Decarboxylation of malate by isolated bundle-sheath cells of certain plants having the C₄-dicarboxylic acid cycle of photosynthesis

Bundle-sheath cells isolated by the grinding and filtration procedure of Edwards and Black (1971b) from species of plants having the C₄-dicarboxylic acid pathway of photosynthesis were tested for the decarboxylation of malate from the C₄-carboxyl position. The bundle-sheath cells, which showed high malic enzyme activity in extracts, decarboxylated 4[¹⁴C]malate at rates sufficient to be involved in photosynthesis. The malate decarboxylation is dependent on the addition of magnesium or manganese and NADP⁺. The activity was increased by raising the temperature from 30 to 50°. The evidence supports the idea that malate may be a carboxyl donor to the reductive pentose-phosphate cycle in bundle-sheath cells in certain C₄-dicarboxylic acid pathway plants such as Zea mays L., Sorghum bicolor L., and Digitaria sanguinalis (L.) Scop.