Millennium Seed Bank Partnership at Royal Botanic Gardens Kew

Dani Ballesteros, Christina Walters, Hugh W. Pritchard

Royal Botanic Gardens Kew, Wellcome Trust Millennium Building, United Kingdom, United States Department of Agriculture., United States

Often various plant propagules (e.g., seeds, pollen and fern spores) can be stored dry (or partially dry) at sub-zero temperatures for extended periods of time. Under such conditions the cell cytoplasm of these propagules solidifies and forms a glass, lethal water freezing does not occur, and metabolic reactions are inhibited. However, dry (or partially dry) plant propagules deteriorate and eventually die during sub- zero storage, including at liquid nitrogen temperatures (i.e. < -150°C). The rates of deterioration are diverse, depend on species and genotypes, and are often influenced by the dry architecture of the propagule’s cells. Probing life and death in the glassy state of cryopreserved materials is challenging, which makes the understanding of the ageing mechanisms of dry plant propagules difficult. However, new techniques in tomography, microscopy and biophysics have been adopted for the study of longevity of cryopreserved dry plant propagules from a structural point of view. Of importance among these tools is: Differential Scanning Calorimetry, Dynamic Mechanical Analysis, micro-Computer Tomography, and Cryo- Scanning Electron Microscopy. They are providing interesting clues about the deterioration mechanisms of seeds, fern spores and pollen during drying and sub-zero exposure and storage. Understanding these deterioration mechanisms will lead to the development of optimized storage protocols to maximize plant germplasm ex situ preservation.

Contributing Author(s): 
Date Recorded: 
Tuesday, July 23, 2019

Daniela Impe, Daniel Ballesteros, Till Ischebeck, Claudia Köpnick, Hardy Rolletschek, Michael Melzer, Manuela Nagel, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) Germany, Royal Botanic Gardens, Kew, United Kingdom, Department of Plant Biochemistry, Georg-August University Göttingen, Germany

Cryopreservation of pollen is used to preserve and exchange nuclear genes of plant genetic resources and to facilitate crosses in breeding programs. For many species, pollen preservation protocols have been established. In wheat breeding programs, long- term pollen preservation would be of high interest to improve the crossing management in hybrid production. However, favorable storage conditions for wheat pollen have not been studied yet and physiological, biochemical and genetic processes in pollen after shedding are hardly understood.

The present project aims to investigate factors that influence wheat pollen viability in order to extend its longevity by cryopreservation. Firstly, a viability test and evaluation scheme based on pollen tube growth in vitro was established and comparisons between in vivo germination, staining methods and impedance flow cytometry showed that more than one test is required to determine wheat pollen viability.

Secondly, storage of wheat pollen under four different non-cryogenic conditions showed that wheat pollen lose germination ability rapidly. At room temperature, viability was lost within one hour at both low and high relative humidity (RH). Under cold temperatures (6-8 °C, both RH) pollen survival was extended moderately. Sugar contents (fructose, glucose and sucrose) increased two- to threefold in pollen stored for one hour under all non-cryogenic conditions. Therefore, we speculate that sugars are actively mobilized during pollen storage. To gain a comprehensive overview of processes contributing to viability loss, a metabolomics and transcriptomic study has been initiated and is complimented by transmission electron microscopy that illustrates ultrastructural differences between fresh, stored and dead wheat pollen.

Finally, storage under ultra-low temperatures (- 196°C) is being investigated in detail. A self-made flash drier was used to control the pollen water content by fast drying. The effects of drying and cryogenic storage are investigated using differential scanning calorimetry and will indicate the feasibility of long-term pollen cryopreservation.

Contributing Author(s): 
Date Recorded: 
Tuesday, July 23, 2019
Michael Way, while exploring Iron Mountain in Oregon, and the vulnerable Brewer’s spruce (Picea breweriana) found there.
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Photo Credit: 
Kew America

Daniel Ballesteros, Millennium Seed Bank Partnership at Royal Botanic Gardens Kew

Wild plant species are highly biodiverse. Biodiversity is typically measured as variation at the genetic, species, and ecosystem levels. But, as a consequence, wild plant species are also highly diverse in their responses to preservation, and ex situ conservation of a wide range of wild plant species can become challenging. For example, ex situ conservation of wild plants, as with most crops, is broadly achieved by conventional dry seed storage at -18°C. Seeds that tolerate desiccation can be stored dry at sub-zero temperatures for extended periods of time. However, dry seeds and other plant propagules still deteriorate and eventually die during sub-zero storage, including at liquid nitrogen temperatures (i.e., < -150°C). The rates of deterioration are diverse depending on species and genotypes, and are influenced by the “dry architecture” of the propagule’s cells. Understanding this variation is essential to design strategies to increase longevity of seeds and other propagules in species with short life spans.

In addition, not all plants produce seeds that tolerate drying and some succumb when stored ‘wet’ at -18°C. For example, about a half of tropical trees and some of the tree species that dominate temperate forests (such as, oaks) produce recalcitrant (i.e., desiccation sensitive) seeds. For these species, cryobiotechnology is the only approach for their long-term ex situ conservation. But cryobiotechnologies are not straight forward. Several challenges related to the manipulation of the plant samples, their drying, cooling, warming and in vitro propagation remain to be resolved. The C-Flora, or Cryo-Flora, defines a range of species and tissues that will enable a wide range of material to be preserved beyond conventional seed storage. Although immediate implementation is possible for diverse materials of the C-Flora, diverse research is needed. To overcome these research challenges, Royal Botanic Gardens, Kew, in its new Science Collection Strategy, highlights the need of a new space within Kew (the Kew Cryosphere), where innovative research, advanced training, and specialized infrastructure are framed to secure the conservation of non-orthodox germplasm of wild plant species using cryobiotechnological approaches.

Contributing Author(s): 
Date Recorded: 
Thursday, May 2, 2019

Michael Way (Royal Botanic Gardens Kew, UK), Clara Holmes (Greenbelt Native Plant Center, USA), and Sean Hoban (The Morton Arboretum)

In 2017, we established a ‘gap analysis working group’ to assess and report the availability and usefulness of online native seed collection data from seven leading online data sources in order to help native seed collectors optimise their targets for additional collections. Volunteers reviewed online data sources and responded to a standardised list of questions to capture their experience of the depth and functionality of the data source. To visualise our findings we transformed results to simple numerical scores and projected on a six-node radar graph within a draft report. In addition, we asked curators of the data sources to fact-check our conclusions. We recommend that collection holders cooperate to publish standardised collection data that can be discovered, mapped, and evaluated using online tools. This will require enhanced cooperation between curators of botanical names, herbarium and seed curators, together with quality communication with the users of seed collections amongst the research, conservation and ecological restoration community. We discuss several innovative solutions addressing these recommendations that include Creative Commons, generalizing longitude and latitude data for widespread dissemination, analysing user communities to develop better tools for collectors, elucidating Seed Transfer Zones, and engaging seed collectors in the development of additional tools to assist seed collections.

Contributing Author(s): 
Date Recorded: 
Thursday, May 3, 2018