It has previously been shown that intracellular ice forms in rapidly cooled embryonic axes of Acer saccharinum (silver maple) but this not necessarily lethal when ice crystals are small. Wesley-Smith et al. cool embryonic axes to liquid nitrogen temperatures without prior dehydration or cryoprotection treatments and thaw them rapidly. Microscopic examination of the cell structure reveals that autophagic degradation and ultimately autolysis of cells following cryo-exposure and formation of small (0.2–0.4 µm) intracellular ice crystals challenges current ideas that ice causes immediate physical damage to cells. Instead, freezing stress may induce a signal for programmed cell death (PCD). Cells that form more ice crystals during cooling have faster PCD responses.
A study of silver maple cools embryonic axes to liquid nitrogen temperatures without prior dehydration or cryoprotection treatments and thaws them rapidly.