ABSTRACT
The living xylem tissue of many temperate species of woody plants exhibits freezing avoidance and survives exposure to freezing temperatures by deep supercooling. In order for deep supercooling to occur, a barrier must exist that allows the cell to remain isolated from the effects of the presence of extracellular ice. Data will be presented that support a major role for the pit membrane of xylem parenchyma in the regulation of deep supercooling and further indicate that pectins may determine the permeability and/or porosity of this region of the cell wall. Research on the movement of various solutions through xylem tissues has been widely reported in the wood technology literature. The shift in the Differential thermal analysis profile of water-soaked tissue was associated with dramatic modifications in cell wall structure in all cell wall layers of the pit membrane. Modifications consisted of a swelling of all cell wall layers and also a partial dissolution of the amorphous layer.
