Conversion of Phosphatidyl Choline to Phosphatidic Acid in Freeze Injured Rye and Wheat Cultivars

The effect of exposure to freezing temperature (?15°C) on leaf phospholipid composition of hardened rye (Secale cereale L.) and hardened wheat cultivars (‘Miranovskaja 808’, ‘Bezostaja 1’, ‘Short Mexican’ and ‘Penjamo 62’), which differ in their resistance to frost, was investigated. Hardening took place under natural conditions. All the seedlings attained an equal level of linolenic acid in their leaves during hardening. Exposure to freezing temperatures resulted in a loss of phosphatidyl choline and accumulation of phosphatidic acid in the leaves. The ratio of phosphatidic acid to phosphatidyl choline, but not the level of poly-unsaturated fatty acids in the leaves, was related to their ability to survive at low temperatures. As freezing injury is caused by the formation of ice crystals in both extra- and intracellular space, it is probable that the plasma membranes of the investigated cultivars differed with respect to their water permeability. It is concluded that the plants, depending on the degree of their resistance to cold, produce an unknown substance of lipidic nature upon exposure to cold, with the aid of which they adjust the transitional state of their membranes to the prevailing temperature and, at the same time, facilitate the efflux of water from the cells.