LIPID SYNTHESIS AND FATTY ACID COMPOSITION IN NANNOCHLOROPSIS SP. (EUSTIGMATOPHYCEAE) GROWN IN A LIGHT-DARK CYCLE1

Chemical composition and lipid biosynthesis were studied in the marine eustigmatophyte Nannochloropsis sp. Grown under a 12:12 h light-dark regime. Cellular division occurred in the dark and was associated with a reduction in cell volume. The cellular content of chlorophyll a and carotenoids increased during the light period and decreased during the dark period. Other cellular components, such as proteins, carbohydrates and lipids, followed a similar pattern. Nannochloropsis sp. Incorporated acetate, mostly into lipids during the light period, whereas a low rate of acetate incorporation was observed during the dark period, mostly into nonlipid compounds. Neutral lipids such as triacylglycerol were synthesized and accumulated in the light and showed a rapid turnover in the dark. Polar structural lipids such as monogalactosyl diacylglycerol were synthesized during the light period and hardly turned over during the dark period. Changes in lipid content were associated with variations in cellular fatty acid composition. The light period was characterized by an increase in the percentage of C16:0 and 16:1 fatty acids associated with triacylglycerols. However, in the dark period, as triglycerides were consumed for cellular maintenance, the relative distribution of the C20:5 fatty acid associated with the galactolipids increased.     

FATTY ACID SIGNATURES DIFFERENTIATE MARINE MACROPHYTES AT ORDINAL AND FAMILY RANKS1

Primary productivity by plants and algae is the fundamental source of energy in virtually all food webs. Furthermore, photosynthetic organisms are the sole source for ω‐3 and ω‐6 essential fatty acids (EFA) to upper trophic levels. Because animals cannot synthesize EFA, these molecules may be useful as trophic markers for tracking sources of primary production through food webs if different primary producer groups have different EFA signatures. We tested the hypothesis that different marine macrophyte groups have distinct fatty acid (FA) signatures by conducting a phylogenetic survey of 40 marine macrophytes (seaweeds and seagrasses) representing 36 families, 21 orders, and four phyla in the San Juan Archipelago, WA, USA. We used multivariate statistics to show that FA composition differed significantly (P < 0.001) among phyla, orders, and families using 44 FA and a subset of seven EFA (P < 0.001). A second analysis of published EFA data of 123 additional macrophytes confirmed that this pattern was robust on a global scale (P < 0.001). This phylogenetic differentiation of macrophyte taxa shows a clear relationship between macrophyte phylogeny and FA content and strongly suggests that FA signature analyses can offer a viable approach to clarifying fundamental questions about the contribution of different basal resources to food webs. Moreover, these results imply that taxa with commercially valuable EFA signatures will likely share such characteristics with other closely related taxa that have not yet been evaluated for FA content.     

EFFECTS OF LOWERING TEMPERATURE DURING CULTURE ON THE PRODUCTION OF POLYUNSATURATED FATTY ACIDS IN THE MARINE DIATOM PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

The composition of fatty acids and contents of eicosapentaenoic acid (EPA) and polyunsaturated fatty acids (PUFAs) of the economically important marine diatom, Phaeodactylum tricornutum (Bohlin), were investigated to see whether reducing the culture temperature enhances the production of EPA and PUFAs. The contents of EPA and PUFAs of P. tricornutum were found to be higher at lower temperature when cultured at 10, 15, 20, or 25°C. When the cells grown at 25°C were shifted to 20, 15, or 10°C, the contents per dry mass of PUFAs and EPA increased to the maximal values in 48, 24, and 12 h, respectively. The highest yields of PUFAs and EPA per unit dry mass (per unit volume of culture) were 4.9% and 2.6% (12.4 and 6.6 mg·L^?1), respectively, when temperature was shifted from 25 to 10°C for 12 h, both being raised by 120% compared with the control. The representative fatty acids in the total fatty acids, when temperature was lowered from 25 to 10°C, decreased proportionally by about 30% in C_16:0 and 20% in C_16:1(n?7) but increased about 85% in EPA. It was concluded that lowering culture temperature of P. tricornutum could significantly raise the yields of EPA and PUFAs.     

Formation of Lyso-glycosphingolipids by Streptomyces sp

The actinomycete strain Streptomyces sp. H37 produces a novel glycosphingolipid-degrading enzyme. This strain was capable of converting ganglioside GM1 to lyso-GM1. After cultivation for 5 days in medium containing GM1, peptone, and detergent, GM1 was found to be almost completely converted to lyso-GM1. The product was purified on a DEAE-Sephadex A-25 column and thin layer chromatographies. The purified lyso-GM1 was hydrolyzed by endoglycoceramidase, and the released oligosaccharide moiety was identified as that of GM1 by HPLC using the pyridylaminoderivative method. The counterpart sphingosine moiety was confirmed with TLC. Moreover, the structure of lyso-GM1 was ascertained by ¹H-NMR analysis. The maximum formation of lyso-GM1 was found in 50mM potassium phosphate buffer (pH 7.5) containing 0.1% glycodeoxycholate. Various lyso-glycoshingolipids, including those of ganglio-, neolacto-, and globo-types, were formed from their parent glycosphingolipids using this strain.     

LIBERATION OF 5,8,11,14,17-EICOSAPENTAENOIC ACID AND OTHER POLYUNSATURATED FATTY ACIDS FROM LIPIDS AS A GRAZER DEFENSE REACTION IN EPILITHIC DIATOM BIOFILMS

Acute grazer toxicity of freshwater diatom biofilms was determined using Thamnocephalus platyurus Packard, an anostracan grazer, as the bioassay organism. The diatoms exhibited toxicity when the cells of the biofilm were freeze–thawed before the assay. The toxicity could be extracted from the biofilms with methanol and acetone, and only minimal toxicity was left in the insoluble residue. Bioassay-guided HPLC separation of the methanolic extract was performed to trace the most toxic components. Analysis by UV spectrometry, gas chromatography, and mass spectrometry showed that 5,8,11,14,17-eicosapentaenoic acid was responsible for most grazer toxicity. The 24-h LC₅₀ of this polyunsaturated fatty acid was 34 μM in the Thamnocephalus platyurus bioassay. The concentrations of other free fatty acids were not high enough to contribute significantly to the toxicity. Procedures that affected the integrity of the cells (e.g. solvent extraction, freezing and thawing, osmotic stress by addition of 20% NaCl, or grinding the cells in a mortar) were taken as model reactions for grazing and had the common effect of resulting in a dramatic increase of free polyunsaturated and saturated fatty acids. Under these conditions, about 30% of the total fatty acids of the diatoms was transformed from the bound into the free form. The time necessary for liberation was very short. With the exception of 5,8,11,14,17-eicosapentaenoic acid, which continued to be liberated, the hydrolysis of the other fatty acids was terminated less than 1 min after initiating the reaction. The classical extraction procedures using methanol and other solvents led to the appearance of a high percentage of free fatty acids in live cells. Treatment of biofilms with these solvents did not stop the hydrolysis of lipids initiated by the disintegration of the cells. However, boiling acetone completely suppressed the hydrolytic reactions, and free polyunsaturated fatty acids were not detected in live biofilm organisms, although nontoxic saturated fatty acids were present in moderate concentrations. These results were interpreted as an indication that the frequently reported existence of free polyunsaturated fatty acids in live biomass is an analytical artifact.     

REGULATION OF FATTY ACID COMPOSITION BY IRRADIANCE LEVEL IN THE EUSTIGMATOPHYTE NANNOCHLOROPSIS SP.1

Chemical composition and quantitative cytological measurements were determined for the eustigmatophyte Nannochloropsis sp. Cultures were grown in turbidostats at three irradiance levels: growth-limiting light, growth-saturating light and photoinhibiting light. Cellular chlorophyll a content decreased as irradiance level increased, concomitant with a disproportionate reduction in carotenoid content. Nannochloropsis sp. grown in saturating light was characterized by a high content of lipid, fatty acids and carbohydrate compared with cells grown in light-limiting conditions. The increase in cellular lipid content coincided with a reduction in the percentage of eicosapentaenoic acid (C20:5) and arachidonic acid (C20:4), fatty acids that are mainly associated with galactolipids, and with an increase in the relative abundance of palmitic acid (C16:0) and palmitoleic acid (C16:1). At growth limiting light conditions, Nannochloropsis sp. preferentially synthesized galactolipids; however, as growth became light saturated, relatively more neutral lipids, mainly triacylglycerols, were synthesized. Changes in lipid content and composition were qualitatively related to changes in cell morphology. Cells grown under low light conditions were characterized by a large relative volume of chloroplast, high surface density of thylakoid membranes and low relative volume of lipid storage bodies. The physiological implications of the changes in cellular lipid composition and ultrastructure are discussed in relation to light/shade adaptation.     

QUANTITATIVE GENETICS OF FATTY ACID VARIATION IN ISOCHRYSIS GALBANA (PRYMNESIOPHYCEAE) AND PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

Fatty acid variation among culture collection strains and 40 new isolates of Isochrysis galbana Parke was analyzed by quantitative genetic methods. Fatty acid variation among strains and among isolates was highly significant for major fatty acids showing the existence of a genetic component in the determination of differences in fatty acid content. The heritabilities for the major fatty acids ranged between 0.68 and 0.99 among collection strains and between 0.31 and 0.43 among isolates. Eicosapentaenoic acid (EPA) had the highest heritability in I. galbana, but the majority of remaining fatty acids also showed high heritability values. A similar experiment with five UTEX strains of Phaeodactylum tricornutum also showed the presence of a genetic component in four out of seven major fatty acids. Nevertheless, the UTEX strains did not differ significantly in EPA content, although they showed a heritability of 0.40 for this fatty acid. An additional experiment culturing the same isolates of I. galbana in larger volumes of media showed that there was a high significant positive linear relation between EPA content in different volumes. Therefore, EPA content in small volume cultures was an unbiased indicator of EPA content in larger volume cultures. Our results provide support for the genetic determination of fatty acid content in microalgae and suggest that selection, and mutation and selection, are likely to improve EPA content in I. galbana and probably in many other microalgae. Such a selection program can be carried out in small-volume cultures with high confidence.     

RADIOLABELING STUDIES OF LIPIDS AND FATTY ACIDS IN NANNOCHLOROPSIS (EUSTIGMATOPHYCEAE), AN OLEAGINOUS MARINE ALGA1

The synthesis of fatty acids and lipids in Nannochloropsis sp. was investigated by labeling cells in vivo with [¹⁴C]-bicarbonate or [¹⁴C]-acetate. [¹⁴C]-bicarbonate was incorporated to the greatest extent into 16:0, 16:1, and 14:0 fatty acids, which are the predominant fatty acids of triacylglycerols. However, more than half of the [¹⁴C]-acetate was incorporated into longer and more desaturated fatty acids, which are constituents of membrane lipids. [¹⁴C]-acetate was incorporated most strongly into phosphatidylcholine, which rapidly lost label during a 5-h chase period. The label associated with phosphatidylethanolamine also decreased during the chase period, whereas label in other membrane lipids and triacylglycerol increased. The dynamics of labeling, along with information regarding the acyl compositions of various lipids, suggests that 1) the primary products of chloroplast fatty acid synthesis are 14:0, 16:0, and 16:1; 2) C₂₀ fatty acids are formed by an elongation reaction that can utilize externally supplied acetate; 3) phosphatidylcholine is a site for desaturation of C₁₈ fatty acids; and 4) phosphatidylethanolamine may be a site for desaturation of C₂₀ fatty acids.     

STUDY ON BIOLOGICAL CHARACTERISTICS OF HETEROTROPHIC MARINE MICROALGA—SCHIZOCHYTRIUM MANGROVEI PQ6 ISOLATED FROM PHU QUOC ISLAND,KIEN GIANG PROVINCE,VIETNAM1

Schizochytrium sp. PQ6, a heterotrophic microalga isolated from Phu Quoc (PQ) Island in the Kien Giang province of Vietnam, contains a high amount of docosahexaenoic acid (DHA, C22:6n‐3). In this study, the culture conditions are developed to maximize biomass and DHA production. Nucleotide sequence analysis of partial 18S rRNA gene from genomic DNA showed that PQ6 has a phylogenetic relationship close to Schizochytrium mangrovei Raghu‐Kumar. The highest growth rate and DHA accumulation of this strain were obtained in 6.0% glucose, 1.0% yeast extract, 50% artificial seawater (ASW), and pH 7 at 28°C. In addition, carbon and nitrogen sources could be replaced by glycerol, ammonium acetate, sodium nitrate, or fertilizer N–P–K. Total lipid content reached 38.67% of dry cell weight (DCW), in which DHA and eicosapentaenoic acid (EPA, C20:5n‐3) contents accounted for 43.58% and 0.75% of the total fatty acid (TFA), respectively. In 5 and 10 L fermenters, the cell density, DCW, total lipid content, and maximum DHA yield were 46.50 × 10⁶ cells · mL^?1, 23.7 g · L^?1, 38.56% of DCW, and 8.71 g · L^?1 (in 5 L fermenter), respectively, and 49.71 × 10⁶ cells · mL^?1, 25.34 g · L^?1, 46.23% of DCW, and 11.55 g · L^?1 (in 10 L fermenter), respectively. Biomass of PQ6 strain possessed high contents of Na, I, and Fe (167.185, 278.3, and 43.69 mg · kg^?1 DCW, respectively). These results serve as a foundation for the efficient production of PQ6 biomass that can be used as a food supplement for humans and aquaculture in the future.     

LIPID,FATTY ACID,AND STEROL COMPOSITION OF EIGHT SPECIES OF KARENIACEAE (DINOPHYTA): CHEMOTAXONOMY AND PUTATIVE LIPID PHYCOTOXINS1

The lipid class, fatty acid, and sterol composition of eight species of ichthyotoxic marine gymnodinioid dinoflagellate (Karenia, Karlodinium, and Takayama) species was examined. The major lipid class in all species was phospholipid (78%–95%), with low levels of triacylglycerol (TAG; 0%–16%) and free fatty acid (FFA; 1%–11%). The common dinoflagellate polyunsaturated fatty acids (PUFA), octadecapentaenoic acid (OPA 18:5ω3), and docosahexaenoic acid (DHA 22:6ω3), were present in all species in varying amounts (14%–35% and 8%–23%, respectively). The very‐long‐chain PUFA (VLC‐PUFA) 28:7ω6 and 28:8ω3 were present at low levels (<1%), and the ratio of these fatty acids may be a useful chemotaxonomic marker at the species level. The typical dinoflagellate sterol dinosterol was absent from all species tested. A predominance of the 4‐methyl and 4‐desmethyl Δ⁸⁽¹⁴⁾ sterols in all dinoflagellate species included 23‐methyl‐27‐norergosta‐8(14),22‐dien‐3β‐ol (Karenia papilionacea A. J. Haywood et Steid, 59%–66%); 27‐nor‐(24R)‐4α‐methyl‐5α‐ergosta‐8(14),22‐dien‐3β‐ol, brevesterol, (Takayama tasmanica de Salas, Bolch et Hallegraeff 84%, Takayama helix de Salas, Bolch, Botes et Hallegraeff 71%, Karenia brevis (C. C. Davis) G. Hansen et Moestrup 45%, Karlodinium KDSB01 40%, Karenia mikimotoi (Miyake et Kominami ex Oda) G. Hansen et Moestrup 38%); and (24R)‐4α‐methyl‐5α‐ergosta‐8(14),22‐dien‐3β‐ol, gymnodinosterol, (K. mikimotoi 48%, Karenia umbella de Salas, Bolch et Hallegraeff 59%, Karlodinium veneficum (D. L. Ballant.) J. Larsen 71%–83%). In Takayama species, five steroid ketones were identified, including for the first time the 3‐keto form of brevesterol and gymnodinosterol. These results indicate a biochemical link between sterol and steroid ketone biosynthesis, suggesting that selected dinoflagellates can make a significant contribution to ketones in marine sediments. The presence of steroid ketones, specific sterols, and fatty acids, and the ratio of VLC‐PUFA may prove to be a useful chemotaxonomic tool for distinguishing between morphologically similar species. The relative levels of the PUFA, OPA, and DHA, coupled with the potential inhibitory action of Δ⁸⁽¹⁴⁾ sterols, may provide an insight into the ichthyotoxicity of these bloom‐forming dinoflagellates.     

DETERMINING BLUBBER FATTY ACID COMPOSITION: A COMPARISON OF IN SITU DIRECT AND TRADITIONAL METHODS

Fatty acids (FAs) are used to make inferences about the foraging behavior and diets of free-ranging marine mammals. However, several methods are currently available for determining the FA composition of blubber and these methods may produce different results. We compared in situ direct transesterification methods, where a small amount of tissue is sampled, with more traditional methods involving prior lipid extraction of the entire sample of interest. Using gray seal ( Halichoerus grypus ) and beluga whale ( Delphinapterus leucas ) blubber, we found that when the direct in situ method was used on a 2-mg sample of blubber, the resulting FA profile differed significantly from that produced when traditional full-extraction methods were employed. Regardless of where the small spot sample was taken within the blubber depth, it was not representative of the entire blubber FA composition, as blubber is non-homogeneous throughout its depth. We also modified the in situ direct method to allow analysis of the entire blubber layer. Results of this full-layer direct method compared quite favorably with traditional extraction methods and may provide a reasonable alternative for analyses. Although application of our full-layer direct method will require further verification in certain marine mammal blubber samples, we conclude that the large differences obtained when using the direct method are not a consequence of the chemical method itself. Rather, they arise from non-representative sampling of the blubber FA composition.     

EFFECT OF NUTRIENT LIMITATION ON FATTY ACID AND LIPID CONTENT OF MARINE MICROALGAE1

Phaeodactylum tricornutum and Chaetoceros sp. (Badllariophyceae), Isochrysis galbana (clone T-Iso) and Pavlova lutheri (Prymnesiophyceae), Nannochloris atomus (Chlorophyceae), Tetraselmis sp. (Prasinophyceae), and Gymnodinum sp. (Dinophyceae) were cultured at different extents of nutrient-limited growth: 50 and 5% of μ_max. The lipid content of the algae was in the range 8.3–29.5% of dry matter and was generally higher in the Prymnesiophyceae than in the Prasinophyceae and the Chlorophyceae. Increasing extent of phosphorus limitation resulted in increased lipid content in the Bacillariophyceae and Prymnesiophyceae and decreased lipid content in the green flagellates N. atomus and Tetraselmis sp. The fatty acid composition of the algae showed taxonomic conformity, especially for the Bacillariophyceae, where the major fatty adds were 14:0, 16:0, 16:1, and 20:5n-3. These fatty acids were dominant also in the Prymnesiophyceae together with 22:6n-3. An exception was I. galbana, in which 18:1 was the major monounsaturated fatty add and 20:5n-3 was absent. The fatty acids of N. atomus and Tetraselmis sp. varied somewhat, but 16:0, 16:1, 18:1, 18:3n-3, and 20:5n-3 were most abundant. Gymnodinum sp. contained mainly 16:0, 18:4n-3, 20: 5n-3, and 22:6n-3. An increased level of nutrient limitation (probably phosphorus) resulted in a higher relative content of 16:0 and 18:1 and a lower relative content of 18:4n-3, 20:5n-3, and 22:6n-3. The nutrient limitation probably reduced the synthesis of n-3 polyunsaturated fatty acids.     

SEASONAL CHANGES IN THE PROXIMATE AND FATTY ACID COMPOSITION OF SOME NATURALLY GROWN FRESHWATER CHLOROPHYTES1

The protein content of the filamentous Cladophora glomerata (L.) Kz., Ulothrix zonata (Web, & Mohr) Kz. and Spirogyra sp., collected from natural populations for 1 year, averaged 8.0–12.4% of the total dry weight; whereas, the corresponding levels of lipid, cellulose and ash were 11.9–16.1%, 10.0–17.8% and 14.6–24.0%, respectively. Mean values for carbohydrates, estimated by difference, ranged from 32.8 to 56.0%. The colonial Scenedesmus dimorphus (Turp.) Kz. and the unicellular Cosmarium laeve Rab., on the other hand, contained more protein, lipid and carbohydrate (estimated by difference) averaging 13–15.0%, 22.5–25.9% and 415–46.8%, respectively, and less cellulose (7.5–9.8%) and ash (8.2–9.8%). A consistent pattern of seasonal variation in the proximate composition was not normally evident for any species, reflecting the influence of several environmental parameters on the algae. Cladophora contained the greatest amount of phospholipid averaging; 10% by weight of total lipid with the smallest quantity (5%) in Scenedesmus. The predominant phospholipid fatty acid in all species was C_18:1 followed by C_18:2, C_18:3 and C_16:1 in Cladophora, Ulothrix and Spirogyra, and C_16:1, C_18:2 and C_16:0 in Scenedesmus and Cosmarium. Oleic (C_18:1) and hexadecanoic (C_16:1) acids were predominant in the neutral lipids of all the algae, followed by C_16:0, C_18:2 and C_18:3. The concentration of the different fatty acids of each Species varied considerably during the year with the proportion of C_16:0 and C_16:1, usually rising and that of C_18:1 failing during the colder months.     

STEROL,FATTY ACID,AND PIGMENT CHARACTERISTICS OF UTEX 2341, A MARINE EUSTIGMATOPHYTE IDENTIFIED PREVIOUSLY AS CHLORELLA MINUTISSIMA (CHLOROPHYCEAE)1

An examination of the sterols of UTEX 2341, a small (ca. 2μm), nonmotile unicellular marine alga identified as Chlorella minutissima Fott et Novakova, yielded results inconsistent with any of 35 Chlorella strains analyzed previously. UTEX 2341 contained cholesterol as the principal sterol, with 24-methylenecholesterol, fucosterol, and isofucosterol also present; these are not dominant sterols in any other Chlorella species. Presence of eicosapentaenoic acid in UTEX 2341 also contrasted with fatty acids of Chlorella strains analyzed previously. Pigment analysis of UTEX 2341 revealed that it contained chlorophyll a, but not chlorophylls b or c; violaxanthin was the only major xanthophyll pigment. Both lipid and pigment compositions suggest that UTEX 2341 is not a member of the genus Chlorella but, rather, belongs in the Eustigmatophyceae; it may be Nannochloropsis sp. Cells with possible extracellular structures were present at an appreciable percentage of the stationary-phase population studied; centrifuging removed or collapsed these structures. The high cholesterol and polyunsaturated fatty acid contents of UTEX 2341 make it attractive as a potential aquaculturefeed, provided it is, or can be made, digestible.     

Lipid droplets formation in human endothelial cells in response to polyunsaturated fatty acids and 1‐methyl‐nicotinamide (MNA); confocal Raman imaging and fluorescence microscopy studies

In this work the formation of lipid droplets (LDs) in human endothelial cells culture in response to the uptake of polyunsaturated fatty acids (PUFAs) was studied. Additionally, an effect of 1‐methylnicotinamide (MNA) on the process of LDs formation was investigated. LDs have been previously described structurally and to some degree biochemically, however neither the precise function of LDs nor the factors responsible for LD induction have been clarified. Lipid droplets, sometimes referred in the literature as lipid bodies are organelles known to regulate neutrophil, eosinophil, or tumor cell functions but their presence and function in the endothelium is largely unexplored. 3D linear Raman spectroscopy was used to study LDs formation in vitro in a single endothelial cell. The method provides information about distribution and size of LDs as well as their composition. The incubation of endothelial cells with various PUFAs resulted in formation of LDs. As a complementary method for LDs identification a fluorescence microscopy was applied. Fluorescence measurements confirmed the Raman results suggesting endothelial cells uptake of PUFAs and subsequent LDs formation in the cytoplasm of the endothelium. Furthermore, MNA seem to potentiate intracellular uptake of PUFAs to the endothelium that may bear physiological and pharmacological significance.

Confocal Raman imaging of HAoEC cell with LDs.     

Climate warming is predicted to reduce omega‐3, long‐chain,polyunsaturated fatty acid production in phytoplankton

Phytoplankton are the main source of energy and omega‐3 (n‐3) long‐chain essential fatty acids (EFA) in aquatic ecosystems. Their growth and biochemical composition are affected by surrounding environmental conditions, including temperature, which continues to increase as a result of climate warming. Increasing water temperatures may negatively impact the production of EFA by phytoplankton through the process of homeoviscous adaptation. To investigate this, we conducted an exploratory data synthesis with 952 fatty acid (FA) profiles from six major groups of marine and freshwater phytoplankton. Temperature was strongly correlated with a decrease in the proportion of n‐3 long‐chain polyunsaturated FA (LC‐PUFA) and an increase in omega‐6 FA and saturated FA. Based on linear regression models, we predict that global n‐3 LC‐PUFA production will be reduced by 8.2% for eicosapentaenoic acid (EPA) and 27.8% for docosahexaenoic acid (DHA) with an increase in water temperature of 2.5 °C. Using a previously published estimate of the global production of EPA by diatoms, which contribute to most of the world's supply of EPA, we predict a loss of 14.2 Mt of EPA annually as a result of ocean warming. The n‐3 LC‐PUFA are vitally important for an array of key physiological functions in aquatic and terrestrial organisms, and these FA are mainly produced by phytoplankton. Therefore, reduced production of these EFA, as a consequence of climate warming, is predicted to negatively affect species that depend on these compounds for optimum physiological function. Such profound changes in the biochemical composition of phytoplankton cell membranes can lead to cascading effects throughout the world's ecosystems.     

Bioavailability and spatial distribution of fatty acids in the rat retina after dietary omega-3 supplementation

Spatial changes of FAs in the retina in response to different dietary n-3 formulations have never been explored, although a diet rich in EPA and DHA is recommended to protect the retina against the effects of aging. In this study, Wistar rats were fed for 8 weeks with balanced diet including either EPA-containing phospholipids (PLs), EPA-containing TGs, DHA-containing PLs, or DHA-containing TGs. Qualitative changes in FA composition of plasma, erythrocytes, and retina were evaluated by gas chromatography-flame ionization detector. Following the different dietary intakes, changes to the quantity and spatial organization of PC and PE species in retina were determined by LC coupled to MS/MS and MALDI coupled to MS imaging. The omega-3 content in the lipids of plasma and erythrocytes suggests that PLs as well as TGs are good omega-3 carriers for retina. However, a significant increase in DHA content in retina was observed, especially molecular species as di-DHA-containing PC and PE, as well as an increase in very long chain PUFAs (more than 28 carbons) following PL-EPA and TG-DHA diets only. All supplemented diets triggered spatial organization changes of DHA in the photoreceptor layer around the optic nerve. Taken together, these findings suggest that dietary omega-3 supplementation can modify the content of FAs in the rat retina.     

THE EFFECT OF GROWTH TEMPERATURE AND CULTURE DENSITY ON THE MOLECULAR SPECIES COMPOSITION OF THE GALACTOLIPIDS IN THE RED MICROALGA PORPHYHDIUM CRUENTUM (RHODOPHYTA)1

The effects of biomass concentration and growth temperature on the molecular species composition of the major galactolipids of the red microalga Porphyridium cruentum Nag. were detmined. At lower biomass concentrations, the Δ17 desaturation of arachidonic acid to eicosapentaenoic acid (20:5) was enhanced in both prokaryotic-type and eukalyotic-type molecular species of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol. We suggest that chloroplastic Δ17 desaturation is correlated with the availability of light. A reduction in the growth temperature led to an increase in the proportion of the eukalyotic molecular species of MGDG, especially for 20:5/ 20:5 MGDG, These results suggest that this molecular species, and perhaps eukaryotic molecular species in general, may play a role in the adaptation of cells to low growth temperatures.     

侧脑室注射胰高血糖素对兔血浆自由脂肪酸、血糖及胰岛素浓度的影响

胰高血糖素是一种脑-肠肽,但它在脑中的生理作用尚不清楚。本工作在家兔侧脑室埋藏慢性套管,并通过注射20μl含0.5—5μg的胰高血糖素溶液,在注射后的15、45、75、105分钟各取血样测定血糖、血浆自由脂肪酸(FFA)和胰岛素的浓度。结果发现:(1)对血糖及血浆胰岛素浓度无明显影响;(2)能引起血浆 FFA 浓度降低,且与剂量有依赖关系,在注射后的45分钟,FFA 降低最明显,以后逐渐恢复;(3)皮下注射阿托品(0.2mg/kg)或静脉注射酚妥拉明(5mg/kg)均不能消除侧脑室注射胰高血糖素降低 FFA 的作用;(4)静脉注射心得安(5mg/kg)能阻断侧脑室注射胰高血糖素的降低 FFA 的作用。这似表明脑中的胰高血糖素可能参与脂代谢的调节,并可能是通过肾上腺素β-受体起作用的。     

ALTERATIONS IN LIPID MOLECULAR SPECIES OF THE MARINE EUSTIGMA TOPHYTE NANNOCHLOROSIS SP.1

The molecular species of triacylglycerol and monogalactosyl diacylglycerol from the marine eustigmatophyte Nannochloropsis were analyzed by high-performance liquid chromatography with a flame ionization detector. Four major molecular species of triacylglycerol composed of C 14:0, C 16:0, and C 16:1 fatty acids at different combinations were identified. Six molecular species of monogalactosyl diacylglycerol were detected. Three of them contained C 20:5 fatty acid in the sn-1 position, and one component accommodated C 20:5 fatty acid in both the sn-1 and sn-2 positions. Variations in the relative distribution of the molecular species were further monitored in Nannochloropsis cultures grown under different irradiance levels and temperatures. The relative distribution of 16: 0/16:1/16:0 triacylglycerol increased in cells grown in high light and in high temperature. Variations in cellular fatty acid composition in Nannochloropsis grown under different environmental conditions of irradiance level and temperature were attributed to alterations in relative cellular content of lipid classes as well as in the relative composition of lipid class molecular species.