First published online January 23, 2003; 10.1104/pp.016386
Plant Physiol, March 2003, Vol. 131, pp. 1347-1359
Expression of a GALACTINOL SYNTHASE Gene in Tomato
Seeds Is Up-Regulated before Maturation Desiccation and Again after
Imbibition whenever Radicle Protrusion Is
Prevented1
Bruce
Downie,*
Sunitha
Gurusinghe,
Petambar
Dahal,
Richard R.
Thacker,
John C.
Snyder,
Hiroyuki
Nonogaki,2
Kyuock
Yim,3
Keith
Fukanaga,
Veria
Alvarado,4 and
Kent J.
Bradford
Department of Horticulture, Agriculture Science Center-North,
University of Kentucky, Lexington, Kentucky 40546 (B.D., R.R.T.,
J.C.S.); and Department of Vegetable Crops, 1 Shields Avenue,
University of California, Davis, California 95616 (S.G., P.D., H.N.,
K.Y., K.F., V.A., K.J.B.)
Raffinose family oligosaccharides (RFOs) have been
implicated in mitigating the effects of environmental stresses on
plants. In seeds, proposed roles for RFOs include protecting cellular integrity during desiccation and/or imbibition, extending longevity in
the dehydrated state, and providing substrates for energy generation during germination. A gene encoding galactinol synthase (GOLS), the
first committed enzyme in the biosynthesis of RFOs, was cloned from
tomato (Lycopersicon esculentum Mill. cv Moneymaker)
seeds, and its expression was characterized in tomato seeds and
seedlings. GOLS (LeGOLS-1) mRNA
accumulated in developing tomato seeds concomitant with maximum dry
weight deposition and the acquisition of desiccation tolerance.
LeGOLS-1 mRNA was present in mature,
desiccated seeds but declined within 8 h of imbibition in
wild-type seeds. However, LeGOLS-1 mRNA
accumulated again in imbibed seeds prevented from completing
germination by dormancy or water deficit. Gibberellin-deficient (gib-1) seeds maintained
LeGOLS-1 mRNA amounts after imbibition unless supplied with gibberellin, whereas abscisic acid (ABA) did not
prevent the loss of LeGOLS-1 mRNA from
wild-type seeds. The presence of LeGOLS-1
mRNA in ABA-deficient (sitiens) tomato seeds indicated
that wild-type amounts of ABA are not necessary for its accumulation
during seed development. In all cases,
LeGOLS-1 mRNA was most prevalent in the
radicle tip. LeGOLS-1 mRNA accumulation was induced by dehydration but not by cold in germinating seeds, whereas both stresses induced LeGOLS-1
mRNA accumulation in seedling leaves. The physiological implications of
LeGOLS-1 expression patterns in seeds and
leaves are discussed in light of the hypothesized role of RFOs in plant
stress tolerance.
1
This work was supported in part by the U.S.
Department of Agriculture National Research Initiative-Competitive
Grants program (grant no. 98-35100-6082), by the Western Regional
Seed Physiology Research Group, and by Regional Research Project
W-168.
2
Present address: Department of Crop and Soil Science,
Oregon State University, Corvallis, OR, 97331-3002.
3
Present address: National Plant Quarantine Service,
433-1 Anyang 6-Dong, Anyhang 430-016, Korea.
4
Present address: Department of Biology, Texas A&M
University, BSBE 201, College Station, TX 77843.
*
Corresponding author; e-mail adownie{at}uky.edu; fax
859-257-2859.
© 2003 American Society of Plant Biologists
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