Regulation of CO2-fixation in Chlorella by light of varied wavelengths and intensities

1) The wavelength effects on ¹⁴CO₂-fixation by Chlorella cellswere studied, using monochromatic light of different light intensities. 2) Blue light (453 mµ) stimulated the incorporation of¹⁴C into aspartate, glutamate and malate. Red light (679 mµ),on the other hand, stimulated its incorporation into P-esters,free sugars and insoluble material. 3) The blue light effect was observed in the presence of CMUat concentrations completely suppressing ordinary photosyntheticCO₂-fixation. 4) The blue light effect in the presence of CMU was inducedat very low intensities. At 453 mµ, 300 erg cm^–2sec^–1 was sufficient for complete saturation. 5) Time courses of ¹⁴C-incorporation into individual compoundswere investigated. Irrespective of the wavelength of the illuminatinglight, the first stable CO₂-fixation product formed under weaklight (400–500 erg cm^–2 sec^–1) was citrulline.At higher light intensities (4,000–7,000 erg cm^–2sec^–1), PGA was the first stable CO₂-fixation product.The incorporation of ¹⁴C into citrulline was not inhibited byCMU. 6) Experimental results indicate that both blue light-inducedincorporation of ¹⁴C into amino and organic acids and the incorporationof ¹⁴C into citrulline induced by low intensity light are operatedby a mechanism(s) independent of ordinary photosynthetic CO₂-fixation.Possible effects of light regulating the carbon metabolism inalgal cells are discussed. (Received July 24, 1969; )     

Effects of disalicylidenepropandiamine and near far-red light on 14CO2-fixation in Chlorella cells

1) With Chlorella ellipsoidea cells, in the presence of 5x10^–6M DSPD, or in its absence, the amounts of ¹⁴CO₂ incorporatedin P-esters, serine-plus-glycine and alanine were larger underred light than under blue light, whereas blue light specificallyincreased ¹⁴CO₂-incorporation in aspartate, glutamate, malateand fumarate (blue light effect). The amount of total ¹⁴C fixedunder blue or red light was greatly decreased by the additionof DSPD. When the concentration of DSPD was raised to 5x10^–4M, practically no radioactivity was found, under blue or redlight, in aspartate, glutamate and fumarate. Radioactivity inalanine was greatly increased. Effects of higher concentrationof DSPD are explained as due to the inhibition of PEP carboxylaseactivity in Chlorella cells. 2) The percentage incorporation of ¹⁴C into aspartate and theother compounds mentioned above, under near infra-red illuminationwas significantly smaller than that under blue light and wasalmost equal to that under red light. These results along withthe effect of 5x10^–6 M DSPD, exclude the possibility thatcyclic photophosphorylation is involved in the "blue light effect"mechanism. (Received December 12, 1969; )     

Cold‐induced organelle relocation in the liverwort Marchantia polymorpha L.

Organelles change their subcellular positions in response to various environmental conditions. Recently, we reported that cold treatments alter the intracellular position of chloroplasts and nuclei (cold positioning) in the fern Adiantum capillus‐veneris; chloroplasts and nuclei localized to the periclinal cell wall relocated to anticlinal cell wall after cold treatments. To further understand organelle positioning under cold conditions, we studied cold‐induced organelle relocation in the liverwort Marchantia polymorpha L. When sporelings and gemmmalings were treated under low temperature (5 °C), chloroplast cold positioning response was successfully induced both in the sporelings and the gemmmalings of M. polymorpha. Using a genetic transformation, nuclei, mitochondria or peroxisomes were visualized with a fluorescent protein, and the transgenic gemmmalings were incubated under the cold condition. Nuclei and peroxisomes, but not mitochondria, clearly relocated from the periclinal cell wall to the anticlinal cell wall after cold treatments. Our findings suggest that several organelles concurrently change their positions in the liverwort cell to cope with cold temperature.     

Effects of dark preincubation and chloramphenicol on blue light-induced CO2 incorporation in Chlorella cells

Chlorella cells incubated in the dark longer than 12 hr showedpronounced blue light-induced ¹⁴CO₂ fixation into aspartate,glutamate, malate and fumarate (blue light effect), whereasthose kept under continuous light showed only a slight bluelight effect, if any. 2) During dark incubation of Chlorellacells, phosphoenolpyruvate carboxylase activity and the capacityfor dark ¹⁴CO₂ fixation decreased significantly, whereas ribulose-1,5-diphosphatecarboxylase activity and the capacity for photosynthetic ¹⁴CO₂fixation (measured under illumination of white light at a highlight intensity) did not decrease. 3) In cells preincubatedin the dark, intracellular levels of phosphoenolpyruvate and3-phosphoglycerate determined during illumination with bluelight were practically equal to levels determined during illuminationwith red light. 4) The blue light effect was not observed incells incubated widi chloramphenicol, indicating that blue light-inducedprotein synthesis is involved in the mechanism of the effect. (Received April 9, 1971; )