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Potential pathways of indole acetic acid (IAA) biosynthesis
in Euphorbia abyssinica

Raf Aerts · Els Prinsen · Bart Muys


Desert candle (Euphorbia abyssinica J.F.
Gmel.) (further referred to as EAG) is a
succulent tree of dry deciduous and
evergreen montane forest, woodland and
shrub savanna. It occurs widely
throughout dryland Africa, where it is
appreciated as a live fence because it is
easily propagated from untreated mature
branch cuttings.
In Negussie et al. (2008) we argue that
the ability of large EAG branches to
regenerate with ease in dry soil may be
related to the natural plant growth
regulator hormone indole acetic acid
(IAA) contained in the latex of the plant.
EAG latex samples from northern
Ethiopia (n = 3) that were chemically
analyzed contained on average ( ρ s.e. of
mean) 350 ρ 117 pmol IAA /g latex (350
pmol/g = 0.06 µg/g = 0.06 mg/l latex),
as well as the IAA metabolites indole
lactate (ILA: 477 ρ 12 pmol/g latex) and
indole ethanol (IEt: 316 ρ 73 pmol/g
latex). One sample also contained IAA
conjugated to amino-acids (108 pmol/g
latex) and glucose (371 pmol/g latex).
Here we present a schematic overview of
the potential pathways of IAA
biosynthesis in EAG (Fig. 1).
The IAA metabolites found in the EAG
latex, ILA and IEt, can be converted to
indole-3-pyruvic acid (IPA) and indole
acetaldehyde (IAAld) respectively. These
molecules suggest that auxin biosynthesis
in EAG is tryptophane (Trp) dependent.
Woodward and Bartel (2005) found
similar pathways in the model plant
Arabidopsis thaliana Schur where de
novo IAA biosynthesis initiates from Trp
or Trp precursors.


R. Aerts (
) · B. Muys
Division Forest, Nature and Landscape, Katholieke Universiteit Leuven, Celestijnenlaan 200E-2411,
BE-3001 Leuven, Belgium
e-mail: raf.aerts@ees.kuleuven.be

E. Prinsen
Department of Biology, University of Antwerp, Groenenborgerlaan 171, BE-2020 Antwerpen,
Belgium
Nature Precedings : doi:10.1038/npre.2008.2212.1 : Posted 21 Aug 2008

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Fig. 1 Potential pathways of IAA biosynthesis in Euphorbia
abyssinica. IAA, its metabolites indole lactate (ILA) and
indole ethanol (IEt) as well as IAA conjugated to amino acids
(IAA-AA) and glucose (IAA-Glu) were found in Euphorbia
abyssinica latex from northern Ethiopia and are marked (*).

NH
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CH
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CCOOH
O
N
H
CH
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CHO
N
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CH
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N
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CH
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NH
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T
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IEt*
IAA*
IAA-AA*
IAA-Glu*
IAld
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Trp
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IAld
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Nature Precedings : doi:10.1038/npre.2008.2212.1 : Posted 21 Aug 2008