Antisense-transformation reveals novel roles for class I ß-1,3-glucanase
in tobacco seed after-ripening and photodormancy
| Gerhard Leubner-Metzger and Frederick Meins, Jr.
| Friedrich Miescher-Institut, P.O. Box 2543, CH-4002 Basel, Switzerland
(G.L.-M., F.M.Jr.) and
Institut für Biologie II, Albert Ludwigs Universität, Schänzlestrasse 1, 79104 Freiburg, Germany (G.L.-M.)
Received: 27 September 2000 / Accepted: 17 May 2001
|Abstract. Little is known about the molecular basis for seed dormancy,
afterripening, and radicle emergence through the covering layers during
germination. In tobacco, endosperm rupture occurs after testa rupture and
is the limiting step in seed germination. Class I ß-1,3-glucanase
(ßGLU I), which is induced in the micropylar endosperm just prior
to its penetration by the radicle, is believed to help weaken the endosperm
wall. Here we provide evidence for a second site of ßGLU I action
during afterripening. Tobacco plants were transformed with antisense ßGLU
I constructs with promoters thought to direct endosperm-specific expression.
Unexpectedly, these transformants were unaffected in endosperm rupture and
did not exhibit reduced ßGLU I expression during germination. Nevertheless
antisense ßGLU I transformation delayed the onset of testa rupture
in light-imbibed, afterripened seeds and inhibited the afterripening-mediated
release of photodormancy. We propose that ßGLU I expression in the
dry seed contributes to the afterripening-mediated release of seed dormancy.
Key words: Abscisic acid, After-ripening, Coat-enhanced seed dormancy, endosperm-limited germination, ß-1,3-Glucanase, Sense- and antisense transformation