Abstract
The malate valve consists of malate dehydrogenase isozymes located in the cytosol and stroma, and a malate/oxaloacetate transporter located in the inner envelope membrane of chloroplasts. The stromal reducing equivalents are exported to the cytosol via the malate valve and provided to cytosolic enzymes and/or intracellular compartments such as peroxisome and mitochondrion. The malate valve also play a role in removing excessive reducing equivalents under the environmental stress conditions. Recently, we identified a gene for plastidic 2-oxoglutarate/malate transporter (OMT) from Arabidopsis. From the results of gene expression patterns and substrate transport properties of the recombinant proteins, OMT was also thought to function as a malate/oxaloacetate transporter in the malate valve. A T-DNA insertion mutant of the OMT gene showed more prominent photoinhibition than wild-type plant under the stress conditions (low temperature and high light). This result suggests that the malate valve plays a crucial role in avoidance of photoinhibiton.
