Metabolism of [14C]Indole-3-Acetic Acid by Coleoptiles ofZea maysL.

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Abstract
Reverse-phase high-performance liquid chromatography was used to analyse [14C]-labelled metabolites of indole-3-acetic acid (IAA) in coleoptile segments of Zeo mays seedlings. After incubation for 2 h in 10−2 mol m−3 [2-14C]IAA, methanolic extracts of coleoptiles contained between six and ten radioactive compounds, one of which co-chromatographed with IAA. The metabolic products in coleoptile extracts appeared to be similar to those in root extracts, with an oxindole-3-acetic-acid-like component as the principal metabolite, but the rate of metabolism was slower in coleoptile than in root segments. Decarboxylation did not appear to play a major role in the metabolism of exogenous IAA during the short incubation periods. Moreover, external IAA concentration had little effect on the pattern of metabolism. Coleoptile segments were also supplied with [14C]IAA from agar donor blocks placed at the apical ends, and agar receiver blocks were placed at the basal ends. After incubation for 4 h, the identity of the single radioactive compound in the receiver blocks was shown to be IAA by both reverse-phase high-performance liquid chromatography and gas chromatography-mass spectrometry techniques.