LIPID CHANGES IN SOYBEAN ROOT MEMBRANES IN RESPONSE TO SALT TREATMENT

Soybean seedlings were grown hydroponically in a nutrient medium with or without 25 mM NaCl. An analysis of proteins, phospholipids, total f atty acids, and sterols was performed at the root level in the whole t issue extract, in the crude microsomal fraction and in the plasma memb rane fraction purified by two-phase partitioning, The free and conjuga ted forms of sterols were analysed, Most of the sterols were found in the free form, whereas steryl glycosides (SG) were detected in small q uantities and steryl esters (SE) did not occur in the membrane fractio ns, The compositions in various moieties of sterols were quite similar among the three materials, i.e. sitosterol was the major sterol accom panied by campesterol, stigmasterol and small quantities of cholestero l and isofucosterol. No changes were detected in the whole root tissue s after salt treatment, Surprisingly, the main lipid changes were obse rved in the microsomal fraction where the phospholipid and sterol cont ent decreased by 50%, accompanied by an increasing saturation of the t otal fatty acids, Only this last parameter was altered in the plasma m embrane 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 i n the plasma membrane increased 56% under salt stress, The different r esponses of the lipid classes induced by salt treatment and their poss ible significance are discussed.