Acid Composition Of Polar Lipids Research Articles

Seasonal lipid dynamics of four Arctic bivalves: Implications for their physiological capacities to cope with future changes in coastal ecosystems.

The Arctic is exposed to unprecedented warming, at least three times higher than the global average, which induces significant melting of the cryosphere. Freshwater inputs from melting glaciers will subsequently affect coastal primary production and organic matter quality. However, due to a lack of basic knowledge on the physiology of Arctic organisms, it remains difficult to understand how these future trophic changes will threaten the long-term survival of benthic species in coastal habitats. This study aimed to gain new insights into the seasonal lipid dynamics of four dominant benthic bivalves (Astarte moerchi, Hiatella arctica, Musculus discors, and Mya truncata) collected before and after sea ice break-up in a high-Arctic fjord (Young Sound, NE Greenland). Total lipid content and fatty acid composition of digestive gland neutral lipids were analyzed to assess bivalve energy reserves while the fatty acid composition of gill polar lipids was determined as a biochemical indicator of interspecies variations in metabolic activity and temperature acclimation. Results showed a decrease in lipid reserves between May and August, suggesting that bivalves have only limited access to fresh organic matter until sea ice break-up. The lack of seasonal variation in the fatty acid composition of neutral lipids, especially essential ω3 fatty acids, indicates that no fatty acid transfer from the digestive glands to the gonads occurs between May and August, and therefore, no reproductive investment takes place during this period. Large interspecies differences in gill fatty acid composition were observed, which appear to be related to differences in species life span and metabolic strategies. Such differences in gill fatty acid composition of polar lipids, which generally influence metabolic rates and energy needs, may imply that not all benthic species will be equally sensitive to future changes in primary production and organic matter quality in Arctic coastal habitats.

Effects of dietary forage-to-concentrate ratio and forage type on milk phospholipids and fatty acid composition of polar lipids

The effects of grass silage and red clover silage on milk fatty acid (FA) composition are extensively studied, but little is known of their effects on minor lipid constituents of milk fat globule membrane. We investigated the effects of forage:concentrate (FC) ratio in grass silage-based diets and forage type (grass silage vs. red clover silage) on selected molecular species of milk phospholipids (PL) and the FA composition of PL. Ten multiparous Nordic Red cows were offered following dietary treatments: grass silage-based diets containing 70:30 (HG) or 30:70 (LG) FC ratio or a red clover silage-based diet (RC) comprising 50:50 FC ratio on a dry matter basis. The most abundant molecular species within the phosphatidylcholines was 16:0-18:1 phosphatidylcholine that was increased by 18% in HG compared with LG milk. Dietary treatments did not affect the relative proportion of 18:1-18:1+18:0-18:2 phosphatidylethanolamine that was the most prevalent species (ca. 44%-45%) in that class. We identified the d18:1-22:0 sphingomyelin as the most abundant sphingomyelin species that tended to increase in HG milk compared with LG. The FC ratio did not affect the relative proportions of saturated FA nor monounsaturated FA in PL, but the proportion of cis-9 18:1 was elevated in HG versus LG milk, whereas the proportion of 18:2n-6 was 50% higher in LG versus HG milk. The RC diet increased monounsaturated FA and 18:3n-3 levels in PL compared with grass silage-based diets and decreased the relative proportion of saturated FA. However, the RC diet did not affect the relative proportion of polyunsaturated FA in PL, although red clover silage typically increases the proportion of polyunsaturated FA in milk fat. This study provides valuable knowledge of the minor lipid components in milk on species level in relation to common feeding strategies in high-forage systems.

Monitoring changes of lipid composition in durum wheat during grain development

The lipid fraction of durum wheat (Triticum turgidum ssp. durum (Desf.) Husn.), cultivar Svevo, was characterized during grain maturation. Growing grain kernels were harvested at five key stages of development between 5 and 30 days post anthesis (dpa). Lipid evolution was assessed during kernel filling by gas chromatography-mass spectrometry (GC-MS) analysis of triacylglycerols and methylated free fatty acids (FFA) as well as by ultra-high performance liquid chromatography coupled to high resolution electrospray ionization tandem mass spectrometry (UHPLC-HRESI-MS/MS) lipid analysis. Major triacylglycerols (TAG) were detected already at early developmental stages, albeit at low abundance. The decrease of FFA during kernel filling corresponded to accumulation of predominantly linoleate (C18:2n6)-containing C52 and C54 TAG. Fatty acid composition of polar lipids including phospholipids and galactolipids also showed the progressive dominance of linoleate, typically since two weeks after anthesis. Conversely, minor sphingolipids (ceramides and glycosylceramides) were constituted mainly by saturated long chain FA, also oxygenated, combined with a restricted set of sphingoid bases, and might play a signaling role during grain development.

The Fatty Acid Composition of Membrane Lipids in Buds of Silver Birch during the Winter–Spring Period under the Conditions of the Cryolithozone

The fatty acid composition of polar lipids, which are the structural and functional bases of cell membranes in the bud of Betula pendula Roth birch, growing under the conditions of the cryolithozone, was studied for the first time. The important role played by lipid metabolism in the winter–spring period, when the apical meristem is at the stage of intrarenal development, was established. It was shown that, during this period, unsaturated fatty acids prevail over saturated in phospholipids and glycolipids in silver birch buds. However, under the conditions of extremely low air temperatures (–40°C and below), the lowest values of double bond index (DBI) and fatty acid unsaturation coefficient (U/S) were recorded. The rise of negative temperatures under the conditions of the cryolithozone (in March) to values usually observed during the winter period throughout the range of silver birch (–20°C and higher) contributed to an increase in the level of membrane lipid unsaturation. It was found that diene fatty acids predominate in phospholipids, and diene and triene acids predominate in glycolipids, the latter reaching maximum values (80.7% of the amount of unsaturated fatty acids) by the beginning of budding. It was hypothesized that, in order to preserve the viability of the apical meristem in buds of silver birch trees under the specific conditions of the cryolithozone, various interrelated adaptive mechanisms were formed. These mechanisms are aimed not only at protecting the rudimentary organs from the effects of sharp fluctuations in daily temperatures during spring, but also at protecting them during winter under conditions of extremely low temperatures (down to –60°С), which do not occur in other parts of its range. One of these mechanisms appeared to be nonspecific, and it was associated with an increase in the unsaturation of the fatty acid composition corresponding to the liquid-crystalline state of membrane lipids. Another adaptive mechanism is probably aimed at protecting cells from dehydration with the involvement of dehydrin proteins, as well as a number of other hydrophilic cryoprotective compounds against the background of increased viscosity of membrane lipids.

Lipid composition of the Antarctic fish Pleuragramma antarcticum. Influence of age class

Larvae and juvenile stages of Pleuragramma antarcticum have been collected in the Dumont D’Urville Sea (East Antarctica) during summer 2008 on board the TRV Umitaka Maru during the CEAMARC survey. Detailed analyses of their lipid class and fatty acid compositions were carried out. P. antarcticum showed a pronounced ontogenic lipid accumulation with increasing size. Larvae displayed a dominance of polar lipids (83% of total lipids) and low percentage of triglycerides (7%). Conversely juveniles showed an increasing accumulation of triglycerides (up to 72.4%). The fatty acid composition of polar lipids remained rather stable between stages with 22:6n−3 and 20:5n−3 as dominant contributors. The relatively minor ontogenic changes, e.g. increase of monounsaturated and decrease of C18 polyunsaturated fatty acids, may reflect the influence of differences in diet. Triglycerides showed that all three age classes are well segregated in term of fatty acid composition. Larvae triglycerides are characterized by significant percentages of 16:0, 20:5n−3, 20:6n−3 and to a minor extent 18:4n−3, which suggest a prymnesiophyte based diet. Juveniles are characterized by larger percentages of C20:1 and C22:1 acids, considered as markers of Calanus type copepods. The increasing contribution of 18:1n−9 in the triglycerides of the older juveniles suggests a gradual and increasing shift from a copepod dominant diet to an euphausiid dominant diet. Fatty acid trophic markers pattern suggests a shift from a phytophagous and omnivorous diet for larvae to a carnivorous diet for juveniles.

Chemical composition and oxidative status of tissues from Iberian pigs as affected by diets: extensive feeding v. oleic acid- and tocopherol-enriched mixed diets

The present work was intended to analyse the chemical composition and oxidative stability of the muscle biceps femoris and adipose tissues from Iberian pigs fed different finishing diets: free-range feeding on grass and acorns in a ‘Montanera’ traditional system (MON), fed in confinement with a mixed diet containing high-oleic sunflower oil (115 g/kg of diet) and supplemented with 250 mg/kg α-tocopherol (HOVE), and fed in confinement with a tocopherol-non-supplemented control mixed diet (CON). Muscles from MON pigs contained significantly (P < 0.05) higher amounts of intramuscular fat than those from HOVE and CON pigs. Muscles from MON and HOVE pigs had significantly higher levels of α-tocopherol than muscles from CON pigs whereas free-range feeding provided significantly higher levels of γ-tocopherol to muscles from MON pigs than the experimental diets did to CON and HOVE pigs. Adipose tissues from MON and HOVE pigs contained significantly lower proportions of saturated fatty acids and significantly higher levels of oleic acid and monounsaturated fatty acids than those from CON pigs. Tissues from MON pigs contained significantly smaller levels of polyunsaturated fatty acids than those from CON and HOVE pigs. To a higher extent, feeding background affected the fatty acid composition of polar lipids from the muscle bicepsfemoris than that of neutral lipids. Tissues from MON pigs contained significantly smaller ω-6/ω-3 values than those from pigs fed mixed diets. Compared to tissues from CON pigs, those from MON and HOVE pigs exhibited a higher oxidative stability as a likely result of a most favourable fatty acid composition and the presence of higher tocopherol levels.

Effect of light intensity on the fatty acid composition of dinoflagellates symbiotic with hermatypic corals

We examined the effects of varying light intensity on fatty acid composition in symbiotic dinoflagellates (SD) isolated from hermatypic corals Millepora intricata , Pocillopora damicornis , Seriatopora caliendrum , Seriatopora hystrix and Stylophora pistillata . The corals were subjected to 95%, 30%, 8% and 2% of incident photosynthetic active radiation (PAR). Irradiance had a significant effect on fatty acid composition of polar lipids and triacylglycerols. SD showed substantial changes in the proportion of 16:0 as a response to variation in PAR. During adaptation to high light, the percentage of 16:0 increased in polar lipids and triacylglycerols. Additionally, the percentage of 14:0, 16:1(n-7) increased in triacylglycerols. Thus, high light conditions lead to an increase in storage products. Polar lipids of SD adapted to low levels of PAR had greater concentrations of 18:4(n-3), 20:5(n-3), 18:5(n-3) and 22:5(n-6) which are commonly involved in the formation of thylakoid membranes. Conversely, the amounts of 20:4(n-6) and 22:6(n-3) increased with increasing irradiance, suggesting an association with photosynthesis. The elevation in percentages of 18:4(n-3), 20:5(n-3) and 18:5(n-3) during exposure to low light was accompanied by an increase in chlorophyll a content in the SD cells. Light-dependent changes in fatty acid composition are probably due to the correlation of activity of photosystems with processes of production and desaturation of fatty acids.

RESPONSES OF APPLE FRUIT TO LOW O2 CONCENTRATIONS INVOLVED IN MEMBRANE LIPID METABOLISM

Experiments were conducted to determine levels of low O2 exposure needed to prevent the occurrence of abnormal respiration, and to characterise the relationship between respiration and membrane lipids of apple fruit. The membrane lipid-associated lipase activity was also measured. Exposure of ‘Braeburn’ apples to 3% and 6% O2 at 10°C markedly reduced CO2 production relative to 21% O2; however, CO2 production rapidly increased when O2 level was further reduced to 1.5 or even 0%, due to anaerobic respiration. Free fatty acids were high in fruits exposed to air atmosphere for 4 days and decreased gradually with the exposure period, whereas a delay in the increase of the fatty acids was observed exposed to 6 or 3% O2 within 12 days. Compared to 6 or 3%, exposure of apples to 1.5 or 0% resulted in higher content of the fatty acids. Furthermore, among these fatty acids analysed, the largest amount was palmitic acid, followed by stearic acid. The change in lipase activity had similar patterns, but a rapid increase in the enzyme activity coincident with the higher content of the fatty acids occurred in apples exposed to 21 or 0% O2 for 4 days. In contrast to the fatty acids, there were more dramatic changes in the fatty acid composition of polar lipids when apples were exposed to various O2 concentrations. Exposure to 6 or 3% O2 exhibited a better maintenance of membrane lipid composition, as judged by relatively stable saturated/unsaturated fatty acid ratios in combination with respiration rates throughout this experiment. The results suggested that responses of apples to reduced O2 concentrations are involved in the breakdown and modification of membrane lipids which may further influence respiratory patterns.

A Biochemical Approach for Assessment of the Diversity of Symbiotic Dinoflagellates

The fatty acid composition of polar lipids and triacetylglycerols was determined in different morphophysiological types of symbiotic dinoflagellates isolated from the hydrocoral Millepora intricata and the scleractinian corals Pocillopora damicornis, Seriatopora caliendrum, Seriatopora hystrix, and Stylophora pistillata. The distribution of fatty acids differed fairly markedly among the investigated morphophysiological types of symbiotic dinoflagellates. The differences were found both in polar lipids, which are the structural components of the cell membranes, and storage lipids—triacetylglycerols. It is shown that fatty acids are useful chemotaxonomic markers for symbiotic dinoflagellates. It is assumed that the biochemical differences among the morphophysiological types of symbiotic dinoflagellates can reflect the genetic diversity of these types.

Effects of Gradual Drought on the Fatty Acid Composition of Polar Lipids, H+-ATPase and 5&amp;prime;-AMPase Activities in the Plasma Membranes of Two Spring Wheat Leaves

研究了田间缓慢干旱胁迫下,抗旱性不同的两个小麦(Triticum aestivum)品种的生长状况、质膜极性脂脂肪酸组成以及质膜关键酶活力的变化.在小麦生长发育的早期,干旱胁迫使其叶片质膜极性脂脂肪酸不饱和度下降、质膜微囊消耗O2的速率升高、膜蛋白含量降低、H+-ATPase (EC 3.6.1.35)活力下降、5′-AMPase (EC 3.1.3.5)活力大幅度升高;在小麦发育的后期,随着干旱的持续,小麦叶片质膜的极性脂脂肪酸不饱和度不变或升高、质膜微囊消耗O2的速率降低、膜蛋白含量与H+-ATPase活力升高、5′-AMPase活力下降.以上结果表明,小麦在发育的早期阶段对干旱较敏感,其细胞质膜流动性降低、细胞中能荷贮备降低;而在后期,则又表现出对干旱的适应.这些结果将有助于阐明自然干旱条件下植物的抗旱机制.

Fatty acid variations in symbiotic dinoflagellates from Okinawan corals

The fatty acid composition of polar lipids and triacylglycerols was determined in different morphophysiological types of symbiotic dinoflagellates (SD) isolated from the hydrocoral Millepora intricata and the scleractinian corals Pocillopora damicornis, Seriatopora caliendrum, Seriatopora hystrix and Stylophora pistillata from a fringing reef of Sesoko Island, Okinawa, Japan. The distribution of the fatty acids among the morphophysiologically distinct types of SD reported in these corals makes it possible to readily distinguish one type of SD from the other. Moreover, differences were found both in polar lipids and triacylglycerols. The polar lipids of SD from M. intricata showed a very distinctive fatty acid profile. A combination of large proportions of 18:4 (n-3), 18:5 (n-3), 22:5 (n-6), and 22:6 (n-3) and negligible amounts of 20:4 (n-6), and 20:5 (n-3) in SD from M. intricata was particularly noteworthy. The fatty acid profiles of SD from P. damicornis and SD isolated from S. caliendrum and S. hystrix differed in the proportion of 18:4 (n-3) and 22:6 (n-3). It is suggested that fatty acids might provide useful information on possible taxonomic differences among symbiotic dinoflagellates. It is assumed that biochemical differences can reflect the genetic diversity of the morphophysiological types of SD associated with several species of hermatypic corals from this region.

The Fatty Acid Composition of Phosphatidylglycerol and Sulfoquinovosyldiacylglycerol of Zea mays Genotypes Differing in Chilling Susceptibility

Summary The content and fatty acid composition of four major chloroplast lipids, monogalactosyldiacylglycerol, digalactosyldiacylglycerol, phosphatidylglycerol and sulfoquinovosyldiacylglycerol, have been measured in the intact leaves of maize inbred lines differing in chilling susceptibility. Visual assessment of chilling injury symptoms during post-chilling recovery of seedlings indicated that both lines CM 7 and Co 151 were more chilling susceptible than lines S 215 and EP l, exhibiting greater chilling tolerance. Fatty acid composition of chloroplast polar lipids was very similar and some small deviation in the content of individual fatty acids did not affect uniformity of the general pattern. In all four lines of maize the content of height-temperature melting fraction of phosphatidylglycerol (htm-PG) and double bond index of polar lipids were equal, while fatty acid composition of polar lipids was very similar despite of small deviations in the content of individual fatty acid. Although the level of the high-temperature melting fraction of sulfoquinovosyldiacylglycerol (htm-SQDG) was lower in CS and CT lines Co 151 and S 215, respectively, than in CS and CT lines CM 7 and EP 1, respectively, this difference could not be related to their chilling sensitivity. All of these data do not support the concepts that the level of htm-PG alone or in combination with low-temperature-melting lipid would differentiate the chilling sensitivity of maize inbred lines. It is likely that some other factors are responsible for differential injury symptoms observed in chilled maize seedlings upon recovery. Discrepancies between the level of htm-PG and chilling sensitivity in several other species as well as various effects of acclimation on the level of htm-PG and temperature of phase transition are discussed.

Osmotic stress induced changes in lipid composition and peroxidation in leaf discs of Brassica napus L.

Summary Leaf discs excised from rape plants ( Brassica napus var. oleifera ) incubated in vitro under moderate osmotic stress (−1.5 MPa) exhibited a significant reduction in the amount of membrane galactolipids. In addition, the phosphatidylethanolamine (PE) and phosphatidylcholine (PC) levels were also decreased, whereas those of phosphatidylglycerol and phosphatidic acid were enhanced. Fatty acid composition of polar lipids was also affected in response to osmotic stress. The percentage of polyunsaturated fatty acids (PUFAs) showed a moderate decrease (in mono- and digalactosyldiacylglycerol, PE and PC) while that of saturated or of monounsaturated fatty acids was not significantly affected. Relative to the total fatty acids of the membrane lipids, the levels of C18:2 and C18:3 were markedly decreased in response to osmotic stress. Under the same conditions the content of malondialdehyde, one of the cytotoxic products of PUFA peroxidation, was enhanced. These responses were associated with decreases in both the relative water content and the internal osmotic potential. Concurrently, lipoxygenase activity was rapidly enhanced, suggesting that lipoxygenase could be responsible for initiation of the lipid peroxidation process. On the other hand, superoxide dismutase and ascorbate peroxidase activities were found to be enhanced in osmotically stressed leaf discs compared with the control. These results indicate that the biochemical adjustments induced by osmotic stress in rape leaf tissues partly rely on changes in membrane lipid composition, which are in part related to a shift in the balance between the production and scavenging of reactive oxygen species.

Dietary lipids modify the fatty acid composition of cartilage, isolated chondrocytes and matrix vesicles

The effects of dietary lipids on the fatty acid composition of hyaline cartilage, epiphyseal chondrocytes (EC) and matrix vesicles (MV) were evaluated in chicks. A basal semipurified diet was fed to chicks containing one of the following lipid sources at 70 g/kg: soybean oil, butter+corn oil, margarine+corn oil or menhaden oil+corn oil (MEC). Articular and epiphyseal growth cartilage were isolated from the proximal tibiotarsus; EC and MV were subsequently released by trypsin (EC 3.4.21.4) and collagenase (EC 3.4.24.3) digestion followed by ultracentrifugation. The fatty acid composition of polar lipids in chick epiphyseal cartilage at three and six weeks, as well as articular cartilage, EC and MV at eight weeks of age revealed the presence of high levels of saturated and monounsaturated fatty acids (up to 85.5%) but low levels of n-6 polyunsaturated fatty acids (PUFA) (2.6-10.2%). Mead acid (20:3n-9, > 3%) was also present in cartilage, EC and MV lipids, and was unaffected by the dietary lipid treatments. Total n-3 PUFA concentrations were the highest in cartilage, EC and MV of chicks consuming MEC. Feeding MEC lowered the levels of 20:4n-6 in cartilage, but increased 20:5n-3 levels. The data are consistent with those reported previously which showed that cartilage tissues are low in n-6 PUFA and that they contain 20:3n-9. We furthermore demonstrated that the PUFA composition of cartilage can be modified by dietary lipids.

Polar lipids in healthy and Phytophthora capsici-infected leaflets of Lycopersicon esculentum

The effects of infection by Phytophthora capsici on the repartition and fatty acid composition of polar lipids in three different foliar tissues of Lycopersicon esculentum (May seedlings) were investigated. The tissues studied were: (i) highly infected tissues, under explant, 6 mm diameter, (ii) infected tissues, margin of the lesions, 9 mm width; and (iii) adjacent peripheral tissues, about 52% total area, apparently sound, compared with uninfected control leaflets. The fatty acid composition of each lipid class was drastically altered in the highly infected area. The desaturation pathway of polyunsaturated fatty acids, specific to plants, was either partly inhibited for glycoglycerolipids, or replaced by the desaturation pathway for the formation of parasite phospholipids. Consequently, the long chain fatty acids characterizing P. capsici increased progressively from peripheral to highly infected tissues and the phosphatidylcholine (PC) of the plant was replaced by the PC of the parasite. The increase in the percentage of parasite PC could be used as an infection index. The amounts of all polar lipid classes were increased in the peripheral zone, except phosphatidic acid. A possible distance effect of infection is enhancement of membrane biosynthesis. Phosphonate treatment was found to favour the synthesis of all polar lipid classes in the control leaflet but to be inactive in preserving the integrity of the fatty acid composition of the lipid classes in infected tissues.

Growth Response and Fatty Acid Composition of Channel Catfish Fry Fed Practical Diets Supplemented with Menhaden Fish Oil

Abstract A 12-week feeding experiment was conducted to investigate the growth and compositional responses of channel catfish fry (Ictalurus punctatus) fed practical diets containing 7.6% fish meal supplemented with 0, 1.5, 3, or 6% menhaden fish oil. Weight gain significantly improved with increasing levels of supplemental menhaden oil up to 3% of diet; fish fed the diet containing 6% fish oil had depressed weight gain. Whole-body dry matter and lipid increased and protein decreased with increasing levels of menhaden oil. Ash content was not affected by dietary treatment. Fatty acid composition of polar lipids from whole-body tissue showed that supplementation of menhaden fish oil at a rate of 1.5% was sufficient to satisfy the essential fatty acid (EFA) requirement of young channel catfish based on the ratio of 20:3 n-9 to 22:6 n-3 fatty acids. Results from this study indicate that practical diets containing fish meal, but without supplemental fish oil, did not meet the n-3 EFA requirement of young chann...

Seasonal variations in the biochemical composition and lipids of muscle and carapace in the shrimp Pleoticus muelleri bate

1. 1. Seasonal variations in the biochemical composition and lipids in the muscle and carapace of the shrimp Pleoticus muelleri from San Jorge Gulf, Argentina, were studied during 1984–1985. 2. 2. The biochemical composition of muscle remained fairly constant throughout the year whereas the carapace showed notable seasonal variations. The carapace contained more water and lesser nitrogenous compounds and mineral salts in spring than in the other seasons, with the suggestion of a higher molt frequency in spring. The carapace could have an additional role as a temporary reservoir of nutrients. 3. 3. Polar lipids were the main fraction of total lipids in both muscle and carapace. Phosphatidylcholine, phosphatidylethanolamine, lysoderivatives of choline, sphingomyelin and pigments were identified; ninhydrine positive components with low R f values were also present. 4. 4. Free sterols and free fatty acids were the major neutral lipid classes in both muscle and carapace in spring; the latter had a higher concentration of astaxanthin and small amounts of sterol esters not detected in muscle. 5. 5. The fatty acid composition of polar lipids varied little in muscle. The neutral lipids of maturing females in summer contained higher levels of saturated fatty acids (16:0 and 18:0). The fatty acid composition of carapace varied markedly in polar and neutral lipids. A low selectivity of fatty acids for carapace formation was observed during the year.

MICROSOMAL MEMBRANE CHANGES IN IRRADIATED CAULIFLOWER DURING STORAGE

Cauliflowers (Brassica oleracea) were irradiated at 0, 2, and 4 kGy and stored 8 days at 13°C. Development of yellow color and browning of the in florescence, increase in membrane electrolyte leakage and reduction of protein recovery in microsomal membranes were observed over the storage period. Changes in membrane free fatty acids, lipid phosphorus content, peroxydation level, and fatty acid composition of polar lipids also occurred. These results indicate an important modification of cellular membranes. The direct effect of gamma rays on membrane lipids via free radical production and subsequent destabilization of the lipid bilayer during storage could be responsable for earlier onset of senescence.

Effect of paclobutrazol on membrane lipids in apple seedlings

The effect of paclobutrazol [(2RS, 3RS)‐1‐(4‐chlorophenyl)‐4,4‐dimethyl‐2‐(1,2, 4‐triazol‐1‐yl) pentan‐3‐ol] on the fatty acid composition of polar lipids and on the sterol content in apple (Malus domestica Borkh. cv. York Imperial) seedlings was determined. Polar lipids isolated from leaves, stems and roots included mono‐ and digalactosyldiglycerides and the phospholipids phosphatidylinositol, phosphatidylcholine, phosphatidylglycerol and phosphatidylethanolamine. The predominant fatty acids in membrane polar lipids were palmitic (C16:0), linolnic (C18:2) and linolenic (C18:3). The predominant sterol, both free and esterified, was β‐sitosterol. There were no significant alterations in the fatty‐acid composition of glyco‐ and phospholipids from paclobutrazol‐treated apple seedlings. In contrast, a significant decrease in the content of β‐sitosterol and campesterol occurred in treated tissues. The decline in sterol content continued with increasing duration of paclobutrazol treatment, and was most pronounced in the root tissue.

Fatty acid composition of polar lipids in goats' milk

Silicic acid column chromatography was used to separate the polar lipids of goats' milk into glycolipid, phosphatidylethanolamine, phosphatidylserine plus phosphatidylinositol, phosphatidylcholine, and sphingomyelin fractions. Each fraction was purified by column chromatography and its fatty acid profile determined by gas liquid chromatography and mass spectrometry. The glycerophospholipids each contained 18:1 as the predominant fatty acid (approximately 45%). The sphingolipids contained a high percentage of long-chain saturated fatty acids (C22 to C24 greater than 45%); the glycolipid fraction also contained ca. 2% 2-hydroxy fatty acids. The data represent a comprehensive cross-sectional study of the major polar lipids found in goats' milks.