Plant Physiology 126: 1299-1313 (2001)

Class I ß-1,3-glucanase and chitinase are expressed in the micropylar endosperm of tomato seeds prior to radicle emergences

Chun-Ta Wu, Gerhard Leubner-Metzger, Frederick Meins, Jr. and Kent J. Bradford

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

Abstract. ß-1,3-Glucanase (EC and chitinase (EC 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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