Seed dormancy occurs during:
Seed dormancy is established and maintained during maturation stage of embryogenesis after heart and torpedo phases when embryo growth ceases and expansion growth stops completely. During maturation ABA accumulates inducing late embryogenesis abundant proteins, oleosins, storage proteins, lipids, and desiccation tolerance mechanisms while gibberellin signaling is suppressed and seed coat hardens imposing physical coat dormancy. Maternal and embryonic factors impose dormancy preventing precocious germination vivipary ensuring effective dispersal and survival through unfavorable season. Germination later occurs upon dormancy break via chilling, light, after-ripening, or gibberellin activation mobilizing stored reserves.
Ref: Finkelstein et al., Plant Physiol 2002; Bewley: seed dormancy established during maturation stage via ABA and LEA proteins.