Survival of Plant Tissue at Super-Low Temperatures. IV. Cell Survival with Rapid Cooling and Rewarming

Abstract

Tissue sections of cortical cells from winter tree [Morus bombyeis] mounted between coverglasses with water were extracellulary prefrozen at the temperatures below-20[degree]C. Sufficiently prefrozen cells could survive immersion in liquid N2, irrespective of rewarming rate. In insufficiently prefrozen cells at temperatures (-5[degree] to -15[degree]), the rewarming rate seriously influenced the survival value. Slow rewarming in air destroyed all of the cells, while rapid rewarming in water at 30[degree] had no effect. An abrupt decrease in the survival of insufficiently prefrozen cells during rewarming following removal from liguid N2 was observed at temperatures above -60[degree]. Tissue sections immersed directly in isopentane bath below -60[degree] for 10 min. following prefreezing at -5[degree] or -10[degree] could survive subsequent rapid rewarming in water at 30[degree]. Thin unmounted tissue sections held with thin forceps and rapidly immersed in isopentane bath kept at various temperature from -5[degree] to 100[degree] from room temperature without prefreezing gave comparable results. It is necessary to go through rapidly a 0[degree] to -60[degree] temperature range in which the growth rate of intracellular crystalization nuclei are great inorder to maintain viability at super-low temperatures.