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

beta -1,3-Glucanase (EC 3.2.1.39) and chitinase (EC 3.2.1.14) mRNAs, protei ns, and enzyme activities were expressed specifically in the micropylar tis sues of imbibed tomato (Lycopersicon esculentum Mill.) seeds prior to radic le emergence. RNA hybridization and immunoblotting demonstrated that both e nzymes were class I basic isoforms. beta -1,3-Glucanase was expressed exclu sively in the endosperm cap tissue, whereas chitinase localized to both end osperm cap and radicle tip tissues. beta -1,S-Glucanase and chitinase appea red in the micropylar tissues of gibberellin-deficient gib-1 tomato seeds o nly when supplied with gibberellin. Accumulation of beta -1,3-glucanase mRN A, protein and enzyme activity was reduced by 100 muM abscisic acid, which delayed or prevented radicle emergence but not endosperm cap weakening. In contrast, expression of chitinase mRNA, protein, and enzyme activity was no t affected by abscisic acid. Neither of these enzymes significantly hydroly zed isolated tomato endosperm cap cell walls. Although both beta -1,3-gluca nase and chitinase were expressed in tomato endosperm cap tissue prior to r adicle emergence, we found no evidence that they were directly involved in cell wall modification or tissue weakening. Possible functions of these hyd rolases during tomato seed germination are discussed.