Abstract:Changes in fatty acid composition of roots of Elymus nutans, Poa sphyondylodes, and Bromus sinensis growing in alpine area were investigated over late fall and early winter. The results indicated that there were marked changes in the fatty acid composition in this period. The content of saturated palmitic acid (16:0) decreased by 40% while the content of unsaturated linolenic acid (18:3) increased by 112%, resulting in an increase in IUFA (index of unsaturated fatty acid) melting level. Membrane fluidities were low at the freezing-melting stage, but higher in the freezing stage. Ca2+, Mn2+ ATPase activities of plasma membranes increased, but Mg2+ ATPase activities decreased. The results suggested that increase in unsaturated fatty acid content of roots may be a very important physiological response to cold acclimation, which is directly associated with changes in the properties of plasma membranes, in maintaining membrane fluidity and controlling the activities of membrane integrated enzymes.