The Role of Maturation Drying in the Transition from Seed Development to Germination

Abstract

lCermode, A. R. and Bewley, J. D. 1988. The role of maturation drying in the transition from seed development to germination. V. Responses of the immature castor bean embryo to isolation from the whole seed: a comparison with premature desiccation.—J. exp. Bot. 39: 487-497. Desiccation is an absolute requirement for germination and post-germinative growth of whole seeds of the castor bean, whether desiccation is imposed prematurely during development, at 35 d after pollination (DAP) or occurs naturally during late maturation (50-60 DAP). Desiccation also plays a direct role in the induction of post-germinative enzyme synthesis in the cotyledons of embryos in the intact seed; this event is not simply due to the presence of a growing axis. Isolation of embryos from the developing castor bean seed at 35 DAP results in both germination and growth, despite the absence of a desiccation event. We have compared the metabolic consequences of premature drying of whole seeds (35 DAP) and isolation of the developing 35 DAP embryos. In both cases, hydrolytic events involved in the mobilization of stored protein reserves proceed in a similar manner and mirror those events occurring within germinated mature seeds. There are differences, however, for post germinative enzyme (LeuN Aase and isocitrate lyase) production occurs to a lesser extent in non-dried isolated embryos than in those from prematurely dried (35 DAP) whole seeds, or from mature dry (whole) seeds. Desiccation of the 35 DAP whole seed does not alter the subsequent response of the embryo upon isolation. Thus, while drying does not affect the metabolism of isolated embryos, it has a profound effect on that of embryos within the intact seed. Tissues surrounding the embryo in the developing intact seed (viz. the endosperm) maintain its metabolism in a developmental mode and inhibit germination. This effect of the surrounding tissues can only be overcome by drying or by their removal. Key words—Metabolism, isolation, desiccation, embryo, endosperm, castor bean, development, germination. Correspondence to: Department of Botany, University of Guelph, Guelph, Ontario NIG 2WI, Canada.