EFFECTS OF PH AND MINERAL-NUTRITION SUPPLY ON LIPID-COMPOSITION AND PROTEIN PATTERN OF PLASMA-MEMBRANES FROM SUGAR-BEET ROOTS

Plasma membranes (PM) were isolated by two-phase-partitioning from roo ts of 21-day-old sugar beet (Beta vulgaris L. cv. Monohill) seedlings cultivated under different conditions. The seedlings were either grown in a complete nutrient solution with a high concentration of nutrient s (H-s roots) and high (6.5) or low (5.3) pH, or in a low concentratio n medium (L-s roots) with a 15 % daily relative addition rate of nutri ents at pH 5.3. The protein pattern, the phospholipids, the glycolipid s and the free sterols were analysed. The protein pattern of plasma me mbranes did not change, but the composition of lipids changed under th e different conditions of cultivation. After cultivation at a low conc entration of nutrients and low pH, the free sterols dominated while af ter cultivation at a high concentration of nutrients, the phospholipid s were the dominant lipids. The Delta(7)-sterols were the most abundan t free sterols representing more than 60 % of the free sterols in PM o f roots growing in a low concentration of nutrients and more than 70 t o 80 % in plasma membranes of roots growing in a high concentration. O ther free sterols present were stigmasterol, sitosterol, campesterol a nd brassicasterol. The ratio of more planar/to less planar sterols inc reased with high salt treatment. Phosphatidylethanolamine and phosphat idylcholine, which were the major phospholipids, increased with high s alt concentration in the growth medium. The glycolipid levels remained substantially unchanged. However, the ratio of phospholipids to glyco lipids increased with high salt and high pH. The relative distribution of fatty acids in the lipid classes also changed after cultivation of the seedlings under different conditions. The results show that the d ifferent growth conditions used in these experiments caused important changes to the plasma membrane lipid composition, which were well corr elated with differences in ATPase activities and K+(Rb-86(+)) influx o bserved under the same experimental conditions.