The auxin conjugate 1-O-indole-3-acetyl-β-D-glucose is synthesized in immature legume seeds by IAGIc synthase and may be used for modification of some high molecular weight compounds

Abstract

Immature seeds of some dicotyledonous plants contain IAGIc synthase catalysing the synthesis of 1-O-IAGIc. This enzyme activity is comparable with 1-O-IAGIc synthase activity investigated earlier in liquid endosperm of Zea mays. Polyclonal antibodies against maize 1-O-IAGIc synthase cross-react with partially purified 1-O-IAGIc synthase from immature pea and rape seeds. Single immunoreactive bands were observed at a locus corresponding to 45.7 KDa and 43.7 KDa from pea and rape enzyme preparations, respectively, unlike that from the 50 KDa molecular mass of the maize enzyme. It was also observed that some high molecular weight compounds of pea seeds are labelled in vivo by [14C] IAA, and unlabelled 1-O-IAGIc inhibits that labelling. In immature pea seeds 43-49.8% of the IAA-modified high molecular weight compounds, obtained after ultracentrifugation, was found in the soluble fraction and 50.1-57% in the insoluble fraction. Ester-linked IAA accounted for about 6-9% and 38-45.6% in soluble and insoluble material, respectively, estimated after hydrolysis in 1 N NaOH. Enzymatic hydrolysis of IAA-labelled high molecular weight compounds gives free IAA and compound(s) corresponding to IAGIc isomers. These results suggest that 1-O-IAGIc synthesized in legume seeds may be used for the modification of some high molecular weight compounds.