Abstract: Intact attached leaves of wheat were illuminated at 2000 μmol m-2·s-1 in CO2-free gas for 3 hours, inhibition percentage of photosynthesis in these leaves by illumination was related lo oxygen concentration in the gas. (1) The damage to the leaves became less gradually when oxygen concentration rose from 0 to 10%. (2) Almost no damage occurred between 10%–50% O2. (3) The damage appeared again when oxygen concentration exceeded 50%. The duration of CO2 outburst of wheat leaves in CO2-free gas containing 8%–11% O2 was 0nly about 15–30 min. However, no photoinhibition could be observed under this condition. Oxygen also could prevent isolated chloroplasts from the damage by strong light. No matter what concentration of oxygen in CO2-free gas was during photoinhibition treatment, the photodamaged site was always in PSⅡ. It is concluded from the results that the way in which photoinhibition was alleviated by oxygen seems not only to be photorespiration, but also the other unknown mechanisms waich may play more important part in it.

Key words: Oxygen, Wheat leaves, Photoinhibition, Photorespiration