Appropriate timing of deacclimation is an important component of winter survival of perennial plants in temperate and boreal zones. The relationship between ambient temperature and the manner of change in freezing resistance of cells is essential information to forecast the timing of deacclimation. In this study, Japanese white birch twigs harvested in mid-February and stored at -20°C were deacclimation-treated at a constant temperature of 0, 4, 10 or 15°C for 3 or 7 days, and then freezing resistance of the cells was determined by an electrolyte leakage test. Birch cells deacclimated in different temperature ranges depending on tissues. Apparent decreases in the freezing resistance of bark cells were observed after deacclimation treatment at 10 or 15°C for 7 days. In contrast, xylem cells initiated deacclimation at 0°C within 7 days. The difference in deacclimation manner between bark and xylem might involve in their freezing behaviors of the cells.
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