Preserving Oak (Quercus sp.) Germplasm to Promote Ex-Situ Conservation

Christina Walters, Lisa Hill, Jennifer Crane, Marcin Michalak, Xia Ke, Jeffrey Carstens, Kevin Conrad, Murphy Westwood, Alison Colwell, Joanna Clines, and Pawel Chmielarz

Published May 2016 International Oaks No. 27: 255–266

Abstract

Germplasm banks are increasingly used as an ex-situ conservation strategy. Studies using seeds – the preferred propagules in plant germplasm banks – have revealed the underlying reasons why some cells are able to survive extreme drying and low temperature. This ability is based on the non-lethal conversion of cytoplasm from fluid to solid, as described from materials sciences principles used in studies of thermoplastics and as applied to preserve dry foods and pharmaceuticals. These fluid to solid transitions are called glass formation or vitrification and the reverse process of solid to fluid is called plasticization. Cells of some seeds, such as acorns, do not survive the amount of drying it takes to form a glass at room temperature. To preserve these so-called recalcitrant seeds a combination of cooling and drying under tightly controlled conditions is required and, ultimately, small tissues such as embryos must be stored cryogenically. Feasibility of successful cryogenic treatments will vary among embryos and depend on sensitivity to desiccation, size of cell mass and a host of other factors. We have observed substantial variation in desiccation and freezing tolerance of embryonic cells from diverse oak species. This variation leads us to hypothesize that cryopreservation success is also likely to vary broadly among species or populations. To date, we have achieved high survival following cryogenic exposure of embryonic axes from cold-adapted trees.

Keywords

recalcitrant seeds, orthodox seeds, vitrification, glass formation, longevity

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