In higher plants aldehyde oxidases (AO) appear to be homo- and heterodimeric assemblies of AO subunits with probably different physiological functions. Involved in the biosynthesis of auxin. H2O + indole-3-acetaldehyde + O2 = (indol-3-yl)acetate + H(+) + H2O2 Binds 2 [2Fe-2S] clusters. Binds 1 Mo-molybdopterin (Mo-MPT) cofactor per subunit. Aldehyde oxidases (AO) are homodimers and heterodimers of AO subunits. Mostly expressed in coleoptiles, and, to a lower extent, in mesocotyl and roots. Belongs to the xanthine dehydrogenase family.