Mass spectrometry, genetics and biochemistry: Understanding the metabolism of indole-3-acetic acid

Abstract

It is the goal of our laboratory to understand the processes that plants use to regulate the level of the naturally occurring auxin, indole-3-acetic acid (IAA). Four basic approaches have been taken that, when applied together, will yield information on the mechanisms and reactions involved in the regulation of the level of this phytohormone. 1) We have developed techniques for the analysis of IAA and related metabolites using GC-MS and stable isotopes for quantitation and in vivo analysis of metabolic reactions. 2) Using chromatographic and spectral analysis we have isolated and identified a variety of conjugates of IAA and have shown these to be important in the regulation of IAA levels. Most unique has been the isolation of a 3 kD peptide with IAA in amide linkage that is the major conjugate in extracts from bean seeds. 3) We have applied genetic techniques in order to extend and refine our metabolic studies. A mutant of Lemna that accumulates large amounts of IAA has been isolated and selections are being made to obtain mutants unable to hydrolyze IAA conjugates. 4) Initial results are presented on the in vitro hydrolysis of IAA-amino acid conjugates by enzyme extracts from bean and from carrot cell cultures.