Transport and Fixation of Inorganic Carbon in the Cells of Chlorella vulgaris 11h Grown under Ordinary Air

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Abstract
Intracellular accumulation of inorganic carbon (Ci) and its fixation in photosynthesis were investigated using silicone oil layer filtering centrifugation technique with the cells of Chlorella vulgaris 11h grown under ordinary air. Both CO2 and HCO3− were transported into the cells from the reaction medium and accumulated in the cells, but the rate of transport was much faster for the former than the latter. 14C-fixation from the total transported Ci was much more efficient when CO2 was added in the external medium than when HCO3− was added. This indicates that CO2 and HCO3− were not converted to the common compound in the cells during the initial period of photosynthesis. Accumulation of Ci into the cells was much less susceptible to low temperature than its fixation. Accumulation of Ci was also observed in the dark. Ethoxyzolamide, an inhibitor of carbonic anhydrase (CA), inhibited the fixation of accumulated CO2 in the cells, suggesting that CA enhanced the supply of CO2 to the reaction site of ribulose bisphosphate carboxylase in the stroma. Mechanism for transport and fixation of Ci during photosynthesis in low-CO2 cells of C. vulgaris 1lh was proposed from these results.