Effect of oxygen on photosynthesis by spinach leaf protoplasts

The photosynthetic CO(2) fixation by spinach leaf (Spinacia oleracea L. var. Kyoho) protoplasts was inhibited by substituting an atmosphere of N(2) with one of either air (21% O(2)) or 100% O(2). The inhibitory effect of 100% O(2) was greater than that of air. The mode of inhibition by 100% O(2) and air was competitive with respect to CO(2); Ki(O(2)) value was 0.32 mM at pH 7 and 0.28 mM at pH 8.5 The labeling patterns of compounds in protoplasts exposed to (14)CO(2) in light after transferring them from N(2) to O(2) atmospheres were examined. There was no detectable (14)CO(2) incorporation into glycolate under anaerobic and O(2) atmospheres; a more marked labeling of glycine occurred under an oxidative environment compared to that under the anaerobic condition, presumably because of a rapid transformation of glycolate to glycine in the protoplasts.