Important as a means of generating NADPH for biosynthetic reactions. D-glyceraldehyde 3-phosphate + H2O + NADP(+) = (2R)-3-phosphoglycerate + 2 H(+) + NADPH Induced by sugar addition. Algae contain three forms of GAPDH: two cytosolic forms which participate in glycolysis and one chloroplastic form which participates in photosynthesis. These three forms are encoded by distinct genes. Belongs to the aldehyde dehydrogenase family.