Abstract
In NADP-malic enzyme-type C4 plants such as maize, efficient transport of oxaloacetate and malate across the chloroplast envelope membranes is indispensable. We have isolated a maize cDNA encoding 2-oxoglutarate/malate transporter (OMT) which express in mesophyll cells and two cDNAs encoding general dicarboxylate transporters (DCT) which express in mesophyll and bundle sheath cells, respectively. In this study, we further investigated the physiological functions of these transports. Genomic Southern analysis revealed that there is one OMT gene in maize. OMT has higher affinity for oxaloacetate than DCT. The Km value for oxaloacetate of mesophyll chloroplasts was remarkably lower than that of bundle sheath chloroplasts. These findings suggest that mesophyll OMT may function in C4 pathway and transport oxaloacetate into chloroplasts. In contrast, bundle sheath DCT may function as a malate transporter in a C4 pathway.
