Osmotic response of individual cells during freezing. I. Experimental volume measurements.

The osmotic response of yeast to freezing was measured as a function of cooling rate and degree of extracellular supercooling. Thirteen experimental trials were conducted on a cryomicroscope in which incremental size changes of individual cells were recorded photographically, and the corresponding volume variations were measured using a digital computer image analysis algorithm. Plots were obtained of normalized cell volume as a function of temperature. Cellular dehydration during freezing was progressively inhibited with increasing values of cooling rate and extracellular supercooling. Normalized cell volume changes were not a function of the relative initial cell size. A constant volume plateau occurred for conditions under which intracellular ice formation was expected.