Use of ionic liquid in fungal taxonomic study of ultrastructure of basidiospore ornamentation

An ionic liquid (IL) is a kind of salt that stays in a molten state even at room temperature. Since ILs do not vaporize even under vacuum conditions and show high ionic conductivity, they can be used in scanning electron microscopy (SEM) studies. The ultrastructural features of basidiospore ornamentation are considered to be important in the delimitation of taxa for fungi. In the present study, we carried out SEM observations on basidiospores that were subjected to an IL treatment, and evaluated the usefulness of this method in comparison with a conventional preparation method in which dehydrating, drying and platinum (Pt) coating were used. Using the conventional method, a considerable number of basidiospores was lost from the gill tissues; however, using the IL method, the decrease in basidiospores was extremely small. No significant differences in ultrastructural morphology or basidiospore size were found between Pt-coated basidiospores and IL-treated ones. SEM images of Pt-coated basidiospores tended to have higher contrast than those of IL-treated ones. Charging effects were observed with Pt-coated basidiospores, especially at the tips of the ornaments, whereas no such effects occurred for the IL-treated ones. In addition, small crinkles were observed in the Pt-coated basidiospores, but not in the IL-treated ones. These results suggest that the IL method is useful for fungal taxonomic studies.