Antisense-transformation reveals novel roles for class I β-1,3-glucanase in tobacco seed after-ripening and photodormancy

Little is known about the molecular basis for seed dormancy, after-ripening, 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 beta -1,3-glucanase (beta GLU I), which is induced in the micropylar endosperm just prior to its penetration by the radicle, is believed to help weaken the endosperm wall. Evidence is presented here for a second site of beta GLU I action during after-ripening. Tobacco plants were transformed with antisense beta GLU I constructs with promoters thought to direct endosperm-specific expression. Unexpectedly, these transformants were unaffected in endosperm rupture and did not exhibit reduced beta GLU I expression during germination. Nevertheless, antisense beta GLU I transformation delayed the onset of testa rupture in light-imbibed, after-ripened seeds and inhibited the after-ripening-mediated release of photodormancy. It is proposed that beta GLU I expression in the dry seed contributes to the after-ripening-mediated release of seed dormancy.