Plant Physiology 126: 1299-1313 (2001)
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Class I ß-1,3-glucanase and chitinase are expressed in the
micropylar endosperm of tomato seeds prior to radicle emergences
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Chun-Ta Wu, Gerhard Leubner-Metzger, Frederick Meins, Jr. and Kent
J. Bradford
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Department of Vegetable Crops, One Shields Avenue, University of California,
Davis, CA 95616-8631, U.S.A. (C.T.W., K.J.B.)
and Friedrich Miescher-Institut, P.O. Box 2543, CH-4002 Basel, Switzerland
(G.L.M., F.M.Jr.)
Received: November 6, 2000 / Accepted: March 14, 2001
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Abstract. ß-1,3-Glucanase (EC 3.2.1.39) and chitinase (EC
3.2.1.14) mRNAs, proteins, and enzyme activities were expressed specifically
in the micropylar tissues of imbibed tomato (Lycopersicon esculentum
Mill.) seeds prior to radicle emergence. RNA hybridization and immunoblotting
demonstrated that both enzymes were class I basic isoforms. ß-1,3-glucanase
was expressed exclusively in the endosperm cap tissue, whereas chitinase
localized to both endosperm cap and radicle tip tissues. ß-1,3-Glucanase
and chitinase appeared in the micropylar tissues of gibberellin-deficient
gib-1 tomato seeds only when supplied with gibberellin. Accumulation of
ß-1,3-glucanase mRNA, protein and enzyme activity was reduced by 100
µM abscisic acid, which delayed or prevented radicle emergence but
not endosperm cap weakening. In contrast, expression of chitinase mRNA,
protein and enzyme activity was not affected by abscisic acid. Neither of
these enzymes significantly hydrolyzed isolated tomato endosperm cap cell
walls. While both ß-1,3-glucanase and chitinase were expressed in
tomato endosperm cap tissue prior to radicle emergence, we found no evidence
that they were directly involved in cell wall modification or tissue weakening.
Possible functions of these hydrolases during tomato seed germination are
discussed.
Key words: Abscisic acid, Gibberellin, ß-1,3-Glucanase, Chitinase,
Seed germination
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