Photorespiration in Air and High CO2-Grown Chlorella pyrenoidosa1

AUTOR(ES)

Shelp, Barry J.

RESUMO

Oxygen inhibition of photosynthesis and CO2 evolution during photorespiration were compared in high CO2-grown and air-grown Chlorella pyrenoidosa, using the artificial leaf technique at pH 5.0. High CO2 cells, in contrast to air-grown cells, exhibited a marked inhibition of photosynthesis by O2, which appeared to be competitive and similar in magnitude to that in higher C3 plants. With increasing time after transfer to air, the photosynthetic rate in high CO2 cells increased while the O2 effect declined. Photorespiration, measured as the difference between 14CO2 and 12CO2 uptake, was much greater and sensitive to O2 in high CO2 cells. Some CO2 evolution was also present in air-grown algae; however, it did not appear to be sensitive to O2. True photosynthesis was not affected by O2 in either case. The data indicate that the difference between high CO2 and air-grown algae could be attributed to the magnitude of CO2 evolution. This conclusion is discussed with reference to the oxygenase reaction and the control of photorespiration in algae.

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