title: A Novel Metabolic Pathway for Indole-3-Acetic Acid in Apical Shoots of Populus tremula (L.) x Populus tremuloides (Michx.).
abstract: Metabolism of indole-3-acetic acid (IAA) in apical shoots of Populus tremula (L.) x Populus tremuloides (Michx.) was investigated by feeding a mixture of [12C]IAA, [13C6]IAA, and [1[prime]-14C]IAA through the base of the excised stem. HPLC of methanolic plant extracts revealed eight major radiolabeled metabolites after a 24-h incubation period. Comparison between feeds with [5-3H]IAA and [1[prime]-14C]IAA showed that all detectable metabolites were nondecarboxylative products. The purified radiolabeled HPLC fractions were screened by frit-fast atom bombardment liquid chromatography-mass spectrometry for compounds with characteristic fragment pairs originating from the application with 12C and 13C isotopes. Samples of interest were further characterized by gas chromatography-mass spectrometry. Using this procedure, oxindole-3-acetic acid (OxIAA), indole-3-acetyl-N-aspartic acid (IAAsp), oxindole-3-acetyl-N-aspartic acid (OxIAAsp), and ring-hydroxylated oxindole-3-acetic acid were all identified as IAA metabolites. Furthermore, a novel metabolic pathway from IAA via IAAsp and OxIAAsp to OxIAA was established on the basis of refeeding experiments with the different IAA metabolites.
authors.affiliation: Department of Forest Genetics and Plant Physiology, The Swedish University of Agricultural Sciences, 90183 Umea, Sweden.
authors.forename: H.
authors.initials: H
authors.lastname: Tuominen
authors.forename: A.
authors.initials: A
authors.lastname: Ostin
authors.forename: G.
authors.initials: G
authors.lastname: Sandberg
authors.forename: B.
authors.initials: B
authors.lastname: Sundberg