The cryopreservation of Chlorella

Following a shift from autotrophic to heterotrophic nutrition, cells of Chlorella protothecoides become sensitive to the stresses of freezing and thawing. The injury then observed at slow rates of cooling cannot be explained by the cellular response to hypertonic solutions, and at faster cooling rates intracellular ice formation was not demonstrated to be damaging. These findings are at variance with suggested mechanisms of injury in other cellular systems. The results are compared with alterations in ultrastructure and in the composition of the cellular fatty acids.