Effect of photoinhibitory treatments on the activity of light-activated enzymes of c(3) and c(4) photosynthetic carbon metabolism.

Exposure of maize leaves to a 3-hour photoinhibitory treatment (photon flux rate of 2,000 microeinsteins meter(-2) second(-1), CO(2)-free air) resulted in lower activities of the light-activated enzymes NADP malate dehydrogenase, pyruvate, Pi dikinase, and ribulose-5-phosphate kinase. The activities could be recovered partially either by incubating enzyme extracts with dithiothreitol or by illuminating the treated leaf in air. Several enzymes which are not light-activated were not affected by the treatment. Ribulose-5-phosphate kinase activity was also reduced when bean plants grown in low light were subjected to a similar photoinhibitory treatment.It is suggested that, although the reactivation of these enzymes may be correlated with the short term increase of CO(2) uptake capacity observed when photoinhibited leaves are returned to illumination in air, inactivation of these enzymes does not contribute significantly to the long term in vivo expression of photoinhibition observed after 2 to 4 hours.The results provide an example of partial inactivation of light-activated enzymes under illumination equivalent to full sunlight.