US EPA

1495665 

Journal Article 

Why plants need more than one type of auxin 

Simon, S; Petrasek, Jan 

2011 

1 

Plant Science
ISSN: 0168-9452
EISSN: 1873-2259 

180 

3 

454-460 

English 

21421392 

10.1016/j.plantsci.2010.12.007 

WOS:000287114500007 

http://://WOS:000287114500007
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The versatile functionality and physiological importance of
the phytohormone auxin is a major focus of attention in contemporary plant science. Recent
studies have substantially contributed to our understanding of the molecular mechanisms
underlying the physiological role of auxin in plant development. The mechanism of auxin action
includes both fast responses not involving gene expression, possibly mediated by Auxin Binding
Protein 1 (ABP1), and slower responses requiring auxin-regulated gene expression mediated by F-
box proteins. These two mechanisms of action have been described to varying degrees for the major
endogenous auxin indole-3-acetic acid (IAA) and for the synthetic auxins 2,4-
dichlorophenoxyacetic acid (2,4-D) and naphthalene-1-acetic acid (NAA). However, in addition to
IAA, plants synthesize three other compounds that are commonly regarded as ""endogenous auxins"",
namely, 4-chloroindole-3-acetic acid (4-Cl-IAA), indole-3-butyric acid (IBA) and phenylacetic
acid (PAA). Although a spectrum of auxinic effects has been identified for all these as well as
several other endogenous compounds, we remain largely ignorant of many aspects of their
mechanisms of action and the extent to which they contribute to auxin-regulated plant
development. Here, we briefly summarize the action of IBA, 4-Cl-IAA and PAA, and discuss the
extent to which their action overlaps with that of IAA or results from their metabolic
conversions to IAA. Other possible pathways for their action are considered. We present a scheme
for homeostatic regulation of IAA levels that embraces other endogenous auxins in terms of the
described mechanism of auxin action including its receptor and downstream signal transduction
events. (C) 2010 Elsevier Ireland Ltd. All rights reserved. 

Auxin; IAA; 4-Cl-IAA; IBA; PAA