Skip to main content
Doctoral thesis, 2002

Metabolism and homeostasis of indole-3-acetic acid in Arabidopsis thaliana

Kowalczyk, Mariusz


The endogenous concentration of a primary auxin, indole-3-acetic acid (IAA) is regulated by a number of biochemical processes, including transport, biosynthesis, catabolism and conjugation. The studies on which this thesis is based focused on an instrumental approach for investigating pathways of IAA metabolism and for examining the IAA biochemistry in various Arabidopsis thaliana mutants. We have identified the major low molecular weight IAA at different concentrations. The endogenous presence of these metabolites was subsequently confirmed and their internal concentrations were measured using highly sensitive liquid chromatography-mass spectrometry (LC-MS) techniques. The results showed that non-decarboxylative oxidation of IAA is a key catabolic pathway in A. thaliana. The levels of selected ester and amide conjugates were very low, indicating either a rapid turnover or a low metabolite flux through the main conjugation pathways. Although the biosynthetic details of IAA amide conjugates remain unknown, an enzyme involved in ester conjugate biosynthesis was cloned and characterised at the biochemical level. The developed methods were subsequently used to analyse two mutants with suspected defects in auxin homeostasis, bus and sur2. In both cases we demonstrated that although IAA metabolism was profoundly altered, the cause of these alterations was not related to the hormone´s conjugation or catabolism. Instead, these mutations distorted the secondary metabolism of specific amino acids (methionine and tryptophan, respectively), which indirectly affected IAA biosynthesis. We also developed analytical tools to investigate proteins involved in IAA metabolism. In conjunction with standard protein analysis techniques, these methods can be used to identify enzymatic activities involved in IAA biosynthesis pathways, either dependent or independent of tryptophan. In relation to this, a second LC-MS technique for the in vivo determination of IAA precursors is also presented.


auxin; conjugation; catabolism; biosynthesis; liquid chromatography; mass spectrometry; multiple reaction monitoring

Published in

Acta Universitatis Agriculturae Sueciae. Silvestria
2002, number: 256
ISBN: 91-576-6340-8
Publisher: Swedish University of Agricultural Sciences

Authors' information

Kowalczyk, Mariusz
Swedish University of Agricultural Sciences, Department of Forest Genetics and Plant Physiology

UKÄ Subject classification

Forest Science

URI (permanent link to this page)