XVI International Botanical Congess

Malic acid synthesized in root nodules from shoot derived sucrose provides the carbon for energy to drive the nitrogenase reaction and the backbone for assimilation of symbiotically fixed nitrogen (N). The synthesis of malate and the assimilation of N requires the coordinated expression of enzymes localized in the cytosol and plastids. Biochemical and molecular analyses have identified the subcellular localization of enzymes involved in root nodule carbon and nitrogeninteractions. Two cycles, one in the cytosol and the other in plastids, linked through plastid localized NADH-dependent glutamate synthase function to channel primary N assimilation in root nodules. Moreover, the discovery of a plastid targeted nodule-enhanced malic dehydrogenase has implications for both carbon and nitrogen metabolism and provides insight into the importance of infected and uninfected cells in carbon metabolism of root nodules.