Planta 199: 282-288 (1999)
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Effects of gibberellins, darkness and osmotica on endosperm rupture
and class I ß-1,3-glucanase induction in tobacco seed germination
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Gerhard Leubner-Metzger, Corinne Fründt, Frederick Meins,
Jr.
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Friedrich Miescher Institute, Box 2543, CH-4002 Basel, Switzerland
Received: 28 August1995 / Accepted: 8 November 1995
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Abstract. The "Havana 425" cultivar of Nicotiana tabacum
L. is photodormant. Gibberellins (e.g. 10-5 M GA4 or GA7) can substitute
for light in releasing dormancy. Measurements of ß-1,3-glucanase activity,
mRNA accumulation and the activity of the class I ß-1,3-glucanase
B promoter indicate that class I ß-1,3-glucanases are induced by GA4
in the dark in association with germination. As in the light, this induction
occurred prior to endosperm rupture and was localized exclusively in the
micropylar region of the endosperm where the radicle will penetrate. Abscisic
acid (ABA, 10-5 M) did not appreciably affect GA-induced release of photodormancy
or seed coat rupture, but it delayed endosperm rupture and inhibited the
rate of class I ß-1,3-glucanase accumulation. Seeds imbibed in the
light in the presence of osmotica, e.g. 0.04 M polyethylene glycol 6000,
showed delayed seed-coat and endosperm rupture, delayed onset of ß-1,3-glucanase
induction, and decreased rates of ß-1,3-glucanase accumulation. These
delays were shortened by GA4 treatment. Our results suggest that GAs and
ABA act at two distinct sites during germination and that expansive growth
of the embryo acts in two ways by triggering ß-1,3-glucanase induction
and by providing force for endosperm penetration. This provides further
support for our working hypothesis that class I ß-1,3-glucanases promote
endosperm weakening and facilitate radicle penetration.
Key words: Endosperm - Germination - Gibberellins - ß-1,3-Glucanase
- Photodormancy - Tobacco
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