Involved in cell redox homeostasis. Required for maintaining a steady state cellular NADH/NAD(+) ratio through a mitochondrial glycerol-3-phosphate redox shuttle. May function with the mitochondrial FAD-dependent glycerol-3-phosphate dehydrogenase SDP6 to shuttle reducing equivalents into the mitochondria for respiration. NAD(+) + sn-glycerol 3-phosphate = dihydroxyacetone phosphate + H(+) + NADH Expressed in roots, leaves, flowers and siliques. By abscisic acid and salt and dehydration treatments. Down-regulated by hypoxia. No visible phenotype under normal growth conditions, but mutant plants have increased NADH/NAD(+) ratios, decreased levels of glycerol-3-phosphate, and produce constitutive high levels of reactive oxygen species (ROS). Belongs to the NAD-dependent glycerol-3-phosphate dehydrogenase family.