The Plant Journal 41: 133-145 (2005)

ß-1,3-Glucanase gene expression in low-hydrated seeds as a mechanism for dormancy release during tobacco after-ripening

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 31 August 2004; revised 9 October 2004; accepted 13 October 2004

Abstract.  An air-dry developmental state with low-hydrated tissues is characteristic for most plant seeds. Seed dormancy is an intrinsic block of germination and can be released during after-ripening, i.e. air-dry storage of mature seeds. Both seed covering layers, testa and endosperm, cause the coat-imposed dormancy of tobacco (Nicotiana tabacum). After-ripening and over-expression of class I ß-1,3-glucanase (ßGlu I) confer maternal effects on testa rupture and dormancy release. Very little is known about the molecular mechanisms of after-ripening and whether gene expression is possible in low-hydrated seeds. Transient, low-level ßGlu I transcription and translation was detected during tobacco seed after-ripening. 1H NMR 2D micro-imaging showed uneven distribution of proton mobility in seeds. ßGlu I gene expression is associated spatially with the inner testa and temporally with the promotion of testa rupture. Local elevation in moisture content seems to permit local, low-level ßGlu I gene transcription and translation in the maternal tissues of air-dry, low-hydrated seeds. De novo gene expression is therefore proposed to be a novel molecular mechanism for the release of coat-imposed dormancy during oilseed after-ripening.

Key words: after-ripening, coat-imposed dormancy, ß-1,3-glucanase, gene expression, low-hydrated state, seed germination, testa rupture

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