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A Novel Metabolic Pathway for Indole-3-Acetic Acid in Apical Shoots of Populus tremula (L.) x Populus tremuloides (Michx.)
Authors:Tuominen H  Ostin A  Sandberg G  Sundberg B
Institution:Department of Forest Genetics and Plant Physiology, The Swedish University of Agricultural Sciences, 90183 Umea, Sweden.
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 1prime]-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 1prime]-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.
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