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, CO₂-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.