Class I beta-1,3-glucanases in the endosperm of tobacco during germination
1995
Leubner-Metzger, G. | Frundt, C. | Vogeli-Lange, R. | Meins, F. Jr
Rupture of the seed coat and rupture of the endosperm are separate events in the germination of Nicotiana tabacum L. cvHavana 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.
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