Planta 199: 282-288 (1999)

Effects of gibberellins, darkness and osmotica on endosperm rupture and class I ß-1,3-glucanase induction in tobacco seed germination

Gerhard Leubner-Metzger, Corinne Fründt, Frederick Meins, Jr.

Friedrich Miescher Institute, Box 2543, CH-4002 Basel, Switzerland

Received: 28 August1995 / Accepted: 8 November 1995

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

Article in PDF format (2.5 MB) Abstract          Fig. 1          Fig. 2          Fig. 3          Tab. 1  

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