036 Cryobiology of the Natural World: Linking the laboratory to the Field

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Life has been found on Earth wherever water is liquid. Whilst considerable attention has been directed at microbes growing in boiling geysers and hydrothermal vents, much of the natural environment is seasonally or permanently cold. The coldest seawater is −1.96 °C, but highly saline aquatic environments may reach −18 °C. On land the interior of Siberia and Alaska may reach −60 °C, a temperature which poses a significant physiological challenge to plants and animals living there. Laboratory physiology has elucidated how temperature affects physiological performance in all organisms. Of particular importance is the temperature dependence in two important processes: ATP synthesis and contractile protein function. These temperature dependencies underpin much of the thermal physiology of cellular performance. They are not, however generally the cause of chilling injury which can lead to impairment or death of many organisms at temperatures above zero. These appear to be membrane events or neurophysiological functions in more complex organisms. Extra factors come into play at the freezing point, as the phase change of water from liquid to solid presents an extra suite of problems. Key challenges for the cell are the freeze-concentration of extracellular solutes, and the need to avoid ice penetration into the cell. Experimental cryobiology in the laboratory has been important in elucidating how organisms cope with these subzero temperatures. Work with model systems has allowed us to define several fundamental aspects, including the effects of low temperature on the structure and function of cell membranes, the circumstances under which intracellular freezing may occur, and the role of vitrification. Work on organisms in the field has revealed the presence of antifreeze molecules, the importance of small molecular weight cryoprotectants, and the importance of dehydration. Bringing laboratory and field cryobiology together is important to allow us to develop a more complete picture of how organisms survive very low temperatures. Source of funding: British Antarctic Survey. Conflict of interest: None declared. accl@bas.ac.uk