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

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Abstract
1) The wavelength effects on 14CO2-fixation by Chlorella cells were studied, using monochromatic light of different light intensities. 2) Blue light (453 mμ) stimulated the incorporation of 14C 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 CMU at concentrations completely suppressing ordinary photosynthetic CO2-fixation. 4) The blue light effect in the presence of CMU was induced at very low intensities. At 453 mμ, 300 erg cm−2 sec−1 was sufficient for complete saturation. 5) Time courses of 14C-incorporation into individual compounds were investigated. Irrespective of the wavelength of the illuminating light, the first stable CO2-fixation product formed under weak light (400–500 erg cm−2 sec−1) was citrulline. At higher light intensities (4,000–7,000 erg cm−2 sec−1), PGA was the first stable CO2-fixation product. The incorporation of 14C into citrulline was not inhibited by CMU. 6) Experimental results indicate that both blue light-induced incorporation of 14C into amino and organic acids and the incorporation of 14C into citrulline induced by low intensity light are operated by a mechanism(s) independent of ordinary photosynthetic CO2-fixation. Possible effects of light regulating the carbon metabolism in algal cells are discussed.

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