Involved in oxidative stress tolerance by detoxifying reactive aldehydes derived from lipid peroxidation. Medium- to long-chain saturated aldehydes are preferred substrates, while the short-chain aldehyde propanal is a weak substrate. Is strictely NAD(+) specific. an aldehyde + H2O + NAD(+) = a carboxylate + 2 H(+) + NADH Thiol-based regulation. Inactivation after dimerization under oxidizing conditions. Optimum pH is 8.0. Homodimer and homomultimer. A number of isoforms are produced. According to EST sequences. An alternative promoter within intron 1 may direct expression of several alternative transcripts, including isoform beta. Isoform alpha is expressed in expanded leaves and flowers. Detected in seedlings. Isoform beta is mainly expressed in flowers. Detected in leaves and seedlings. By abscisic acid (ABA), dehydration and salt stress in roots. Isoform alpha is up-regulated in leaves but not in roots upon salt treatment. Isoforn beta is up-regulated by salt treatment in both roots and leaves. Increased sensitivity to salt stress. Major isoform. Produced by alternative splicing. Maybe not translated into a protein or accumulates at a level below detection. Belongs to the aldehyde dehydrogenase family.