Abstract
Freezing behavior of xylem ray parenchyma cells in several hardwood and softwood species that inhabit in cold areas changes from supercooling in summer to extracellular freezing in winter. It was suggested that the seasonal changes in the freezing behavior were due to changes of the cell wall properties as a result of seasonal cold acclimation, although at ultrastructural level little changes of the cell walls were detected among seasons. The property of the cell walls may also have important roles for occurrence and/or inhibition of freezing injury in plant cells by extracellular freezing, in which close apposition of membranes as a result of cellular shrinkage and cellular deformation produces injury, because cellular deformation is mainly produced by deformation of cell walls. For understanding more precisely about the mechanisms of freezing adaptation of plant cells, it is necessary to clarify changes of the cell wall properties by cold acclimation.
