Transport and Fixation of Inorganic Carbon during Photosynthesis in Cells of Anabaena Grown under Ordinary Air Grown under Ordinary Air

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In cells of cyanobacterium Anabaena variabilis grown under ordinary air (low-CO_2 cells), the transport of both CO_2 and HCO^-_3 was significantly enhanced by Na^+. This effect was pronounced as the external pH increased. When low-CO_2 cells were treated with an inhibitor of carbonic anhydrase (CA), only CO_2 transport but not HCO^-_3 transport, was inhibited. The initial rate of photosynthetic carbon fixation as a function of the concentration of internal inorganic carbon (IC) was practically the same irrespective of whether CO_2 or HCO^-_3 was externally supplied. These results suggest that IC is actively transported through the plasma membrane in a form of HCO^-_3 probably by some transporter and that the transmembrane Na^+ gradient is involved in this IC transport system. Free CO_2 may be hydrated by CA to HCO^-_3 and then transported to the cells by this transporter. On the other hand, CO_2 is actively taken up by cells grown with air containing 5% CO_2 (high-CO_2 cells) though the enhancing effect of Na^+ was much smaller in high-CO_2 cells than in low-CO_2 cells. The initial rate of fixation as a function of internal IC concentration indicated that the rate of the carboxylation reaction of accumulated IC is higher in low-CO_2 cells than in high-CO_2 cells. The studies with ethoxyzolamide indicated that even in low-CO_2 cells, CA does not function inside Anabaena cells. These results suggest that inside the low-CO_2 cells of Anabaena, some mediatdr(s) facilitates the transport of IC to RuBPCase.
日本植物生理学会の論文

Transport and Fixation of Inorganic Carbon during Photosynthesis in Cells of Anabaena Grown under Ordinary Air Grown under Ordinary Air

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