Induction of biosynthetic enzymes for avenanthramides in elicitor-treated oat leaves |
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Authors: | Atsushi Ishihara Yoshiaki Ohtsu Hajime Iwamura |
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Institution: | (1) Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan, JP |
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Abstract: | The accumulation of oat (Avena sativa L.) phytoalexins, avenanthramides, occurred in leaf segments treated with oligo-N-acetylchitooligosaccharides. The amount of avenanthramide A, the major oat phytoalexin, reached a maximum 36–48 h after elicitor
treatment. This accumulation was preceded by a marked increase in enzyme activities of phenylpropanoid pathway members, including
phenylalanine ammonia-lyase (EC 4.3.1.5), cinnamate 4-hydroxylase (EC 1.14.13.11) and 4-coumarate:CoA ligase (EC 6.2.1.12).
These enzyme activities reached a maximum 6–12 h after elicitor treatment, when the avenanthramides were produced most rapidly.
Both phenylalanine ammonia-lyase and 4-coumarate:CoA ligase activities decreased thereafter to undetectable levels 72 h after
treatment, while cinnamate 4-hydroxylase activity showed a second increase 48 h after treatment. Among the chitooligosaccharides
tested, tetra- and pentasaccharides most effectively induced these enzyme activities in a dose-dependent manner. The elicitor-induced
4-coumarate: CoA ligase accepted all hydroxycinnamic acids occurring in the avenanthramides as substrates, with the exception
of avenalumic acid. These findings indicate that accumulation of the avenanthramides results from de-novo synthesis through
the general phenylpropanoid pathway and that early biosynthetic enzymes function as regulatory points of carbon flow to the
avenanthramides.
Received: 3 December 1998 / Accepted: 27 January 1999 |
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Keywords: | : Avenanthramide Avena Cinnamate 4-hydroxylase 4-Coumarate:CoA ligase Elicitor Phenylalanine ammonia-lyase |
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