In the dark, chloroplast/cytosolic glycolysis and the TCA cycle become more active. The sucrose and malate that accumulated during the day are released from the vacuole and can serve as sources of reducing equivalents. Sucrose can supply NADPH to chloroplasts and the cytosol via OPPP and NADH (via chloroplast GAPDH [GAPDHp] and cytosolic GAPDH, respectively) via glycolysis. Whether np-GAPDH can provide cytosolic NADPH at night requires validation. Malate stored in the vacuole during the day can be released to the cytosol during the night to supply cytosolic NADPH and NADH via NADP-ME13 and cyNAD-MDH, respectively. In addition, cytosolic malate can enter chloroplasts, mitochondria, and peroxisomes to supply NADH and NADPH via their respective MDHs and MEs. Specifically, clNAD-MDH and NADP-ME4 provide NADH and NADPH for chloroplasts, pNAD-MDH provides NADH for peroxisomes, and mtNAD-MDH and light-inactivated mtNAD-ME provide mitochondrial NADH. In mitochondria, OGDH in the TCA cycle also provides NADH. Pyruvate generated from glycolysis and cytosolic NADP-MEs enters the mitochondria to feed the TCA cycle. Citrate is exported from the mitochondria and stored in the vacuole during the night. Isocitrate can serve as a source of NADPH in the cytosol, mitochondria, peroxisomes, and chloroplasts via their respective NADP-ICDHs. NADH and NADPH in the matrix can be consumed by NDA1-2 (A1-2) and NDC1 (C1), respectively. During the night, the incomplete OPPP pathway in peroxisomes is driven by the import of plastid G6PD1 to provide NADPH. NADPH can participate in oxidative reactions throughout the day. Cytosolic NADH can be consumed by NDB2-4 (B2-4). Cytosolic NADPH can be consumed by NDB1 (B1), RboH, and NTRA; plastid-localized NADPH can be consumed through NTRC; and mitochondrial NADPH can be consumed through NTRB. The AsA–GSH cycle can consume both NADH and NADPH in the cytosol, chloroplasts, peroxisomes, and mitochondria regardless of light conditions. Actyl-CoA, acetyl coenzyme A; AsA–GSH, ascorbate–glutathione cycle; BPGA, 1,3-bisphosphoglycerate; cyNAD-MDH, cytosolic NAD-dependent malate dehydrogenase; clNAD-MDH, chloroplast NAD-dependent malate dehydrogenase; clNADP-MDH, chloroplast NADP-dependent malate dehydrogenase; cmNADP-ICDH, chloroplast-mitochondrial NADP-dependent isocitrate dehydrogenase; cyNADP-ICDH, cytosolic NADP-dependent isocitrate dehydrogenase; ETC, electron transport chain; FNR, ferredoxin-NADP(H) oxidoreductase; GAPDH, cytosolic NAD-specific glyceraldehyde 3-phosphate dehydrogenase; GAPDHp, plastidic NAD-specific glyceraldehyde 3-phosphate dehydrogenase; G6P, glucose 6-phosphate; GAP, glyceraldehyde 3-phosphate; mETC, mitochondrial electron transport chain; mPDC, mitochondrial pyruvate dehydrogenase complex; mNAD-ME, mitochondrial NAD-dependent malate enzyme; mtNAD-MDH, mitochondrial NAD-dependent malate dehydrogenase; mNAD-ICDH, mitochondrial NAD-dependent isocitrate dehydrogenase; np-GAPDH, non-phosphorylating glyceraldehyde 3-phosphate dehydrogenase; NADP-ME, NADP-dependent malate enzyme; NDA1-2 (A1-2), alternative NADH dehydrogenases A1-2; NDB1 (B1), alternative NADPH dehydrogenase B1; NDB2-4 (B2-4), alternative NADPH dehydrogenase B2-4; NDC1 (C1), alternative NADPH dehydrogenase C1; NTRA, NADPH-dependent thioredoxin reductase A; NTRB, NADPH-dependent thioredoxin reductase B; NTRC, NADPH-dependent thioredoxin reductase C; OGDH, 2-oxoglutarate dehydrogenase complex; OAA, oxaloacetate; OPPP, oxidative pentose phosphate pathway; pNAD-MDH, peroxisomal NAD-dependent malate dehydrogenase; pNADP-ICDH, peroxisomal NADP-dependent isocitrate dehydrogenase; RboH, respiratory burst oxidase homologs; Succinyl CoA, succinyl-coenzyme A; TCA cycle, tricarboxylic acid cycle; 3-PGA, 3-phosphoglycerate; 2-OG; 2-oxoglutarate.
