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RESEARCH PRODUCT

Calorimetric properties of water and triacylglycerols in fern spores relating to storage at cryogenic temperatures.

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Abstract Storing spores is a promising method to conserve genetic diversity of ferns ex situ . Inappropriate water contents or damaging effects of triacylglycerol (TAG) crystallization may cause initial damage and deterioration with time in spores placed at −15 °C or liquid nitrogen temperatures. We used differential scanning calorimetry (DSC) to monitor enthalpy and temperature of water and TAG phase transitions within spores of five fern species: Pteris vittata , Thelypteris palustris , Dryopteris filix-mas , Polystichum aculeatum , Polystichum setiferum . The analyses suggested that these fern spores contained between 26% and 39% TAG, and were comprised of mostly oleic ( P. vittata ) or linoleic acid (other species) depending on species. The water contents at which water melting events were first observable ranged from 0.06 ( P. vittata ) to 0.12 ( P. setiferum ) g H 2 O g −1  dry weight, and were highly correlated with water affinity parameters. In spores containing more than 0.09 ( P. vittata ) to 0.25 ( P. setiferum ) g H 2 O g −1  dry weight, some water partitioned into a near pure water fraction that melted at about 0 °C. These sharp peaks near 0 °C were associated with lethal freezing treatments. The enthalpy of water melting transitions was similar in fern spores, pollen and seeds; however, the unfrozen water content was much lower in fern spores compared to other forms of germplasm. Though there is a narrow range of water contents appropriate for low temperature storage of fern spores, water content can be precisely manipulated to avoid both desiccation and freezing damage.