(go
to KOMUGI Home) (go
to WIS List) (go
to NO.76 Contents)
Wheat Information
Service
Number 76: 83-84 (1993)
Embryonic
mRNA related to seed dormancy in wheat
Kaz. Noda and N. Kawakami
Kihara Institute for Biological Research, Yokohama City
University, Minami-ku, Yokohama, Japan 232
Grain dormancy is a major factor involved in the resistance of
preharvest sprouting of wheat. Among the characteristics such as seed
color, endogenous germination inhibitors and pericarp structure,
which have been studied in relation to dormancy, response of the
embryos to abscisic acid (ABA) is the one that differentiate clearly
dormant grains from nondormant ones (Stoy and Sundin 1976). Embryos
of the dormant grains respond to ABA and do not germinate in ABA
solution, but those of nondormant grains do. Embryo responsiveness to
ABA also decrease in concert with the loss of grain dormancy during
afterripening (Walker-Simmons 1987, Noda and Kanzaki 1988). In a
field, preharvest sprouting is induced when grains absorb water at
low temperatures. Imbibition at low temperature is the primary factor
in breaking dormancy and resulted in preharvest sprouting. Noda et al
(1992) reported that severe chilling of grains also changed the
embryo responsiveness to ABA.
Besides the above physiological studies, plant mutants have the
potential to provide insight into the mechanism of seed dormancy.
Seeds of ABA-deficient mutants from maize (vp), Arabidopsis (aba) and
tomato (sit) exhibit viviparous germination or non-dormancy
(Robichaud et al 1980, Koornneef et al 1982, Karssen et al 1987).
Additionally, ABA-insensitive mutants of Arabidopsis (abi3) and maize
(vpl) produce non-dormant seeds (Koornneef et al 1984, Robichaud et
al 1980). These findings suggest that responsiveness of the embryo to
ABA plays an important role in developing and maintaining seed
dormancy.
To identify factors related to responsiveness of seed embryos to ABA,
we tried to obtain non-dormant mutant lines of wheat after
mutagenized seeds of pre-harvest sprouting resistant and dormant
Kitakei- 1354 with EMS. Three lines (EH 47-1, EH 47-2-5, EH 47-2-6)
of non-dormant mutants were established (Table1).
All three lines were susceptible to pre-harvest sprouting in the
field. Also, mature seed embryos from these lines showed only weak
responsiveness to 10 microM ABA, compared with the wild type
Kitakei-1354 (Table
2).
We compared the embryonic mRNAs of Kitakei-1354 and the three mutant
lines. Poly (A)+RNA was extracted from embryos at 30 and
60 days post-anthesis (DPA) seeds. mRNAs were translated in a wheat
germ cell-free system and the polypeptide products were compared
using two-dimensional polyacrylamide gel electrophoresis. Several
mRNAs were expressed differently in the Kitakei-1354 and mutant
lines. One polypeptide designated as e was not expressed in
embryosfrom the mutant lines, but existed in Kitakei-1354. This mRNA
is also up-regulated by ABA in embryos from dormant, but not
afterripened Kitakei-1354 seeds (Table
2). We conclude
that polypeptide e is a candidate for the factor that positively
regulates dormancy in wheat seeds.
References
Karssen CM, Groot SPC and Koornneef M (1987) Hormone mutants and
seed dormancy in Arabidopsis and tomato. In: Developmental Mutants in
Higher Plants. H Thomas and D Grierson, eds. Cambridge University
Press, Cambridge, UK, pp 119-133.
Koornneef M, Jorna MI, Brinkhorst-van der Swan DLC and Karssen CM
(1982) The isolation of abscisic acid (ABA) deficient mutants by
selection of induced revertants in non-germinating gibberellin
sensitive lines of Arabidopsis thaliana (L.) Heyrth. Theor Appl Genet
61: 385-393.
Koornneef M, Reuling G and Karssen CM (1984) The isolation and
characterization of abscisic acid insensitive mutants of Arabidopsis
thaliana. Physiol Plant 61: 377-383.
Noda K and Kanzaki K (1988) Fluorescence staining technique for
evaluating embryo sensitivity to abscisic acid of sprouting resistant
wheat cultivars. Jpn J Breed 38: 301-308.
Noda K, Kawabata C and Kawakami N (1992) Wheat grain imbibition at
low temperatures and embryo responsiveness to ABA. In: 6th Int.Symp.
on Pre- Harvest sprouting in Cereals. in press.
Robichaud CS, Wong J and Sussex IM (1980) Control of in vivo growth
of viviparous embryo mutants of maize by abscisic acid. Develop Genet
1: 325-330.
Stoy V and Sundin K (1976) Effects of growth regulating substances in
cereal seed germination. Cereal Res Commun 4: 157-163.
Walker-Simmons M (1987) ABA levels and sensitivity in developing
wheat embryo of sprouting resistant and susceptible. cultivars. Plant
Physiol 84: 61-66.
(go
to KOMUGI Home) (go
to WIS List) (go
to NO.76 Contents)