A new chemically mutagenic mutant ofSynechococcus PCC7942 named high-CO2 requiring mutant, which could grow at 4% CO2 but could not grow at air levels of CO2, was isolated. Comparative studies on some physiological aspects of the mutant and high-CO2 growing cells (growing at 4% CO2) were conducted. The result showed that the mutant had lower growing rate, about 1/40th photosynthetic affinity to inorganic carbon, 25% lower carbonic anhydrase (CA) activity, lower quenching rate of chlorophyll fluorescence, and about 1/2 alkalinization rate of the medium. The CA activity responses of the two types of cells to different concentration of CO2 were determined. Upon the addition, of inorganic carbon (Ci), the rate of active Ci uptake described by the rate of chlorophyll fluorescence quenching of the mutant was obviously lower compared with that of the high-CO2 growing cells; the size of the internal inorganic carbon pool size detemined by the extent of fluorescence quenching of the mutant was also smaller.
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