Distinct expression patterns of β-1,3-glucanases and chitinases during the germination of Solanaceous seeds

The expression patterns of beta-1,3-glucanases (betaGlu) and chitinases (Chn) were investigated during the seed germination of members of the Cestroideae (three Nicotiana species, Petunia hybrida) and the Solanoideae (Capsicum annuum, Physalis peruviana) subgroups of Solanaceous species. Rupture of the micropylar testa (seed coat) and rupture of the micropylar endosperm, i.e. radicle emergence, were distinct and temporally separate events during the germination of Cestroideae-type seeds. betaGlu accumulation in imbibed Cestroideae-type seeds, occurring after testa rupture but prior to endosperm rupture, was inhibited by abscisic acid (ABA) and promoted by gibberellins (GA) and light, in strict association with germination, and appeared to be caused by transcriptional regulation of the class I betaGlu genes. The micropylar cap of Solanoideae-type seeds does not allow a distinction between testa and endosperm rupture, but betaGlu accumulation occurred prior to radicle emergence of pepper and P. peruviana seeds. ABA inhibited endosperm rupture and betaGlu accumulation in the micropylar cap of pepper seeds. In contrast to tomato, betaGlu accumulation in pepper seeds was not only confined to the micropylar cap, was due to distinct, tissue-specific betaGlu isoforms, and was not accompanied by Chn accumulation. In conclusion, ABA inhibition of germination and betaGlu accumulation in the micropylar endosperm appears to be a widespread event during the seed germination of Solanaceous species. In contrast, accumulation of Chn and distinct betaGlu isoforms in the embryo, prior to germination, appears to be a species-specific phenomenon within the Solanaceae. In addition, a post-germination co-induction of betaGlu and Chn in the root of the emerged seedling was found in endospermic and non-endospermic species and could represent an evolutionarily conserved event during dicot seedling development.