Sense transformation reveals a novel role for class I beta-1,3-glucanase in tobacco seed germination

'Coat-enhanced' seed dormancy of many dicotyledonous species, including tob acco, is released during after-ripening. Rupture of the endosperm, which is the limiting step in tobacco seed germination, is preceded by induction of class I beta-1,3-glucanase (beta GLU I) in the micropylar endosperm where the radicle will penetrate. Treating after-ripened tobacco seeds with absci sic acid (ABA) delays endosperm rupture and inhibits beta GLU I induction. Sense transformation with a chimeric ABA-inducible beta GLU I transgene res ulted in over-expression of beta GLU I in seeds and promoted endosperm rupt ure of mature seeds and of ABA-treated after-ripened seeds. Taken together, these results provide direct evidence that beta GLU I contributes to endos perm rupture. Over-expression of beta GLU I during germination also replace d the effects of after-ripening on endosperm rupture. This suggests that re gulation of beta GLU I by ABA signalling pathways might have a key role in after-ripening.