Freezing behavior of xylem ray parenchyma cells in softwood species with differences in the organization of cell walls

By cryo-scanning electron microscopy we examined the effects of the organiz ation of the cell walls of xylem ray parenchyma cells on freezing behavior, namely, the capacity for supercooling and extracellular freezing, in vario us softwood species. Distinct differences in organization of the cell wall were associated with differences in freezing behavior. Xylem ray parenchyma cells with thin, unlignified primary walls in the entire region (all cells in Sciadopitys verticillata and immature cells in Pinus densiflora) or in most of the region (mature cells in P. densiflora and all cells in P. parif lora var. pentaphylla) responded to freezing conditions by extracellular fr eezing, whereas xylem ray parenchyma cells with thick, lignified primary wa lls (all cells in Crytomeria japonica) or secondary walls (all cells in Lar ix leptolepis) in most regions responded to freezing by supercooling. The f reezing behavior of xylem ray parenchyma cells in L. leptolepis changed sea sonally from supercooling in summer to extracellular freezing in winter, ev en though no detectable changes in the organization of cell walls were appa rent. These results in the examined softwood species indicate that freezing behavior of xylem ray parenchyma cells changes in parallel not only with c lear differences in the organization of cell walls but also with subtle sub -electron-microscopic differences, probably, in the structure of the cell w all.