Lipids of Plasma Membranes Prepared from Oat Root Cells

Abstract

Plasma membranes were isolated from oat (Avena sativa) roots by the phase-partitioning method. The membranes were exposed to repeated periods of moderate water-deficit stress, and a waterdeficit tolerance was induced (acclimated plants). The plasma membranes of the controls (nonacclimated plants) were characterized by a high phospholipid content, 79% of total lipids, cerebrosides (9%) containing hydroxy fatty acids (>90% 24:1-OH) and free sterols, acylated sterylglucosides, sterylglucosides, and steryl esters, together amounting to 12%. Major phospholipids were phosphatidylcholine and phosphatidylethanolamine with lesser amounts of phosphatidylglycerol, phosphatidylinositol, and phosphatidic acid. After the membranes were acclimated to dehydration, the lipid to protein ratio decreased from 1.3 to 0.7 micromoles per milligram. Furthermore, the cerebrosides decreased to 5% and free sterols increased from 9% (nonacclimated plants) to 14%. Because the total phospholipids did not change significantly, the free sterol to phospholipid ratio increased from 0.12 to 0.19. There was no change in the relative distribution of sterols after acclimation. The ratio of phosphatidylcholine to phosphatidylethanolamine changed from 1.1 in the nonacclimated plants to 0.69 in the acclimated plants. The results show that acclimation to dehydration implies substantial alterations in the lipid composition of the plasma membrane.Lipids play a fundamental role in determining the physical and chemical properties of biomembranes. The total cellular metabolic activity is affected by permeability, transfer activity, enzyme reactions, and lipid phase transition characteristics of the membranes. Plant cell membranes are dynamic with composition changing with the developmental stage (1 1, 30) and with variation in environment (1 2, 14, 31). Ofthe cellular membranes the plasma membrane, by its localization limiting the cytoplasm, is the initial critical target when the cells are exposed to abiotic environmental stress. However, information concerning lipid composition of plant cell plasma membranes is quite limited because of difficulties in isolating plasma membranes with a high degree of purity and in quantities needed for detailed studies.Water water stress and changed membrane lipid composition (12,13,19,28). Oat (Avena sativa) plants repeatedly exposed to a moderate water-deficit stress followed by a recovery period of rewatering will induce tolerance against subsequent exposure to a prolonged water stress period (P. Norberg and C. Liljenberg, unpublished data). The repeated stress cycle which is regarded as an acclimation process to dehydration is characterized by prolonged survival and prolonged continued growth ofthe roots as compared with the nonacclimated plants during exposure to a long period of severe stress. Furthermore, the root cell membranes had reduced permeability as measured by ion leakage. The roots of the acclimated plants had a lower relative water content as well as absolute water content compared with the controls...

Signal Perception and Mechanism of Salt Toxicity/Tolerance in Photosynthetic Organisms: Cyanobacteria to Plants

“…A salt-tolerant plant generally has an increased ratio of phosphatidylcholine (PC) to phosphatidylethanolamine (PE) (Wu et al 2005) while reverse is true for the sensitive plant (Norberg and Liljenberg 1991;Mansour et al 2002). This is in accordance with the fact that PE in contrast to PC readily attains a non-lamellar-inverted hexagonal structure that may introduce hydrophilic water channels throughout the biological membrane (Caffrey 1985) altering its stability and permeability thereby making plants more vulnerable to salt stress.…”

5 Sterol metabolism and functions in higher plants

“…Very little attention has been paid so far to plant GlcCer (see Heinz in this volume). GlcCer are important components of plant PM (Norberg and Liljenberg 1991), but their biosynthetic pathway has not yet been established. According to Lynch et al (1997), SG can serve as donors of glucosyl groups for GlcCer synthesis at the level of the PM.…”

Phosphate-limited Oat

“…Vital) were soaked in deionized water overnight and sown on and covered with vermiculite. The plants were grown in a full nutrient solution (13) or in a nutrient solution in which KH 2 PO 4 was replaced with KCl, in a climate chamber with a 16-h light/8-h dark period. The temperature was 20°C/17°C and the relative humidity was 70%/80% during the light/dark periods.…”

“…Except for a few reports (11)(12)(13), the content of 1-5 mol% DGDG has been ascribed to plastid contamination. We recently established that DGDG indeed is a plasma membrane constituent because it was the dominant acyl lipid of plasma membranes isolated from shoots and roots of oat that had been cultivated for 4 weeks in a phosphate-free medium (9).…”