• abscisic acid;
  • after-ripening;
  • endosperm-limited seed germination;
  • gene function;
  • β-1;
  • 3-glucanase;
  • sense transformation


‘Coat-enhanced’ seed dormancy of many dicotyledonous species, including tobacco, 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 β-1,3-glucanase (βGLU I) in the micropylar endosperm where the radicle will penetrate. Treating after-ripened tobacco seeds with abscisic acid (ABA) delays endosperm rupture and inhibits βGLU I induction. Sense transformation with a chimeric ABA-inducible βGLU I transgene resulted in over-expression of βGLU I in seeds and promoted endosperm rupture of mature seeds and of ABA-treated after-ripened seeds. Taken together, these results provide direct evidence that βGLU I contributes to endosperm rupture. Over-expression of βGLU I during germination also replaced the effects of after-ripening on endosperm rupture. This suggests that regulation of βGLU I by ABA signalling pathways might have a key role in after-ripening.