LIGHT-DEPENDENT PHOSPHORYLATION OF PHOSPHOENOLPYRUVATE CARBOXYLASE AND ITS ROLE IN THE REGULATION OF C-4 PHOTOSYNTHESIS

This paper deals with the regulatory phosphorylation for the C-4 cycle enzyme, cytosolic phosphoenolpyruvate carboxylase (PEPC) in mesophyll cells from C-4 plants. Emphasis is put on the organization of the lig ht signal-transduction chain which upregulates PEPC-kinase activity an d the phosphorylation of PEPC. Initiation of the signalling pathway in mesophyll cells involves 3-P-glycerate formed in the Calvin cycle of the neighbouring bundle sheath cells. Downstream elements: cytosolic p H, tonoplast InsP3-gated calcium channel, cytosolic calcium, a calcium -dependent protein kinase and the calcium-independent PEPC-kinase have been identified by a confocal microscopy/flux cytometry/protoplast ph armacology approach. The post-translational modulation of PEPC strongl y iinfluences its regulation by photosynthesis-related metabolites (L- malate, feedback inhibitor and glucose-6P, allosteric activator). The physiological significance of this process is discussed in the context of C-4 photosynthesis.