title: Class I [beta]-1,3-Glucanases in the Endosperm of Tobacco during Germination.
abstract: Rupture of the seed coat and rupture of the endosperm are separate events in the germination of Nicotiana tabacum L. cv Havana 425 seeds. Treatment with 10-5 M abscisic acid (ABA) did not appreciably affect seed-coat rupture but greatly delayed subsequent endosperm rupture by more than 100 h and resulted in the formation of a novel structure consisting of the enlarging radicle with a sheath of greatly elongated endosperm tissue. Therefore, ABA appears to act primarily by delaying endosperm rupture and radicle emergence. Measurements of [beta]-1,3-glucanase activity, antigen content, and mRNA accumulation together with reporter gene experiments showed that induction of class I [beta]-1,3-glucanase genes begins just prior to the onset of endosperm rupture but after the completion of seed-coat rupture. This induction was localized exclusively in the micropylar region of the endosperm, where the radicle will penetrate. ABA treatment markedly inhibited the rate of [beta]-1,3-glucanase accumulation but did not delay the onset of induction. Independent of the ABA concentration used, onset of endosperm rupture was correlated with the same [beta]-1,3-glucanase content/seed. These results suggest that ABA-sensitive class I [beta]-1,3-glucanases promote radicle penetration of the endosperm, which is a key limiting step in tobacco seed germination.
authors.affiliation: Friedrich-Miescher Institute, Box 2543, CH-4002 Basel, Switzerland.
authors.forename: G.
authors.initials: G
authors.lastname: Leubner-Metzger
authors.forename: C.
authors.initials: C
authors.lastname: Frundt
authors.forename: R.
authors.initials: R
authors.lastname: Vogeli-Lange
authors.forename: F.
authors.initials: F
authors.lastname: Meins