Species- and age-dependent sensitivity to ozone in young plants of pea,wheat and spinach: Effects on acyl lipid and pigment content and metabolism

Acyl lipids and pigments were analyzed in young plants of garden pea, spring wheat and spinach exposed to < 5 or 65 nl l^?1 ozone 12 h per day for 6 days. In one set of experiments, the plants were exposed to ¹⁴CO₂ for 2 h 3 days prior to ozone exposure. The plants responded differently to the moderately enhanced level of ozone used Spinach was not at all sensitive while in both pea and wheat, leaves of different ages differed in ozone sensitivity. In pea, ozone sensitivity increased with leaf age. In the second and third oldest leaves, the amounts of galactolipids per leaf area and the proportions of 18:3 of the total lipid extract and of phosphatidylglycerol decreased. In the second oldest leaf, ozone also caused a decreased proportion of 18:3 of monogalactosyldiacylglycerol. In the fourth oldest leaf, lipid composition and galactolipid unsaturation was unaffected, but ozone caused decreased leaf expansion resulting in increased acyl lipid content per leaf area. In both the first and second leaves of wheat, ozone fumigation caused a marked decrease in the content of monogalactosyldiacylglycerol and in the first leaf, the contents of phosphatidylcholine and phosphatidylethanolamine increased. The proportion of 18:3 in phosphatidylcholine was larger in ozone-fumigated than in control plants, while the reverse applied for phosphatidylglycerol. In the oldest sampled leaves of pea and wheat, ozone caused an increase in the radioactivity associated with β-carotene, indicating increased turnover. Thus, while spinach was unaffected, in both pea and wheat ozone caused a decrease in the proportion of chloroplast membrane lipids to non-chloroplast membrane lipids in older leaves while younger leaves were less sensitive.     

Constraints to growth of annual nettle (Urtica urens) in an elevated CO2 atmosphere: Decreased leaf area ratio and tissue N cannot be explained by ontogenetic drift or mineral N supply

Plant sterols differ from cholesterol in having an alkyl group at Δ-24, and, in the case of stigmasterol, also a Δ-22 double bond. The effects of 10 mol% of three plant sterols (campesterol, β -sitosterol, stigmasterol) and cholesterol on the molecular dynamics and phase behavior in multilamellar liposomes made from different phosphatidylcholine (PC) molecular species have been compared, utilizing the fluorescent probe Laurdan (2-dimethyl-amino-6-laurylnaphthalene). Laurdan reports the molecular mobility in the hydrophilic/hydrophobic interface of the membrane by determining the rate of dipolar relaxation of water molecules close to the glycerol backbone of PC. Our results showed that the Δ-24 alkyl group of plant sterols did not affect their ability to reduce molecular mobility in this region of the PC membranes. However, the plant sterols had a decreased capacity compared to cholesterol to inhibit formation of co-existing domains of gel and liquid-crystalline phases in membranes composed of equimolar dilauroyl-PC and dipalmitoyl-PC. The Δ-22 double bond present in stigmasterol decreased the ability of this sterol, compared to the other phytosterols, to reduce the molecular mobility at the hydrophobic/hydrophilic interface in membranes made of a saturated PC molecular species. However, in membranes made from 16:0/18:2-PC, a lipid species common in plant plasma membranes, stigmasterol was as efficient as other sterols in affecting the polarity and molecular mobility at the hydrophilic/hydrophobic interface of the membrane at 25°C, but was, in contrast to the other sterols, without effect at 0°C. Our results thus confirm as well as contradict the results of previous studies of the interactions between saturated PC and sterols, where other membrane regions were probed. The physiological relevance of the findings is discussed.     

Effects of moderately enhanced levels of ozone on the acyl lipid composition of leaves of garden pea (Pisum sativum)

Plants of garden pea ( Pisum sativum L.) were exposed to charcoal-filtered air with or without addition of 65 ± 5 l⁻¹ ozone. Plants were harvested daily for 9 days and lipids were extracted from the second-oldest leaf. Visible injury of this leaf was evident from day 5 on, while the differences in lipids between ozone and control treatments were observed earlier. Ozone caused large decreases in the contents of monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and sulfoquinovosyldiacylglycerol (SQDG), a slower decrease in the content of phosphatidylcholine (PC), but an increase in the content of phosphatidylethanolamine (PE) per leaf area, compared with exposure to charcoal-filtered air. The content of phosphatidylglycerol (PG) was unaffected by ozone. Compared with charcoal-filtered air, fumigation with ozone resulted in a decrease in the proportion of linolenic acid (18:3) of the total lipid extract, with a concomitant increase in the proportion of linoleic acid (18:2). For individual lipids, ozone caused a similar pattern of decreased 18:3 and increased 18:2 in MGDG, SQDG, PC and PE, while the fatty acid composition of DGDG was unaffected. In PG, ozone decreased the proportions of 18:3 and trans -Δ³-decenoic acid (16:1_trans), balanced by increased proportions of palmitic and oleic acids. The contents of chlorophylls and carotenoids were unaffected by ozone. Our results show that moderately elevated levels of ozone cause significant changes in the polar lipid composition of garden pea leaves and in the level of unsaturation of the lipid acyl groups and, furthermore, that ozone has different effects, which could be direct or indirect, on chloroplast lipids (MGDG, DGDG, SQDG, PG acylated with 16:1_trans) and cytosolic membrane lipids.     

Soybean phosphatidylcholine vesicles containing plant sterols: a fluorescence anisotropy study

The typical plant sterols (sitosterol, stigmasterol and campesterol) were compared with respect to their ability to regulate membrane fluidity of soybean phosphatidylcholine (PC) vesicles. Fluidity changes were monitored by the steady-state fluorescence anisotropy with 1,6-diphenyl-1,3,5-hexatriene as a probe and assigned to a measure of the acyl chain orientational order. Sitosterol and campesterol appear to be the most suitable sterols in ordering the acyl chains of soybean lecithin bilayers, even more efficient than cholesterol, the standard of reference for sterol effects on membranes, suggesting that they play a significant role in the regulation of plant membrane properties. Stigmasterol is shown to be much less active. Cycloartenol, a biosynthetic precursor of plant sterols, increases the acyl chain order with the same efficiency as cholesterol. We also investigated the effects of two unusual sterols, 24-methylpollinastanol and 14 alpha,24-dimethylcholest-8-en-3 beta-ol, which were shown to accumulate in plants treated with fungicides belonging to two important classes, N-substituted morpholines and triazoles, respectively. These two sterols exhibit a behavior very similar to that of stigmasterol. The results are discussed in terms of sterol effects on the molecular packing of soybean PC bilayers.     

Fluidity and lipid composition of oat and rye shoot plasma membrane: effect of sterol perturbation by xenobiotics

Oat and rye plants were treated with either tetcyclacis (an experimental plant growth regulator), nuarimol (a fungicide) or gamma-ketotriazole (an experimental herbicide). These treatments reduced shoot growth and changed the lipid composition of the shoot plasma membranes. In oat, both tetcyclacis and nuarimol treatments increased plasma membrane cholesterol and increased the phosphatidylethanolamine/phosphatidylcholine (PE/PC) ratio, whereas gamma-ketotriazole treatment reduced cholesterol and the PE/PC ratio. In rye, all treatments reduced the PE/PC ratio. Generally, the sterol/phospholipid ratio was less in oat than in rye but the cholesterol/phospholipid ratio was greater. With all treatments in oat and rye, increases were observed in unsaturation of the phospholipid acyl chains. The fluidity of membranes was measured by steady-state fluorescence polarisation of the probe diphenylhexatriene; oat membranes were more fluid than rye. Membrane fluidity was greater in plasma membranes from plants treated with the xenobiotics than the controls. The results are discussed in the context of the effect of plasma membrane lipid composition on membrane fluidity, and it is concluded that there appears to be no overall simple relationship between membrane lipid composition and fluidity that holds for all treatments in both species.     

Lipid and Sterol Composition of Plasma Membranes Isolated from Stele and Cortex of Maize Roots

The phospholipid and sterol contents of plasma membranes isolatedfrom stele and cortex of maize roots were compared. The majorsterol present in both tissues was stigmasterol which was foundin significantly higher quantities in the cortex (27·4µg mg^–1 membrane protein) compared to the stele(17·4 µg mg^–1). Other sterols detected includedsitosterol, campesterol and small quantities of cholesterol.The major phospholipids found were phosphatidylethanolamine(PE) and phosphatidylcholine (PC), with PC more abundant inthe stele. The fatty acid composition indicated that the majorfatty acid in both stele and cortex was 16:0 (palmitic), withothers found in lesser amounts. Key words: Zea mays, cortex, phospholipids, plasma membrane, stele, sterols     

Stress tolerance in the marsh plant Spartina patens: Impact of NaCl on growth and root plasma membrane lipid composition

The C‐4 salt marsh grass, Spartina patens , thrives in the upper portion of the marsh where soil salinities may be equal to coastal seawater. Spartina patens was grown in hydroponic culture in a greenhouse at 0, 340, and 510 m M NaCl, and measured for growth, tissue cation content, and root plasma membrane (PM) lipid composition. From 0 to 340 and 510 m M , the shoot growth decreased, but root growth was not affected. The Na⁺ content increased in both shoots and roots when plants were grown in salt, while the shoots had a decreased K⁺ content and the roots had a decreased Ca²⁺ content. Spartina patens root plasma membrane was isolated with an aqueous polymer two‐phase system. The purity of the plasma membrane was verified with cytochemical tests on membrane enzyme markers. Plasma membrane lipids were stable relative to the membrane protein content. Molar percentages of sterols (including free sterols) and phospholipid decreased with increasing salinity. However, glycolipid showed a statistically significant increase in the total lipid as salinity in the medium was increased from 0 to 510 m M . Even at a salinity of 510 m M , the plasma membrane sterol/phospholipid ratio was unaffected by NaCl. When the plants were grown in NaCl media, the plasma membrane had a decreased phosphatidylcholine (PC) and phosphatidylethanolamine (PE) content, but the PC/PE ratios were not affected. The plasma membrane molar percentage of sitosterol in total free sterol increased when plants were grown in salt media. The predominant membrane fatty acids were C11 and C14, and the major unsaturated one was C14:1. An increase in growth medium salinity resulted in a decreased root plasma membrane fluidity.     

The relationship between plasma membrane lipid composition and physical-chemical properties. III. Detailed physical and biochemical analysis of fatty acid-substituted EL4 plasma membranes

Murine leukemia EL4 cells were modified by supplementation of culture media with fatty acids for 24 h. A plasma membrane-enriched fraction was prepared from substituted and normal cells. Analyses were performed to determine fatty acyl composition, phospholipid headgroup composition and cholesterol content. The two major membrane phospholipids, phosphatidylethanolamine (PE) and phosphatidylcholine (PC) were isolated by thin-layer chromatography and ESR measurements were done on liposomes prepared from these lipids as well as on the intact plasma membrane preparations. Slight perturbations in overall plasma membrane lipid composition were observed when EL4 cells were supplemented with a single exogenous fatty acid. This may be consistent with the idea that the incorporation of exogenous fatty acid induces compensatory changes in membrane lipid composition. On the other hand, we observed no significant difference in two ESR motional parameters between the unsubstituted control and various fatty acid-substituted plasma membranes. ESR measurements carried out on PE and PC liposomes derived from 17:0- and 18:2c-substituted membranes also failed to detect major differences between these liposomes and those made from normal EL4 phospholipids. In the case of liposomes prepared from 18:2t,-substituted membranes, the order parameter was significantly changed from the normal. However, the change was in opposite directions in PE and PC, perhaps accounting for the fact that no change parameter is seen in intact 18:2t-substituted plasma membrane. Measurements of order parameter (S) in mixed lipid vesicles showed that at up to 50 mol% mixture of a synthetic PC with plasma membrane PC, the value of S was only marginally different from that of the plasma membrane PC vesicles. We interpret these data as an indication that the two ESR parameters used are not sufficiently sensitive to detect changes due to modifications of the acyl chain composition of a complex biological membrane.     

A comparison of the influence of sterols on the specific activity of the H+-ATPases in isolated plasma membrane vesicles from oat, rye and rice shoots

Plasma membrane vesicles were extracted from the shoots of 10-day-old oat, rye and rice plants and incubated with either cholesterol, stigmasterol or a mixture of sitosterol ⁺ campesterol (60:40). After ascertaining that the sterol composition of the vesicles had been altered by this treatment, the specific hydrolytic activity of the membrane-bound H⁺-ATPase (EC 3. 6. 1. 35) was measured. The results indicated that, although all sterols were taken up, cholesterol was best integrated into the plasma membrane of the species tested. After treatment, ATPase activity was altered in oat and rice, but not in rye. The results are discussed in the context of sterol/lipid and sterol/protein interactions in the plasma membrane.     

Greening-related lipid changes in leaves,protoplasts and a plasmamembrane-enriched fraction of pea

Light-induced changes in the membrane lipid compositions were studied in pea leaves and in protoplasts and a plasmamembrane-enriched fraction (PMEF)* of pea leaves. PC, PE, PI, PG, PA, MGDG, DGDG and SL were identified as the glycerolipids. The relative levels of various membrane lipids changed due to light-induced greening. There was an increase in the galactolipids of leaves and leaf protoplasts. The galactolipid constituent of the PMEF was very low and showed no change. Among the plasmamembrane phospholipids, PI increased with a concomitant decrease in PC.     

Pathway for the synthesis of triacylglycerols from monogalactosyldiacylglycerols in ozone-fumigated spinach leaves

When the upper leaf surface of spinach (Spinacia oleracea L.) plants was treated with [1-(14)C]acetate and grown for 2 days, (14)C was effectively incorporated into acyl moieties of leaf lipids in ratios approximately their composition by mass. Fumigation of the plants with ozone (0.5 microliter per liter) caused a redistribution of (14)C among lipid classes, i.e. a marked increase of (14)C content in triacylglycerol (TG) and 1,2-diacylglycerol (1,2-DG) and a decrease of label in monogalactosyldiacylglycerol (MGDG) without affecting (14)C distribution in leaf fatty acids. Label in both TG and 1,2-DG was found predominantly in their polyene molecular species. Since MGDG consists of similar polyene molecular species, the results indicate the synthesis of TG from MGDG via 1,2-DG. Label was also accumulated in tri- and tetragalactosyldiacylglycerol, products of galactolipid:galactolipid galactosyltransferase (GGGT). Moreover, there was a close relation between increases in the amounts of TG and the oligogalactolipids in ozonetreated leaves. These results indicate that MGDG was converted to 1,2-DG by GGGT and then to TG. In intact chloroplasts isolated from ozone-treated leaves, there was an enhanced production of free fatty acid (FFA), which was diminished by the addition of coenzyme A (CoA) and ATP, indicating that ozone stimulated the hydrolysis of MGDG to liberate FFA, which was in turn converted to acyl-CoA. The final step of TG synthesis, acylation of 1,2-DG with acyl-CoA, was confirmed by feeding with [1-(14)C]linolenic acid in leaf discs excised from ozone-fumigated leaves; (14)C was effectively incorporated into TG but not into 1,2-DG. These results demonstrate the synthesis of TG from 1,2-DG and FFA which were liberated from MGDG in ozone-fumigated spinach leaves.     

Lipid composition of plasma membranes isolated from light-grown barley (Hordeum vulgare) leaves: identification of cerebroside as a major component

The total lipid composition of highly purified plasma membranes from light-grown barley (Hordeum vulgare) leaves was investigated. The plasma membranes were separated from intracellular membranes by subfractionation of the microsomal fraction using aqueous polymer two-phase partitioning. A novel finding was that glucocerebroside was a major lipid of the plasma membrane (23 mol%). The most abundant lipid class in the plasma membrane was phospholipid (42 mol%), consisting mainly of phosphatidylcholine and phosphatidylethanolamine, together with free sterols at a level of 28 mol%. The only free sterols of the plasma membrane were campesterol (15%), stigmasterol (23%), and sitosterol (62%). The plasma membrane contained a relatively high proportion of saturated fatty acids compared to the bulk of intracellular membranes, the major components of the plasma membrane being palmitic (16:0), linoleic (18:2), and linolenic (18:3) acids in approximately equal amounts.     

植物在缺钾胁迫中膜稳定性的变化

植物维持膜的功能是其抵御胁迫的关键问题,而维持膜功能必须要保持膜的稳定性和合适的流动性。我们前期的研究发现植物主要是通过积累叶片膜脂和保持根部膜脂基本不变来适应长期缺钾。在本研究中,以拟南芥和其具有耐受缺钾胁迫特性的近缘种须弥芥为对象,研究了与膜的流动性密切相关的双键指数（double bond index,DBI）的变化,发现长期缺钾条件下,两种植物叶片中总的DBI保持不变,根部总的DBI略有降低。同时研究了与膜稳定性密切相关的溶血磷脂的含量和DGDG/MGDG以及PC/PE这两个比值的变化,发现长期缺钾后拟南芥和须弥芥叶片中溶血磷脂的总量呈上升趋势,根部溶血磷脂总量基本保持不变;无论在对照还是缺钾条件下,拟南芥溶血磷脂的总含量要高于须弥芥。须弥芥叶片具有更高的DGDG/MGDG值,根部具有更高的PC/PE值,说明长期缺钾条件下须弥芥膜的稳定性可能更好。这可能是须弥芥耐缺钾的原因之一。     

Changes of Membrane Stability in Potassium Stressed Plants

The maintenance of membrane function is critical to the ability of plants to resist environmental stresses; specifically, the stability and appropriate fluidity of membranes are crucial to their normal function. We previously demonstrated that plants adapt to long term potassium (K+) deficiency by accumulation of membrane lipids in leaves and maintenance of the lipid composition in roots. In this study, which involved Arabidopsis thaliana and its K+ deficiency tolerant relative Crucihimalaya himalaica, we first calculated the double bond index (DBI) as an indicator of membrane fluidity. After exposure to long term K+ deficiency stress, the DBI of the total lipids in leaves of Athaliana and Chimalaica showed no significant changes, whereas the DBI of the total lipids in the roots of these species showed slight increases. Changes in lysophospholipids (lysoPLs) levels, and digalactosyldiacylglycerol/monogalactosyldiacylglycerol (DGDG/MGDG) and phosphatidylcholine/phosphatidylethanolamine (PC/PE) ratios, all of which strongly reflect membrane stability, were also studied in K+ stressed Athaliana and Chimalaica. After long term K+ deficiency, total lysoPLs levels increased in Athaliana and Chimalaica leaves, but showed no significant changes in roots. DGDG/MGDG and PC/PE ratios were higher in Chimalaica leaves and roots than in those of Athaliana. These results indicate that Chimalaica exhibits superior membrane stability compared with Athaliana. This may explain its superior growth and tolerance under K+ deficient conditions.     

Changes in plasma-membrane lipid composition: a strategy for acclimation to copper stress

Wheat seedlings were grown hydroponically in the presence of 50 microM Cu2+. The copper stress resulted in plasma-membrane (PM) changes of the root cells as altered lipid composition, a decreased phosphatidylcholine (PC)/phosphatidylethanolamine (PE) ratio from 0.7 to 0.3, a decreased fatty acyl unsaturation and a decrease in the lipid/protein ratio. Membrane vesicles made from total lipid extracts of isolated PMs of wheat grown under copper excess showed a remarkably low permeability to polar molecules like glucose, as compared with the control, and no difference in proton permeability. Permeability studies of vesicles of plasma-membrane lipids, which were selectively modified by addition of specific lipids such as PC and PE, were also performed. The results are discussed with emphasis on the role of the increased PE proportion.     

Permeability behaviour of lipid vesicles prepared from plant plasma membranes--impact of compositional changes

Exposure of oat seedlings to repeated moderate water deficit stress causes a drought acclimation of the seedlings. This acclimation is associated with changes in the lipid composition of the plasma membrane of root cells. Here, plasma membranes from root cells of acclimated and control plants were isolated using the two-phase partitioning method. Membrane vesicles were prepared of total lipids extracted from the plasma membranes. In a series of tests the vesicle permeability for glucose and for protons were analysed and compared with the permeability of model vesicles. Further, the importance of critical components for the permeability properties was analysed by modifying the lipid composition of the vesicles from acclimated and from control plants. The purpose was to add specific lipids to vesicles from acclimated plants to mimic the composition of the vesicles from control plants and vice versa. The plasma membrane lipid vesicles from acclimated plants had a significantly increased permeability for glucose and decreased permeability for protons as compared to control vesicles. The results point to the importance of the ratio phosphatidylcholine (PC)/phosphatidylethanolamine (PE), the levels of cerebrosides and free sterols and the possible interaction of these components for the plasma membrane as a permeability barrier.     

Modification of the root plasma membrane lipid composition of cadmium-treated Pisum sativum

The effects of in vivo Cd treatments on pea root plasma membrane(PM) lipid composition were studied. In the long-term experiment,plants were supplied with Cd: moderate stress (10 µM)or strong stress (50 µM) for 10 d. Growth of root andshoot was severely affected in 50 µM Cd-treated plants,as evidenced by the approximately 7-fold reduction in theirRelative Growth Increment (RGI). Treatment with Cd (10 µM)resulted in changes to the lipid composition of the pea rootPM, including increases in the degree of unsaturation of phospholipid-associatedfatty acids and in the relative amount of stigmasterol (30–42%).This change was accompanied by a reduction in sitosterol content(26.8 to 17.4 µg mg^–1 protein). However, the sterolcomposition was not altered in plants treated with 50 µMCd for 10 d. The content of phosphatidylethanolamine and phosphatidylcholine(major phospholipids present in pea root PM) decreased as Cdlevel increased, but the ratio between them remained unaffected.In the short-term experiment, plants exposed to Cd (50 µM)accumulated less sitosterol (from 27.7 to 14.0 µg g mg^–1protein) over 72 h, but no significant effect on other measuredlipids was observed. The physiological repercussions of changesin plasma membrane lipid composition, as a result of Cd exposureare discussed. Key words: Cadmium, lipids, pea, Pisum sativum, plasma membranes     

Lipid Composition of Citrus Leaves from Plants Resistant and Susceptible to Citrus Bacterial Canker

The contents and composition of lipids in citrus leaves in relation to their general resistance to infection by strains of Xanthomonas campestris pv. citri (Xcc) were determined. The composition and contents of total polar lipids and phospholipids and the degree of fatty acid unsaturation were significantly different between resistant and susceptible species. Leaves from resistant plants had less phospholipids, but more free sterols than those from susceptible plants. The predominant fatty acids in the phospholipids were palmitic (16:0), linoleic (18:2) and α-linolenic acid (18:3). The degree of fatty acid unsaturation was higher in susceptible plants than in resistant plants. Major phospholipids in citrus leaves were phosphatidylchloline (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and phosphatidylinositol (PI). β-Sitosterol, campesterol and lanosterol were major sterols in the leaves of citrus plants with resistant species having a higher ratio of free sterols to total phospholipids than susceptible species. Differences in lipid metabolism may contribute to differences in Xcc-resistance of citrus leaves.     

Interaction of the polyene antibiotic filipin with model and natural membranes containing plant sterols

The interaction of the polyene antibiotic, filipin, with individual or mixed plant sterols (stigmasterol, sitosterol, campesterol and 24-methylpollinastanol) incorporated into large unilamellar vesicles (LUV) of soybean phosphatidylcholine (PC) as well as the filipin interaction with purified membrane fractions from maize roots containing these sterols was investigated by ultraviolet (UV) absorption and and circular dichroism (CD) spectroscopy. With both types of membrane preparation, dramatic changes in the UV absorption and CD spectra of the antibiotic were evidenced. When LUV containing stigmasterol, sitosterol and/or campesterol were incubated with low filipin concentrations (i.e., for filipin/sterol molar ratios (rst) lower than 1), CD signal characteristic of the formation of filipin-sterol complexes were observed. At higher rst values, the filipin-sterol interaction was shown to be in competition with a filipin-phospholipid interaction. With 24-methylpollinastanol-containing LUV, the filipin-phospholipid interaction was detected even at rst values lower than 1, which suggests a lower affinity of filipin for this sterol and emphasizes the structural differences between delta 5-sterols and 9 beta,19-cyclopropylsterols. With sterol-free soybean PC LUV, a filipin-phospholipid interaction could also be evidenced. With maize root cell membranes containing either delta 5-sterols or 9 beta,19-cyclopropylsterols, CD spectra similar to those obtained in the presence of LUV having these sterols as components were observed. Thus, the protein component of the membranes does not appear to be an important feature.     

The response of plasma membrane lipid composition in callus of the halophyte Spartina patens (Poaceae) to salinity stress

Callus cultures of the salt marsh grass Spartina patens were examined to determine changes and consistencies in membrane lipid composition in response to salt. Major membrane lipid classes remained stable at all salinity levels (0, 170, 340 mmol/L). However, the membrane protein to lipid ratio decreased significantly in response to elevated NaCl. Callus plasma membrane (PM) consisted predominantly of sterols, about 60% (mol%) of the total lipids. Glycolipid was the second largest lipid class, making up about 20% (mol%) of the total. With increasing salinity, the relative percentage of sitosterol decreased, while that of campesterol increased. The phospholipid species detected were phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylinositol (PI). When callus was grown at 340 mmol/L NaCl, PC increased significantly. PI and PS were also significantly elevated in salinity treatments. Only 24-32% of the PM fatty acids were common plant membrane fatty acids, C16, C18, C20, and C22, while over 60% were the less common fatty acids, C11 and C14. Membrane fluidity remained stable in response to growth medium salinity. The findings on membrane responses to salinity will facilitate a better understanding of this halophyte's tactics for salt tolerance.