Role of cell wall in freezing tolerance of cultured potato cells and their protoplasts

Cultured potato ( Solanum tuberosum L., cv. Red Pontiac) cells suspended in PEG 1000 solutions of 0.6 and O.S osmol exhibited significantly different freezing tolerance from the same cells when suspended in PEG 6000 solutions of the same osmolalities. Cells suspended in PEG 6000 showed cytorhysis instead of plasmolysis. Cells in 0.2 and 0.4 osmol PEG 1000 had LT₅₀(1 of −2.5°C, but the LT₅₀ decreased to −7.50C as the osmolality increased to 0.8 osmol. In PEG 6000 the LT₅₀ remained at −2.50C for all osmolalities used, up to and including 0.8 osmol.
Released protoplasts suspended in 0.5 M sucrose had LT₅₀ of −21.5°C, compared to −12°C for whole cells suspended in the same medium. These results lend credence to an involvement of the cell wall in freezing injury of cultured potato cells, and are interpreted in terms of the generation of a mechanical stress between cell wall and plasma membrane during the freeze-thaw cycle.