Supercooling-Facilitating Hydrolyzable Tannins Isolated from Xylem Tissues of Cercidiphyllum japonicum

Parenchyma cells in xylem of boreal woody plants respond to subzero temperatures by deep supercooling, which is distinct from extracellular freezing observed in bark cells and herbaceous plant cells. It is known that the cell wall is essential for the deep supercooling capability of xylem parenchyma cells (XPCs). Additionally, we have shown the contribution of intracellular substances to deep supercooling capability and have detected supercooling-facilitating activities in xylem extracts of several woody plants in the presence of ice-nucleating bacteria, Erwinia ananas. Further studies revealed the presence of four kinds of flavonol glycosides as novel supercooling-facilitating substances in xylem extracts of Cercidiphyllum japonicum. Recently, four kinds of hydrolyzable tannins were additionally identified as novel supercooling-facilitating substances in the xylem extracts. These findings suggest that supercooling-facilitating substances contribute to the deep supercooling capability of XPCs in connection with the roles of cell wall structure.