The role of the membrane lipid component in the chilling tolerance of cucumber plants

The effect of chilling temperature (6 degrees C) on the composition and con tent of polar lipids and esterified fatty acids as well as on the chloropla st ultrastructure in the palisade parenchyma of cucumber (Cucumis sativus L .) leaves was investigated. Chilling was shown to cause irreversible damage to plants that subsequently led to their death. After this treatment, the total content of polar lipids declined by about 30% when calculated per pro tein basis. The decrease in the content of galacto- and sulfolipids was muc h more significant than that of phospholipids. Among the phospholipids, pho sphatidylglyceroll content was diminished most significantly. Thus, low tem perature affected the content of chloroplast lipids to a greater extent: mo nogalactosyl-, digalactosyl-, and sulfoquinovosyldiacylglycerols, as well a s phosphatidylglycerols. Low-temperature treatment resulted in a minor decr ease in the unsaturated to saturated acid content ratio and in an increase in the linolenic to linoleic acid content ratio. The possible role of these alterations in the lipid components of cell membranes, especially the chlo roplast membranes, in the irreversible damage to heat-loving plants by chil ling temperatures is discussed.