Carboxylation reactions and photosynthesis of carbon compounds in isolated mesophyll and bundle sheath cells of [formula omitted] (L.) Scop

Abstract

Bundle sheath and mesophyll cells were successfully separated from fully developed leaves of Digitaria sanguinalis (L.) Scop. to study the photosynthetic metabolism of these distinct cell types. Ribulose-1,5-diphosphate and ribose-5-phosphate enhanced CO 2 fixation by bundle sheath cells and had little effect on CO 2 fixation in mesophyll cells. In contrast, pyruvate induced CO 2 fixation in mesophyll cells and had no effect in bundle sheath cells. Phosphoenolpyruvate carboxylase is localized in mesophyll cells and ribulose-1,5-diphosphate carboxylase is localized in bundle sheath cells. The results establish that mesophyll cells fix CO 2 by a β-carboxylation while the bundle sheath cells fix CO 2 by carboxylation of ribulose-1,5-diphosphate.