Catalyzes a reversible NAD-dependent dehydrogenase reaction involved in central metabolism and redox homeostasis between organelle compartments (Probable). Plays a key role in the metabolism of dark chloroplasts and non-green plastids. Essential for embryo viability (PubMed:24198233, PubMed:24453164). Plays an essential role in heterotrophic metabolism in embryos, and autotrophic metabolism in photosynthetic tissues as well (PubMed:24453164). (S)-malate + NAD(+) = H(+) + NADH + oxaloacetate Homodimer. Expressed in rosette leaves (PubMed:20876337). Expressed in meristematic regions of roots and shoots, cotyledons, young leaves, trichomes, stamen, pollen, tapetum, gynoecium and ovules (PubMed:24198233). During pollen development, expressed in mature pollen grains and early in pollen-tube growth. Not expressed in immature pollen grains and fully grown pollen tubes (PubMed:24198233). During embryo development, expressed from the heart stage to mature embryo. Not expressed at the beginning of embryo development up to the globular stage (PubMed:24198233, PubMed:24453164). Embryonic lethality when homozygous due to embryo development arrest at globular stage. Belongs to the LDH/MDH superfamily. MDH type 1 family.