Model for the Relationships between CO_2-Concentrating Mechanism, CO_2 Fixation, and Glycolate Synthesis during Photosynthesis in Chlamydomonas reinhardtii

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Photosynthetically competent chloroplasts were isolated from cells of Euglena gracilis Z grown photoautotrophically in 1.5% CO_2. The isolated chloroplasts were intact and substantially free from cytosolic, mitochondrial and microbody materials. The effects of some compounds on the activity of photosynthetic ^<14>CO_2 fixation were examined. The optimal pH and sorbitol concentration were 8.0 and 0.33 _M, respectively. The chloroplasts required a high level of P_i (5 to 20 m_M) for the maximal rate of photosynthesis. They were insusceptible to 10 m_M of free Mg^<2+>. ATP, ADP and AMP at 1 to 5 m_M notably stimulated photosynthesis, although high concentrations of AMP were unfavorable. In the assay medium developed for this study, the chloroplasts exhibited photosynthetic activity of 120 μmoles・mg^<-1> Chl・h^<-1> at 30℃. Chloroplasts could also be isolated from cells grown under ordinary air. The rate of photosynthetic ^<14>CO_2 fixation at 1 m_M NaH^<14>CO_3 was higher in these chloroplasts than in those isolated from cells grown in 1.5% CO_2, whereas at 10 m_M NaH^<14>CO_3, the rates of the two types of chloroplasts were nearly the same. These results suggest that the CO_2 concentration given during growth of the algal cells affects the affinity for dissolved inorganic carbon at the chloroplast level.
日本植物生理学会の論文