Plant Journal 23: 215-221 (2000)
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Sense transformation reveals a novel role for class I ß-1,3-glucanase
in tobacco seed germination
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Gerhard Leubner-Metzger and Frederick Meins, Jr.
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Friedrich Miescher Institute, Maulbeerstr. 66, CH-4058 Basel, Switzerland
Received: 21 March 2000 / Accepted: 5 April 2000
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Abstract. 'Coat-enhanced' seed dormancy of many dicotyledonous
species, including tobacco, is released during afterripening. Rupture of
the endosperm, which is the limiting step in tobacco seed germination, is
preceded by induction of class I ß-1,3-glucanase (ßGLU I) in
the micropylar endosperm where the radicle will penetrate. Treating after-ripened
tobacco seeds with abscisic acid (ABA) delays endosperm rupture and inhibits
ßGLU I induction. Sense transformation with a chimeric ABA-inducible
ßGLU I transgene resulted in over-expression of ßGLU I in seeds
and promoted endosperm rupture of mature seeds and of ABA-treated after-ripened
seeds. Taken together, these results provide direct evidence that ßGLU
I contributes to endosperm rupture. Over-expression of ßGLU I during
germination also replaced the effects of after-ripening on endosperm rupture.
This suggests that regulation of ßGLU I by ABA signaling pathways
might have a key role in after-ripening.
Key words: Abscisic acid, After-ripening, Endosperm-limited seed
germination, Gene function, ß-1,3-Glucanase, Sense transformation
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