Lipid dependence of diadinoxanthin solubilization and de-epoxidation in artificial membrane systems resembling the lipid composition of the natural thylakoid membrane

In the present study, the solubility and enzymatic de-epoxidation of diadinoxanthin (Ddx) was investigated in three different artificial membrane systems: (1) Unilamellar liposomes composed of different concentrations of the bilayer forming lipid phosphatidylcholine (PC) and the inverted hexagonal phase (H_II phase) forming lipid monogalactosyldiacylglycerol (MGDG), (2) liposomes composed of PC and the H_II phase forming lipid phosphatidylethanolamine (PE), and (3) an artificial membrane system composed of digalactosyldiacylglycerol (DGDG) and MGDG, which resembles the lipid composition of the natural thylakoid membrane. Our results show that Ddx de-epoxidation strongly depends on the concentration of the inverted hexagonal phase forming lipids MGDG or PE in the liposomes composed of PC or DGDG, thus indicating that the presence of inverted hexagonal structures is essential for Ddx de-epoxidation. The difference observed for the solubilization of Ddx in H_II phase forming lipids compared with bilayer forming lipids indicates that Ddx is not equally distributed in the liposomes composed of different concentrations of bilayer versus non-bilayer lipids. In artificial membranes with a high percentage of bilayer lipids, a large part of Ddx is located in the membrane bilayer. In membranes composed of equal proportions of bilayer and H_II phase forming lipids, the majority of the Ddx molecules is located in the inverted hexagonal structures. The significance of the pigment distribution and the three-dimensional structure of the H_II phase for the de-epoxidation reaction is discussed, and a possible scenario for the lipid dependence of Ddx (and violaxanthin) de-epoxidation in the native thylakoid membrane is proposed.     

The lipid dependence of diadinoxanthin de-epoxidation presents new evidence for a macrodomain organization of the diatom thylakoid membrane

The present study shows that thylakoid membranes of the diatom Cyclotella meneghiniana contain much higher amounts of negatively charged lipids than higher plant or green algal thylakoids. Based on these findings, we examined the influence of SQDG on the de-epoxidation reaction of the diadinoxanthin cycle and compared it with results from the second negatively charged thylakoid lipid PG. SQDG and PG exhibited a lower capacity for the solubilization of the hydrophobic xanthophyll cycle pigment diadinoxanthin than the main membrane lipid MGDG. Although complete pigment solubilization took place at higher concentrations of the negatively charged lipids, SQDG and PG strongly suppressed the de-epoxidation of diadinoxanthin in artificial membrane systems. In in vitro assays employing the isolated diadinoxanthin cycle enzyme diadinoxanthin de-epoxidase, no or only a very weak de-epoxidation reaction was observed in the presence of SQDG or PG, respectively. In binary mixtures of the inverted hexagonal phase forming lipid MGDG with the negatively charged bilayer lipids, comparable suppression took place. This is in contrast to binary mixtures of MGDG with the neutral bilayer lipids DGDG and PC, where rapid and efficient de-epoxidation was observed. In complex lipid mixtures resembling the lipid composition of the native diatom thylakoid membrane, we again found strong suppression of diadinoxanthin de-epoxidation due to the presence of SQDG or PG. We conclude that, in the native thylakoids of diatoms, a strict separation of the MGDG and SQDG domains must occur; otherwise, the rapid diadinoxanthin de-epoxidation observed in intact cells upon illumination would not be possible.     

Role of hexagonal structure-forming lipids in diadinoxanthin and violaxanthin solubilization and de-epoxidation

In this study, we have examined the influence of different lipids on the solubility of the xanthophyll cycle pigments diadinoxanthin (Ddx) and violaxanthin (Vx) and on the efficiency of Ddx and Vx de-epoxidation by the enzymes Vx de-epoxidase (VDE) from wheat and Ddx de-epoxidase (DDE) from the diatom Cyclotella meneghiniana, respectively. Our results show that the lipids MGDG and PE are able to solubilize both xanthophyll cycle pigments in an aqueous medium. Substrate solubilization is essential for de-epoxidase activity, because in the absence of MGDG or PE Ddx and Vx are present in an aggregated form, with limited accessibility for DDE and VDE. Our results also show that the hexagonal structure-forming lipids MGDG and PE are able to solubilize Ddx and Vx at much lower lipid concentrations than bilayer-forming lipids DGDG and PC. We furthermore found that, in the presence of MGDG or PE, Ddx is much more solubilizable than Vx. This substantial difference in Ddx and Vx solubility directly affects the respective de-epoxidation reactions. Ddx de-epoxidation by the diatom DDE is saturated at much lower MGDG or PE concentrations than Vx de-epoxidation by the higher-plant VDE. Another important result of our study is that bilayer-forming lipids DGDG and PC are not able to induce efficient xanthophyll de-epoxidation. Even in the presence of high concentrations of DGDG or PC, where Ddx and Vx are completely solubilized, a strongly inhibited Ddx de-epoxidation is observed, while Vx de-epoxidation by VDE is completely absent. This indicates that the inverted hexagonal phase domains provided by lipid MGDG or PE are essential for de-epoxidase activity. We conclude that in the natural thylakoid membrane MGDG serves to solubilize the xanthophyll cycle pigments and furthermore provides inverted hexagonal structures associated with the membrane bilayer, which are essential for efficient xanthophyll de-epoxidase activity.     

Effects of natural shade on soybean thylakoid membrane composition

The effect of natural shade on chloroplast thylakoid membrane activity and composition was examined for soybean (Glycine Max. cv. Young) grown under field conditions. Plots with high (10 plants m^–1 row) or low (1 plant m^–1 row) plant density were established. Expanding leaves were tagged at 50, 58 and 65 days after planting (DAP). At 92 DAP, tagged leaves were used as reference points to characterize canopy light environments and isolate thylakoid membranes. Light environments ranged from a photosynthetic photon flux density (PPFD) of 87% of full sun to a PPFD of 10% of full sun. The decline in PPFD was accompanied by an increase in the far-red/red (735 nm/645 nm) ratio from 0.9 to approximately six. The major effects of shade on chloroplast thylakoid membranes were a reduction in chloroplast coupling factor and a shift in light-harvesting capacity from Photosystem I to Photosystem II. Photosynthetic electron transport capacity was not affected by differences in PPFD, but was 20 to 30% higher in the 1 plant m^–1 row treatment. The plant density effect on electron transport was associated with differences in plastocyanin concentration, suggesting that plastocyanin is a limiting factor in soybean. Shade did not have a significant effect on the concentration of Photosystem II, Cyt b₆f, or Photosystem I complexes.Abbreviations CF₁ chloroplast coupling factor - DAP days after planting - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCIP 2,6-dichlorophenolindophenol - FR/R far-red/red - PBS 10 mM sodium phosphate (pH 7.0), 150 mM NaCl - PPFD photosynthetic photon flux density - PS I Photosystem I - PS II Photosystem II - P700 reaction center of Photosystem I - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - TBS 20 mM Tris-HCl (pH 7.5), 500 mM NaCl - TTBS 20 mM Tris-HCl (pH 7.5), 500 mM NaCl, 0.05% (w/v) polyoxyethylenesorbitan monolaurate (Tween-20) The US Government right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.The US Government right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

The kinetics of P515 in relation to the lipid composition of the thylakoid membrane

Flash-induced P515 absorbance changes have been studied in dark-adapted chloroplasts isolated from spinach plants grown under two different light intensities. The slow component (reaction 2), normally present in the P515 response of chloroplasts isolated from plants grown at an intensity of 60 W · m^–2, was largely reduced in chloroplasts isolated from plants grown at an intensity of 6 W · m^–2. This reduction of the slow component in the P515 response appeared to be coincident with an alteration in the lipid composition of the thylakoid membrane. Mainly the ratio monogalactosyldiacylglycerol to digalactosyldiacylglycerol appeared to be altered. In thylakoids from plants grown at 6 W · m^–2, the ratio was approximately 35% lower than that of plants grown at 60 W · m^–2. The amount of both cytochromeb ₅₆₃ and cytochromef was largely reduced in chloroplasts isolated from plants grown at low light intensity. These results may indicate a possible correlation between structural organization of the thylakoid membrane and the kinetics of the flash-induced P515 response.     

The main thylakoid membrane lipid monogalactosyldiacylglycerol (MGDG) promotes the de-epoxidation of violaxanthin associated with the light-harvesting complex of photosystem II (LHCII)

In higher plants, the major part of the xanthophyll cycle pigment violaxanthin (Vx) is non-covalently bound to the main light-harvesting complex of PSII (LHCII). Under saturating light conditions Vx has to be released from its binding site into the surrounding lipid phase, where it is converted to zeaxanthin (Zx) by the enzyme Vx de-epoxidase (VDE). In the present study we investigated the influence of thylakoid lipids on the de-epoxidation of Vx, which was still associated with the LHCII. We isolated LHCII with different concentrations of native, endogenous lipids and Vx by sucrose gradient centrifugation or successive cation precipitation. Analysis of the different LHCII preparations showed that the concentration of LHCII-associated Vx was correlated with the concentration of the main thylakoid lipid monogalactosyldiacylglycerol (MGDG) associated with the complexes. Decreases in the MGDG content of the LHCII led to a diminished Vx concentration, indicating that a part of the total Vx pool was located in an MGDG phase surrounding the LHCII, whereas another part was bound to the LHCII apoproteins. We further studied the convertibility of LHCII-associated Vx in in-vitro enzyme assays by addition of isolated VDE. We observed an efficient and almost complete Vx conversion in the LHCII fractions containing high amounts of endogenous MGDG. LHCII preparations with low concentrations of MGDG exhibited a strongly reduced Vx de-epoxidation, which could be increased by addition of exogenous, pure MGDG. The de-epoxidation of LHCII-associated Vx was saturated at a much lower concentration of native, endogenous MGDG compared with the concentration of isolated, exogenous MGDG, which is needed for optimal VDE activity in in-vitro assays employing pure isolated Vx.     

Lipid peroxidation in the rat-liver S9 fraction: influence of membrane lipid composition

These studies describe the influence of membrane fatty acid composition on peroxidation processes in rat-liver S9 fractions. Lipid peroxidation may be expected to affect enzyme activity and cofactors of importance for the performance of the Salmonella Mutagenicity Test, as well as to contribute to the formation of chemically reactive degradation products that are mutagenic. Lipid peroxidation products were measured as derivatives of 2-thiobarbituric acid (TBA). The amount of TBA-reactive compounds (TBA-C), formed during incubation of S9 fractions from rats fed a diet containing sunflower-seed oil, was 8 times higher than that produced in S9 fractions prepared from rats fed diets containing coconut oil or hydrogenated lard as their only sources of fat. S9 fractions from livers of Aroclor 1254 treated rats showed a marked increase in peroxidation yields for all 3 dietary groups investigated as compared to S9 fractions from non-induced animals. The coconut oil and hydrogenated lard dietary groups showed a 13-fold increase in the yield of TBA-reactive material, while a 2-fold increase was found for the sunflower-seed oil group. The variations in the glutathione (GSH) levels and the degradation of unsaturated fatty acids were also studied in response to Aroclor 1254 treatment, fatty acid composition of the diets and incubation at 37 degrees C. Pronounced variations in the GSH levels were observed in response to Aroclor 1254 treatment and incubation conditions. A positive correlation between production of TBA-reactive material and degradation of unsaturated fatty acids was verified for S9 fractions from the coconut oil and hydrogenated lard dietary groups. Furthermore, the effect of Fe2+ on lipid peroxidation was studied in all 3 dietary groups. The rate of lipid peroxidation was increased in all groups but only the coconut oil and hydrogenated lard dietary groups showed increased total yields of TBA-C upon administration of Aroclor 1254 to rats. Lipid peroxidation processes cause chemical alterations in liver homogenates. Therefore, these effects ought to be considered both in the preparation and in the use of the S9 fraction in different test systems.     

Effect of monogalactosyldiacylglycerol and other thylakoid lipids on violaxanthin de-epoxidation in liposomes

In this study we present evidence that one of two reactions of the xanthophyll cycle, violaxanthin de-epoxidation, may occur in unilamellar egg phosphatidylcholine vesicles supplemented with monogalactosyldiacylglycerol (MGDG). Activity of violaxanthin de-epoxidase (VDE) in this system was found to be strongly dependent on the content of MGDG in the membrane; however, only to a level of 30 mol%. Above this concentration the rate of violaxanthin de-epoxidation decreased. The effect of individual thylakoid lipids on VDE-independent violaxanthin transformation was also investigated and unspecific effects of phosphatidylglycerol and sulphoquinovosyldiacyglycerol, probably related to the acidic character of these lipids, were found. The presented results suggest that violaxanthin de-epoxidation most probably takes place inside MGDG-rich domains of the thylakoid membrane. The described activity of the violaxanthin de-epoxidation reaction in liposomes opens new possibilities in the investigation of the xanthophyll cycle and may contribute to a better understanding of this process.     

Photosynthetic electron transport in relation to thylakoid membrane composition and organization

Abstract. A review is given of the organization and properties of thylakoid membrane proteins and lipids as a basis for understanding the factors which regulate the light reactions of photosynthesis. Particular emphasis is placed on the lateral organization of the major intrinsic multipeptide complexes and on the importance of diffusional processes in controlling the kinetics of electron transport and the distribution of light energy between photosystems 1 and 2.     

Comparison of violaxanthin de-epoxidation from the stroma and lumen sides of isolated thylakoid membranes from Arabidopsis: implications for the mechanism of de-epoxidation

The enzyme violaxanthin de-epoxidase (VxDE) is localized in the thylakoid lumen and catalyzes the de-epoxidation of membrane-bound violaxanthin (Vx) to zeaxanthin. De-epoxidation from the opposite, stroma side of the membrane has been investigated in the npq1 mutant from Arabidopsis thaliana (L.) Heynh. - which lacks VxDE - by adding partially purified VxDE from spinach thylakoids. The accessibility of Vx to the exogenously added enzyme (exoVxDE) and the kinetics of Vx conversion by the exoVxDE in thylakoids from npq1 plants were very similar to the characteristics of Vx conversion by the endogenous enzyme (endoVxDE) in thylakoids from wild-type plants. However, the conversion of Vx by exoVxDE was clearly retarded at lower temperatures when compared with the reaction catalyzed by endoVxDE. Since the exoVxDE - in contrast to the endoVxDE - has no access to the stacked regions of the membrane, where the xanthophylls bound to photosystem II are located, these results support the assumption of pronounced diffusion of xanthophylls within the thylakoid membrane.     

Lipid transfer proteins in the study of artificial and natural membranes

Summary Lipid transfer proteins, differing in their specificity for the transfer of lipids and for the surfaces on which they act, have been purified from various mammalian tissues and subsequently characterized. Several of their properties make them useful research tools. They have been used alone or with other techniques to study the distribution and mobility of phospholipids in artificial vesicles and in natural membranes, and have been used to create asymmetric phospholipid vesicles.Lipid transfer proteins are capable of altering the lipid composition of membranes by introducing new lipids or by depletion of existing lipids. Some of the transfer proteins can effect a net transfer of phospholipids, glycosphingolipids and cholesterol from one structure to another, whereas others appear to act primarily in promoting exchange. Some lipid transfer proteins are capable of introducing spin labeled and fluorescent lipid analogs into the outer surface of membranes. Because lipid transfer proteins do not seem to alter membrane lipid asymmetry or permeability of membranes, they are useful tools for studying the effect of lipid substitution on membrane-mediated transport processes and on various membrane-bound enzyme systems.Abbreviations PA phosphatidic acid - PC phosphatidylcholine - PE phosphatidylethanolamine - PI phosphatidylinositol - PG phosphatidylglycerol - PS phosphatidylserine - DPG diphosphatidylglycerol - SPH sphingomyelin - G_{m t} II³--N-Acetylneuraminosylgangliotetraglycosylceramide - GbOse₄Cer globotetraglycosylceramide Career Investigator of C.O.N.I.C.E.T. (Argentina)Career Investigator of the American Heart Association.     

Molecular architecture of the thylakoid membrane: lipid diffusion space for plastoquinone

We have determined the stoichiometric composition of membrane components (lipids and proteins) in spinach thylakoids and have derived the molecular area occupied by these components. From this analysis, the lipid phase diffusion space, the fraction of lipids located in the first protein solvation shell (boundary lipids), and the plastoquinone (PQ) concentration are derived. On the basis of these stoichiometric data, we have analyzed the motion of PQ between photosystem (PS) II and cytochrome (cyt.) bf complexes in this highly protein obstructed membrane (protein area about 70%) using percolation theory. This analysis reveals an inefficient diffusion process. We propose that distinct structural features of the thylakoid membrane (grana formation, microdomains) could help to minimize these inefficiencies and ensure a non-rate limiting PQ diffusion process. A large amount of published evidence supports the idea that higher protein associations exist, especially in grana thylakoids. From the quantification of the boundary lipid fraction (about 60%), we conclude that protein complexes involved in these associations should be spaced by lipids. Lipid-spaced protein aggregations in thylakoids are qualitatively different to previously characterized associations (multisubunit complexes, supercomplexes). We derive a hierarchy of protein and lipid interactions in the thylakoid membrane.     

Lipid-mediated interactions between intrinsic membrane proteins: dependence on protein size and lipid composition.

The present study is an application of an approach recently developed by the authors for describing the structure of the hydrocarbon chains of lipid-bilayer membranes (LBMs) around embedded protein inclusions ( Biophys. J. 79:2867-2879). The approach is based on statistical mechanical integral equation theories developed for the study of dense liquids. First, the configurations extracted from molecular dynamics simulations of pure LBMs are used to extract the lateral density-density response function. Different pure LBMs composed of different lipid molecules were considered: dioleoyl phosphatidylcholine (DOPC), palmitoyl-oleoyl phosphatidylcholine (POPC), dipalmitoyl phosphatidylcholine (DPPC), and dimyristoyl phosphatidylcholine (DMPC). The results for the lateral density-density response function was then used as input in the integral equation theory. Numerical calculations were performed for protein inclusions of three different sizes. For the sake of simplicity, protein inclusions are represented as hard smooth cylinders excluding the lipid hydrocarbon core from a small cylinder of 2.5 A radius, corresponding roughly to one aliphatic chain, a medium cylinder of 5 A radius, corresponding to one alpha-helix, and a larger cylinder of 9 A radius, representing a small protein such as the gramicidin channel. The lipid-mediated interaction between protein inclusions was calculated using a closed-form expression for the configuration-dependent free energy. This interaction was found to be repulsive at intermediate range and attractive at short range for two small cylinders in POPC, DPPC, and DMPC bilayers, whereas it oscillates between attractive and repulsive values in DOPC bilayers. For medium size cylinders, it is again repulsive at intermediate range and attractive at short range, but for every model LBM considered here. In the case of a large cylinder, the lipid-mediated interaction was shown to be repulsive for both short and long ranges for the DOPC, POPC, and DPPC bilayers, whereas it is again repulsive and attractive for DMPC bilayers. The results indicate that the packing of the hydrocarbon chains around protein inclusions in LBMs gives rise to a generic (i.e., nonspecific) lipid-mediated interaction which favors the association of two alpha-helices and depends on the lipid composition of the membrane.     

Photosynthetic functions and thylakoid membrane polypeptide composition in light-sensitive mutants of Chlamydomonas reinhardii

In this paper we compared the pigment composition, photochemical activity, chloroplast ultrastructure, thylakoid membrane polypeptide composition and ribosomal content of wild-type and seven light-sensitive mutants of Chlamydomonas reinhardii.All the mutants had low chlorophyll and carotenoid content compared to wild-type. Mutants lts-30 and lts-135 were also characterized by a complete absence of visible carotenoids, while mutant lts-19 was fully deficient in chlorophylls.In most mutants, the chloroplast fragment could not carry out any DCIP photoreduction and O₂ evolution was also blocked. The PSI/P₇₀₀/activity was decreased in most cases.The mutant strains contained mostly single lamellae in their plastids, that is the stacking capacity of the thylakoid membranes was very decreased or fully absent. In most cases the number of lamellae was also very low.The relative amounts of 70 S ribosomes were decreased in all of the mutants. The thylakoid membranes showed anomalies in the region of 24 000–30 000 dalton polypeptides. The common characteristic for them was the relatively higher amount of the 30 000 dalton polypeptide and considerably decreased level of the 27 000 and 24 000 dalton polypeptides relative to the wild-type. These polypeptides were probably constituents of the chlorophyll-protein complex II which has been suggested to be the light harvesting pigment complex for PSII. The polypeptide of 30 000 daltons is the precursor for the LHCP apoprotein (24 000 dalton protein). It may be that the lighstimulated conversion of this precursor into LHCP apoprotein was blocked in our pigment-deficient mutants.Abbreviations CPI Chlorophyll-protein complex I - PSI Photosystem I - PSII Photosystem II - LHCP Light-harvesting pigment complex - DCIP 2,6-dichlorophenolindophenol - RuDPC-ase Ribulose-1,5-biphosphate-carboxylase - SDS Sodium dodecyl sulfate - LIDS Lithium dodecyl sulfate - PAG Polyacrylamide gel - TKM buffer 25 mM Tris-HCl, pH 7.S; 25 mM KCl; 25 mM Mg acetate     

Lipid composition and lipid metabolism of Spiroplasma citri.

In a horse serum-based medium containing a full complement of fatty acids, cells of Spiroplasma citri were seen to preferentially incorporate palmitic acid. In the same medium, which had a steryl ester-to-sterol ratio of 3.64, a steryl ester-to-sterol ratio of 0.23 was seen in the cells, cholesterol being preferentially incorporated over cholesteryl ester. Like most other mycoplasmas, S. citri was shown to be unable to synthesize fatty acids or esterify cholesterol. The neutral lipids of S. citri grown in a medium containing horse serum consisted of free cholesterol, cholesteryl ester, free fatty acids, triglycerides and diglycerides. All polar lipids were phospholipids, with no glycolipids detected. These phospholipids, which are characteristic of many mycoplasmas, are phosphatidyl glycerol, diphosphatidyl glycerol, and their lyso derivatives. Sphingomyelin was also incorporated when cells were grown on horse serum. A sterol requirement for the growth of S. citri was confirmed using a serum-free medium supplemented with bovine serum albumin, palmitic acid, and various concentrations of sterols dissolved in Tween 80. The addition of palmitic acid stimulated growth but was not essential for growth. S citri was shown to grow best on cholesterol and beta-sitosterol and was able to grow on stigmasterol and ergosterol to a lesser degree. No growth was obtained using mevalonate, deoxycholate, or taurodeoxycholate as an alternative to sterol. S. citri was also able to grow when palmitic acid was replaced with oleic acid, linoleic acid, or linolenic acid. Alterations in the lipid composition of the growth medium and hence in the lipid composition of S. citri induced changes in the characteristic helical morphology of the cells, concurrent with loss of cell viability. Culture, age, and pH were also factors in determining cell morphology and viability.     

Lipid composition of the isolated rat intestinal microvillus membrane

1. Rat intestinal microvillus plasma membranes were prepared from previously isolated brush borders and the lipid composition was analysed. 2. The molar ratio of cholesterol to phospholipid was greatest in the membranes and closely resembled that reported for myelin. 3. Unesterified cholesterol was the major neutral lipid. However, 30% of the neutral lipid fraction was accounted for by glycerides and fatty acid. 4. Five phospholipid components were identified and measured, including phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine, sphingomyelin and lysophosphatidylcholine. Though phosphatidylethanolamine was the chief phospholipid, no plasmalogen was detected. 5. In contrast with other plasma membranes in the rat, the polar lipids of the microvillus membrane were rich in glycolipid. The cholesterol:polar lipid (phospholipid+glycolipid) ratio was about 1:3 for the microvillus membrane. Published data suggest that this ratio resembles that of the liver plasma membrane more closely than myelin or the erythrocyte membrane. 6. The fatty acid composition of membrane lipids was altered markedly by a single feeding of safflower oil. Membrane polar lipids did not contain significantly more saturated fatty acids than cellular polar lipids. Differences in the proportion of some fatty acids in membrane and cellular glycerides were noted. These differences may reflect the presence of specific membrane glycerides.     

Growth temperature effects on thylakoid membrane lipid and protein content of pea chloroplasts

The lipid composition and level of unsaturation of fatty acids has been determined for chloroplast thylakoid membranes isolated from Pisum sativum grown under cold (4°/7°C) or warm (14°/17°C) conditions. Both the relative amounts of lipid classes and degree of saturation were not greatly changed for the two growth conditions. In cold-grown plants, there was a slightly higher linolenic and lower linoleic acid content for the glycolipids monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), and sulfoquinovosyldiacylglycerol. In contrast to thylakoid membranes, a non-thylakoid leaf membrane fraction including the chloroplast envelope, had a higher overall level of fatty acid unsaturation in cold-grown plants due mainly to an increase in the linolenic acid content of MGDG, DGDG, phosphatidylglycerol, and phosphatidylcholine. The most clear cut change in the thylakoid membrane composition was the lipid to protein ratio which was higher in the cold-grown plants.