ULTRASTRUCTURAL CHANGES OF CHLOROPLASTS IN ATTACHED AND DETACHED,AGING PRIMARY WHEAT LEAVES

Degradation of chloroplasts is shown in mesophyll cells of primary leaves of wheat. The sequence of ultrastructural changes in chloroplasts of naturally senescing leaves is compared with that of detached, aging leaves. In chloroplasts of naturally senescing leaves, the first indications of aging are the appearance of osmiophilic globuli and reorientation of the thylakoidal system. The membranes of the grana and intergrana lamellae then become distended and later dissociate into distinct vesicles. Concurrent with these membrane changes, osmiophilic globuli increase in size and number, and the stroma breaks down. Finally, the chloroplast envelope ruptures and plastid contents disperse throughout the cell's interior. In chloroplasts of mesophyll cells in detached, aging leaves, initial changes also include appearance of osmiophilic globuli, but later stages of chloroplast degradation are different. The chloroplast envelope ruptures before the lamellae break down. Swelling of grana and intergrana lamellae is not pronounced and, additionally, the thylakoidal system degenerates without forming vesicles or numerous osmiophilic globuli. These differences in the sequence of chloroplast degradation indicate that naturally senescing leaves rather than detached, aging leaves should be used in studies of chloroplast senescence.     

Development of ultrastructure and experimental change in carotene composition of the eyespot in Chlamydomonas reinhardtii mutants

Biogenesis of the ultrastructure of the eyespot in chloroplasts of a unicellular green alga Chlamydomonas reinhardtii has been studied. It has been ascertained that the development of eyespot structure correlates with the accumulation of carotenoids. Owing to their accumulation, the eyespot may have one to four layers of lipid/carotenoid globuli. It has been shown that only carotenes are accumulated in the eyespot globuli. It has been found for the first time that in mutants, the composition of carotenes in the eyespot may change together with the changes of their composition in chloroplast membranes.     

Action of actinomycin D on Euglena gracilis ultrastructure

Effects of 1 and 10 mkg/ml concentrations of actinomycin D, an inhibitor of RNA synthesis, on the ultrastructure of a phytoflagellate Euglena gracilis were followed during 48 hours. Similar changes were observed with both the concentrations, but the effect of the higher dose appeared in a short time and was more expressed. The effect of actinomycin D becomes obvious as early as half an hour after its adding; the cell nucleus, chloroplasts and mitochondria show definite responses. Chromatin condensation is seen in the nucleus, the nucleolus is enlarged in size, compressed and fragmented. Chloroplasts react to the action of actinomycin D by swelling, accumulation of osmiophilic globuli, disorganization and reduction of lamellar systems, formation of the myelin figures and gran-like structures and by the decomposition of pyrenoid. The mitochondrial matrix is compressed, the structure and orientation of the cristae become abnormal, and some electron-dense bodies appear.     

Three-dimensional organization of higher-plant chloroplast thylakoid membranes revealed by electron tomography

The light-harvesting and energy-transducing functions of the chloroplast are performed within an intricate lamellar system of membranes, called thylakoid membranes, which are differentiated into granum and stroma lamellar domains. Using dual-axis electron microscope tomography, we determined the three-dimensional organization of the chloroplast thylakoid membranes within cryo-immobilized, freeze-substituted lettuce (Lactuca sativa) leaves. We found that the grana are built of repeating units that consist of paired layers formed by bifurcations of stroma lamellar sheets, which fuse within the granum body. These units are rotated relative to each other around the axis of the granum cylinder. One of the layers that makes up the pair bends upwards at its edge and fuses with the layer above it, whereas the other layer bends in the opposite direction and merges with the layer below. As a result, each unit in the granum is directly connected to its neighbors as well as to the surrounding stroma lamellae. This highly connected morphology has important consequences for the formation and function of the thylakoid membranes as well as for their stacking/unstacking response to variations in light conditions.     

Änderungen der Ultrastrukturen in den Grünalgen Ankistrodesmus braunii und Chlorella fusca var. rubescens bei Stickstoffmangel

Summary Ultrastructural changes as well as changes in pigment and lipid content induced by nitrogen deficiency in the green algae Ankistrodesmus braunii and Chlorella fusca var. rubescens have been studied. Electron micrographs (freezeetching technique) and analyses show that the content of chlorophylls and the number of thylakoids decrease under these conditions synchronously with the increase of secondary carotenoids (astaxanthin-like type) and lipid vacuoles. However, there is no change, as compared with the green control, in the number and structure of the plastoglobuli localized in the chloroplasts. After addition of nitrogen, synthesis of the thylakoids and chlorophylls begins. The lipid vacuoles and secondary carotenoids disappear gradually. These extraplastidic lipid vacuoles do not correspond with the intraplastidic plastoglobuli (lipid globuli) found in higher plants and in Acetabularia.     

Lipid‐polymorphism of plant thylakoid membranes. Enhanced non‐bilayer lipid phases associated with increased membrane permeability

Earlier experiments, using ³¹P‐NMR and time‐resolved merocyanine fluorescence spectroscopy, have shown that isolated intact, fully functional plant thylakoid membranes, in addition to the bilayer phase, contain three non‐bilayer (or non‐lamellar) lipid phases. It has also been shown that the lipid polymorphism of thylakoid membranes can be characterized by remarkable plasticity, i.e. by significant variations in ³¹P‐NMR signatures. However, changes in the lipid‐phase behaviour of thylakoids could not be assigned to changes in the overall membrane organization and the photosynthetic activity, as tested by circular dichroism and 77 K fluorescence emission spectroscopy and the magnitude of the variable fluorescence of photosystem II, which all showed only marginal variations. In this work, we investigated in more detail the temporal stability of the different lipid phases by recording ³¹P‐NMR spectra on isolated thylakoid membranes that were suspended in sorbitol‐ or NaCl‐based media. We observed, at 5°C during 8 h in the dark, substantial gradual enhancement of the isotropic lipid phases and diminishment of the bilayer phase in the sorbitol‐based medium. These changes compared well with the gradually increasing membrane permeability, as testified by the gradual acceleration of the decay of flash‐induced electrochromic absorption changes and characteristic changes in the kinetics of fast chlorophyll a‐fluorescence transients; all variations were much less pronounced in the NaCl‐based medium. These observations suggest that non‐bilayer lipids and non‐lamellar lipid phases play significant roles in the structural dynamics and functional plasticity of thylakoid membranes.     

Fatty aldehyde and fatty alcohol metabolism: Review and importance for epidermal structure and function

Normal fatty aldehyde and alcohol metabolism is essential for epidermal differentiation and function. Long-chain aldehydes are produced by catabolism of several lipids including fatty alcohols, sphingolipids, ether glycerolipids, isoprenoid alcohols and certain aliphatic lipids that undergo α- or ω-oxidation. The fatty aldehyde generated by these pathways is chiefly metabolized to fatty acid by fatty aldehyde dehydrogenase (FALDH, alternately known as ALDH3A2), which also functions to oxidize fatty alcohols as a component of the fatty alcohol:NAD oxidoreductase (FAO) enzyme complex. Genetic deficiency of FALDH/FAO in patients with Sjögren–Larsson syndrome (SLS) results in accumulation of fatty aldehydes, fatty alcohols and related lipids (ether glycerolipids, wax esters) in cultured keratinocytes. These biochemical changes are associated with abnormalities in formation of lamellar bodies in the stratum granulosum and impaired delivery of their precursor membranes to the stratum corneum (SC). The defective extracellular SC membranes are responsible for a leaky epidermal water barrier and ichthyosis. Although lamellar bodies appear to be the pathogenic target for abnormal fatty aldehyde/alcohol metabolism in SLS, the precise biochemical mechanisms are yet to be elucidated. Nevertheless, studies in SLS highlight the critical importance of FALDH and normal fatty aldehyde/alcohol metabolism for epidermal function. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.     

Importance of trimer-trimer interactions for the native state of the plant light-harvesting complex II

Aggregates and solubilized trimers of LHCII were characterized by circular dichroism (CD), linear dichroism and time-resolved fluorescence spectroscopy and compared with thylakoid membranes in order to evaluate the native state of LHCII in vivo. It was found that the CD spectra of lamellar aggregates closely resemble those of unstacked thylakoid membranes whereas the spectra of trimers solubilized in n-dodecyl-beta,D-maltoside, n-octyl-beta,D-glucopyranoside, or Triton X-100 were drastically different in the Soret region. Thylakoid membranes or LHCII aggregates solubilized with detergent exhibited CD spectra similar to the isolated trimers. Solubilization of LHCII was accompanied by profound changes in the linear dichroism and increase in fluorescence lifetime. These data support the notion that lamellar aggregates of LHCII retain the native organization of LHCII in the thylakoid membranes. The results indicate that the supramolecular organization of LHCII, most likely due to specific trimer-trimer contacts, has significant impact on the pigment interactions in the complexes.     

The Lamellar Systems of Cytoplasmic Membranes in Dividing Spermatogenic Cells of Drosophila virilis

Spermatogenic cells of Drosophila virilis were studied by light and electron microscopy. The persistence of a "nuclear wall" during the meiotic divisions has been reported by a number of early cytologists, but this interpretation has been a subject of debate. Electron micrographs of dividing spermatocytes reveal the presence of multiple layers of paired membranes surrounding the nuclear region. These lamellar membrane systems are not typical of the nuclear envelope, but were interpreted as such by light microscopists. The membranes constituting a pair are separated by an interspace of ~ 100 A and successive pairs are 200 to 400 A apart. These spacings are similar but not identical to those found in the lamellar systems of the Golgi complex. The cisternae of the endoplasmic reticulum in this material are devoid of attached ribonucleoprotein particles, are more precisely ordered than in vertebrate cells, and show a uniform, narrow intracisternal space of ~ 100 A. The conspicuous asters appear to be made up of similar paired membranes radiating from the centriolar region. The primary spermatocyte has numerous dictyosomes and a well developed endoplasmic reticulum in cisternal form, but no typical Golgi complex or endoplasmic reticulum is found during the meiotic division stages of metaphase to telophase. Evidence is presented that these cytoplasmic organelles contribute to the formation of the extensive lamellar systems that appear during meiosis. The results of the Golgi silver staining methods and staining tests for phospholipids, basophilia, and the PAS reaction, indicate that the lamellar arrays of membranes present during meiosis are indistinguishable from the Golgi complex in their tinctorial properties.     

Importance of trimer-trimer interactions for the native state of the plant light-harvesting complex II

Aggregates and solubilized trimers of LHCII were characterized by circular dichroism (CD), linear dichroism and time-resolved fluorescence spectroscopy and compared with thylakoid membranes in order to evaluate the native state of LHCII in vivo. It was found that the CD spectra of lamellar aggregates closely resemble those of unstacked thylakoid membranes whereas the spectra of trimers solubilized in n-dodecyl-β,d-maltoside, n-octyl-β,d-glucopyranoside, or Triton X-100 were drastically different in the Soret region. Thylakoid membranes or LHCII aggregates solubilized with detergent exhibited CD spectra similar to the isolated trimers. Solubilization of LHCII was accompanied by profound changes in the linear dichroism and increase in fluorescence lifetime. These data support the notion that lamellar aggregates of LHCII retain the native organization of LHCII in the thylakoid membranes. The results indicate that the supramolecular organization of LHCII, most likely due to specific trimer-trimer contacts, has significant impact on the pigment interactions in the complexes.     

THE FINE STRUCTURE OF CHLOROPLASTS FROM MINERAL-DEFICIENT LEAVES OF PHASEOLUS VULGARIS

Thomson , W. W., and T. E. Weier . (U. California, Davis.) The fine structure of chloroplasts from mineral-deficient leaves of Phaseolus vulgaris. Amer. Jour. Bot. 49(10): 1047–1055. Illus. 1962.—An electron microscopic study of the changes in chloroplast structure as affected by the stress of nutrient deficiencies is described. Each deficiency produces characteristic changes in the ultrastructure of the chloroplast. In phosphorus and potassium deficiency the plastids develop fully before changes occur; then the grana break down into diffuse, electron-dense masses, forming a highly ordered lamellar system. The plastids of plants low in nitrogen and magnesium do not reach full development before changes occur. In nitrogen-deficient plastids, the stroma is greatly diminished and the grana compartments are swollen and reduced in number. In magnesium deficiency, the grana-fretwork system becomes disorganized and many star-bodies are formed. The absence of zinc blocks the full development of a grana-fretwork system, and large vacuoles are formed in conjunction with grana compartments.     

Structure and function of lamellar bodies, lipid-protein complexes involved in storage and secretion of cellular lipids.

This review article attempts to present an overview of the occurrence and function of lipid storage and secretory organelles: the lamellar bodies. Morphologically these organelles vary considerably in size (100 nm to 2400 nm); they are surrounded by a membrane and contain multilamellar lipid membranes. Lamellar bodies may also contain apolipoproteins and lytic enzymes and have an acidic pH, which confers on them a lysosomal character. Under normal physiological conditions, the main function of lamellar bodies is the supply of extracellular domains with specialized lipid components related to a specialized function. The lamellar bodies of the lung epithelium are best investigated in their functional and structural features and are the storage form of the lung surfactant. They provide a monomolecular lipid film of dipalmitoyl phosphatidylcholine (DPPC) on the surface of lung alveoli to lower surface tension necessary for optimal gas exchange and a hydrophobic protective lining against environmental influences. Additional cells of the respiratory system such as the mucosa of the human nose and the bronchi contain lamellar bodies. Lamellar bodies are also found in the gastrointestinal tract, in tongue papillae, oral epithelium, and mucosa cells of the stomach. The major phospholipid of lamellar bodies in mucosa cells of the stomach is DPPC, providing a hydrophobic protective lipid film against the tissue-damaging activities of gastric juice. The hydrophobic water-protective barrier of the skin, which consists mainly of neutral lipids, however, also originates from lamellar bodies secreted by epithelial cells. Lamellar bodies, mainly consisting of DPPC, also occur in mesodermal cell layers of sliding surfaces to provide the lubrication of joints, of the peritoneum, pericardium, and pleural mesothelium. In certain pathological conditions, such as atherosclerosis, Niemann-Pick disease, lecithin:cholesterol acyltransferase (LCAT) deficiency, cholestasis, degeneration of nerves and brain, and regeneration of nerves and wound healing, lipid-containing lamellar bodies have been observed in various cells, the function of which still remains to be elucidated. In early and late lesions of atherosclerotic plaques, lamellar bodies, consisting of unesterified cholesterol and phospholipids, are associated with the extracellular matrix of the intima. During regression of fatty streaks, lamellar bodies are seen intracellularly in macrophages and smooth muscle cells. Inherited metabolic disorders, such as Niemann-Pick disease type I and type II, result in the excessive accumulation of lamellar body-containing cells, for example in bone marrow, spleen, and lymphoid tissue. Type I is a deficiency in sphingomyelinase and type II is a defect in intracellular trafficking of lipoprotein-derived cholesterol.(ABSTRACT TRUNCATED AT 400 WORDS)     

Transmembrane electrical potential affects the lipid composition of Acholeplasma laidlawii

In membranes of Acholeplasma laidlawii, lipid composition is regulated as a function of several stimuli affecting the volume and length of the hydrocarbon chains and the hydrocarbon-water interfacial area. This regulation is vizualized as changes in the relative amounts of the major polar lipids monoglucosyl diglyceride and diglucosyl diglyceride. These lipids form reversed hexagonal and lamellar phases with water, respectively. However, mixtures of the two lipids, in the molar proportions found in the A. laidlawii membrane, form a lamellar phase. By adjustment of the glycolipid ratio as a response to environmental stimuli, a certain stability of the lamellar membrane is maintained. In growing cells with oleoyl membrane lipids, a transmembrane electrical potential of approximately -50 mV (inside negative), but no transmembrane pH difference, was found. Addition of the K+ ionophore valinomycin caused a rapid and dose-dependent hyperpolarization remaining for at least 7 h. Simultaneously, a rapid and lasting metabolic decrease in the ratio monoglucosyl diglyceride/diglucosyl diglyceride occurred. The increase in potential and the decrease in the lipid ratio were both reversed in a dose-dependent manner by extracellular KCl. Likewise, the lipophilic cation tetraphenylphosphonium caused a dose-dependent decrease in membrane potential and an increase in the monoglucosyl diglyceride/diglucosyl diglyceride ratio, respectively. The ionophores monensin and particularly nigericin had similar but less pronounced effects on the potential and lipid ratios as valinomycin. The uncoupler carbonyl cyanide m-chlorophenylhydrazone had no effect on cell growth, membrane potential, or lipid regulation at 10 microM. These dissimilar structures and the low concentrations used make a direct disturbance of drug molecules on lipid packing in membranes less likely.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phospholipid content and lamellar structures in the epididymal epithelial cells of rats treated chronically with lead acetate [Pb(II)].

The electron-microscopic observations accomplished covered epididymal epithelial cells of rats receiving lead acetate for five times longer than the duration of one spermatogenesis. These cells were found to possess a large number of vacuoles and conglomerates containing plicated membranes or tightly packed myelin-like lamellar formations. Further observations also revealed the formation of lamellar structures in mitochondria, dilatation of cisternae in the Golgi apparatus, and increased phagocytosis of spermatozoa by epithelial cells. The presence of a large amount of membranous material correlated with the increased content of phospholipids in epididymal epithelial cells. It may be suggested that the presence of such a great quantity of lamellar structures in epididymal epithelial cells of rats treated chronically with lead is the result of several processes, including the augmented synthesis of membranes associated with encircling the deposits of lead, autophagy in the cells, as well as intensified phagocytosis of spermatozoa.     

Lipophilic penetration enhancers and their impact to the bilayer structure of stratum corneum lipid model membranes: neutron diffraction studies based on the example oleic acid

The present study analyzes the effect of the lipophilic penetration enhancer oleic acid on the bilayer structure of stratum corneum (SC) lipid model membranes based on Ceramide AP by using the neutron diffraction technique. Our results indicate the formation of a single lamellar phase in the presence of oleic acid under the chosen experimental conditions; a separated fluid-like oleic acid-rich phase was not detected in the present study. By comparing the internal membrane structure received from Fourier synthesis with the model system lacking oleic acid, considerable structural changes in terms of impairment of the lamellar order were found after incorporation of the penetration enhancer into the bilayers. In addition, by using specifically deuterated oleic acid we were able to prove the integration of the enhancer molecules into the model bilayers and moreover, to determine the exact position of oleic acid inside the SC lipid model membrane. From the present results we conclude a strong perturbation of lamellar SC lipid arrangement due to the intercalated penetration enhancer which can account for the promoting effects on drug penetration across the SC known for oleic acid.     

日本沼虾高尔基体在精子发生过程中的变化

用岸民镜技术研究了日本沼虾精子发生过程中生精细胞内高尔基体变化。结果表明：精原细胞内,高尔基体结构典型,分布在核膜附近,许多膜囊通过过连接小管相互连接。初级精母细胞内,高尔基体结构紧凑且更典型,更造近核膜,在反面的分泌活动旺盛,产生大量初级溶酶体;     

Structure and thermotropic phase behaviour of detergent-resistant membrane raft fractions isolated from human and ruminant erythrocytes

Detergent-resistant membrane raft fractions have been prepared from human, goat, and sheep erythrocyte ghosts using Triton X-100. The structure and thermotropic phase behaviour of the fractions have been examined by freeze-fracture electron microscopy and synchrotron X-ray diffraction methods. The raft fractions are found to consist of vesicles and multilamellar structures indicating considerable rearrangement of the original ghost membrane. Few membrane-associated particles typical of freeze-fracture replicas of intact erythrocyte membranes are observed in the fracture planes. Synchrotron X-ray diffraction studies during heating and cooling scans showed that multilamellar structures formed by stacks of raft membranes from all three species have d-spacings of about 6.5 nm. These structures can be distinguished from peaks corresponding to d-spacings of about 5.5 nm, which were assigned to scattering from single bilayer vesicles on the basis of the temperature dependence of their d-spacings compared with the multilamellar arrangements. The spacings obtained from multilamellar stacks and vesicular suspensions of raft membranes were, on average, more than 0.5 nm greater than corresponding arrangements of erythrocyte ghost membranes from which they were derived. The trypsinization of human erythrocyte ghosts results in a small decrease in lamellar d-spacing, but rafts prepared from trypsinized ghosts exhibit an additional lamellar repeat 0.4 nm less than a lamellar repeat coinciding with rafts prepared from untreated ghosts. The trypsinization of sheep erythrocyte ghosts results in the phase separation of two lamellar repeat structures (d=6.00; 5.77 nm), but rafts from trypsinized ghosts produce a diffraction band almost identical to rafts from untreated ghosts. An examination of the structure and thermotropic phase behaviour of the dispersions of total polar lipid extracts of sheep detergent-resistant membrane preparations showed that a reversible phase separation of an inverted hexagonal structure from coexisting lamellar phase takes place upon heating above about 30 degrees C. Non-lamellar phases are not observed in erythrocytes or detergent-resistant membrane preparations heated up to 55 degrees C, suggesting that the lamellar arrangement is imposed on these membrane lipids by interaction with non-lipid components of rafts and/or that the topology of lipids in the erythrocyte membrane survives detergent treatment.     

Calcium-dependent self-association of annexin II: a possible implication in exocytosis.

Alveolar type II cells secrete lung surfactant through exocytosis of lamellar bodies. We previously showed that the annexin II tetramer (Anx IIt) mediates the fusion of lamellar bodies with liposomes. The present study examined the possible involvement of membrane proteins in this process. Pre-treatment of lamellar bodies with trypsin and alpha-chymotrypsin reduced Anx IIt-mediated membrane fusion. With the use of an Anx IIt-conjugated Sepharose column, three Anx IIt-binding proteins with molecular weights of 67,000, 36,000 and 34,000 were isolated froM the Triton X-100 extract of bovine lung tissue membranes. These proteins were identified as annexins VI, II and IV by Western blot. The interaction of Anx IIt with annexins II and IV was confirmed by ligand blot assay. An EGTA-resistant membrane-bound annexin II was present in lung type II cells. Anx IIt preferentially hound to membranous annexin II compared with cytosolic annexin II of type II cells. With the use of immunofluorescence, annexin II was found to translocate from cytoplasm to plasma membranes in type II cells upon stimulation with phorbol 12-myristate 13-acetate. These results suggest that cytosolic annexin II may bind to membranous annexin II and form a protein-protein bridge to bring two membranes together.     

Thematic review series: skin lipids. The role of epidermal lipids in cutaneous permeability barrier homeostasis

The permeability barrier is required for terrestrial life and is localized to the stratum corneum, where extracellular lipid membranes inhibit water movement. The lipids that constitute the extracellular matrix have a unique composition and are 50% ceramides, 25% cholesterol, and 15% free fatty acids. Essential fatty acid deficiency results in abnormalities in stratum corneum structure function. The lipids are delivered to the extracellular space by the secretion of lamellar bodies, which contain phospholipids, glucosylceramides, sphingomyelin, cholesterol, and enzymes. In the extracellular space, the lamellar body lipids are metabolized by enzymes to the lipids that form the lamellar membranes. The lipids contained in the lamellar bodies are derived from both epidermal lipid synthesis and extracutaneous sources. Inhibition of cholesterol, fatty acid, ceramide, or glucosylceramide synthesis adversely affects lamellar body formation, thereby impairing barrier homeostasis. Studies have further shown that the elongation and desaturation of fatty acids is also required for barrier homeostasis. The mechanisms that mediate the uptake of extracutaneous lipids by the epidermis are unknown, but keratinocytes express LDL and scavenger receptor class B type 1, fatty acid transport proteins, and CD36. Topical application of physiologic lipids can improve permeability barrier homeostasis and has been useful in the treatment of cutaneous disorders.     

The role of ceramide chain length distribution on the barrier properties of the skin lipid membranes

The skin barrier function is provided by the stratum corneum (SC). The lipids in the SC are composed of three lipid classes: ceramides (CERs), cholesterol (CHOL) and free fatty acids (FFAs) which form two crystalline lamellar structures. In the present study, we investigate the effect of CER chain length distribution on the barrier properties of model lipid membranes mimicking the lipid composition and organization of SC. The membranes were prepared with either isolated pig CERs (PCERs) or synthetic CERs. While PCERs have a wide chain length distribution, the synthetic CERs are quite uniform in chain length. The barrier properties were examined by means of permeation studies using hydrocortisone as a model drug. Our studies revealed a reduced barrier in lipid membranes prepared with PCERs compared to synthetic CERs. Additional studies revealed that a wider chain length distribution of PCERs results in an enhanced hexagonal packing and increased conformational disordering of the lipid tails compared to synthetic CERs, while the lamellar phases did not change. This demonstrates that the chain length distribution affects the lipid barrier by reducing the lipid ordering and density within the lipid lamellae. In subsequent studies, the effect of increased levels of FFAs or CERs with a long acyl chain in the PCERs membranes was also studied. These changes in lipid composition enhanced the level of orthorhombic packing, reduced the conformational disordering and increased the barrier of the lipid membranes. In conclusion, the CER chain length distribution is an important key factor for maintaining a proper barrier.