Presence of a Pathway for the Biosynthesis of Auxin via Indole-3-Acetamide in Trifoliata Orange

概要

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The auxin-biosynthetic pathway from L-tryptophan to indole-3-acetic acid via indole-3-acetamide (IAM), found in plant-pathogenic bacteria such as Agrobacterium tumefaciens and Pseudomonas savastanoi, has not been found in plants. We attempted to detect the enzymatic activities for this pathway in cell-free systems from various tissues of trifoliata orange (Poncirus trifoliata Rafin.). A high level of activity of IAM hydrolase, which catalyzes the conversion of IAM to indole-3-acetic acid, was observed in a crude extract prepared from young fruits one week after full bloom. Using α-naphthaleneacetamide as a competitor of IAM hydrolase, a simple assay system was developed for the detection of the conversion of L-tryptophan to IAM (tryptophan monooxygenase activity). When this system was used to assay cell-free extracts of young fruit of P. trifoliata, the conversion of L-tryptophan to IAM was clearly demonstrated by the presence of IAM among reaction products, as demonstrated by GC/MS analysis and the incorporation of ^<14>C-labeled L-tryptophan into an IAM fraction. This is the first report indicating the presence of an auxin-biosynthetic pathway via IAM in P. trifoliata. Furthermore, it is shown that both enzyme activities in auxin biosynthesis increased transiently during fruit development.
日本植物生理学会の論文