Functions and regulation of ß-1,3-glucanases during seed germination, dormancy release and after-ripening

Figure 1.   A speculative model integrating tobacco class I ß-1,3-glucanase (ßGlu I), seed dormancy, after-ripening and germination. According to the model, ßGlu I expression is transcriptionally down-regulated by abscisic acid (ABA) in dormant seeds. Expression of ßGlu I contributes to the release of coat-imposed dormancy and the promotion of germination by acting at two sites. First, decrease in ABA level and sensitivity during after-ripening eventually permit ßGlu I expression in seeds. Upon sufficient moisture increase ßGlu I action contributes to the release of coat-imposed dormancy and promotes testa rupture in the light. Second, ßGlu I is induced by the light/gibberellin (GA) pathway in the micropylar endosperm and facilitates endosperm rupture. Endosperm-specific ßGlu I expression and endosperm rupture are inhibited by ABA and promoted by light, GA and ethylene (C2H4). The light/GA pathway also promotes ABA degradation. In addition, photodormancy is manifested as a block prior to testa rupture during dark-imbibition. It can either be released during after-ripening or by the light/GA pathway early during imbibition. ßGlu I is one of several key factors that regulate dormancy and germination in response to environmental and hormonal conditions. A 'plus' sign designates promotion and a 'minus' sign inhibition of a process.

© Gerhard Leubner-Metzger, Seed Science Research 13: 17-34 (2003)

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