engleski

Metabolism of exogenous auxin by Arabidopsis thaliana : identification of the conjugate N(alpha)-(indol-3-ylacetyl)glutamine and initiation of a mutant screen

The accumulation of conjugates of indole-3-acetic acid (IAA) in Arabidopsis thaliana was studied by incubating tissues with high concentrations of exogenous IAA, followed by reverse phase HPLC analysis of the extracts. Using fluorescence detection, indole-3-acetyl-aspartate, indole-3-acetyl-glutamate, and indole-3-acetyl-glucose were observed and quantitated in extracts of of tissue after 24 h incubation with 500 micromol/L IAA. In addition, a new metabolite was detected and positively identified as indole-3-acetyl-glutamine by fast atom bombardment mass spectrometry, exact mass measurement, and tandem mass spectrometry in comparison with a synthetic standard. The amounts of individual conjugates formed differed between leaves, shoot axes and roots. In all three tissues, indole-3-acetyl-aspartate was the most abundant conjugate, the highest level being observed in roots. Highest levels of indole-3-acetyl-glutamine were observed in leaves, where it was the second most abundant conjugate and comprised approximately 12% of the fluorescent metabolites. Accumulation of the three amide conjugates was dramatically inhibited by cycloheximide, whereas accumulation of indole-3-acetyl-glucose was little affected. Based on these data, a screen for Arabidopsis mutants altered in the IAA-inducible system for auxin conjugate formation was initiated. The first mutant to be isolated and characterized produces more indole-3-acetyl-glutamine and less indole-3-acetyl-aspartate than wild-type, and is allelic to an existing class of photorespiration mutants (gluS) deficient in chloroplastic glutamate synthase.

Arabidopsis thaliana; Cruciferae; indole-3-acetic acid; IAA; N-(indol-3-ylacetyl)aspartate; N-(indol-3-ylacetyl)glutamate; N(alpha)-(indol-3-ylacetyl)glutamine; indole-3-ylacetylglucose; gluS mutant

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