Gamma linolenic acid--occurrence and physical and chemical properties

Fatty acid content and juice characteristics in black currant (Ribes nigrum L.) genotypes

The fatty acid compositions of seeds from 29 black currant genotypes were determined using a rapid small-scale procedure. There was interest in alpha-linolenic, stearidonic, and, especially, gamma-linolenic acid (GLA) contents, and most samples showed values between 11.1 and 18.7%, between 2.5 and 4.5%, and between 11.6 and 17.4%, respectively. However, six genotypes exhibited gamma-linolenic contents >18%, and values >20% were recorded in four of these genotypes. The fatty acid contents of the six genotypes were also analyzed by using a conventional procedure, and only slight differences in fatty acid composition were found between the two methods. Although GLA content was not strongly correlated with juice parameters, some genotypes had both high GLA contents and desirable juice characteristics. The results obtained provide evidence that it is possible to select for GLA contents without negatively affecting juice quality, and both aspects can be combined in a single cultivar, thereby increasing the added value of the whole fruit.

Plants as 'chemical factories' for the production of polyunsaturated fatty acids

Polyunsaturated fatty acids (PUFAs) are valuable products because of their involvement in several aspects of human health. Market demand for most PUFAs is growing continually and current sources are considered insufficient for satisfying this demand; alternative sources are actively sought after. Oilseed plants can be a potential source of PUFAs if they are appropriately gene engineered. Most of the basic tools for genetic engineering of oilseed plants for giving them the ability to produce PUFAs are already developed. Here we review the prospects of genetic engineering of oilseed plants for producing some valuable long-chain polyunsaturated fatty acids. Genetic transformation for GLA production seems to be a near-term possibility, but gene engineering seems considerably more difficult for the other long-chain PUFAs. Nevertheless, with the current rapid pace of biotechnological advancement, the remaining difficulties may be surmounted in the near future.

γ-Linolenic acid enrichment from Borago officinalis and Echium fastuosum seed oils and fatty acids by low temperature crystallization

Solvent winterization of seed oil and free fatty acids (FFAs) was employed to obtain gamma-linolenic acid (GLA; 18:3omega6) concentrates from seed oils of two Boraginaceae species, Echium fastuosum and Borago officinalis. Different solutions of seed oils and FFAs from these two oils at 10%, 20% and 40% (w/w) were crystallized at 4 degrees C, -24 degrees C and -70 degrees C, respectively, using hexane, acetone, diethyl ether, isobutanol and ethanol as solvents. Best results were obtained for B. officinalis FFAs in hexane, reaching a maximum GLA concentration of 58.8% in the liquid fraction (LF). In E. fastuosum, the highest GLA concentration (39.9%) was also achieved with FFAs in hexane.

Lipids of the hexane extract from the roots of medicinal boraginaceous species

The chemical compositions of hexane extracts of the lipid fraction of the roots of the medicinal Boraginaceous species Alkanna tinctoria, Onosma heterophylla, Macrotomia densiflora and Onosma hispidium are presented and their phytochemical relevance evaluated. The predominating fatty acids in all of the root lipids were stearic, palmitic, oleic, linoleic and gamma-linolenic acids, while the latter and stearidonic acid predominated in the seeds and leaves of various Boraginaceous species. The indigenous presence of methyl, ethyl and isopropyl esters of fatty acids, reported for the first time in the roots of higher plants, is considered to be of particular importance in the biosynthesis of fatty substances. The results suggest the use of fatty acids as chemotaxonomic markers for Boraginaceous species and the utilisation of Boraginaceous species as new commercial sources for fatty acids with valuable medicinal and nutritional properties.

A Mucor rouxii mutant with high accumulation of an unusual trans-linoleic acid (9c,12t-C18:2)

Genetic and biochemical approaches reveal the existence of a gamma-linolenic acid biosynthetic pathway in Mucor rouxii. By treatment with ultraviolet light, combined with low temperature cultivation and filtration enrichment, a mutant defective in polyunsaturated fatty acid synthesis was isolated. Genetic analysis and fatty acid supplementation indicate that the defect occurred in the Delta(12)-desaturation resulting in the absence of cis-linoleic acid and gamma-linolenic acid and in the accumulation of monounsaturated fatty acids. In addition, an unusual fatty acid, trans-linoleic acid (9c,12t-C18:2), which has not been reported previously in this fungus, was found to increase in the mutant. The information gained from the mutant was used to develop the hypothetical pathway of fatty acid desaturation in M. rouxii.

High-level production of gamma-linolenic acid in Brassica juncea using a delta6 desaturase from Pythium irregulare

gamma-Linolenic acid (GLA), a nutritionally important fatty acid in mammals, is synthesized by a delta6 desaturase. Here, we report identification of PiD6, a new cDNA from the oleaginous fungus, Pythium irregulare, encoding a 459-amino acid protein that shares sequence similarity to carboxyl-directed desaturases from various species. Expression of PiD6 in yeast (Saccharomyces cerevisiae) revealed that it converts exogenously supplied linoleic acid into GLA, indicating that it encodes a delta6 fatty acid desaturase. Expression of the desaturase in Brassica juncea under the control of the Brassica napus napin promoter resulted in production of three delta6 unsaturated fatty acids (18:2-6, 9; 18:3-6, 9, 12; and 18:4-6, 9, 12, 15) in seeds. Among them, GLA (18:3-6, 9, 12) is the most abundant and accounts for up to 40% of the total seed fatty acids. Lipid class and positional analysis indicated that GLA is almost exclusively incorporated into triacylglycerol (98.5%) with only trace amounts found in the other lipids. Within triacylglycerols, GLA is more abundant at the sn-2 position.

Cloning and molecular characterization of the delta6-desaturase from two echium plant species: production of GLA by heterologous expression in yeast and tobacco

The synthesis of GLA (delta6,9,12-1-8:3) is carried out in a number of plant taxa by introducing a double bond at the delta6 position of its precursor, linoleic acid (delta9,12-18:2), through a reaction catalyzed by a delta6-desaturase enzyme. We have cloned genes encoding the delta6-desaturase (D6DES) from two different Macaronesian Echium species, E. pitardii and E. gentianoides (Boraginaceae), which are characterized by the accumulation of high amounts of GLA in their seeds. The Echium D6DES genes encode proteins of 438 amino acids bearing the prototypical cytochrome b(5) domain at the N-terminus. Cladistic analysis of desaturases from higher plants groups the Echium D6DES proteins together with other delta6-desaturases in a different cluster from that of the highly related delta8-desaturases. Expression analysis carried out in E. pitardii shows a positive correlation between the D6DES transcript level and GLA accumulation in different tissues of the plant. Although a ubiquitous expression in all organs is observed, the transcript is particularly abundant in developing fruits, whereas a much lower level is present in mature leaves. Functional characterization of the D6DES gene from E. gentianoides has been achieved by heterologous expression in tobacco plants and in the yeast Saccharomyces cerevisiae. In both cases, overexpression of the gene led to the synthesis of GLA. Biotechnological application of these results can be envisaged as an initial step toward the generation of transgenic oleaginous plants producing GLA.

Structured lipids via lipase-catalyzed incorporation of eicosapentaenoic acid into borage (Borago officinalis L.) and evening primrose (Oenothera biennis L.) oils

Enzymatic acidolysis of borage oil (BO) or evening primrose oil (EPO) with eicosapentaenoic acid (20:5n-3; EPA) was studied. Of the six lipases that were tested in the initial screening, nonspecific lipase PS-30 from Pseudomonas sp. resulted in the highest incorporation of EPA into both oils. This enzyme was further studied for the influence of enzyme load, temperature, time, type of organic solvent, and mole ratio of substrates. The products from the acidolysis reaction were analyzed by gas chromatography (GC). The highest incorporation of EPA in both oils occurred at 45-55 degrees C and at 150-250 enzyme activity units. One unit of lipase activity was defined as nanomoles of fatty acids (oleic acid equivalents) produced per minute per gram of enzyme. Time course studies indicated that EPA incorporation was increased up to 26.8 and 25.2% (after 24 h) in BO and EPO, respectively. Among the solvents examined, n-hexane served best for the acidolysis of EPA with both oils. The effect of the mole ratio of oil to EPA was studied from 1:1 to 1:3. As the mole ratio of EPA increased, the incorporation increased from 25.2-26.8 to 37.4-39.9% (after 24 h). The highest EPA incorporations of 39.9 and 37.4% in BO and EPO, respectively, occurred at the stoichiometric mole ratio of 1:3 for oil to EPA.

Genotypic variation in fatty acid content of blackcurrant seeds

The fatty acid composition and total fatty acid content of seeds from 36 blackcurrant genotypes developed at the Scottish Crop Research Institute were examined. A rapid small-scale procedure, involving homogenization of seeds in toluene followed by sodium methoxide transesterification and gas chromatography, was used. There was considerable variation between genotypes. The gamma-linolenic acid content generally varied from 11 to 19% of the total fatty acids, but three genotypes had higher values of 22-24%, levels previously not reported for blackcurrant seed and similar to those for borage seed. Other nutritionally important fatty acids, stearidonic acid and alpha-linolenic acid, varied from 2 to 4% and 10-19%, respectively. The mean total fatty acid contents ranged from 14 to 23% of the seed, but repeatability was poor. The results are discussed. Blackcurrant seeds are mainly byproducts from juice production, and the study shows the potential for developing blackcurrant genotypes with optimal added value.

Expression of borage Δ6 desaturase in Saccharomyces cerevisiae and oilseed crops

The borage Δ6 desaturase is a modular protein that contains a cytochrome b5-like domain attached to the N-terminus of the main catalytic domain. When the full-length open reading frame was expressed in two types of Saccharomyces cerevisiae strains, the endogenous cytochrome b5-disrupted strain and the cytochrome b5-competent wild type strain, the expressed enzyme introduced a double bond at the Δ6 position into the endogenous substrates 16:1(9) and 18:1(9), and also into the exogenously fed fatty acid substrates 18:2(9,12) and 18:3(9,12,15). However, the preferred substrates of the enzyme when expressed in yeast were 18:2(9,12) and 18:3(9,12,15), whereas 16:1(9) and 18:1(9) were relatively poor substrates. When the partial desaturase sequence with a deletion of the cytochrome b5-like domain at the N-terminus was introduced into the yeast strains, the truncated enzyme could not desaturate any of the supplied substrates. Introduction of the full-length cDNA into flax (Linum usitatissimum L.) under the control of a constitutive (35S) promoter resulted in accumulation of the two Δ6 desaturated fatty acids (18:3(6,9,12) and 18:4(6,9,12,15)), in one elite line, forming up to 22% of the total fatty acids in the stem, 19% in the root, and 11% in the leaf. Introduction of the desaturase into Brassica juncea (L.) Czern. under the control of the Brassica napus L. napin promoter resulted in accumulation of the Δ6 desaturated fatty acids at levels of up to 13% of the total fatty acids in mature seeds.Key words: borage, Δ6 desaturase, γ-linolenic acid, stearidonic acid, Brassica juncea, flax.

Occurrence and characterization of oils rich in gamma-linolenic acid (III): the taxonomical value of the fatty acids in Echium (Boraginaceae)

Fourteen species of the genus Echium (Fam. Boraginaceae) collected in the Macaronesia were surveyed in a search for high levels of gamma-linolenic acid (GLA, 18:3omega6) in the seed oil. High amounts of this fatty acid were found in all of them, ranging from 18.85% (E. pitardii var. pitardii) to 27.42% (E. gentianoides) on total seed fatty acids. The GLA content related to total seed weight was also significant, ranging from 1.26% (E. handiense) to 8.22% (E. gentianoides). In addition, considerable amounts of stearidonic acid (SA, 18:4omega3) were detected, ranging from 3.78% (E. bonnetii var. bonnetii) to 8.81% (E. pininana) on total fatty acids. Besides all the perennial species, the four herbaceous Echium taxa endemic to the Macaronesia also showed high GLA percentages. This is in contrast to the low GLA level found in continental Echium species, all of them bearing an herbaceous habit. These results are in good agreement with the available genetic data and show the ability of GLA to discriminate between Macaronesian and continental Echium species. The analysis of five other Macaronesian species belonging to plant families rich in GLA are also reported.

Occurrence and characterization of oils rich in gamma-linolenic acid Part I: Echium seeds from Macaronesia

Nineteen species of the genus Echium (Fam. Boraginaceae) collected in Macaronesia were surveyed in a search for new sources of gamma-linolenic acid (GLA, 18:3omega6). High amounts of this acid were found in all of them, ranging from 9.15% (E. plantagineum) to 26.31% (E. callithyrsum) of total seed fatty acids. The amounts of GLA related to total seed weight were also significant, ranging from 1.77% (E. sventenii) to 5.02% (E. nervosum). In addition, considerable amounts of stearidonic acid (SA, 18:4omega3) were detected, ranging from 3.03% (E. auberianum) to 12.94% (E. plantagineum) of total fatty acids. These data allow us to consider tile members of the genus Echium from Macaronesia as one of the richest sources of gamma-linolenic acid found so far in nature. The results obtained from multivariable data analysis and the taxonomic relationships among the species is discussed.

A rapid and quantitative method for total fatty acid analysis of fungi and other biological samples

A quantitative method for the one-step esterification and determination of absolute amounts of polyunsaturated fatty acids in biotechnologically produced fungal mycelia is proposed. A system of two internal standards was used to quantify the total fatty acid content of the samples by gas chromatography. The degree of methylation of the analyzed fatty acids was calculated using the internal standards, and subsequently this quotient was used to validate the derivatization and extraction reactions. By utilizing this degree of methylation, the corrected amounts of the various fatty acids in the sample can be calculated.

Delta6-fatty acid desaturase from an arachidonic acid-producing Mortierella fungus. Gene cloning and its heterologous expression in a fungus, Aspergillus

A DNA fragment was cloned from the fungal strain, Mortierella alpina 1S-4 (which is used industrially to produce arachidonic acid), after PCR amplification with oligonucleotide primers designed based on the sequence information for delta6-desaturase genes (from borage and Caenorhabditis elegans), which are involved in the desaturation of linoleic acid (delta9, delta12-18:2) to gamma-linolenic acid (delta6, delta9, delta12-18:3). This fragment was used as a probe to isolate a cDNA clone with an open reading frame encoding 457 amino acids from a M. calpina 1S-4 library. The predicted amino-acid sequence showed similarity to those of the above delta6-desaturases, and contained a cytochrome b5-like domain at the N-terminus, being different from the yeast delta9-desaturase which has the corresponding domain at the C-terminus. The full-length cDNA clone was expressed under the control of the amyB promoter in a filamentous fungus, Aspergillus oryzae, resulting in the accumulation of gamma-linolenic acid (which was not detected in the control Aspergillus) to the level of 25.2% of the total fatty acids. These findings revealed that the recombinant product has delta6-desaturase activity. The Mortierella delta6-desaturase is the first to be reported in fungi.

Occurrence of gamma-linolenic acid in compositae: a study of Youngia tenuicaulis seed oil

Seeds of Youngia tenuicaulis and other species from the plant family Compositae (Asteraceae) were studied for their oil content and fatty acid composition. The seed oil of Y. tenuicaulis growing in Mongolia was found to contain 5.6% gamma-linolenic acid (18:3delta6cis,9cis,12cis) in addition to common fatty acids. The oil was analyzed using chromatographic [capillary gas-liquid chromatography (GLC), thin-layer chromatography] and spectroscopic (infrared, gas chromatography-mass spectrometry) techniques. Seed oil fatty acids of Saussurea amara (containing gamma-linolenic acid) and of Arctium minus (containing 18:3delta3trans,9cis,12cis), as well as delta5cis- and delta5trans-18:3 were used as GLC reference substances. The evolution in this plant family of a large number of different 18:3 acids as well as the corresponding evolution of unusual desaturases should be investigated. On the other hand, the delta6cis-desaturase required for the biosynthesis of gamma-linolenic acid may have evolved independently several times in unrelated families of the plant kingdom.

Enhancement of gamma-linolenic acid production by the fungus Mucor sp LB-54 by growth temperature

As a relatively prolific producer of GLA, the strain of Mucor sp LB-54 was selected for a study at different growth temperatures in shaker flask culture. The strain used in our experiment was capable to accumulate a relatively high amount of intracellular lipid, 20.73 % of dry cell weight, and GLA content of 15 % of total fatty acids after 5 days of incubation at 28°C. As the growth temperature was decreased from 28 to 12°C the percentage of GLA increased from 15 to 24 % of total fatty acids. In order to optimize the culture conditions for rapid biomass production and lipid production with a high proportion of GLA, the fungus was grown at two temperature combinations associated supplies of carbon source (glucose) in the culture medium. Maximal production of GLA (74 mg/l) was obtained from the Mucor sp LB-54 strain after 5 days of incubation at 28°C in basal medium following glucose addition (7 % w/v) and incubation for an additional 3 days at 12°C. The identity of GLA found in the strain of Mucor sp LB-54 was confirmed by the coupled gas chromatography-mass spectrometry

Expression of a borage desaturase cDNA containing an N-terminal cytochrome b5 domain results in the accumulation of high levels of delta6-desaturated fatty acids in transgenic tobacco

gamma-Linolenic acid (GLA; C18:3 delta(6,9,12)) is a component of the seed oils of evening primrose (Oenothera spp.), borage (Borago officinalis L.), and some other plants. It is widely used as a dietary supplement and for treatment of various medical conditions. GLA is synthesized by a delta6-fatty acid desaturase using linoleic acid (C18:2 delta(9,12)) as a substrate. To enable the production of GLA in conventional oilseeds, we have isolated a cDNA encoding the delta6-fatty acid desaturase from developing seeds of borage and confirmed its function by expression in transgenic tobacco plants. Analysis of leaf lipids from a transformed plant demonstrated the accumulation of GLA and octadecatetraenoic acid (C18:4 delta(6,9,12,15)) to levels of 13.2% and 9.6% of the total fatty acids, respectively. The borage delta6-fatty acid desaturase differs from other desaturase enzymes, characterized from higher plants previously, by the presence of an N-terminal domain related to cytochrome b5.

Separation of gamma- and alpha-linolenic acid containing triacylglycerols by capillary supercritical fluid chromatography

The separation of gamma- and alpha-linolenic acid containing triacylglycerols with an identical acyl carbon number and degree of unsaturation was obtained on capillary supercritical fluid chromatography using a 25% cyanopropyl-75% methylpolysiloxane stationary phase. The resolution of 1,3-dioleoyl-2-alpha-linolenoyl-sn-glycerol was 1.35 on a 10 m x 50 microns i.d. column, whereas the resolution was enhanced to 1.66 by combining two 10-meter columns in series. The difference in the position of double bonds in one linolenic acid residue of triacylglycerols resulted in two series of peaks in the separation of alpine currant (Ribes alpinum) and black currant (R. nigrum) seed oils. The use of the 10-meter column was found to be appropriate for the screening of the triacylglycerol profile in both seed oils studied.

Cholesterol condensation of alpha-linolenic and gamma-linolenic acid-containing phosphatidylcholine monolayers and bilayers

Cholesterol is demonstrated to condense phosphatidylcholine (PC) monolayers and bilayers containing stearic acid in the sn-1 position and alpha-linolenic acid in the sn-2 position (18:0, alpha-18:3 PC) but has no effect when gamma-linolenic acid occupies the sn-2 position (18:0,gamma-18:3 PC). Cholesterol-induced condensation is measured by area/molecule determinations made on monolayers using a Langmuir trough, while condensation in bilayers is followed by the fluorescent dyes merocyanine (MC540) and dansyllysine. Permeability to erythritol is also demonstrated to be diminished by cholesterol for the condensable 18:0,alpha-18:3 PC bilayer membranes but not the 18:0,gamma-18:3 PC membranes. alpha- and gamma-linolenic acid are isomers containing 18 carbons and three unsaturations. Both fatty acids have unsaturations at positions 9 and 12 and differ only in the location of the third unsaturation, at either position 6 for gamma-linolenic acid (an omega-6 fatty acid) and at position 15 for alpha-linolenic acid (an omega-3 fatty acid). Here lipid-cholesterol interaction is used to distinguish the effect of position of unsaturation on membrane structure.

Gamma-linolenic acid suppression of hepatic Ito cell mitogenesis: post-PDGF receptor prostaglandin-independent mechanism

Ito cell mitogenesis occurs during liver injury and fibrogenesis in vivo. Platelet-derived-growth factor (PDGF)-induced mitogenesis was studied in cultured rat hepatic Ito cells, which resemble the myofibroblast associated with liver injury. Pretreatment with gamma-linolenic acid (GLA), an essential fatty acid prostanoid precursor, markedly suppressed the PDGF response in a dose-dependent reversible fashion. Prostaglandins E1 and E2 were found to be the predominant prostanoids formed by cultured Ito cells. GLA depressed endogenous PG production, suggesting that the antimitogenic effect was independent of GLA conversion to a prostanoid metabolite. The PDGF-induced cascade was studied with and without GLA to determine the level of regulation that induced the observed suppression. GLA caused no apparent diminution in the abundance of the surface PDGF-beta receptor nor its subsequent activation and tyrosine phosphorylation after PDGF stimulation. Raf kinase activation and Raf perinuclear translocation were also intact despite the presence of GLA. PDGF induction of nuclear Egr and Fos also occurred with or without GLA. Activation of the serine threonine kinase c-Raf has previously been found to be sufficient to activate egr and fos and to induce mitogenesis. Therefore, the GLA suppressive effect is likely to be operative at a parallel non-Raf pathway or distal to Raf-induced early gene expression.