Cryopreservation of spinach chloroplast membranes by low-molecular-weight carbohydrates. I. Evidence for cryoprotection by a noncolligative-type mechanism.

In freezing experiments with isolated spinach thylakoids (Spinacia oleracea L. cv. Monatol) the cryoprotective efficiency of various low-molecular-weight polyols was determined. The activity of cyclic photophosphorylation was used as an assay for the functional integrity of the membranes. The results were compared with the osmotic behavior of the cryoprotectants at high concentrations. Equimolal concentrations of polyols which exhibit nearly comparable freezing point depressions even at high concentrations differed considerably in their protective capacity during a freeze-thaw cycle. This was particularly distinct when glucose, galactose, and ethylene glycol monomethyl ether were compared, but was also evident when various pentoses and deoxy-hexoses were used as cryoprotectants. Even in the absence of freezing, carbohydrates exerted a stabilizing influence on biomembranes. From the data it is suggested that in addition to colligative action of the compounds, a specific noncolligative mechanism contributes to membrane protection during freezing.