Lipid changes in soybean root membranes in response to salt treatment

Abstract

Soybean seedlings were grown hydroponically in a nutrient medium with or without 25 mM NaCl. An analysis of proteins, phospholipids, total fatty acids, and sterols was performed at the root level in the whole tissue extract, in the crude microsomal fraction and in the plasma membrane fraction purified by two-phase partitioning. The free and conjugated forms of sterols were analysed. Most of the sterols were found in the free form, whereas steryl glycosides (SG) were detected in small quantities and steryl esters (SE) did not occur in the membrane fractions. The compositions in various moieties of sterols were quite similar among the three materials, i.e. sitosterol was the major sterol accompanied by campesterol, stigmasterol and small quantities of cholesterol and isofucosterol. No changes were detected in the whole root tissues after salt treatment. Surprisingly, the main lipid changes were observed in the microsomal fraction where the phospholipid and sterol content decreased by 50%, accompanied by an increasing saturation of the total fatty acids. Only this last parameter was altered in the plasma membrane fraction and to a lesser extent. The saturated fatty acids (16:0) and (18:0) which both accounted for 49% of the total fatty acids in the plasma membrane increased 56% under salt stress. The different responses of the lipid classes induced by salt treatment and their possible significance are discussed.