Plant and Cell Physiology 47: 864-877 (2006)

Endosperm-limited Brassicaceae seed germination: Abscisic acid inhibits embryo-induced endosperm weakening of Lepidium sativum (cress) and endosperm rupture of cress and Arabidopsis thaliana

Kerstin Müller, Stefanie Tintelnot, Gerhard Leubner-Metzger

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

Received April 3, 2006; accepted May 3, 2006

Abstract.  The endosperm is a barrier for radicle protrusion of many angiosperm seeds. Rupture of the testa (seed coat) and rupture of the endosperm are two sequential events during the germination of Lepidium sativum L. and Arabidopsis thaliana (L.) Heyhn. Abscisic acid (ABA) specifically inhibits the endosperm rupture of these two closely related Brassicaceae species. Lepidium seeds are large enough to allow the direct measurement of endosperm weakening by the puncture force method. We found that the endosperm weakens prior to endosperm rupture and that ABA delays the onset and decreases the rate of this weakening process in a dose-dependent manner. An early embryo signal is required and sufficient to induce endosperm weakening, which afterwards appears to be an organ-autonomous process. Gibberellins (GA) can replace this embryo signal, de novo GA biosynthesis occurs in the endosperm and weakening is regulated by the GA-ABA ratio. Our results suggest that the control of radicle protrusion during the germination of Brassicaceae seeds is mediated, at least in part, by endosperm weakening. We propose that Lepidium is an emerging Brassicaceae model system for endosperm weakening and that the complementary advantages of Lepidium and Arabidopsis can be used in parallel experiments to investigate the molecular mechanisms of endosperm weakening.

Key words: abscisic acid, Arabidopsis thaliana, embryo signal, endosperm weakening, gibberellin, Lepidium sativum (garden cress)

Article in PDF format (1.1 MB)
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