Seedlings of winter wheat (Triticum aestivum L. cv. Jubilejnaja 50) were grown under normal and dry conditions. Frost resistance (LT50) of 10‐day‐old control seedlings was −6°C. LT50 of the subsequently drought‐stressed leaves shifted to −16°C. In plants of the same physiological age (28 days) but grown without stress, LT50 was −12°C. Phosphatidylcholine accumulated and phosphatidylethanolamine decreased in drought‐stressed leaves. Fatty acid unsaturation of these phospholipids increased with leaf age, independently of water supply. Both ageing and drought stress produced a decrease in the apparent phase separation temperature of isolated total phospholipids as determined by electron spin resonance. The possible role of dehydration‐induced structural changes in the bilayer matrix in triggering adaptive alterations in membrane composition, similar to those observed during cold hardening, is discussed.

The lipid composition of leaves has been investigated in different genotypes of cucumber (Cucumis sativus L.), which differ in temperature requirement for cultivation. In addition the effects of hardening by low but non‐chilling temperature, soil heating and grafting (on the chilling‐resistant C. ficifolia L.) on lipid composition have been studied. Content and composition of phospholipids and sterols were determined as well as phospholipid/sterol ratio, and fatty acid composition of total lipids and the different phospholipids. The effects of genetic differentiation and of the various culture treatments on lipid composition of the leaves were very different. Genetic differentiation was evident as higher levels of Iinolenic acid in several phospholipids in the more cold‐tolerant cultivars. Hardening the plants by low temperature resulted in a higher phospholipid level (especially phosphatidyl choline), more unsaturated phospholipid, and lowering of the sterol/phiospholipid ratio, all properties which may contribute to a higher membrane fluidity and lower growth temperature limit. Soil healing reduced the phospholipid level of the leaves slightly, and a higher content of 3‐trans‐hexadece‐noic acid in phosphatidyl glycerol was observed. Grafting cucumber on the cold‐resistant rootstock of C. ficifolia also raised the level of trans‐hexadecenoic acid in phosphatidyl glycerol. The role of this fatty acid in the functioning of the chloroplast is discussed.

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Phospholipid multibilayers, obtained from two cultivars of thermally acclimated wheats of different frost resistances (Triticum aestivum L. cv. Penjamo 62, the sensitive cultivar, and T. aestivum L. cv. Miranovskaja 808, the frost-resistant cultivar), were investigated using electron-spin-resonance and X-ray-diffraction techniques. The former technique revealed two breaks in the motion of the spin-labelled fatty acid 2-(14-carboxyte-tradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxyl, for both cultivars (+3°C,-17° C and +5° C,-18° C, respectively) when grown at 22° C. The resistant cultivar compensated for exposure to cold (+2° C) by shifting the onset of the apparent phase-separation temperature from +3° C to-16° C. The sensitive cultivar was unable to do so. X-ray diffraction did not reveal fluid-to-gel transitions between +20° C and-10° C in any of the samples. The possible role of the formation of relatively ordered aggregates or clusters of lipid molecules discerned by spin probe within the otherwise freely dispersed liquid-like lipids is discussed in terms of freezing injury of plants.