Seed Science Research 13: 17-34 (2003)
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Invited review:
Functions and regulation of ß-1,3-glucanases during seed germination,
dormancy release and after-ripening
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Gerhard Leubner-Metzger
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Albert-Ludwigs-Universität Freiburg, Institut für Biologie
II, Botanik, Schänzlestr. 1, D-79104 Freiburg i. Br., Germany
Received: 20 February 2002 / Accepted: 8 November 2002
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Abstract. ß-1,3-Glucanase (ßGlu) expression
in seeds plays important roles in the regulation of seed germination and
dormancy and in the defense against seed pathogens. A thick ß-1,3-glucan
layer is typical for the seed envelope of Cucurbitaceous species, confers
seed semipermeability and is degraded during germination. In many species
with coat-imposed dormancy, the seed envelope confers a physical constraint
to radicle emergence. In the Solanaceous species the micropylar endosperm
and testa have this function and endosperm weakening appears to be a prerequisite
for germination. Class I ßGlu is transcriptionally induced in the
micropylar endosperm of tobacco, tomato and other Solanaceous seeds just
prior to radicle emergence. ßGlu induction and germination are tightly
linked in response to plant hormones and environmental factors, e.g. they
are both promoted by gibberellins and inhibited by abscisic acid (ABA).
Sense and antisense transformation of tobacco reveals two sites of ßGlu
action: after-ripening-mediated release of testa-imposed dormancy and endosperm
rupture during germination. The use of an ABA-inducible chimeric sense-transgene
resulted in over-expression of class I ßGlu in seeds and provided
direct evidence that ßGlu contributes to endosperm rupture. A model
integrating ßGlu, seed dormancy, after-ripening and germination is
presented and possible mechanisms for ßGlu action are discussed. It
is proposed that ßGlu not only helps defend seeds against pathogens,
but is also a key factor in regulating coat-imposed dormancy and germination
of seeds in response to environmental and hormonal cues.
Table of Contents:
1. Introduction
2. Structure, regulation and function of plant ß-1,3-glucanases
(ßGlu I)
3. Nicotiana seeds as a model system for the hormonal
regulation of dormancy, after-ripening and germination
4. ßGlu I contributes to endosperm rupture
5. Occurrence and functions of ß-1,3-glucans
in seeds
6. Effects of ßGlu I and after-ripening on
testa rupture and photodormancy
7. ß-1,3-Glucanases during the germination
of non-endospermic dicot seeds
8. ß-1,3-Glucanases during the germination
of cereal caryopses
9. Seed pathogen-related functions of ß-1,3-glucanase
10. A speculative model for tobacco seed dormancy and germination
11. References
Key words: Abscisic acid - After-ripening - Gibberellin - ß-1,3-Glucanase
- Nicotiana seeds - Seed dormancy - Seed germination
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