Planta 215: 959-968 (2002)
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Seed after-ripening and over-expression of class I ß-1,3-glucanase
confer maternal effects on tobacco testa rupture and dormancy release
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Gerhard Leubner-Metzger
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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
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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.
Keywords.
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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