This inhibition is partially reversed in transgenic tobacco (Nicotiana tabacum) seeds that over-express βGlu I in the seed-covering layers under the control of an ABA-inducible transgene promoter. βGlu I is therefore causally involved in the promotion of endosperm rupture.
EREBP, ethylene-responsive element binding protein transcription factor.
Part (a) is modified from Leubner-Metzger (2006) and reprinted with permission from The Haworth Press, Inc.; article copies are available from The Haworth Document Delivery Service:1-800-HAWORTH; Email: docdelivery@haworthpress.com.
(b) Brassica napus seed germination is one-step.
The mature seeds of these species are without an endosperm and so testa rupture plus initial radicle elongation result in the completion of germination.
ABA does not inhibit testa rupture, but inhibits subsequent radicle growth (Schopfer & Plachy, 1984; for a review, see Kucera et al., 2005).