DISTRIBUTION OF EXCITATION-ENERGY BETWEEN PHOTOSYSTEM-2 AND PHOTOSYSTEM-1 UPON ADAPTATION OF HIGH-CO2 GROWN CELLS OF CHLORELLA-VULGARIS SP K TO LOW CO2

The 77 K fluorescence emission was measured on Chlorella cells at regu lar intervals during adaptation of high CO2 (1.8 % CO2 V/V) grown cell s to air level of CO2. The ratios of the peaks at 686 and 697 nm (phot osystem 2, PS 2, fluorescence) to the peak at 720 nm (PS 1 fluorescenc e) decreased and approached a constant level in about 1.5 h. The exter nal concentration of dissolved inorganic carbon (DIC) required for the half-maximum rates of CO2-dependent O2 evolution, K0.5, also decrease d and reached a constant level after the same period of adaptation. He nce the increased demand for ATP/NADPH during the CO2 assimilation by the ''CO2-concentrating mechanism'' induces the redistribution of exci tation energy from PS 2 to PS 1 and increases formation of ATP by the cyclic photophosphorylation.