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

Abstract

The expression patterns of ␤-1,3-glucanases (␤Glu) 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 Cestroideaetype seeds. ␤Glu accumulation in imbibed Cestroideaetype 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 ␤Glu genes. The micropylar cap of Solanoideae-type seeds does not allow a distinction between testa and endosperm rupture, but ␤Glu accumulation occurred prior to radicle emergence of pepper and P. peruviana seeds. ABA inhibited endosperm rupture and ␤Glu accumulation in the micropylar cap of pepper seeds. In contrast to tomato, ␤Glu accumulation in pepper seeds was not only confined to the micropylar cap, was due to distinct, tissue-specific ␤Glu isoforms, and was not accompanied by Chn accumulation. In conclusion, ABA inhibition of germination and ␤Glu 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 ␤Glu isoforms in the embryo, prior to germination, appears to be a speciesspecific phenomenon within the Solanaceae. In addition, a post-germination co-induction of ␤Glu 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. Web site: 'The Seed Biology Place' http://www.leubner.ch Abbreviations: ABA = abscisic acid; Chn = chitinase; Chn I = class I chitinase; GA = gibberellin; ␤Glu = ␤-1,3-glucanase; ␤Glu I = class I ␤-1,3-glucanase.

Water Uptake and Distribution in Germinating Tobacco Seeds Investigated in Vivo by Nuclear Magnetic Resonance Imaging

“…ABA inhibits the induction of bGlu I in the micropylar endosperm just before its rupture but does not affect testa rupture of tobacco. ABA also inhibits endosperm rupture, but not testa rupture, of several other Nicotiana species and of petunia (Petunia hybrida; Grappin et al, 2000;Krock et al, 2002;Petruzzelli et al, 2003;Schwachtje and Baldwin, 2004). Transgenic TKSG7 tobacco seeds overexpress bGlu I in the seed-covering layers under the control of a chimeric ABA-inducible transgene promoter (Leubner-Metzger, 2003).…”

Emerging and established model systems for endosperm weakening.

“…In contrast, endo-β-1,4-mannanase in tomato seeds is associated with the first phase of endosperm weakening and is not inhibited by ABA (Nonogaki et al, 2000;Toorop et al, 2000). Expression of endo-β-1, 3-glucanase in the micropylar endosperm, its inhibition by ABA and the inhibition of endosperm rupture by ABA is widespread among the Solanaceae (Wu et al, 2000;Leubner-Metzger, 2003;Petruzzelli et al, 2003). The ABA inhibition of endosperm rupture is partially reverted in transgenic tobacco seeds that overexpress endo-β-1,3-glucanase in the seed-covering layers under the control of an ABA-inducible transgene promoter LeubnerMetzger, 2002;Manz et al, 2005).…”

“…Another phenomenon of endospermic seeds is that endosperm rupture is inhibited by ABA (Karssen, 1976;Finch-Savage and McQuistan, 1991;Toorop et al, 2000;Petruzzelli et al, 2003). In the established model systems of the asterid clade it has been shown that ABA inhibits endosperm rupture, at least in part, by acting in an inhibitory manner on the micropylar endosperm (Ni and Bradford, 1993;LeubnerMetzger, 2003;da Silva et al, 2004).…”

“…A typical feature of Cestroideae-type seeds like tobacco is a two-step germination with a visible distinction between testa rupture and endosperm rupture (Fig. 20.3;Leubner-Metzger, 2003;Petruzzelli et al, 2003). Two-step germination with separate testa and endosperm rupture is widespread over the entire phylogenetic tree and has been described for many species, including Trollius (Ranunculaceae, Ranunculales, basal eudicots) (Hepher and Roberts, 1985), Chenopodium (Amaranthaceae, Caryophyllales, caryophyllids) (Karssen, 1976) and Nicotiana (Cestroideae, Solanaceae, Solanales, asterids) (Leubner-Metzger, 2003).…”

“…initial embryo elongation) even in the presence of 1000 µM ABA (Liptay and Schopfer, 1983). The Solanaceae family can be divided into two large subgroups ( Judd et al, 2002;Petruzzelli et al, 2003): (i) the Solanoideae (e.g. Capsicum, Lycopersicon and Datura); and (ii) the Cestroideae (e.g.…”