The mechanism of inhibition of photosynthesis by high partial pressures of oxygen inChlorella

The decrease in rate of photosynthesis of $^{14}$CO$_{2}$ following a transition from 20 to 99$\cdot $96% oxygen with 0$\cdot $04% carbon dioxide was associated with a decrease in radioactivity of the sugar phosphates and an increase in that of glycollic acid. The effect of increasing the partial pressure of oxygen was greater at higher light intensities. At the highest light intensities used the inhibition became irreversible. When carbon-14 was incorporated into the sugar phosphates and the further metabolism of these compounds studied in carbon dioxide free conditions the main products in 20% oxygen were polyglucan and sucrose, but in the presence of high oxygen partial pressure they were glycollate and glycine. Radioactive glucose was fed in the presence of oxygen free of carbon dioxide. At low light intensities the main product was a polyglucan; at higher light intensitie sglycollic acid was formed and radioactive carbon dioxide was produced.