Journal of Experimental Botany 58: 3047-3060 (2007)

1-Aminocyclopropane-1-carboxylic acid and abscisic acid during the germination of sugar beet (Beta vulgaris L.) - a comparative study of fruits and seeds

Katrin Hermann, Juliane Meinhard, Peter Dobrev, Ada Linkies, Bedrich Pesek, Barbara Heß, Ivana Machácková, Uwe Fischer, Gerhard Leubner-Metzger

Institute of Biology II, Botany / Plant Physiology, Albert-Ludwigs-University Freiburg, Schänzlestr. 1, D-79104 Freiburg i. Br., Germany, Web: 'The Seed Biology Place' (K.H., A.L., B.H., G-L.-M.)
KWS SAAT AG, Grimsehlstr. 31, D-37555 Einbeck, Germany, Web: (J.M., U.F.)
Institute of Experimental Botany CAS, Rozvojová 263, CZ-16502 Prague 6, Czech Republic, Web: (P.D., B.P., I.M.)

Received June 15, 2007; accepted June 25, 2007

Abstract.  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. In 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. In 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, Beta vulgaris (sugar beet), ethylene, ethylene-ABA interaction, pericarp, radicle emergence, seed and fruit covering layers, sugar beet germination

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   Abstract    Fig. 1               Fig. 2
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Fig. 3               Fig. 4                Tab. 1
Fig. 7               Suppl. Fig. S1
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