Antisense-transformation reveals novel roles for class I beta-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 s tep 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 r adicle, is believed to help weaken the endosperm wall. Evidence is presente d here for a second site of beta GLU I action during after-ripening. Tobacc o plants were transformed with antisense beta GLU I constructs with promote rs thought to direct endosperm-specific expression. Unexpectedly, these tra nsformants 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, afte r-ripened seeds and inhibited the after-ripening-mediated release of photod ormancy. It is proposed that beta GLU I expression in the dry seed contribu tes to the after-ripening-mediated release of seed dormancy.