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Tryptophan-dependent indole-3-acetic acid biosynthesis by 'IAA-synthase' proceeds via indole-3-acetamide

Pollmann, Stephan, Duchting, Petra, Weiler, Elmar W.
Phytochemistry 2009 v.70 no.4 pp. 523-531
Arabidopsis thaliana, biosynthesis, gas chromatography, indole acetic acid, mass spectrometry, tryptophan
Plants are suggested to produce their major growth promoting phytohormone, indole-3-acetic acid (IAA), via multiple redundantly operating pathways. Although great effort has been made and plenty of possible routes have been proposed based on experimental evidence, a complete pathway for IAA production has yet to be demonstrated. In this study, an in-vitro approach was taken to examine the conversion of L-tryptophan (L-trp) to IAA by gas chromatography-mass spectrometry (GC-MS). Especially the influence of putative reaction intermediates on the enzymatic conversion of L-trp to IAA was analyzed. Among the substances tested only indole-3-acetamide (IAM) showed a pronounced effect on the l-trp conversion. We additionally report that IAM is synthesized from L-trp and that it is further converted to IAA by the utilized cell free Arabidopsis extract. Together, our results underscore the functionality of an IAM-dependent auxin biosynthesis pathway in Arabidopsis thaliana.