Abstract
In this study, we examined the low temperature behavior and dehydration tolerance of xylem ray parenchyma cells from several hardwood species that grow from tropical to cold-temperate zones by observation using cryo-scanning electron microscopy and freeze-fracture replica technique in addition to differential thermal analysis (DTA). We found that the freezing behavior of ray parenchyma cells changed discontinuously from shallow supercooling (in the tropical zone), through deep supercooling (in the temperate zone) to extracellular freezing (in the cold-temperate zone) depending upon the temperature reduction in the growing areas. Conversely, dehydration tolerance increased continuously in parallel with the reduction of temperature in growing areas, despite the presence of supercooling ability. These results suggest that the responses of xylem ray parenchyma cells in wide variety of hardwood species to freezing temperatures can be explained as a continuum, the specifies of which depend upon the temperatures of growing conditions.
