Catalyzes the NAD-dependent reduction of a carbon-carbon double bond in an enoyl moiety that is covalently linked to an acyl carrier protein (ACP). Catalyzes the last reduction step in the de novo synthesis cycle of fatty acids. Involved in the elongation cycle of fatty acids which are used in lipid metabolism. Required for normal plant growth. a 2,3-saturated acyl-[ACP] + NAD(+) = a (2E)-enoyl-[ACP] + H(+) + NADH Inhibited by the phytotoxin cyperin and the synthetic antimicrobial compound triclosan. Lipid metabolism; fatty acid biosynthesis. Homotetramer. Expressed in flowers and siliques and at lower levels in roots and leaves (at protein level). Premature cell death in several organs, chlorotic and curly leaves, semidwarfism, distorted siliques, premature senescence of primary inflorescences, reduced fertility and decrease in total lipid content. Belongs to the short-chain dehydrogenases/reductases (SDR) family. FabI subfamily.