Reciproca1 crosses between aba mutants and wild-type
plants show that dormancy is initiated only when the em-
bryo itself produces ABA; ABA-deficient seeds (abalaba) on
ABA-producing parent plants (Abalaba) are not dormant.
Maternal ABA does not play a role in preventing germination
in developing maize kernels either, and embryos of vp5 and
vp8 mutants are even viviparous in the presence of a normal
endosperm (McCarty, 1995). That in situ ABA synthesis in
the embryo is necessary for the imposition of dormancy has
been demonstrated in sunflower as well (LePage-Degivry
and Garello, 1992). Although applied ABA prevented germi-
nation of isolated developing sunflower embryos, this inhibi-
tion was overcome upon their transfer to water; only ABA
synthesized within the embryo imposed a lasting dormancy
(LePage-Degivry and Garello, 1992).