Studies on thermal adaptation of Tetrahymena lipids : Alteration in fatty acid composition and its mechanism in the growth temperature shift-up

Abstract

A rise in the growth temperature of Tetrahymena pyriformis strain NT-1 from 15 to 34°C resulted in changes in the fatty acid composition of membrane lipids toward higher saturation after a shift-up. The proportion of palmitate (16:0) increased and γ-linolenate (18:3 (6,9,12)) decreased. Alteration in phospholipid composition was completed by a marked increase in phosphatidylethanolamine, with a compensatory decrease in 2-aminoethylphosphonolipid. However, the level of phosphatidylcholine remained unchanged. The rate of incorporation of [1- 14C]acetate into saturated fatty acids (myristate, 14:0; palmitate; stearate, 18:0) was maximum at 1 h after a shift, while formation of 14C-labeled unsaturated fatty acids (palmitoleate, 16:1 (9); linoleate, 18:2 (9,12); γ-linolenate) decreased by about 50%. These findings could be explained by the reduced desaturase activities which were due principally to the decrease in the terminal component, cyanide-sensitive factor (CSF), of the microsomal desaturase system. Furthermore, changes induced by temperature shift-up in activities of microsomal reductases and the content of cytochrome b 5 were observed to behave comparably with changes in activities of desaturases.