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Bio-precipitation or self-cryopreservation: Why does pollen nucleate ice?

Project Description

Project Highlights:
• Work with Royal Botanic Gardens Kew to understand how the biosphere influences weather and climate
• Discover how the evolutionary history of plants interacts with our atmosphere
• Develop a diverse and up-to-date skill set by working with chemists, plant scientists and atmospheric scientists

Nucleation of crystalline ice from supercooled water plays a critical role in the glaciation of mixed-phase clouds and thereby impacts both weather and climate (Murray et al., 2012, Vergara-Temprado et al., 2018). Ice-active polysaccharides (IAPs) associated with pollen grains of some plant species are known to nucleate ice effectively and are present in the atmosphere in potentially significant quantities (Dreischmeier et al., 2017, Pummer et al., 2012, O′Sullivan et al., 2015, Diehl et al., 2002, von Blohn et al., 2005).
Ice nucleation caused by birch pollen IAPs is remarkably specific in nature, occurring sharply at around -16°C, indicating that IAPs have evolved to interact with ice. It is not known why birch pollen produces IAPs or how well the vast majority of pollens nucleate ice as less than 10 species have been studied (von Blohn et al., 2005). There are two obvious reasons for pollens to evolve IAPs.
1) To control precipitation and aid return to the ground having been lofted to altitude by wind. This is an example of ‘bio-precipitation’ where life interacts with clouds to propagate itself.
2) To improve tolerance of cold temperatures by controlling ice formation, be it in clouds or at ground level. Different species pollens are known to be desiccation tolerant to varying extents, depending on the specific dispersal methods they employ. This may be related to their ability to nucleate ice.

The student will collect pollen from plant species held in the collections at Royal Botanic Gardens (RGB) Kew and measure their ice nucleation ability and freeze tolerance to generate a comprehensive multi-species dataset. Armed with this dataset the student will conduct an analysis of the phylogenetic background and ecological role of pollen ice nucleation, allowing an assessment of why pollen nucleates ice. This information will be of ecological interest and improve understanding of biosphere/atmosphere interaction.

Methodology: Pollen grains from a wide range of plant species will be obtained from the RGB Kew collections and their ice nucleation ability assessed using droplet freezing techniques (Whale et al., 2015). The polysaccharides responsible for ice nucleation will be isolated by ice chromatography and characterized. A test for the presence of pollen IAPs and a method for selectively denaturing them will then be developed. The relationship between ice nucleation and pollen desiccation tolerance will be obtained from the literature and empirical determination (Nebot et al., 2018). Pollen grains will be frozen in liquid water after Williams (2013), and post-thaw viability assessed. Pollen viability tests will be optimized at the species level. This will show whether the IAPs help pollen grains to survive freezing. Results will be compared with existing phylogenetic and ecological datasets to assess which plant families nucleate ice and to trace back the genetic origin of plant ice nucleation (e.g. Colville and Pritchard, 2019).

Training and skills: At the University of Warwick (UoW) students will receive training in ice specific analytical techniques and biomacromolecule characterisation as well as general chemical analytical techniques such as Raman and IR spectroscopy, differential scanning calorimetry and X-ray diffraction, amongst others.
RBG Kew will provide extensive relevant training in plant science. RGB Kew also has particular expertise in science communication with specific training provided and opportunities to write for the RGB Kew website and social media channels and engage with media outlets.
Skills developed in the course of the PhD will be interdisciplinary and relevant to a wide range of fields in industry and academia including atmospheric science, plant science, analytical chemistry and science communication.

Funding Notes

This funding provides full tuition fees at the Home/EU rate, pays an annual stipend in line with UK Research Councils (currently £15,009) and a research training support grant (RTSG) of £8,000


Further reading:
COLVILLE, L; PRITCHARD, H.W. (2019) Seed life span and food security. New Phytologist 224: 557–562
DIEHL, K., MATTHIAS-MASER, S., JAENICKE, R. & MITRA, S. K. 2002. The ice nucleating ability of pollen: Part II. Laboratory studies in immersion and contact freezing modes. Atmospheric Research, 61, 125-133.
DREISCHMEIER, K., BUDKE, C., WIEHEMEIER, L., KOTTKE, T. & KOOP, T. 2017. Boreal pollen contain ice-nucleating as well as ice-binding ‘antifreeze’ polysaccharides. Scientific Reports, 7, 41890.
MURRAY, B. J., O'SULLIVAN, D., ATKINSON, J. D. & WEBB, M. E. 2012. Ice nucleation by particles immersed in supercooled cloud droplets. Chemical Society Reviews, 41, 6519-6554.
NEBOT, A., PRITCHARD, H.W., BALLESTEROS. D 2018 Desiccation tolerance and the hydration window for the cryopreservation of woody species’ pollen. Cryobiology 85: 139.
O′SULLIVAN, D., MURRAY, B. J., ROSS, J. F., WHALE, T. F., PRICE, H. C., ATKINSON, J. D., UMO, N. S. & WEBB, M. E. 2015. The relevance of nanoscale biological fragments for ice nucleation in clouds. Scientific Reports, 5, 8082.
PUMMER, B. G., BAUER, H., BERNARDI, J., BLEICHER, S. & GROTHE, H. 2012. Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen. Atmospheric Chemistry and Physics, 12, 2541-2550.
VERGARA-TEMPRADO, J., MILTENBERGER, A. K., FURTADO, K., GROSVENOR, D. P., SHIPWAY, B. J., HILL, A. A., WILKINSON, J. M., FIELD, P. R., MURRAY, B. J. & CARSLAW, K. S. 2018. Strong control of Southern Ocean cloud reflectivity by ice-nucleating particles. Proceedings of the National Academy of Sciences 115 (11) 2687-2692.
VON BLOHN, N., MITRA, S. K., DIEHL, K. & BORRMANN, S. 2005. The ice nucleating ability of pollen: Part III: New laboratory studies in immersion and contact freezing modes including more pollen types. Atmospheric Research, 78, 182-189.
WHALE, T. F., MURRAY, B. J., O'SULLIVAN, D., WILSON, T. W., UMO, N. S., BAUSTIAN, K. J., ATKINSON, J. D., WORKNEH, D. A. & MORRIS, G. J. 2015. A technique for quantifying heterogeneous ice nucleation in microlitre supercooled water droplets. Atmospheric Measurement Techniques, 8, 2437-2447.
WILLIAMS, C. G. 2013. Forest tree pollen dispersal via the water cycle. American Journal of Botany 100, 1184-1190.

Related Subjects

How good is research at University of Warwick in Agriculture, Veterinary and Food Science?

FTE Category A staff submitted: 12.60

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