LIGHT-INDUCED CHANGES IN CONTENT OF SOME ENZYMES OF C4-DICARBOXYLIC ACID PATHWAY OF PHOTOSYNTHESIS AND ITS EFFECT ON OTHER CHARACTERISTICS OF PHOTOSYNTHESIS

Various effects of light and light-intensity on the content of several photosynthetic enzymes were examined. Included amongst the enzymes were, pyruvate, Pi dikinase, phosphopyruvate carboxylase, adenylate kinase and alkaline pyrophosphatase, enzymes believed to have specific roles in the C4-dicarboxylic acid pathway of photosynthesis. Maize and Amaranthus plants were grown at high or low light intensities for prolonged periods and their enzyme contents examined before and after transfer of high-light-grown plants to low light or vice versa. Ribulose 1,5-diphosphate carboxylase activity was unaffected by these treatments, but the contents of glyceraldehyde 3-phosphate dehydrogenase, adenylate kinase and pyrophosphatase were approximately 2 fold higher and pyruvate, Pi dikinase and phosphopyruvate carboxylase between 5- and 10-fold higher in plants grown at the higher light intensities. During the 6 days following changes in the light regime the enzyme contents adapted almost completely to the new light conditions. These changes in enzyme activities were accompanied by changes in maximum photosynthesis rates and light-saturation characteristics of leaves. However studies with 14CO2 provided no evidence for significant changes in the pathway of photosynthesis operative in these leaves. Other studies showed that the content of these and other photosynthetic enzymes were low in the leaves of maize plants germinated and grown in the dark but increased up to 15-fold, together with chlorophyll, following transfer of plants to the light for 35 hr. The possible regulatory significance of these findings are discussed. © 1970.