Changes In Membrane Lipid Composition Research Articles

Tolerance to Changes in Membrane Lipid Composition as a Selected Trait of Membrane Proteins

Membrane lipid composition can vary dramatically across the three domains of life and even within single organisms. Here we review evidence that the lipid-exposed surfaces of membrane proteins have generally evolved to maintain correct structure and function in the face of major changes in lipid composition. Such tolerance has allowed evolution to extensively remodel membrane lipid compositions during the emergence of new species without having to extensively remodel the associated membrane proteins. The tolerance of membrane proteins also permits single-cell organisms to vary their membrane lipid composition in response to their changing environments and allows dynamic and organelle-specific variations in the lipid compositions of eukaryotic cells. Membrane protein structural biology has greatly benefited from this seemingly intrinsic property of membrane proteins: the majority of structures determined to date have been characterized under model membrane conditions that little resemble those of native membranes. Nevertheless, with a few notable exceptions, most experimentally determined membrane protein structures appear, to a good approximation, to faithfully report on native structure.

Longevity, lipids and C. elegans

Longevity, lipids and C. elegans

Abeta Peptide Toxicity is Reduced After Treatments Decreasing Phosphatidylethanolamine Content in Differentiated Neuroblastoma Cells

We investigated whether the toxicity of oligomeric amyloid-beta peptide (Abeta1-42) upon differentiated human neuroblastoma SH-SY5Y cells, can be affected by changes of membrane lipid composition. An immunostaining technique, using lipids extracted from the cells and separated by thin layer chromatography, suggested that Abeta preferentially binds to phosphatidylethanolamine (PE), one of the major lipids in the cell extract. For this reason, we utilized treatments with putative inhibitors of phosphatidylethanolamine biosynthesis (choline, phosphocholine, R59949) to decrease its proportion in the cell membrane; choline treatment (2.5mM, 24h) showed the best performance, reducing phosphatidylethanolamine content from 5.7 to 3.3μg phosphorous/mg protein. Either the extent of Abeta binding or its toxicity decreased onto choline-treated cells. These data may open the possibility to develop future strategies aiming to reduce Abeta toxicity in Alzheimer disease.

Effect of growth temperature on yeast lipid composition and alcoholic fermentation at low temperature

The loss of viability of wine yeast strains due to low-temperature fermentations could be overcome by increasing their stress tolerance and adaptability. Changes in membrane lipid composition are one of the first responses to cold stress. The aim of this study was to analyze the various adaptation mechanisms to low temperatures by comparing the better adapted Saccharomyces species. The viability, vitality, fermentation capacity, and lipid composition of different Saccharomyces species (S. cerevisiae, S. bayanus, S. uvarum, and a hybrid S. cerevisiae/S. uvarum) with different fermentative origins (wine, beer, and baker’s strains together with a laboratory strain) were compared after culturing at low (13 °C) and optimal (25 °C) temperatures. In spite of specific responses of the different strains/species, the results showed that at low temperature, the medium-chain fatty acid and the triacylglyceride content increased, whereas the phosphatidic acid content and the phosphatidylcholine/phosphatidylethanolamine ratio decreased. Only the laboratory strain was not able to ferment the sugars, and after growing at both temperatures, its lipid composition was very different from that of the other strains. The hybrid strain showed the highest sugar consumption at 13 °C and the best vitality whatever the preculture temperature used. The rest of the species needed a preadaptation at low temperature involving a change in their lipid composition to improve their fermentation rate at 13 °C.

Arachidonic Acid: An Evolutionarily Conserved Signaling Molecule Modulates Plant Stress Signaling Networks

Fatty acid structure affects cellular activities through changes in membrane lipid composition and the generation of a diversity of bioactive derivatives. Eicosapolyenoic acids are released into plants upon infection by oomycete pathogens, suggesting they may elicit plant defenses. We exploited transgenic Arabidopsis thaliana plants (designated EP) producing eicosadienoic, eicosatrienoic, and arachidonic acid (AA), aimed at mimicking pathogen release of these compounds. We also examined their effect on biotic stress resistance by challenging EP plants with fungal, oomycete, and bacterial pathogens and an insect pest. EP plants exhibited enhanced resistance to all biotic challenges, except they were more susceptible to bacteria than the wild type. Levels of jasmonic acid (JA) were elevated and levels of salicylic acid (SA) were reduced in EP plants. Altered expression of JA and SA pathway genes in EP plants shows that eicosapolyenoic acids effectively modulate stress-responsive transcriptional networks. Exogenous application of various fatty acids to wild-type and JA-deficient mutants confirmed AA as the signaling molecule. Moreover, AA treatment elicited heightened expression of general stress-responsive genes. Importantly, tomato (Solanum lycopersicum) leaves treated with AA exhibited reduced susceptibility to Botrytis cinerea infection, confirming AA signaling in other plants. These studies support the role of AA, an ancient metazoan signaling molecule, in eliciting plant stress and defense signaling networks.

PUFAs enhance oxidative stress and apoptosis in tumour cells exposed to hypericin-mediated PDT

Since many studies have suggested the impact of dietary polyunsaturated fatty acids on cancer progression and prognosis, there is an assumption of possible pre-sensitizing effects of their application in combined treatment. The present work evaluates modulation of photodynamic therapy (PDT) with hypericin by pre-treatment with n-3 and n-6 fatty acids in HT-29 and HeLa tumour cells. We observed stimulation of cytotoxic effects by docosahexaenoic acid (n-3) and arachidonic acid (n-6) in several stages of action in both cell lines. Treatment with either fatty acids or photodynamic therapy alone induced apoptosis in a dose- and time-dependent manner; however the effect was even more striking in mutual combination applied as pre-treatment with fatty acids prior to photodynamic therapy. Moreover, the combination also induced changes in membrane lipid composition leading to alteration in cell membrane fluidity. Increased toxicity of combined treatment was also confirmed by the presence of oxidative stress demonstrated by ROS production, RNS accumulation and increased presence of lipoperoxides. In conclusion, we suggest that pre-treatment with polyunsaturated fatty acids may contribute to cytotoxic effects induced by photodynamic therapy with hypericin.

家族性lecithin:cholesterol acyltransferase欠損症の一例

Lecithin: cholesterol acyltransferase (LCAT) is an enzyme that catalyzes the esterifying reaction of cholesterol in plasma high density lipoprotein (HDL). Deficiency of LCAT is a rare hereditary disease characterized by several clinical symptoms such as proteinuria, corneal opacity, and anemia due to a shortened life span of erythrocytes. In this communication, we report a case of 40 year-old female patient of LCAT deficiency. She visited a hospital for work-up of proteinuria, corneal opacity and anemia. Activity of her serum LCAT was found to be extremely low, and characteristic changes in plasma lipids due to deficiency of LCAT was observed: those were marked decreases in HDL-cholesterol, degree of esterification in serum cholesterol, and apoprotein A-I, A-II, B and C-II levels. The diagnosis of LCAT deficiency was finally made. We studied about histopathological changes in the patient's kidney, and erythrocyte membrane lipid composition and fluidity. Histopathological findings in renal biopsy were follows: a) Light microscopy showed spherical deposits stained with periodic acid-Schiff in mesangial matrix and adjacent capillary loops, and hyaline deposits in arterioles, b) Electron microscopy showed vacuoles in mesangial matrix and along the glomerular basement membranes. In erythrocyte membrane lipids, increase of cholesterol to phospholipid molar ratio was evident, being accompanied by changes in phospholipid fractions: increase of phosphatidylcholine, and decreases of phosphatidylethanolamine, sphingomyelin and lysophosphatidylcholine. In phospholipid acyl chains, increase of C18:2 and decreased of C18:1 were evident in the patient. Erythrocyte membrane fluidity was found to be decreased in the patient in a measurement by pyrene, probably being related to the changes in membrane lipid composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cholesterol-loaded cyclodextrin during freezing step of cryopreservation with TCGY extender containing bovine serum albumin on quality of goat spermatozoa

The susceptibility of mammalian spermatozoa to cold shock and freezing damage is due to changes in membrane lipid composition, particularly cholesterol depletion in plasma membrane during cryopreservation. The aim of this study was to investigate the effects of different concentrations of cholesterol-loaded cyclodextrin (CLC) and bovine serum albumin (BSA) on the cryopreservation of goat spermatozoa in tris-citrate egg yolk extender. Semen was collected from four mature goats and divided into seven aliquots prior to cryopreservation. The first aliquot remained untreated and was mixed with TCG, the second aliquot was mixed with TCG and egg yolk (TCGY), third aliquot was mixed with TCGY and 2.5% BSA (TCGYB) and other aliquots were mixed with TCGYB containing 0.75, 1.5, 2.5 and 3 mg/ml CLC. All samples were cryopreserved in straws over liquid nitrogen vapor and sperm motion Kinetics were measured by computer-assisted semen analysis (CASA) (percent motility (MOT), curvilinear velocity (VCL), straight-line velocity (VSL), average path velocity (VAP), linearity (LIN), and amplitude of lateral head displacement (ALH)). Acrosome status and vitality was observed by the triple-stain technique. CLC addition to extender resulted in significant ( p < 0.05) enhancement of MOT, STR, and VCL of post-thawing sperm. Post-thawed motility, progressive motility and recovery rate were significantly ( p < 0.05) higher in 1.5 mg/ml CLC with 2.5% BSA in TCGY extender compared to other groups. The 1.5 CLC sperm yielded a significant increase in percentage of spermatozoa with intact acrosome ( P > 0.05). These results indicate that treating goat sperm with CLC and BSA in TCGY extender improved motility and vitality after freezing and thawing.

Altered lipid content inhibits autophagic vesicular fusion

The autophagic/lysosomal system includes a variety of vesicular compartments that undergo dynamic fusion events. However, the characteristics and factors modulating these interactions remain, for the most part, unknown. To gain insights on the properties that govern lysosomal fusion events, we have established an in vitro fusion assay using different lysosomal/autophagic compartments isolated from mouse liver. We have found that autophagosome/lysosome fusion is a temperature-dependent process (fusion increment of 0.2+/-0.01%/degrees C), which requires ATP (1-3 mM), GTP (1-2 mM), Ca(2+) (0.2-2 mM), and an acidic lysosomal pH (pH 5.2). Furthermore, changes in membrane lipid composition, induced either in vitro, by treatment with 25 mM methyl-beta-cyclodextrin, or in vivo, by subjecting animals to a high-fat-diet challenge (60% kcal in fat) reduce autophagosome/lysosome fusion up to 70% of that observed in untreated fractions or from animals under a normal regular diet. These findings reveal a novel role for lipids in autophagic fusion and provide a mechanism for the reduced macroautophagic rates observed during exposure to a chronic lipid challenge. Changes in the intracellular lipid content (i.e., metabolic disorders) may thus have pronounced effects on the fusion step of macroautophagy and affect the overall activity of this intracellular proteolytic pathway.

Running the hypothesis of a bio molecular approach to psychiatric disorder characterization and fatty acids therapeutical choices

Beyond the conviction that Major Depression can found its origin in genetics [1-3] a bio molecular mechanism could be hypothesized from what emerged from the studies on platelets fatty acid composition in human (normal and depressive subjects) which allowed classifying the depressive disorder [4] using an Artificial Neural Network (Self Organizing Map-SOM) [5], as mathematical tool, because of the complexity of the membrane dynamics. Rapid changes in membrane lipid composition or in the cytoskeleton could modify neuronal signalling. In the knowledge to have found something that could have implications in the understanding of some aspects of psychiatric disorders and a very suggestive hypothesis was build as summarized in Figure ​Figure1.1. In figure ​figure11 is described the molecular depression hypothesis made according to Cocchi and collegues [4], Donati and collegues [6], Hameroff and Penrose [7]. The membrane viscosity can modify the Gsα protein status. The Gsα protein is connected with Tubulin. Tubulin, depending on local membrane lipid fase concentration, may serve as a positive or negative regulator of phosphatidylinositol bisphosphate (PIP2) hydrolysis, such as Gsα protein does. Tubulin is known to form high-affinity complexes with certain G proteins. The formation of such complexes allows tubulin to activate Gsα, which, in turn, can activate the Protein Kinase C and fosters a system whereby elements of the cytoskeleton can influence G-protein signalling. Rapid changes in membrane lipid composition or in the cytoskeleton might modify neuronal signalling. We have hypothesized that through this mechanism is possible to modify the consciousness state and that it is mesurable through gamma syncrony EEG. Figure 1 The molecular depression hypothesis. There are strong reasons to think that each fatty acid combination of Palmitic Acid (PA), Linoleic Acid (LA) and Arachidonic Acid (AA), in platelet, is responsible of the membrane viscosity and, therefore, of the molecular conditioning of the cellular stuctures (Gsα and Tubulin) and that the main therapeutic target is the reduction of the Arachidonic Acid.

Rapid Cold Hardening in Drosophila requires MAPK signaling

Increasing evidence supports the hypothesis that rapid cold hardening (RCH) protects insects in nature. However, the cellular/biochemical mechanisms of RCH remain unclear. In Sarcophaga crassipalpis RCH involves accumulation of glycerol and Mitogen Activated Protein Kinase (MAPK) signaling pathways. For Drosophila melanogaster RCH correlates with changes in membrane lipid composition, but does not appear to involve the production of low‐molecular weight cryoprotectants. The present study utilized a pharmacological approach to determine whether RCH in D. melanogaster involves MAPK signaling. Rearing D. melanogaster on yeast paste containing the MAPK inhibitor SB203580 for 2 days following eclosion impaired their ability to rapidly cold harden (evaluated as resistance to mortality caused by cold shock injury), in a dose dependent manner. These data suggest that MAPK signaling is important to RCH in D. melanogaster.

Insect overwintering in a changing climate

Insects are highly successful animals inhabiting marine, freshwater and terrestrial habitats from the equator to the poles. As a group, insects have limited ability to regulate their body temperature and have thus required a range of strategies to support life in thermally stressful environments, including behavioural avoidance through migration and seasonal changes in cold tolerance. With respect to overwintering strategies, insects have traditionally been divided into two main groups: freeze tolerant and freeze avoiding, although this simple classification is underpinned by a complex of interacting processes, i.e. synthesis of ice nucleating agents, cryoprotectants, antifreeze proteins and changes in membrane lipid composition. Also, in temperate and colder climates, the overwintering ability of many species is closely linked to the diapause state, which often increases cold tolerance ahead of temperature-induced seasonal acclimatisation. Importantly, even though most species can invoke one or both of these responses, the majority of insects die from the effects of cold rather than freezing. Most studies on the effects of a changing climate on insects have focused on processes that occur predominantly in summer (development, reproduction) and on changes in distributions rather than winter survival per se. For species that routinely experience cold stress, a general hypothesis would be that predicted temperature increases of 1 degree C to 5 degrees C over the next 50-100 years would increase winter survival in some climatic zones. However, this is unlikely to be a universal effect. Negative impacts may occur if climate warming leads to a reduction or loss of winter snow cover in polar and sub-polar areas, resulting in exposure to more severe air temperatures, increasing frequency of freeze-thaw cycles and risks of ice encasement. Likewise, whilst the dominant diapause-inducing cue (photoperiod) will be unaffected by global climate change, higher temperatures may modify normal rates of development, leading to a decoupling of synchrony between diapause-sensitive life-cycle stages and critical photoperiods for diapause induction. In terms of climate warming and potential heat stress, the most recent predictions of summer temperatures in Europe of 40 degrees C or higher in 50-75 years, are close to the current upper lethal limit of some insects. Long-term data sets on insect distributions and the timing of annual migrations provide strong evidence for 'positive' responses to higher winter temperatures over timescales of the past 20-50 years in North America, Europe and Asia.

Stress-Induced Changes of Phospholipids in Betaproteobacterium Aromatoleum aromaticum Strain EbN1 due to Alkylbenzene Growth Substrates

The denitrifying betaproteobacterium strain EbN1 degrades toluene and ethylbenzene under anoxic conditions. Alkylbenzenes are unusual substrates, since their extraordinary chemical stability necessitates complex reactions and their toxic properties as solvents challenge cellular viability. To study the solvent impact on membrane lipid composition, strain EbN1 was grown at low, standard and semi-inhibitory concentrations of toluene (70, 240, and 740 µM) and ethylbenzene (80, 210, and 315 µM). At semi-inhibitory concentrations, phosphatidylglycerol increased at the expense of phosphatidylethanolamine. Moreover, phosphatidylcholine proportions increased and tentatively identified N-hexanoyl-phosphatidylethanolamine was detected. All observed changes in membrane lipid composition are interpreted as the organism’s response to prevent the maceration of the cell membrane.

Cholesterol efflux stimulates metalloproteinase-mediated cleavage of occludin and release of extracellular membrane particles containing its C-terminal fragments

That changes in membrane lipid composition alter the barrier function of tight junctions illustrates the importance of the interactions between tetraspan integral tight junction proteins and lipids of the plasma membrane. Application of methyl-β-cyclodextrin to both apical and basolateral surfaces of MDCK cell monolayers for 2 h, results in an ∼80% decrease in cell cholesterol, a fall in transepithelial electrical resistance, and a 30% reduction in cell content of occludin, with a smaller reduction in levels of claudins-2, -3, and -7. There were negligible changes in levels of actin and the two non-tight junction membrane proteins GP-135 and caveolin-1. While in untreated control cells breakdown of occludin, and probably other tight junction proteins, is mediated by intracellular proteolysis, our current data suggest an alternative pathway whereby in a cholesterol-depleted membrane, levels of tight junction proteins are decreased via direct release into the intercellular space as components of membrane-bound particles. Occludin, along with two of its degradation products and several claudins, increases in the basolateral medium after incubation with methyl-β-cyclodextrin for 30 min. In contrast caveolin-1 is detected only in the apical medium after adding methyl-β-cyclodextrin. Release of occludin and its proteolytic fragments continues even after removal of methyl-β-cyclodextrin. Sedimentation and ultrastructural studies indicate that the extracellular tight junction proteins are associated with the membrane-bound particles that accumulate between adjacent cells. Disruption of the actin filament network by cytochalasin D did not diminish methyl-β-cyclodextrin-induced release of tight junction proteins into the medium, suggesting that the mechanism underlying their formation is not actin-dependent. The 41- and 48-kDa C-terminal occludin fragments formed during cholesterol depletion result from the action of a GM6001-sensitive metalloproteinase(s) at some point in the path leading to release of the membrane particles.

Metabolic depression during aestivation does not involve remodelling of membrane fatty acids in two Australian frogs

Changes in membrane lipid composition (membrane remodelling) have been associated with metabolic depression in some aestivating snails but has not been studied in aestivating frogs. This study examined the membrane phospholipid composition of two Australian aestivating frog species Cyclorana alboguttata and Cyclorana australis. The results showed no major membrane remodelling of tissue in either frog species, or in mitochondria of C. alboguttata due to aestivation. Mitochondrial membrane remodelling was not investigated in C. australis. Where investigated in C. alboguttata, total protein and phospholipid content, and citrate synthase (CS) and cytochrome c oxidase (CCO) activities in tissues and mitochondria mostly did not change with aestivation in liver. In skeletal muscle, however, CS and CCO activities, mitochondrial and tissue phospholipids, and mitochondrial protein decreased with aestivation. These decreases in muscle indicate that skeletal muscle mitochondrial content may decrease during aestivation. Na(+)K(+)ATPase activity of both frog species showed no effect of aestivation. In C. alboguttata different fat diets had a major effect on both tissue and mitochondrial phospholipid composition indicating an ability to remodel membrane composition that is not utilised in aestivation. Therefore, changes in lipid composition associated with some aestivating snails do not occur during aestivation in these Australian frogs.

Expression and Activity of SGLT2 in Diabetes Induced by Streptozotocin: Relationship with the Lipid Environment

Background/Aims: Diabetes mellitus may impact on the regulation of renal Na⁺-glucose cotransporter type 2 (SGLT2), however, previous studies have yielded conflicting results on the effects of streptozotocin (STZ)-induced diabetes on SGLT-mediated glucose transport. Methods: Diabetes was induced in male Wistar rats. The studies were performed at 3 (D3), 7 (D7) and 14 (D14) days after a single i.p. injection of STZ. SGLT2 activity was measured using α-¹⁴C-methyl glucose uptake in brush-border vesicles (BBV) from renal cortex, and SGLT2 expression was assessed by immunoblotting. Phospholipids were quantified by a modification of Fiske-Subarow‘s method after being separated by thin-layer chromatography. Results: Glucose uptake was reduced in all groups of diabetic rats. SGLT2 expression decreased in D3 and D7. There was a decrease in sphingomyelin (SM) content and an increase in phosphatidylcholine (PC) content in BBV from D14 versus control, without differences in phosphatidylinositol (PI), phosphatidylserine (PS) and phosphatidylethanolamine (PE). Conclusion: The downregulation of SGLT2 activity during STZ-induced diabetes may be a protective mechanism to control the excess of circulating glucose and could be a consequence of a decrease in SGLT2 expression in D3 and D7, whereas altered activity of SGLT2 in D14 could be a consequence of changes in membrane lipid composition. However, we cannot discard the possibility that the decrease in SGLT2 activity could be due to a covalent modification of the active site of the protein.

Changes in membrane lipid composition in ethanol- and acid-adapted Oenococcus oeni cells: characterization of the cfa gene by heterologous complementation

Cyclopropane fatty acid (CFA) synthesis was investigated in Oenococcus oeni. The data obtained demonstrated that acid-grown cells or cells harvested in the stationary growth phase showed changes in fatty acid composition similar to those of ethanol-grown cells. An increase of the CFA content and a decrease of the oleic acid content were observed. The biosynthesis of CFAs from unsaturated fatty acid phospholipids is catalysed by CFA synthases. Quantitative real-time-PCR experiments were performed on the cfa gene of O. oeni, which encodes a putative CFA synthase. The level of cfa transcripts increased when cells were harvested in stationary phase and when cells were grown in the presence of ethanol or at low pH, suggesting transcriptional regulation of the cfa gene under different stress conditions. In contrast to Escherichia coli, only one functional promoter was identified upstream of the cfa gene of O. oeni. The function of the cfa gene was confirmed by complementation of a cfa-deficient E. coli strain. Nevertheless, the complementation remained partial because the conversion percentage of unsaturated fatty acids into CFA of the complemented strain was much lower than that of the wild-type strain. Moreover, a prevalence of cycC19 : 0 was observed in the membrane of the complemented strain. This could be due to a specific affinity of the CFA synthase from O. oeni. In spite of this partial complementation, the complemented strain of E. coli totally recovered its viability after ethanol shock (10 %, v/v) whereas its viability was only partly recovered after an acid shock at pH 3.0.

Differential Degradation of Extraplastidic and Plastidic Lipids during Freezing and Post-freezing Recovery in Arabidopsis thaliana

Changes in membrane lipid composition play important roles in plant adaptation to and survival after freezing. Plant response to cold and freezing involves three distinct phases: cold acclimation, freezing, and post-freezing recovery. Considerable progress has been made toward understanding lipid changes during cold acclimation and freezing, but little is known about lipid alteration during post-freezing recovery. We previously showed that phospholipase D (PLD) is involved in lipid hydrolysis and Arabidopsis thaliana freezing tolerance. This study was undertaken to determine how lipid species change during post-freezing recovery and to determine the effect of two PLDs, PLDalpha1 and PLDdelta, on lipid changes during post-freezing recovery. During post-freezing recovery, hydrolysis of plastidic lipids, monogalactosyldiacylglycerol and plastidic phosphatidylglycerol, is the most prominent change. In contrast, during freezing, hydrolysis of extraplastidic phospholipids, phosphatidylcholine and phosphatidylethanolamine, occurs. Suppression of PLDalpha1 decreased phospholipid hydrolysis and phosphatidic acid production in both the freezing and post-freezing phases, whereas ablation of PLDdelta increased lipid hydrolysis and phosphatidic acid production during post-freezing recovery. Thus, distinctly different changes in lipid hydrolysis occur in freezing and post-freezing recovery. The presence of PLDalpha1 correlates with phospholipid hydrolysis in both freezing and post-freezing phases, whereas the presence of PLDdelta correlates with reduced lipid hydrolysis during post-freezing recovery. These data suggest a negative role for PLDalpha1 and a positive role for PLDdelta in freezing tolerance.

Regulation of desaturase gene expression, changes in membrane lipid composition and freezing tolerance in potato plants

Irreversible damage of the plant plasma membrane is the primary cause of freezing injury. Changes in lipid unsaturation have being largely studied as one of the major components aimed at preserving the integrity and functionality of plasma membranes, and increasing freezing tolerance. In the present study, the potato stearoyl-ACP desaturase (ω-9) gene, encoding the first enzyme involved in plant lipid unsaturation, was cloned and used to monitor its expression during cold acclimation in plants of two Solanum species, known to differ in their ability to cold acclimate. Although up-regulated upon cold acclimation in both potato species, freezing tolerant S. commersonii plants had a constitutive level of the ω-9 desaturase gene transcripts and of other known stress protective proteins (dhn2 and cpn60β) remarkably higher than plants of the not freezing tolerant potato species (S. tuberosum). Transcript levels of oleoyl-desaturase (ω-6) and linoleyl CoA desaturase (ω-3), microsomal desaturases involved in further plasma membrane fatty acid (FA) unsaturation, did not vary appreciably during cold acclimation in both potato species. S. tuberosum potato plants overexpressing the ω-9 desaturase gene were generated, to change FA lipid composition and measure the effect on the basal level freezing tolerance of cultivated potato varieties. Unsaturation level of total leaf polar lipids of one of best ω-9 desaturase overexpressing line, with a high transcript level of the exogenous gene and related protein, was slightly higher compared to potato plants transformed with the empty vector, with the notable appearance of cis-vaccenic acid (C18:1 Δ11), an unusual monoic FAs in plants. Freezing tolerance, estimated as an increase in LT50 (2°C), derived from the electrolyte leakage test, enhanced in ω-9 desaturase overexpressing transgenic potato plants only upon cold acclimation. These results indicate that modifications in lipid unsaturation account for only a small fraction of the acquired freezing tolerance, while interaction with other protective proteins (dhn2, cpn60β) is necessary to fulfil a higher level of freezing tolerance.

Changes in membrane lipid composition in azuki bean epicotyls under hypergravity conditions: Possible role of membrane sterols in gravity resistance

Seedlings of azuki bean ( Vigna angularis Ohwi et Ohashi) were cultivated under hypergravity conditions, and changes in membrane lipid composition in their epicotyls were analyzed. Under hypergravity conditions at 300 g, the levels of total sterols, phospholipids, and fatty acids per fresh weight were kept higher, as compared with 1 g controls. In particular, sterol levels were prominently increased by hypergravity. On the other hand, hypergravity did not clearly influence the levels of each phospholipid and glycolipid class, or their fatty acid compositions. Thus, the effect of hypergravity on membrane lipid metabolism was specific for sterol biosynthesis. In various regions of azuki epicotyls, high growth rate was associated with high sterol levels. Hypergravity suppressed elongation growth and stimulated lateral expansion of azuki epicotyls. In the presence of lovastatin, an inhibitor of sterol biosynthesis, at 30 μM, such changes in growth parameters occurred even under 1 g conditions, suggesting that lovastatin made epicotyls hypersensitive to the gravitational force. These results support the hypothesis that membrane sterols are involved in maintenance of normal growth capacity of plant organs against gravity.