The CO2 compensation points of Coccochloris peniocystis, a blue-green alga and Chlamydomonas reinhardtii, a green alga, were determined at pH 8.0 in a closed system by a gas chromatographic technique. The compensation point of Chlamydomonas increased markedly with temperature, rising from 0.79 microliter per liter CO2 at 15 C to 2.5 microliters per liter CO2 at 35 C. In contrast, the compensation point of Coccochloris at 20 C was 0.71 microliter per liter CO2 and rose to only 0.95 microliter per liter CO2 at 40 C.The compensation point of the green alga was significantly reduced at low O2 concentrations (1 to 2%) when measured over the temperature range of 15 to 35 C. The compensation point of the blue-green alga, over the temperature range of 20 to 40 C, was unaffected by lowering the O2 concentration.The whole cell CO2 affinity of Chlamydomonas decreased substantially with increasing temperature at 21% O2 whereas little change was observed over the same temperature regime when the CO2 affinity was determined at O2 concentrations of 1 to 2%. The CO2 affinity of Coccochloris did not decrease significantly with either increasing temperature or O2 concentration.These results suggest that while photorespiration is undetectable in Coccochloris some photorespiratory CO2 release occurs in Chlamydomonas.
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