Abstract
The ability of pollen to withstand freezing and freeze-drying is dependent on the interaction of a large number of variables such as freezing rate, thawing rate, freeze-drying temperature and duration, storage temperature and environment and rehyeration rates. A change in any of these variables will most likely affect the others directly Freezing of pollen at rates of approximately 200℃/min maintains the highest degree of viable pollen when combined with rapid thawing or freeze-drying. These results suggest that freezable water enucleates within the cells and grows during subsequent slow rewarming into larger ice masses. However, Davies and Dickinson (Plant Physiol., 24 5-9, 1971) maintain that pollen has a normal water content of 9-10% and also a high sucrose concentration which makes it unlikely that intracellular freezing occurs. Although Dickinson makes no statement of freezing rates, immersion in dry ice and acetone baths at -60℃ to -70℃ might suggest a freezing rate rapid enough to produce minute ice crystals.
