Freezing behavior of free protoplasts of winter rye

Free protoplasts prepared from the epicotyls of nonhardened rye seedlings were subjected to fast and slow freezing on a microscope-adapted thermoelectric stage. During rapid freezing to ?12 °C, ice formation occurred inside the protoplasts causing lethal disruption of cell and membrane organization. Under slow freezing to ?12 °C, ice formation occurred outside the protoplast with accompanying dehydration and contraction of the protoplast. Complete rehydration and recovery of the protoplasts occurred upon thawing after slow freezing. Free protoplasts therefore afford a new system for the study of mechanisms of plant cell freezing injury and resistance free of the complications presented by a cell wall.