenicol can be shown after short incubation periods. Cycloheximide treatment of the cells within 30 and 60 min and up to the 10-fold concentration of protein synthesis inhibition (Morris, 1967) results in no effect on labeling of ribosomal RNA and of ribosomal particles in Chlorella with uridine. Only after prolonged treatment of the cells with cycloheximide is some effect on uridine incorporation observed.The comparison of the incorporation patterns of 6-(14C)-orotate, (6-14C)-uridine and 5-(3H)-uridine into nucleic acids in the presence of rifampin, chloramphenicol and cycloheximide shows some similarities. After 60 min incubation with the precursors, the incorporation is reduced by all three antibiotics. In rifampin treated cells, orotate and both uridines are preferentially incorporated into DNA. With chloramphenicol, the relative incorporation of orotate and of uridine into the 5 S and the 16 S RNA is higher as compared with the 23 S RNA. Cycloheximide results in an increase in the relative incorporation of orotate as well of uridine into DNA. The similarities of the effects of the three antibotics indicate that the preferential incorporation of uridine into chloroplast ribosomes of Chlorella is not due to a compartmentation of the uridine-UMP-pathway.ZusammenfassungChlorella pyrenoidosa inkorporiert unter normalen Anzuchtbedingungen kurzfristig angebotenes Uridin fast ausschließlich in plastidäre ribosomale RNA. Es lassen sich rasch markierte Ribosomen und deren Untereinheiten von 70 S, 50 S und 30 S nachweisen. Diese Markierung wird durch Rifampin in geringen Konzentrationen bereits nach wenigen Minuten unterbunden. Auf das Zellwachstum hat Rifampin bei heterotropher Anzucht dagegen auch in höheren Konzentrationen keinen Einfluß. Chloramphenicol hemmt den kurzfristigen Uridin-Einbau in ribosomale Partikeln von 70 S, 50 S und 30 S, nur geringfügig dagegen denjenigen in ribosomale RNA. Auch die Wirkung des Chloramphenicols tritt rasch ein. Cycloheximid beeinflußt den Kurzzeit-Einbau von Uridin in ribosomale Partikeln und in RNA nicht, wenn die Inkubationszeit 60 min nicht überschreitet.Die Markierung der Nucleinsäuren von Chlorella mit 6-(14C)-Orotsäure zeigt vergleichbare Empfindlichkeiten gegen die drei Antibiotica wie der Einbau von 6-(14C)-Uridin und 5-(3H)-Uridin.Chlorella pyrenoidosa inkorporiert unter normalen Anzuchtbedingungen kurzfristig angebotenes Uridin fast ausschlieslich in plastidare ribosomale RNA. Es lassen sich rasch markierte Ribosomen und deren Untereinheiten von 70 S, 50 S und 30 S nachweisen. Diese Markierung wird durch Rifampin in geringen Konzentrationen bereits nach wenigen Minuten unterbunden. Auf das Zellwachstum hat Rifampin bei heterotropher Anzucht dagegen auch in hoheren Konzentrationen keinen Einflus. Chloramphenicol hemmt den kurzfristigen Uridin-Einbau in ribosomale Partikeln von 70 S, 50 S und 30 S, nur geringfugig dagegen denjenigen in ribosomale RNA. Auch die Wirkung des Chloramphenicols tritt rasch ein. Cycloheximid beeinflust den Kurzzeit-Einbau von Uridin in ribosomale Partikeln und in RNA nicht, wenn die Inkubationszeit 60 min nicht uberschreitet.

Vorstufen der plastidären ribosomalen RNA und ihre Reifung bei Chlorella

SummaryIn Chlorella pyrenoidosa, tritiated uridine is incorporated specifically into the RNA of the chloroplast. The 16 S and 23 S ribosomal RNA become labeled after at least 15 min. Short pulse labeling of 5 min results in peaks of radioactivity in the 17 S region and at the heavy side of the 23 S peak, as shown by polyacrylamide electrophoresis.During chase treatment with unlabeled uridine after the pulse labeling, a shift of radioactivity from the 17 S to the 16 S region is observed. At the same time, the radioactivity over the 23 S speak becomes symmetrical. In the 17 S region, there are at least two peaks which appear and disappear during chase treatment. From data of specific radioactivity a precursor—end product relation can be deduced.After blocking of the chloroplast translation with spectinomycin, the RNA in the 17 S region is accumulated. This product is not stringently the same as that from pulse labeling experiments, because it migrates slightly faster than 17 S RNA. Removal of the antibiotic results in a shift of the radioactivity to the 16 S region. At the same time, the previously blocked chloroplast ribosome synthesis is reinitiated.Attempts have been made to localize the precursor molecules of 17 S and 23 S within the cell. By means of differential centrifugation it has been shown that the precursor RNA components are located in ribosomal particles. No free precursor molecules are found in the ribosome-free supernatant. This is the case in normal as well as in spectinomycin-treated cells.The results are discussed in view of the possible role of chloroplast ribosomal particles as processing agents for the maturation of chloroplast ribosomal RNA.In Chlorella pyrenoidosa, tritiated uridine is incorporated specifically into the RNA of the chloroplast. The 16 S and 23 S ribosomal RNA become labeled after at least 15 min. Short pulse labeling of 5 min results in peaks of radioactivity in the 17 S region and at the heavy side of the 23 S peak, as shown by polyacrylamide electrophoresis.During chase treatment with unlabeled uridine after the pulse labeling, a shift of radioactivity from the 17 S to the 16 S region is observed. At the same time, the radioactivity over the 23 S speak becomes symmetrical. In the 17 S region, there are at least two peaks which appear and disappear during chase treatment. From data of specific radioactivity a precursor-end product relation can be deduced.After blocking of the chloroplast translation with spectinomycin, the RNA in the 17 S region is accumulated. This product is not stringently the same as that from pulse labeling experiments, because it migrates slightly faster than 17 S RNA. Removal of the antibiotic results in a shift of the radioactivity to the 16 S region. At the same time, the previously blocked chloroplast ribosome synthesis is reinitiated.Attempts have been made to localize the precursor molecules of 17 S and 23 S within the cell. By means of differential centrifugation it has been shown that the precursor RNA components are located in ribosomal particles. No free precursor molecules are found in the ribosome-free supernatant. This is the case in normal as well as in spectinomycin-treated cells.The results are discussed in view of the possible role of chloroplast ribosomal particles as processing agents for the maturation of chloroplast ribosomal RNA.

Stimulierung des Aminosäure-Einbaus in vitro durch niedermolekulare RNA in Chlorella

The nucleic acids of the particle-fraction (pellet 30,000 g) of Chlorella enhance the amino acid incorporation in vitro in cell-free systems of the same organism.After sucrose density gradient centrifugation, the most stimulating RNA component is found to be a low molecular weight RNA sedimenting between the soluble RNA and the smaller ribosomal RNA component. This stimulating RNA is not identical with transfer-RNA.SummaryThe nucleic acids of the particle-fraction (pellet 30,000 g) of Chlorella enhance the amino acid incorporation in vitro in cell-free systems of the same organism.After sucrose density gradient centrifugation, the most stimulating RNA component is found to be a low molecular weight RNA sedimenting between the soluble RNA and the smaller ribosomal RNA component. This stimulating RNA is not identical with transfer-RNA.ZusammenfassungDie Nucleinsäuren der Grobpartikelfraktion (Sediment 30 000 g) von Chlorella stimulieren den Aminosäure-Einbau im zellfreien, Proteinsynthetisierenden System desselben Organismus. Auftrennung dieser Nucleinsäuren im Rohrzucker-Dichtegradienten ergibt unterschiedliche Stimulierung des Einbaus durch die einzelnen RNA-Komponenten. Die stärkste Förderung wird mit einer niedermolekularen RNA erreicht, die zwischen der löslichen und der leichteren ribosomalen RNA sedimentiert und die nicht mit transfer-RNA identisch ist.

Die Wirkung von Neomycin auf Zellteilung, Wachstum und Nucleinsäuren synchronisierter Chlorellen

SummarySynchronously grown Chlorella cells show no more cell division after autotrophic and mixotrophic culture in the presence of 0.5 mg/ml neomycin. At the same time, the production of dry matter and of cell nitrogen is nearly unaffected by the drug.After colorimetric determination, the DNA-content of the cells can be shown to be 20 to 30 per cent, the RNA-content to be 16 per cent lower than in the untreated control cells. The chromatography of the nucleic acid preparations from neomycin-treated and untreated cells on MAK-columns shows no nucleic acid fraction which is specially affected by the antibiotic treatment.The preparation of ribosomes from treated and untreated cells and their separation in sucrose density gradients results patterns which show an increase of polysomes after neomycin-treatment of the cells.The results are discussed with respect to the possible site of action of neomycin in the cell division process.ZusammenfassungAutotrophe und mixotrophe Synchronkulturen von Chlorella pyrenoidosa zeigen in Lösungen, die mehr als 0,5 mg/ml an Neomycin enthalten, am Ende eines Zellcyclus keine Zellteilung. Die Produktion von Trockensubstanz und Zellstickstoff ist dabei nur geringfügig verringert. Hierin lassen sich ebenfalls keine Unterschiede zwischen autotrophen und mixotrophen Anzuchten feststellen.Nach 24 Std Behandlung mit 1 mg/ml an Neomycin ist der DNA-Gehalt um 20–30%, der RNA-Gehalt um 16% niedriger als bei der Kontrolle. Durch Chromatographie kann keine Nucleinsäure-Fraktion festgestellt werden, die durch die Neomycin-Behandlung besonders betroffen wäre.Bei Auftrennung der Ribosomen aus behandelten Zellen ergibt sich ein gegenüber der Kontrolle deutlich erhöhter Gehalt an Polysomen der cytoplasmatischen Ribosomen.Der Wirkungsort des Neomycins auf die Teilungshemmung wird diskutiert.

Einbau von 3H-Uracil in die RNA steriler Anzuchten von Utricularia stellaris mit und ohne Rohrzucker

Sucrose has been shown to increase the growth of Utricularia stellaris in axenic culture (HARDER and ZEMLIN, 1967). Comparable cultures of Utricularia were incubated for 3 and 7 hours with tritiated uracil, and then nucleic acids were prepared. With sucrose, the incorporation is about 5 times higher than that with the inorganic salt cultures. After chromatographic separation of the nucleic acids on MAK-columns, different peaks of short time labelled RNA with high specific activity were found. These peaks indicate the presence of two low molecular weight RNA components in the inorganic culture. These peaks also have been found in cultures with sucrose, but in these cultures there is another predominant peak of high molecular weight RNA which is eluted from the column after the greater ribosomal RNA component.SummarySucrose has been shown to increase the growth of Utricularia stellaris in axenic culture (Harder and Zemlin, 1967). Comparable cultures of Utricularia were incubated for 3 and 7 hours with tritiated uracil, and then nucleic acids were prepared. With sucrose, the incorporation is about 5 times higher than that with the inorganic salt cultures. After chromatographic separation of the nucleic acids on MAK-columns, different peaks of short time labelled RNA with high specific activity were found. These peaks indicate the presence of two low molecular weight RNA components in the inorganic culture. These peaks also have been found in cultures with sucrose, but in these cultures there is another predominant peak of high molecular weight RNA which is eluted from the column after the greater ribosomal RNA component.

Endogene Produktivitätsschwankungen bei Scenedesmus acutus und ihre Beziehung zum Nucleinsäure-Stoffwechsel

Summary1.In Scenedesmus acutus Tomaselli, endogenous variations in cell progeny production and chlorophyll formation have been found which are very similar to those previously described in Chlorella by Hesse (Z. Pflanzenphysiol. 67, 58–77, 1972). When the dark phase of the light-dark-cycle is prolonged to a certain extent, cell productivity drops to a minimal value during the next normal light-dark-cycle. If the duration of the supplementary dark treatment comes near to 24 h, cell productivity is almost normal during the next cycle.2.Nucleic acid labeling with radioactive precursors is very similar in Scenedesmus acutus and Chlorella pyrenoidosa. Short time labeling with uridine results in labeled chloroplastic RNA and DNA, the cytoplasmic RNA being almost unlabeled. With guanosine, both chloroplastic and cytoplasmic RNA as well as DNA are labelled. In nucleic acid separation on acrylamide gels special caution must be taken, since endocellular RNases are particularely active in some cell stages of Scenedesmus. Optimal results are obtained with ripe mother cells; during nucleic acid purification, cell homogenates have to be frozen together with the phenol-cresol mixture.3.Large differences in guanosine incorporation are found after treatment of the cells with supplementary dark time. After the normal 10:12 h light-dark-cycle, and also after 24 h of supplementarry dark time, much more radioactive guanosine is incorporated into chloroplastic RNA than into cytoplasmic RNA. After 12 h of supplementary dark time, however, cytoplasmic RNA is more extensively labeled than chloroplastic RNA.4.When the specific radioactivity of guanosine is diluted to one half, the incorporation into the rRNA of cytoplasm and chloroplast is strongly reduced. This is due to the filling up of the guanosine pool in the two compartments. In contrast, DNA labeling is hardly influenced by reduced specific radioactivity of the precursor. This may be interpreted as meaning that the radioactive labeling reflects the rate of DNA synthesis rather than the size of the guanosine pool in the nucleus. Differences found in the labeling of DNA after 12 and 24 h of supplementary dark time can than be interpreted as variations in DNA synthesis rate.1. In Scenedesmus acutus Tomaselli, endogenous variations in cell progeny production and chlorophyll formation have been found which are very similar to those previously described in Chlorella by Hesse (Z. Pflanzenphysiol. 67, 58-77, 1972). When the dark phase of the light-dark-cycle is prolonged to a certain extent, cell productivity drops to a minimal value during the next normal light-dark-cycle. If the duration of the supplementary dark treatment comes near to 24 h, cell productivity is almost normal during the next cycle. 2. Nucleic acid labeling with radioactive precursors is very similar in Scenedesmus acutus and Chlorella pyrenoidosa. Short time labeling with uridine results in labeled chloroplastic RNA and DNA, the cytoplasmic RNA being almost unlabeled. With guanosine, both chloroplastic and cytoplasmic RNA as well as DNA are labelled. In nucleic acid separation on acrylamide gels special caution must be taken, since endocellular RNases are particularely active in some cell stages of Scenedesmus. Optimal results are obtained with ripe mother cells; during nucleic acid purification, cell homogenates have to be frozen together with the phenol-cresol mixture. 3. Large differences in guanosine incorporation are found after treatment of the cells with supplementary dark time. After the normal 10:12 h light-dark-cycle, and also after 24 h of supplementarry dark time, much more radioactive guanosine is incorporated into chloroplastic RNA than into cytoplasmic RNA. After 12 h of supplementary dark time, however, cytoplasmic RNA is more extensively labeled than chloroplastic RNA. 4. When the specific radioactivity of guanosine is diluted to one half, the incorporation into the rRNA of cytoplasm and chloroplast is strongly reduced. This is due to the filling up of the guanosine pool in the two compartments. In contrast, DNA labeling is hardly influenced by reduced specific radioactivity of the precursor. This may be interpreted as meaning that the radioactive labeling reflects the rate of DNA synthesis rather than the size of the guanosine pool in the nucleus. Differences found in the labeling of DNA after 12 and 24 h of supplementary dark time can than be interpreted as variations in DNA synthesis rate.

Endogene Produktivittsschwankungen bei Scenedesmus acutus und ihre Beziehung zum Nucleinsure-Stoffwechsel@@@Endogenous variations of productivity in Scenedesmus acutus and their relation to the nucleic acid metabolism

Summary1.In Scenedesmus acutus Tomaselli, endogenous variations in cell progeny production and chlorophyll formation have been found which are very similar to those previously described in Chlorella by Hesse (Z. Pflanzenphysiol. 67, 58–77, 1972). When the dark phase of the light-dark-cycle is prolonged to a certain extent, cell productivity drops to a minimal value during the next normal light-dark-cycle. If the duration of the supplementary dark treatment comes near to 24 h, cell productivity is almost normal during the next cycle.2.Nucleic acid labeling with radioactive precursors is very similar in Scenedesmus acutus and Chlorella pyrenoidosa. Short time labeling with uridine results in labeled chloroplastic RNA and DNA, the cytoplasmic RNA being almost unlabeled. With guanosine, both chloroplastic and cytoplasmic RNA as well as DNA are labelled. In nucleic acid separation on acrylamide gels special caution must be taken, since endocellular RNases are particularely active in some cell stages of Scenedesmus. Optimal results are obtained with ripe mother cells; during nucleic acid purification, cell homogenates have to be frozen together with the phenol-cresol mixture.3.Large differences in guanosine incorporation are found after treatment of the cells with supplementary dark time. After the normal 10:12 h light-dark-cycle, and also after 24 h of supplementarry dark time, much more radioactive guanosine is incorporated into chloroplastic RNA than into cytoplasmic RNA. After 12 h of supplementary dark time, however, cytoplasmic RNA is more extensively labeled than chloroplastic RNA.4.When the specific radioactivity of guanosine is diluted to one half, the incorporation into the rRNA of cytoplasm and chloroplast is strongly reduced. This is due to the filling up of the guanosine pool in the two compartments. In contrast, DNA labeling is hardly influenced by reduced specific radioactivity of the precursor. This may be interpreted as meaning that the radioactive labeling reflects the rate of DNA synthesis rather than the size of the guanosine pool in the nucleus. Differences found in the labeling of DNA after 12 and 24 h of supplementary dark time can than be interpreted as variations in DNA synthesis rate.1. In Scenedesmus acutus Tomaselli, endogenous variations in cell progeny production and chlorophyll formation have been found which are very similar to those previously described in Chlorella by Hesse (Z. Pflanzenphysiol. 67, 58-77, 1972). When the dark phase of the light-dark-cycle is prolonged to a certain extent, cell productivity drops to a minimal value during the next normal light-dark-cycle. If the duration of the supplementary dark treatment comes near to 24 h, cell productivity is almost normal during the next cycle. 2. Nucleic acid labeling with radioactive precursors is very similar in Scenedesmus acutus and Chlorella pyrenoidosa. Short time labeling with uridine results in labeled chloroplastic RNA and DNA, the cytoplasmic RNA being almost unlabeled. With guanosine, both chloroplastic and cytoplasmic RNA as well as DNA are labelled. In nucleic acid separation on acrylamide gels special caution must be taken, since endocellular RNases are particularely active in some cell stages of Scenedesmus. Optimal results are obtained with ripe mother cells; during nucleic acid purification, cell homogenates have to be frozen together with the phenol-cresol mixture. 3. Large differences in guanosine incorporation are found after treatment of the cells with supplementary dark time. After the normal 10:12 h light-dark-cycle, and also after 24 h of supplementarry dark time, much more radioactive guanosine is incorporated into chloroplastic RNA than into cytoplasmic RNA. After 12 h of supplementary dark time, however, cytoplasmic RNA is more extensively labeled than chloroplastic RNA. 4. When the specific radioactivity of guanosine is diluted to one half, the incorporation into the rRNA of cytoplasm and chloroplast is strongly reduced. This is due to the filling up of the guanosine pool in the two compartments. In contrast, DNA labeling is hardly influenced by reduced specific radioactivity of the precursor. This may be interpreted as meaning that the radioactive labeling reflects the rate of DNA synthesis rather than the size of the guanosine pool in the nucleus. Differences found in the labeling of DNA after 12 and 24 h of supplementary dark time can than be interpreted as variations in DNA synthesis rate.

Endogenous variations of productivity in Scenedesmus acutus and their relation to the nucleic acid metabolism

Summary1.In Scenedesmus acutus Tomaselli, endogenous variations in cell progeny production and chlorophyll formation have been found which are very similar to those previously described in Chlorella by Hesse (Z. Pflanzenphysiol. 67, 58–77, 1972). When the dark phase of the light-dark-cycle is prolonged to a certain extent, cell productivity drops to a minimal value during the next normal light-dark-cycle. If the duration of the supplementary dark treatment comes near to 24 h, cell productivity is almost normal during the next cycle.2.Nucleic acid labeling with radioactive precursors is very similar in Scenedesmus acutus and Chlorella pyrenoidosa. Short time labeling with uridine results in labeled chloroplastic RNA and DNA, the cytoplasmic RNA being almost unlabeled. With guanosine, both chloroplastic and cytoplasmic RNA as well as DNA are labelled. In nucleic acid separation on acrylamide gels special caution must be taken, since endocellular RNases are particularely active in some cell stages of Scenedesmus. Optimal results are obtained with ripe mother cells; during nucleic acid purification, cell homogenates have to be frozen together with the phenol-cresol mixture.3.Large differences in guanosine incorporation are found after treatment of the cells with supplementary dark time. After the normal 10:12 h light-dark-cycle, and also after 24 h of supplementarry dark time, much more radioactive guanosine is incorporated into chloroplastic RNA than into cytoplasmic RNA. After 12 h of supplementary dark time, however, cytoplasmic RNA is more extensively labeled than chloroplastic RNA.4.When the specific radioactivity of guanosine is diluted to one half, the incorporation into the rRNA of cytoplasm and chloroplast is strongly reduced. This is due to the filling up of the guanosine pool in the two compartments. In contrast, DNA labeling is hardly influenced by reduced specific radioactivity of the precursor. This may be interpreted as meaning that the radioactive labeling reflects the rate of DNA synthesis rather than the size of the guanosine pool in the nucleus. Differences found in the labeling of DNA after 12 and 24 h of supplementary dark time can than be interpreted as variations in DNA synthesis rate.1. In Scenedesmus acutus Tomaselli, endogenous variations in cell progeny production and chlorophyll formation have been found which are very similar to those previously described in Chlorella by Hesse (Z. Pflanzenphysiol. 67, 58-77, 1972). When the dark phase of the light-dark-cycle is prolonged to a certain extent, cell productivity drops to a minimal value during the next normal light-dark-cycle. If the duration of the supplementary dark treatment comes near to 24 h, cell productivity is almost normal during the next cycle. 2. Nucleic acid labeling with radioactive precursors is very similar in Scenedesmus acutus and Chlorella pyrenoidosa. Short time labeling with uridine results in labeled chloroplastic RNA and DNA, the cytoplasmic RNA being almost unlabeled. With guanosine, both chloroplastic and cytoplasmic RNA as well as DNA are labelled. In nucleic acid separation on acrylamide gels special caution must be taken, since endocellular RNases are particularely active in some cell stages of Scenedesmus. Optimal results are obtained with ripe mother cells; during nucleic acid purification, cell homogenates have to be frozen together with the phenol-cresol mixture. 3. Large differences in guanosine incorporation are found after treatment of the cells with supplementary dark time. After the normal 10:12 h light-dark-cycle, and also after 24 h of supplementarry dark time, much more radioactive guanosine is incorporated into chloroplastic RNA than into cytoplasmic RNA. After 12 h of supplementary dark time, however, cytoplasmic RNA is more extensively labeled than chloroplastic RNA. 4. When the specific radioactivity of guanosine is diluted to one half, the incorporation into the rRNA of cytoplasm and chloroplast is strongly reduced. This is due to the filling up of the guanosine pool in the two compartments. In contrast, DNA labeling is hardly influenced by reduced specific radioactivity of the precursor. This may be interpreted as meaning that the radioactive labeling reflects the rate of DNA synthesis rather than the size of the guanosine pool in the nucleus. Differences found in the labeling of DNA after 12 and 24 h of supplementary dark time can than be interpreted as variations in DNA synthesis rate.