Planta 215: 959-968 (2002)


Seed after-ripening and over-expression of class I ß-1,3-glucanase confer maternal effects on tobacco testa rupture and dormancy release

Gerhard Leubner-Metzger

Institut für Biologie II, Botanik, Albert-Ludwigs-Universität, Schänzlestrasse 1, D-79104 Freiburg, Germany

Received: 19 January 2002 / Accepted: 4 May 2002 / Published online: 25 July 2002

Abstract. 'Coat-imposed' seed dormancy of many non-endospermic and endospermic species is released during after-ripening. After-ripening-mediated promotion of tobacco (Nicotiana tabacum L.) seed germination is mainly due to a promotion of testa rupture and a similar promotion of subsequent endosperm rupture. Treatment of after-ripened or freshly harvested mature seeds with abscisic acid (ABA) delays endosperm rupture and inhibits the induction of class I ß-1,3-glucanase (ßGlu I) in the micropylar endosperm, but does not affect the kinetics of testa rupture. After-ripening-mediated release of photodormancy is correlated with a decreased gibberellin (GA) requirement for testa rupture during dark-imbibition. Reciprocal crosses between wild-type tobacco and sense-ßGlu I transformant lines showed that ßGlu I over-expression in the seed covering layers can replace the promoting effect of after-ripening on testa rupture in light, but only if the mother plant is a sense-ßGlu I line. This maternal effect supports the model of two sites for ßGlu I action: (i) ßGlu I contribution to the after-ripening-mediated release of dormancy in the dry seed state, which is manifested in the promotion and ABA-insensitivity of testa rupture during imbibition. (ii) ABA-sensitive expression of ßGlu I in the micropylar endosperm, which contributes to endosperm rupture. The importance of GA-signaling and testa characteristics appear to be a common feature during the after-ripening-mediated release of coat-imposed dormancy in endospermic and non-endospermic seeds.
Abbreviations. ABA: abscisic acid DAP: days after pollination GA: gibberellin ßGlu I: class I -1,3-glucanase WT: wild type

Key words: Abscisic acid - After-ripening - Gibberellin requirement - ß-1,3-Glucanase - Maternal effect - Nicotiana (seed dormancy) - Photodormancy - Testa rupture

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Abstract Fig. 1 Fig. 2 Fig. 3 Table 1          Maternal   crosses
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