Effects of pH and Mineral Nutrition Supply on Lipid Composition and Protein Pattern of Plasma Membranes from Sugar Beet Roots

Abstract

Summary Plasma membranes (PM) were isolated by two-phase-partitioning from roots 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 nutrients (H-s roots) and high (6.5) or low (5.3) pH, or in a low concentration medium (L-s roots) with a 15% daily relative addition rate of nutrients at pH 5.3. The protein pattern, the phospholipids, the glycolipids and the free sterols were analysed. The protein pattern of plasma membranes did not change, but the composition of lipids changed under the different conditions of cultivation. After cultivation at a low concentration of nutrients and low pH, the free sterols dominated while after cultivation at a high concentration of nutrients, the phospholipids were the dominant lipids. The Δ 7 -sterols were the most abundant free sterols representing more than 60% of the free sterols in PM of roots growing in a low concentration of nutrients and more than 70 to 80% in plasma membranes of roots growing in a high concentration. Other free sterols present were stigmasterol, sitosterol, campesterol and brassicasterol. The ratio of more planar/to less planar sterols increased with high salt treatment. Phosphatidylethanolamine and phosphatidylcholine, which were the major phospholipids, increased with high salt concentration in the growth medium. The glycolipid levels remained substantially unchanged. However, the ratio of phospholipids to glycolipids 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 different growth conditions used in these experiments caused important changes to the plasma membrane lipid composition, which were well correlated with differences in ATPase activities and K + ( 86 Rb + ) influx observed under the same experimental conditions.