Tansley Review - New Phytologist 171: 501-523 (2006)

Seed dormancy and the control of germination

William E. Finch-Savage (1), Gerhard Leubner-Metzger (2)

(1) Warwick HRI, Warwick University, Wellesbourne, Warwick CV35 9EF, United Kingdom, Web: 'Seed Science Group' http://www2.warwick.ac.uk/fac/sci/hri2/research/seedscience/

(2) Institut für Biologie II (Botanik/Pflanzenphysiologie), Albert-Ludwigs-Universität Freiburg, Schänzlestr. 1, D-79104 Freiburg i. Br., Germany, Web: 'The Seed Biology Place' http://www.seedbiology.de

Received February 23, 2006; accepted March 27, 2006

Hormonal interactions seed dormancy release and germination

Figure 2. Hormonal interactions during the regulation of seed dormancy release and germination of Nicotiana (A) and Brassica (B)model species. (A) Nicotiana sp. seed germination is two-step: testa rupture and then endosperm rupture. Dormancy release and germination promotion occur during seed after-ripening (dry storage at room temperature for several months) or by the light-gibberellin (GA) pathway during imbibition. Abscisic acid (ABA) inhibits endosperm rupture, but not testa rupture. GA, ethylene and brassinosteroids (BR) promote endosperm rupture and counteract the inhibitory effects of ABA. The ABA-inhibited class I ß-1,3-glucanase genes (ßGlu I) are transcriptionally induced in the micropylar endosperm just prior to endosperm rupture (reviewed in Leubner-Metzger, 2003). This induction is highly localized in the micropylar endosperm at the site of radicle emergence. Light, GA and ethylene promote and ABA, osmotica and darkness inhibit ßGlu I expression and endosperm rupture. This inhibition is partially reversed in transgenic tobacco seeds that over-express ßGlu I in the seed covering layers under the control of an ABA-inducible transgene promoter. ßGlu I is therefore causally involved in the promotion of endosperm rupture. EREBP = "ethylene-responsive element binding protein" transcription factor. Modified reprint with permission: G. Leubner-Metzger, Hormonal interactions during seed dormancy release and germination in A. Basra (Ed.), Handbook of Seed Science. © 2006, The Haworth Press, Inc., Binghamton, NY, USA; article copies available from The Haworth Document Delivery Service: 1-800-HAWORTH, E-mail address: docdelivery@haworthpress.com. (B) Brassica napus seed germination is one-step. The mature seeds of these species are without endosperm and so testa rupture plus initial radicle elongation result in the completion of germination. ABA does not inhibit testa rupture, but inhibits subsequent radicle growth (Schopfer & Plachy, 1984). Review: Kucera et al. (2005).

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