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Submitted to: International Society for Biological and Environmental Repositories Newslet
Publication Type: Abstract Only Publication Acceptance Date: 5/20/2003 Publication Date: 5/4/2003 Citation: Walters, C. 2003. Longevity and Genetic stability of cryopreserved materials. International Society for Biological and Environmental Repositories Newsletter, May 4-7, 2003, Philadelphia, PA. pp. 14. Interpretive Summary: Though cryogenic storage is presumed to provide nearly infinite longevity to cells, the actual time scale for changes in viability has not been addressed theoretically or empirically. In this presentation, theoretical aspects of storage stability at cryogenic temperatures are discussed in terms of molecular mobility within aqueous amorphous matrices. Empirical aspects are discussed using results of an experiment in which seeds were stored in liquid nitrogen vapor or liquid (-135 and-196C, respectively) for about 20 years. We show that molecular mobility and deterioration of germplasm are indeed limited at cryogenic temperatures, decreasing by about 8 orders of magnitude over a 100C temperature range. However, the extreme cold is not sufficient to stop either process. Molecular mobility in seeds at low temperatures is more rapid than predicted by the Vogel-Tamman-Fulcher (VTF) model for relaxation of ideal glasses and considerations using Adams-Gibbs configurational entropy demonstrated that the temperature dependency of aqueous glasses in seeds changed from fragile to strong behavior (i.e., VTF to Arrhenius kinetics) at temperatures below the glass transition temperature (Tg) and the Kauzman temperature (TK). A similar change in temperature dependency was noted for seed aging rates. The benefit of low temperature storage (-18C or -135C) on seed longevity was progressively lost if seeds were first stored at 5C, and this result has serious implications for processing samples intended for cryogenic storage. Collectively, our results indicate that molecular motion must be regarded as unavoidable in vitrified biological materials, implying that indefinite shelf life may not be possible using current cryogenic technologies. If this is true, the desired or achievable shelf-life for preserved materials must be more concretely defined by the user and genebank operator and time scales for biological change must be determined for an array of materials and preservation strategies. This work contributes to reliable assessments of the potential benefit and cost of different genebanking strategies. Technical Abstract: Though cryogenic storage is presumed to provide nearly infinite longevity to cells, the actual time scale for changes in viability has not been addressed theoretically or empirically. In this presentation, theoretical aspects of storage stability at cryogenic temperatures are discussed in terms of molecular mobility within aqueous amorphous matrices. Empirical aspects are discussed using results of an experiment in which seeds were stored in liquid nitrogen vapor or liquid (-135 and-196C, respectively) for about 20 years. We show that molecular mobility and deterioration of germplasm are indeed limited at cryogenic temperatures, decreasing by about 8 orders of magnitude over a 100C temperature range. However, the extreme cold is not sufficient to stop either process. Molecular mobility in seeds at low temperatures is more rapid than predicted by the Vogel-Tamman-Fulcher (VTF) model for relaxation of ideal glasses and considerations using Adams-Gibbs configurational entropy demonstrated that the temperature dependency of aqueous glasses in seeds changed from fragile to strong behavior (i.e., VTF to Arrhenius kinetics) at temperatures below the glass transition temperature (Tg) and the Kauzman temperature (TK). A similar change in temperature dependency was noted for seed aging rates. The benefit of low temperature storage (-18C or -135C) on seed longevity was progressively lost if seeds were first stored at 5C, and this result has serious implications for processing samples intended for cryogenic storage. Collectively, our results indicate that molecular motion must be regarded as unavoidable in vitrified biological materials, implying that indefinite shelf life may not be possible using current cryogenic technologies. If this is true, the desired or achievable shelf-life for preserved materials must be more concretely defined by the user and genebank operator and time scales for biological change must be determined for an array of materials and preservation strategies. This work contributes to reliable assessments of the potential benefit and cost of different genebanking strategies. |
