Ice-Encasement Injury to Microsomal Membranes Isolated from Winter Wheat Crowns : II. Changes in Membrane Lipids during Ice Encasement.

The physical properties and chemical composition of microsomal membranes were examined during a 7 day period of ice encasement in crown tissue of winter wheat (Triticum aestivum L. cv Norstar). Membrane damage, detected as an increase in microviscosity and electrolyte leakage, began between 1 and 3 days of icing, and was associated with a reduction in the recovery of microsomal membranes from stressed tissue, an increase in the microsomal free fatty acid:total fatty acid ratio, and a decrease in the phospholipid:total fatty acid ratio. These trends were amplified between 3 and 7 days of ice encasement. Examination of the free and total fatty acid fractions showed there was a slight, but not statistically significant (P = 0.05) reduction in the degree of unsaturation of the total fatty acid fraction. The composition of the free and total fatty acid fractions were very similar during ice encasement. Furthermore, analysis of phospholipid classes revealed no significant change in the relative amounts of phosphatidylcholine, phosphatidylethanolamine, phosphatidic acid, or lysophospholipids in microsomal membranes during icing. Membrane injury during ice encasement apparently involves hydrolysis of the ester bond between glycerol and the acyl groups of the phospholipid resulting in loss of the phosphate-containing polar head group and a concomitant accumulation of free fatty acids in the bilayer.