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

Abstract

Kermode, A. R. and Bewley, J. D. 1986. The role of maturation drying in the transition from seed development to germination. IV. Protein synthesis and enzyme activity changes within the cotyledons of Ricinus communis L. seeds.—J. exp. Bot. 37: 1887-1898. Drying of immature seeds of Ricinus communis L. cv. Hale (castor bean) during the desiccation tolerant phase of development causes them to germinate upon subsequent rehydration. This desiccation-induced switch from development to germination is also mirrored by a change in the pattern of soluble and insoluble protein synthesis within the cotyledons of the castor bean. Following rehydration of seeds prematurely dried at 40 d after pollination (DAP), cotyledonary proteins characteristic of development (e.g. storage proteins) are no longer synthesized; hydrolytic processes resulting in their degradation commence (after 12 h) in a manner similar to that observed following imbibition of the mature seed. A pattern of protein synthesis recognizable as germination/growth associated occurs; premature drying has elicited a redirection in metabolism from a developmental to a germinative mode. Desiccation is also required for the induction (within cotyledons of 35 DAP seeds) of enzymes involved in protein reserve breakdown (leucyl /i-naphthylamidase; LeuNAase) and lipid utilization (isocitrate lyase; ICL), an event intimately associated with the post-germinative (growth) phase of seedling development. Thus, at a desiccation-tolerant stage of development, premature drying results in the suppression of the developmental metabolic programme and a permanent switching-on of the germination/growth metabolic programme. Key words—Desiccation, metabolism, seed development, seed germination, castor bean, cotyledons. Correspondence to: Department of Botany, University of Guelph, Guelph, Ontario NIG 2W1, Canada.