The role of PEPC phosphorylation in theregulation of C4 photosynthesis

Abstract Leaves of C plants are characterized by concentrically organized photosynthetic tissues, i.e. an outer mesophyll (M) surrounding inner bundle sheath (BS) cells in which two metabolic cycles, the C and Calvin cycles, are working in concert to achieve CO assimilation. In ‘L-malate formers’, the primary fixation of CO (in its hydrated form) is carried out by the enzyme phosphoenolpyruvate carboxylase (E.C. 4.1.1.31, PEPC) in the cytoplasm ofM-cells to form oxaloacetic acid (OAA) which will be reduced to L-malate in the M chloroplasts; diffusive transport of Lmalate to BS-cells and its decarboxylation by NADP-malic enzyme in the chloroplast stroma make CO available for incorporation by ribulose bisphosphate carboxylase/oxygenase (Rubisco) in the Calvin cycle (Fig. 4.1) (Hatch 1987).