Figure 3.

Metabolic coordination of chloroplasts and mitochondria in the light. NADPH formed in the photosynthetic ETC drives the Calvin–Benson cycle and fuels the malate valve in the reaction catalyzed by NADP-MDH. Oxidation of malate in the chloroplasts, cytosol, peroxisomes, and mitochondria by corresponding isoforms of NAD-MDH generates NADH in these compartments. In mitochondria, the increase of NADH level fuels the mitochondrial ETC and stimulates the efflux of citrate, which is transformed into 2-OG by the cytosolic aconitase and NADP-isocitrate dehydrogenase. The increase in the cytosolic NADPH level results in stimulation of the cytochrome P450-dependent monooxygenase reactions leading to the synthesis of secondary metabolites, xenobiotic degradation, and other processes. The rise in the 2-OG level results in glutamate synthesis and 2ODD reactions, which also generate secondary metabolites. Oxygen produced in photosynthesis is used not only for mitochondrial respiration but also in Rubisco oxygenase reaction (photorespiration), glycolate oxidase in peroxisomes, and in mono- and dioxygenase reactions, leading to the formation of secondary metabolites. OAA, oxaloacetate; PEP, phosphoenolpyruvate; PGA, 3-phosphoglyceric acid; TP, triose phosphate. The oxygen consumption or release is shown by the red arrows, and the light blue thick arrows indicate the formation of secondary compounds. The biochemical reactions and transport processes are represented by the solid thin lines, and the dotted line indicates the reduction of hydroxypyruvate in peroxisomes by NADH.