Photorespiration and Oxygen Inhibition of Photosynthesis in Chlorella pyrenoidosa1

AUTOR(ES)

Shelp, Barry J.

RESUMO

The inhibition of photosynthesis by O2 in air-grown Chlorella pyrenoidosa was investigated using three experimental techniques (artificial leaf, aqueous method, and O2 electrode) to measure carbon assimilation. CO2 response curves were determined under different O2, pH, and temperature conditions. Regardless of the experimental technique and condition, O2 inhibition was not evident until a concentration of 50% was reached; Vmax values were reduced whereas Km (CO2) values were unaffected by the increasing O2 concentration. The response of photosynthesis to O2 was independent of CO2 and HCO3− concentrations as well as temperature. Relative rates of photosynthesis showed a 4 to 5% stimulation in 2% O2, a 12% inhibition in 50% O2, and a 24% inhibition in 100% O2. The inhibition by 50% O2 was still reversible after 20 minutes exposure whereas 100% O2 caused irreversible inhibition after only 4 minutes.

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