Effect of choline chloride on fatty acid chain ordering in membranes of wheat (Triticum aestvium L. cv. Miranovskaja 808).

A winter variety (Miranovskaja 808) of wheat (Triticum aestivum L.) was grown in water cultures containing 0, 5, 15, 30, and 60 mM choline chloride. There was an increase in the phosphatidylcholine level at the expense of phosphatidic acid, parallel with an increasing choline concentration in the cultivating medium. While the ratio of free sterols to phospholipids remained essentially constant in the seedlings, there was an increase in the ratio of saturated-to-unsaturated fatty acids of the phospholipid fraction. Probing the protoplasts obtained from the leaves of the seedlings, with spin labeled 5-doxyl- and 16-doxyl stearic acids, indicated a progressive rigidifying of the hydrophobic core of the plasmalemma. It is suggested that this is a manifestation of compensatory mechanisms by which plants attempt to maintain unchanged average membrane fluidity across their membranes in response to the fluidizing effect of choline head groups.