PHOTOSYNTHETIC O-2 EXCHANGE IN CHLORELLA CELLS ADAPTED TO LOW CO2 CONCENTRATION UNDER BLUE OR RED-LIGHT

The effect of light quality on the adaptation to low atmospheric CO2 c oncentration was studied on the cells of unicellular green al,oa Chlor ella pyrenoidosa 82T grown under 2% CO2 concentration and white light. The adaptation of Chlorella cells was more successful under blue than under red light. Thus, the air-adapted cells under blue light showed a higher affinity for CO2, a higher quantum efficiency of apparent pho tosynthesis at CO2 limitation, and acceleration of O-2 evolution at li ght saturation, as compared to the red-light-adapted cells. In air-ada pted cells, the photosynthetic rates at low CO2 concentration were enh anced with increased intensities of both blue and red light, but the d ifferences between the two treatments were retained. It was inferred t hat Chlorella cell adaptation depended on both light intensity and its spectral composition. The light intensity exerts its action via photo synthetic apparatus while spectral composition of light exerts its eff ect via a system of photoreception, which absorbs blue light. This add itional blue light absorption is considered favorable for Chlorella ce ll adaptation to low CO2 concentration.