JXB Advance Access first published online on August 30, 2007
This version published online on September 4, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erm162
© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
1-Aminocyclopropane-1-carboxylic acid and abscisic acid during the germination of sugar beet (Beta vulgaris L.): a comparative study of fruits and seeds
ková3
1Institute of Biology II, Botany/Plant Physiology, Faculty of Biology, Albert-Ludwigs-University Freiburg, Schänzlestr. 1, D-79104 Freiburg i. Br., Germany
2KWS SAAT AG, Grimsehlstr. 31, D-37555 Einbeck, Germany
3Institute of Experimental Botany CAS, Rozvojová 263, CZ-16502 Prague 6, Czech Republic
* To whom correspondence should be addressed. E-mail: gerhard.leubner{at}biologie.uni-freiburg.de. Web: ‘The Seed Biology Place’; http://www.seedbiology.de
The control of sugar beet (Beta vulgaris L.) germination by plant hormones was studied by comparing fruits and seeds. Treatment of sugar beet fruits and seeds with gibberellins, brassinosteroids, auxins, cytokinins, and jasmonates or corresponding hormone biosynthesis inhibitors did not appreciably affect radicle emergence of fruits or seeds. By contrast, treatment with ethylene or the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) promoted radicle emergence of fruits and seeds. Abscisic acid (ABA) acted as an antagonist of ethylene and inhibited radicle emergence of seeds, but not appreciably of fruits. High endogenous contents of ACC and of ABA were evident in seeds and pericarps of dry mature fruits, but declined early during imbibition. ABA-treatment of seeds and fruits induced seed ACC accumulation while ACC-treatment did not affect the seed ABA content. Transcripts of ACC oxidase (ACO, ethylene-forming enzyme) and ABA 8'-hydroxylase (CYP707A, ABA-degrading enzyme) accumulate in fruits and seeds upon imbibition. ABA and ACC and the pericarp did not affect the seed CYP707A transcript levels. By contrast, seed ACO transcript accumulation was promoted by ABA and by pericarp removal, but not by ACC. Quantification of the endogenous ABA and ACC contents, ABA and ACC leaching, and ethylene evolution, demonstrate that an embryo-mediated active ABA extrusion system is involved in keeping the endogenous seed ABA content low by ‘active ABA leaching’, while the pericarp restricts ACC leaching during imbibition. Sugar beet radicle emergence appears to be controlled by the pericarp, by ABA and ACC leaching, and by an ABA–ethylene antagonism that affects ACC biosynthesis and ACO gene expression.
Key words: Abscisic acid (ABA), ABA 8'-hydroxylase (CYP707A), 1-aminocyclopropane-1-carboxylic acid (ACC), ACC oxidase (ACO), ACC and ABA leaching, ethylene, ethylene–ABA interaction, pericarp, radicle emergence, seed and fruit covering layers, sugar beet germination
This version of the paper is now Open Access.
Received 30 March 2007; Revised 15 June 2007 Accepted 25 June 2007
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