Effects of glycerol on intracellular ice formation and dehydration of onion epidermis.

Microscopic observations of freezing processes of onion epidermis have been carried out using a directional solidification stage. Effects of cryoprotectant on the intracellular ice formation and the dehydration were examined for several kinds of concentrations of glycerol in a wide range of cooling rate. With an increase of the glycerol concentration the ice formation due to the surface-catalyzed nucleation (SCN) at the plasma membrane was suppressed and the freezing temperature decreased. Especially, under a rapid cooling condition, a large supercooling should be achieved and we observed a different type of freezing in the lower temperature conditions. At the slower cooling rate, on the other hand, the use of glycerol can not prevent the cell shrinkage caused by the dehydration. It is also found that the intracellular ice formation and the dehydration under the ordinary cooling condition can be estimated based on the SCN theory by Toner et al. and Mazuar's dehydration model.