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Molecular Plant 2009 2(1):108-119; doi:10.1093/mp/ssn092
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© The Author 2009. Published by the Molecular Plant Shanghai Editorial Office in association with Oxford University Press on behalf of CSPP and IPPE, SIBS, CAS.

ABA-Mediated Inhibition of Germination Is Related to the Inhibition of Genes Encoding Cell-Wall Biosynthetic and Architecture: Modifying Enzymes and Structural Proteins in Medicago truncatula Embryo Axis

Christine Gimeno-Gillesa,2, Eric Lelièvrea,2, Laure Viaua, Mustafa Malik-Ghulama, Claudie Ricoulta, Andreas Niebelb, Nathalie Leducc and Anis M. Limamia,1

a University of Angers, UMR_A 1191, Physiologie Moléculaire des Semences (PMS), 2 Bd Lavoisier, F-49045, Angers, France
b UMR 441 CNRS-INRA, Laboratoire de Biologie Moléculaire des Relations Plantes Micro-organismes (LIPM), Castanet-Tolosan 31326 cedex, France
c University of Angers, UMR Sciences Agronomiques Appliqués à l'Horticulture (SAGAH), 2 Bd Lavoisier, F-49045, Angers, France

1 To whom correspondence should be addressed. E-mail anis.limami{at}univ-angers.fr, fax +33 2 41 73 53 52, phone +33 241 73 54 46

Radicle emergence and reserves mobilization are two distinct programmes that are thought to control germination. Both programs are influenced by abscissic acid (ABA) but how this hormone controls seed germination is still poorly known. Phenotypic and microscopic observations of the embryo axis of Medicago truncatula during germination in mitotic inhibition condition triggered by 10 µM oryzalin showed that cell division was not required to allow radicle emergence. A suppressive subtractive hybridization showed that more than 10% of up-regulated genes in the embryo axis encoded proteins related to cell-wall biosynthesis. The expression of {alpha}-expansins, pectin-esterase, xylogucan-endotransglycosidase, cellulose synthase, and extensins was monitored in the embryo axis of seeds germinated on water, constant and transitory ABA. These genes were overexpressed before completion of germination in the control and strongly inhibited by ABA. The expression was re-established in the ABA transitory-treatment after the seeds were transferred back on water and proceeded to germination. This proves these genes as contributors to the completion of germination and strengthen the idea that cell-wall loosening and remodeling in relation to cell expansion in the embryo axis is a determinant feature in germination. Our results also showed that ABA controls germination through the control of radicle emergence, namely by inhibiting cell-wall loosening and expansion.

Key Words: ABA • cell-wall expansion • germination • Medicago truncatula • radicle emergence • XET

2 These authors contributed equally to this work.


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