Relationship between Phospholipid Breakdown and Freezing Injury in a Cell Wall-Less Mutant of Chlamydomonas reinhardii.

The effects of freezing and thawing on a cell wall-less mutant (CW15+) of Chlamydomonas reinhardii were investigated by monitoring enzyme release, cell viability, cell ultrastructure, and lipid composition. Cells suspended in Euglena gracilis medium were extremely susceptible to freezing injury, the median lethal temperature in the presence of extracellular ice being -5.3 degrees C. Cell damage was associated with a release of intracellular enzymes and massive breakdown of cellular organization. Changes in phospholipid fatty acid composition consistent with either a peroxidation process or phospholipase A(2) activity were evident, but the time course of these changes showed clearly that alterations in phospholipid fatty acid composition were a secondary, pathological event and not the the primary cause of freeze-thaw injury in Chlamydomonas reinhardii CW15+.