Unique Fatty Acid Composition Research Articles

Lipid rafts enriched in phosphatidylglucoside direct astroglial differentiation by regulating tyrosine kinase activity of epidermal growth factor receptors

Membrane lipid rafts provide a specialized microenvironment enriched with sphingolipids and phospholipids containing saturated fatty acids and serve as a platform for various intracellular signalling pathways. PtdGlc (phosphatidylglucoside) is a type of glycophospholipid localized in the outer leaflet of the plasma membrane. Owing to PtdGlc's unique fatty acid composition, exclusively composed of C(18:0) at sn-1 and C(20:0) at sn-2 of the glycerol backbone, it tends to form PGLRs (PtdGlc-enriched lipid rafts). Previously, we demonstrated that PGLRs reside on the cell surface of astroglial cells from fetal rat brain [Nagatsuka, Horibata, Yamazaki, Kinoshita, Shinoda, Hashikawa, Koshino, Nakamura and Hirabayashi (2006) Biochemistry 45, 8742-8750]. In the present study, we observed PGLRs in astroglial lineage cells at mid-embryonic to early-postnatal stages of developing mouse cortex. This suggests that PGLRs are developmentally correlated with astroglial differentiation during fetal cortical development. Our cell culture studies with multipotent neural progenitor cells prepared from fetal mouse telencephalon demonstrated that treatment with EGF (epidermal growth factor) or anti-PtdGlc antibody caused recruitment of EGFRs (EGF receptors) into lipid raft compartments, leading to activation of EGFRs. Moreover, the activation of EGFRs by antibody triggered downstream tyrosine kinase signalling and induced marked GFAP (glial fibrillary acidic protein) expression via the JAK (Janus kinase)/STAT (signal transducer and activator of transcription) signalling pathway. These findings strongly suggest that PGLRs are physiologically coupled to activated EGFRs on neural progenitor cells during fetal cortical development, and thereby play a distinct role in mediating astrogliogenesis.

Clostridium lavalense sp. nov., a glycopeptide-resistant species isolated from human faeces

Two vancomycin-resistant, strictly anaerobic, Gram-positive, rod-shaped, spore-forming organisms (strains CCRI-9842(T) and CCRI-9929) isolated from human faecal specimens in Québec, Canada, and Australia were characterized using phenotypic, biochemical and molecular taxonomic methods. Pairwise analysis of the 16S rRNA gene sequences showed that both strains were closely related to each other genetically (displaying 99.2 % sequence similarity) and represented a previously unknown subline within the Clostridium coccoides rRNA group of organisms (rRNA cluster XIVa of the genus Clostridium). Strains CCRI-9842(T) and CCRI-9929 used carbohydrates as fermentable substrates, producing acetic acid as the major product of glucose metabolism. The novel strains were most closely related to Clostridium asparagiforme, Clostridium bolteae and Clostridium clostridioforme, but morphological, biochemical and phylogenetic studies demonstrated that they represent a previously unidentified species of the genus Clostridium. This was confirmed by the unique cellular fatty acid composition of strains CCRI-9842(T) and CCRI-9929. Therefore, on the basis of data from the polyphasic taxonomic analysis, it is proposed that strains CCRI-9842(T) and CCRI-9929 represent a novel species of the genus Clostridium, for which the name Clostridium lavalense sp. nov. is proposed. The type strain is CCRI-9842(T) (=CCUG 54291(T)=JCM 14986(T)=NML 03-A-015(T)).

Morphology of the melon and its tendinous connections to the facial muscles in bottlenose dolphins (Tursiops truncatus)

The melon is a lipid-rich structure located in the forehead of odontocetes that functions to propagate echolocation sounds into the surrounding aquatic environment. To date, the melon's ability to guide and impedance match biosonar sounds to seawater has been attributed to its unique fatty acid composition. However, the melon is also acted upon by complex facial muscles derived from the m. maxillonasolabialis. The goal of this study was to investigate the gross morphology of the melon in bottlenose dolphins (Tursiops truncatus) and to describe how it is tendinously connected to these facial muscles. Standard gross dissection (N = 8 specimens) and serial sectioning (N = 3 specimens) techniques were used to describe the melon and to identify its connections to the surrounding muscles and blubber in three orthogonal body planes. The dolphin forehead was also thin-sectioned in three body planes (N = 3 specimens), and polarized light was used to reveal the birefringent collagen fibers within and surrounding the melon. This study identified distinct regions of the melon that vary in shape and display locally specific muscle-tendon morphologies. These regions include the bilaterally symmetric main body and cone and the asymmetric right and left caudal melon. This study is the first to identify that each caudal melon terminates in a lipid cup that envelopes the echolocation sound generators. Facial muscles of the melon have highly organized tendon populations that traverse the melon and insert into either the surrounding blubber, the connective tissue matrix of the nasal plug, or the connective tissue sheath surrounding the sound generators. The facial muscles and tendons also lie within multiple orthogonal body planes, which suggest that the melon is capable of complex shape change. The results of this study suggest that these muscles could function to change the frequency, beam width, and directionality of the emitted sound beam in bottlenose dolphins. The echolocation sound propagation pathway within the dolphin forehead appears to be a tunable system.

Fatty acid and oil variation in seed from kenaf ( Hibiscus cannabinus L.)

Kenaf ( Hibiscus cannabinus L.) is a fibre plant native to east-central Africa. The potential for using kenaf seeds as a source of edible oil is often overlooked when considering kenaf as a fibre and feed crop. The aim of this research was to study and compare the fatty acid composition and oil content of eight commercial kenaf varieties from various countries. Linoleic, oleic, and palmitic acid were the predominant fatty acids in all cultivars. Percentages of fatty acids varied greatly among different kenaf varieties. Gregg had the highest percentage of linoleic acid whilst El Salvador had the lowest. El Salvador had the highest percentage of oleic acid and Endora had the highest percentage of palmitic acid. Stearic acid and palmitic acid were positively correlated, as well as stearic and linoleic acid. Increasing stearic and linolenic acid and reducing palmitic acid at the same time therefore might be difficult through conventional breeding. The oil content was 19.84% on average and there was not much difference between the varieties. The relatively high oil content and the unique fatty acid composition, suggested that kenaf seed could be used as a source of edible oil. Kenaf oil can be considered nutritionally healthy because of the relatively high amount of monounsaturated and polyunsaturated fatty acids.

The small domain of cytochromeffrom the psychrophileChlamydomonas raudensisUWO 241 modulates the apparent molecular mass and decreases the accumulation of cytochromefin the mesophileChlamydomonas reinhardtii

Cytochrome f from the psychrophile Chlamydomonas raudensis UWO 241 has a lower thermostability of its c-type heme and an apparent molecular mass that is 7 kDa lower than that of the model mesophilic green alga Chlamydomonas reinhardtii. We combined chloroplast transformation, site-directed mutagensis, and the creation of chimeric fusion constructs to assess the contribution of specific domains and (or) amino acids residues to the structure, stability, and accumulation of cytochrome f, as well as its function in photosynthetic intersystem electron transport. We demonstrate that differences in the amino acid sequence of the small domain and specific charged amino acids in the large domain of cytochrome f alter the physical properties of this protein but do not affect either the thermostability of the c-type heme, the apparent half-life of cytochrome f in the presence of the chloroplastic protein synthesis inhibitor chloramphenicol, or the capacity for photosynthetic intersystem electron transport, measured as e-/P700. However, pulse-labeling with [14C]acetate, combined with immunoblotting, indicated that the negative autoregulation of cytochrome f accumulation observed in mesophilic C. reinhardtii transformed with chimeric constructs from the psychrophile was likely the result of the defective association of the chimeric forms of cytochrome f with the other subunits of the cytochrome b6/f complex native to the C. reinhardtii wild type. These results are discussed in terms of the unique fatty acid composition of the thylakoid membranes of C. raudensis UWO 241 adapted to cold environments.

Confirmation of a new food chain utilizing geothermal energy: Unusual fatty acids of a deep‐sea bivalve, Calyptogena phaseoliformis

Neutral and polar lipids of the cold‐seep clam Calyptogena phaseoliformis were determined to assess the trophic relationship at hydrothermal vents. The clam obtained many of its lipids from the chemosynthetic microorganisms within the bacteriocytes on its gill filaments. The major fatty acids in the triacylglycerols and phospholipids in the clam consisted only of the n‐4 family polyunsaturated fatty acids (PUFA) plus saturated and n‐7 monounsaturated fatty acids and were completely lacking n‐3 PUFA, such as docosahexaenoic acid (22:6n‐3) and icosapentaenoic acid (20:5n‐3). Such unique fatty acid composition markedly differs from those reported for other marine animals, which depend on organic matter derived from surface‐layer phytoplankton. The relationship between C. phaseoliformis and its symbiotic bacteria is documented and revealed a closed novel food chain, independent of the photosynthetic food chain. The fluidity of the fatty acids in the animal’s membrane are maintained by adaptation of the exogenous n‐4 family PUFA. These unusual but dominant fatty acids are assimilated from the symbiotic chemosynthetic bacteria, which use only geothermal energy and minerals from the cold‐seep vents.

Identification of novel n-4 series polyunsaturated fatty acids in a deep-sea clam, Calyptogena phaseoliformis

Novel fatty acids originated from the cold-seep clam Calyptogena phaseoliformis, collected from hydrothermal vents in the Japan Trench at a depth of 6354–6367 m, were determined by using gas chromatography–mass spectrometry analysis of the 4,4-dimethyloxazoline derivatives. The major fatty acids present in the C. phaseoliformis lipids belong to the n-4 family non-methylene interrupted polyunsaturated fatty acids (NMI-PUFA): 20:3 n-4,7,15, 20:4 n-1,4,7,15, and 21:3 n-4,7,16, with significant levels of 20:2 n-7,15 and 21:2 n-7,16 as non-methylene interrupted n-7 dienes. Compared with the lipids of shallow-water clam Mactra chinensis, which contains photosynthetic n-3 PUFA, such as docosahexaenoic acid and icosapentaenoic acid, C. phaseoliformis might have an intrinsic mechanism in vivo so as to maintain the fluidity of the high-melting fatty acids in the membrane lipids by exogenous n-4 family PUFA adaptation as substitutes. Such special kinds of fatty acids are assimilated by the symbiotic chemosynthetic bacteria, which use geothermal energy and minerals from the cold-seep vents. Its unique fatty acid composition corresponding to the novel n-4 family NMI-PUFA markedly differs from those of the reported lipid compositions of other marine animals, which depend on the marine grazing food chain originating from phytoplankton. Thus, the present findings confirm a perfect and closed novel food chain in the cold-seep bivalve and in its symbionts, which is independent from the photosynthetic food chain.

Atopy, eczema and breast milk fatty acids in a high‐risk cohort of children followed from birth to 5 yr

The incidence of atopic diseases such as eczema is increasing in westernized societies. The suggestion that there is a "protective" association between the unique fatty acid composition of breast milk, particularly the omega-3 (n-3) and omega-6 (n-6) essential polyunsaturated fatty acid content, and the development of atopic disease in children was investigated in a cohort study of 263 infants born into families with a history of allergy (one or both parents had asthma, hayfever, eczema). The objectives of this study were to determine the lipid profile [specifically in relation to long-chain polyunsaturated fatty acid (LC-PUFA) composition] in maternal breast milk samples collected at 6 wk and at 6 months following birth, and to investigate the potential role of these fatty acids in modulating the phenotype of children at high genetic risk of developing atopic disease. Breast milk samples were available from 91 atopic mothers at their child's ages of 6 wk and 6 months. These samples were analysed for the fatty acid spectrum. Analysis of variance was used to detect differences between groups of outcomes (no atopy or eczema, non-atopic eczema, atopy, atopic eczema) at ages 6 months and 5 yr, and a multiple comparisons procedure was conducted to isolate the parameters producing the different results (F-test, LSD test). For the exposure variables, n-3 and n-6 fatty acids are expressed as weight percentage and as a ratio (at both time-points). The fatty acid profiles of maternal breast milk at 6 wk and 6 months were similar. An increased ratio of n-6: n-3 fatty acids in both 6 wk and 6 month milk samples was associated with non-atopic eczema (p < 0.005) but not atopy alone or atopic eczema. We found milk fatty acids were a significant modulator of non-atopic eczema but not atopy or atopic eczema in infants at 6 months. In mothers with a history of asthma, hayfever or eczema, their 6-month-old infants were more likely to develop non-atopic eczema if their milk had a higher ratio of n-6: n-3 LC-PUFA.

Oxidative stability and phenolic content of virgin olive oil: An analytical approach by traditional and high resolution techniques

The characteristic resistance to oxidation of virgin olive oil is related to its unique fatty acid composition in addition to several minor components that have antioxidant properties. Among the latter, phenols are the most important. Several factors can influence the chemical or enzymatic oxidative processes that extend or shorten the shelf-life of olive oil. Furthermore, the amount of phenolic compounds extracted during production is fundamental for the oxidative and nutritional quality of the oil. In fact, it is well known that different steps used for preparation of virgin olive oil may determine differences in the quantities of phenol. At present, various analytical methods are available to analyze the hydrophilic components, including spectrophotometric assays (traditional) and high resolution chromatographic techniques (HRGC, HPLC, HPCE). In this review we summarize these different methodologies and demonstrate that the amount of phenolic compounds in virgin olive oil as determined by both traditional and high resolution techniques can be influenced by different factors including the olive cultivar and degree of ripeness, as well as by production and extraction technologies.

Influence of fatty acid methyl esters from hydroxylated vegetable oils on diesel fuel lubricity

Current and future regulations on the sulfur content of diesel fuel have led to a decrease in lubricity of these fuels. This decreased lubricity poses a significant problem as it may lead to wear and damage of diesel engines, primarily fuel injection systems. Vegetable oil based diesel fuel substitutes (biodiesel) have been shown to be clean and effective and may increase overall lubricity when added to diesel fuel at nominally low levels. Previous studies on castor oil suggest that its uniquely high level of the hydroxy fatty acid ricinoleic acid may impart increased lubricity to the oil and its derivatives as compared to other vegetable oils. Likewise, the developing oilseed Lesquerella may also increase diesel lubricity through its unique hydroxy fatty acid composition. This study examines the effect of castor and Lesquerella oil esters on the lubricity of diesel fuel using the High-Frequency Reciprocating Rig (HFRR) test and compares these results to those for the commercial vegetable oil derivatives soybean and rapeseed methyl esters.

Three Novel Soybean Germplasms with Unique Fatty Acid Composition using Multiple Mutant Alleles

Three soybean [Glycine max (L.) Merr.] germplasms were previously developed for unique fatty acid content: LPKKC-3 has fap1 and sop1 alleles for reduced palmitic acid, HPKKC-7 has fap2 and fapx alleles for elevated palmitic acid and DHL has the ol allele for elevated oleic acid, and fan and fanxa alleles for reduced linolenic acid. If these loci are independently inherited, soybean germplasms with useful combinations of these fatty acids could be developed that would result in a novel oil quality of great value for the food industry. Crosses were made between DHL and LPKKC-3, and DHL and HPKKC-7. The data from F2 seed and F2 progeny of DHL X LPKKC-3 indicated that the loci controlling reduced palmitic acid (fap1 and sop1) were independently inherited from the locus controlling elevated oleic acid (ol), and the loci controlling reduced linolenic acid (fan and fanxa). Thus, the germplasm (LPDHL) with 4.0% palmitic, 51.0% oleic and 2.9% linolenic acids was easily developed. The data from F2 seeds and F2 progeny of DHL X HPKKC-7 indicated that the loci controlling elevated palmitic acid (fap2 and fapx), and reduced linolenic acid (fan and fanxa) were independently inherited. The locus controlling elevated oleic acid (ol) was also distinctly segregated but the contents of oleic acid were found to be reduced due to the presence of loci for elevated palmitic acid. Thus, one germplasm (HPLL) with 22.5% palmitic acid and 2.7% linolenic acid, and another germplasm (MHPDHL) with 17.1% palmitic acid, 41.8% oleic and 2.9% linolenic acids were developed.

Charting molecular composition of phosphatidylcholines by fatty acid scanning and ion trap MS3 fragmentation

The molecular composition of phosphatidylcholines (PCs) in total lipid extracts was characterized by a combination of multiple precursor ion scanning on a hybrid quadrupole time-of-flight mass spectrometer and MS3 fragmentation on an ion trap mass spectrometer. Precursor ion spectra for 50 acyl anion fragments of fatty acids (fatty acid scanning) acquired in parallel increased the specificity and the dynamic range of the detection of PCs and identified the fatty acid moieties in individual PC species. Subsequent analysis of detected PC peaks by MS3 fragmentation on an ion trap mass spectrometer quantified the relative amount of their positional isomers, thus providing the most detailed and comprehensive characterization of the molecular composition of the pool of PCs at the low-picomole level. The method is vastly simplified, compared with conventional approaches, and does not require preliminary separation of lipid classes or of individual molecular species, enzymatic digestion, or chemical derivatization. The approach was validated by the comparative analysis of the molecular composition of PCs from human red blood cells. In the total lipid extract of Madin-Darby canine kidney II cells, we detected 46 PC species with unique fatty acid composition and demonstrated that the presence of positional isomers almost doubled the total number of individual molecular species.

Marine lipids in a cold coastal ecosystem: Gilbert Bay, Labrador

Some organisms living in coastal bays in Newfoundland and Labrador have to contend with sub-zero temperatures for most of the year. The goal of this study was to examine the lipid composition of the food web in such an environment in order to obtain information on essential nutrients and trophic relations. In August 2000, plankton, 16 species of macroinvertebrates, and sediments were collected in a shallow, sheltered bay, Gilbert Bay, southern Labrador (52°35′N; 55°50′W). Plankton had higher proportions of ω3 fatty acids (39±5%) and lower proportions of bacterial fatty acids (5±2%), while sediments had 12±5% ω3 fatty acids and 15±9% bacterial fatty acids. Plankton ω3 fatty acids levels and sediment bacterial fatty acid levels were higher than in equivalent samples previously collected further south, in Newfoundland. Benthic macroinvertebrates contained 0.5±0.4% of their wet weight as lipid, of which 45±15% was triacylglycerol. Levels of ω3 fatty acids were high and relatively constant across phyla, accounting for 36±11% of the total fatty acids. Compared to other invertebrates, echinoderms had a unique fatty acid composition, which was characterized by high levels of 20:4ω-6 (9±6%), bacterial fatty acids (8±4%), and ∑20:1+22:1 monoenoic fatty acids (13±6%). Baseline lipid data from plankton and macroinvertebrates showed constantly high levels of polyunsaturated fatty acids, indicating their physiological importance at low temperatures.

Fatty acid composition of the adipose tissue of polar bears and of their prey: ringed seals, bearded seals and harp seals

Polar bears Ursus maritimus are predators of phocid seals, but they also forage oppor- tunistically on a variety of other species. In the Barents Sea — Svalbard area, their diet is thought to consist almost exclusively of ringed seals Phoca hispida, bearded seals Erignathus barbatus and harp seals P. groenlandica. When a seal is killed, polar bears preferentially consume the blubber. The fatty acid (FA) compositions of the outer, middle and inner adipose layer of 18 polar bears were compared to each other and also with the FA composition of the blubber of their prey, represented by 10 ringed seals, 10 harp seals and 9 bearded seals. The composition of the FAs in the inner layer of the bear adi- pose tissue differed from the composition of the outer layer, and was also distinctly different from the composition of the blubber from the prey. Fifteen of the 28 FAs analysed were found in lower relative amounts in the polar bears than in any of the 3 seal species. Eight of the FAs were found in higher rel- ative amounts in polar bears when compared to the 3 prey species. Only 5 of the FAs in polar bears were within the range of relative values found in the prey. This strongly suggests that polar bear adi- pose tissue has a unique FA composition that is not a straightforward mixture of what they consume, but rather is the result of selective processes prior to and during deposition of lipids in the tissue.

The Surface of Lipid Droplets Is a Phospholipid Monolayer with a Unique Fatty Acid Composition

We found that caveolin-2 is targeted to the surface of lipid droplets (Fujimoto, T., Kogo, H., Ishiguro, K., Tauchi, K., and Nomura, R. (2001) J. Cell Biol. 152, 1079-1085) and hypothesized that the lipid droplet surface is a kind of membrane. To elucidate the characteristics of the lipid droplet surface, we isolated lipid droplets from HepG2 cells and analyzed them by cryoelectron microscopy and by mass spectrometry. By use of cryoelectron microscopy at the stage temperature of 4.2 K, the lipid droplet surface was observed as a single line without any fixation or staining, indicating the presence of a single layer of phospholipids. This result appeared consistent with the hypothesis that the lipid droplet surface is derived from the cytoplasmic leaflet of the endoplasmic reticulum membrane and may be continuous to it. However, mass spectrometry revealed that the fatty acid composition of phosphatidylcholine and lysophosphatidylcholine in lipid droplets is different from that of the rough endoplasmic reticulum. The ample presence of free cholesterol in lipid droplets also suggests that their surface is differentiated from the bulk endoplasmic reticulum membrane. On the other hand, although caveolin-2beta and adipose differentiation-related protein, both localizing in lipid droplets, were enriched in the low density floating fraction, the fatty acid composition of the fraction was distinct from lipid droplets. Collectively, the result indicates that the lipid droplet surface is a hemi-membrane or a phospholipid monolayer containing cholesterol but is compositionally different from the endoplasmic reticulum membrane or the sphingolipid/cholesterol-rich microdomain.

The accumulation pattern in developing seeds and its relation to fatty acid variation in soybean

AbstractSixty soybean cultivars from Japan and the USA formed five maturity groups (IIb‐Vc) based on number of days from sowing to flowering and number of days from flowering to maturity. Highly significant intervarietal differences in fatty acid composition were found in all the maturity groups, especially in IIc. Stearic and oleic acids showed a larger variation than palmitic, linoleic and linolenic acids. Principal component analysis suggested that the total variation of fatty acid composition depended mainly on the desaturation levels from oleic to linoleic acid. Three cultivars exhibiting unique fatty acid composition, together with a standard cultivar, were examined for the contents of the five fatty acids, as well as crude oil at eight seed‐filling stages. For all four cultivars, it was found that crude oil content increased sigmoidally with advancing filling stage, and that the accumulation patterns of palmitic, linoleic and linolenic acids were similar to that of crude oil. However, the accumulation pattern of stearic acid was different from that of crude oil and divided the cultivars into two distinct groups. For oleic acid, only the cultivar ‘Aburamame’ showed a rapid increase in proportion with advancing filling stage, although not differing markedly in accumulated content from the other cultivars. These results indicate that analysing the accumulation patterns of fatty acids could explain the latent genetic variation in fatty acid composition of soybean seeds.

Biological properties of lipid A isolated from Flavobacterium meningosepticum.

The biological properties of the lipid A from Flavobacterium meningosepticum, which we recently isolated and whose complete chemical structure has been determined (H. Kato, T. Iida, Y. Haishima, A. Tanaka, and K. Tanamoto. J. Bacteriol. 180:3891--3899, 1998), were studied. The lipid A exhibited generally moderate activity compared to Salmonella enterica subsp. enterica serovar abortus equi lipopolysaccharide (LPS) used as a control in the assay systems tested; lethal toxicity in galactosamine-sensitized mice, mitogenicity in mouse spleen cells, induction of tumor necrosis factor alpha (TNF-alpha) release from mouse peritoneal macrophages and J774-1 mouse macrophage-like and human THP-1 line cells, nitric oxide induction activity from J774-1 cells, and Limulus gelation activity. The moderate activity of the F. meningosepticum lipid A may be explained by its unique fatty acid composition and the lack of a phosphate group in position 4'. It is noteworthy that the lipid A apparently induced TNF-alpha release from peritoneal macrophages in LPS-unresponsive C3H/HeJ mice and that the activation was suppressed by the LPS-specific antagonist, succinylated lipid A precursor. Significant splenocyte mitogenicity in C3H/HeJ mice was also observed with the lipid A. Taken together with the previous results concerning Porphyromonas gingivalis lipid A, which has a high level of structural similarity to the lipid A of F. meningosepticum, and the induction of TNF-alpha release in macrophages from C3H/HeJ mice, the lipid A of F. meningosepticum, which has novel fatty acids, may possibly play an role for the activation of C3H/HeJ macrophages.

Electron microscopy may reveal structure of docosahexaenoic acid-rich oil within Schizochytrium sp.

Schizochytrium sp. is an algae-like microorganism utilized for commercial production of docosahexaenoic acid (DHA)-rich oil and dried microalgae for use as a source of DHA in foods, feeds, and nutritional supplements. Electron microscopic analysis of whole cells of Schizochytrium sp. employing sample preparation by high-pressure freeze substitution suggests the presence of secondary and tertiary semicrystalline structures of triacylglycerols within the oil bodies in Schizochytrium sp. A fine secondary structure consisting of alternating light- and dark-staining bands was observed inside the oil bodies. Dark bands were 29 +/- 1 A in width, and light bands were 22 +/- 1 A in width. The tertiary (three-dimensional) structure may be a multilayered ribbon-like structure which appears coiled and interlaced within the oil body. In freeze-fracture photomicrographs, Schizochytrium oil bodies exhibited fracture planes with terraces averaging 52 +/- 7 A in height which could correspond to the combined width of two halves of two light bands and one dark band observed in the high-pressure freeze substitution photomicrographs. The results suggest that triacylglycerols within Schizochytrium sp. oil bodies may be organized in a triple chain-length structure. High-pressure freeze substitution electron micrographs of two other highly unsaturated oil-producing species of microalgae, Thraustochytrium sp. and Isochrysis galbana, also revealed this fine structure, whereas microalgae containing a higher proportion of saturated oil did not. The results suggest that the staining pattern is not an artifact of preparation and that the triple chain-length conformation of triacylglycerols in Schizochytrium sp. oil bodies may be caused by the unique fatty acid composition of the triacylglycerols.

Response to divergent mass selection for plant architecture and earliness and its effect on seed yield in Dimorphotheca pluvialis

Seeds of Dimorphotheca pluvialis contain oil with a unique fatty acid composition, making it a potential raw material for several industrial applications. So far, the species has not been used in arable farming. The currently available plant populations show considerable variation for morphological and agronomic traits. Divergent mass selection for plant architecture and earliness was performed, aiming at the creation of more uniform populations and subsequently the determination of the plant ideotype. Three cycles of combined selection for plant architecture and earliness resulted in a significant response for both traits in both directions, even at a low selection pressure. Selection for early flowering or procumbent plant architecture showed a better response and a higher realised heritability than selection for late flowering or upright plant architecture. At low plant densities (4 plants/m 2), as used during selection, differences in plant architecture between procumbent and upright selections were clearly visible. However, at densities used in cultivation practice (50 plants/m 2), the crops produced by the two plant types looked remarkably similar; between the plots no clear differences in plant architecture could be seen. The different plant architecture selections showed similar flowering development and seed yield, and therefore no ideal plant architecture type could be defined with regard to breeding for increased seed yield. Earliness, however, had a significant effect on seed yield; early flowering selections showed the highest yields. Since genotype by year interactions could not be determined, no firm conclusions on the ideotype with regard to earliness should be drawn. Nevertheless, (very) late flowering selections in general are undesired in the Netherlands because of an increased risk of experiencing unfavourable weather conditions during flowering and seed set.

Unsaturated fatty acids.

There is good scientific evidence that dietary fatty acid composition is involved in the aetiology of many diseases. Increasing the supply of n-3 polyunsaturated fatty acids (PUFA) may reduce the risk of CHD. Several scientific organizations (for example, see Department of Health, 1991, 1994; British Nutrition Foundation, 1992; Scientific Committee for Food, 1993; Food and Agriculture Organization/World Health Organization, 1998) have made recommendations for n-3 PUFA; however, there is a high degree of variation both in terms of the type and amount of n-3 PUFA (up to 7-fold). This variation reflects the different scientific axioms which underlie the different recommendations. Optimal nutrition may be defined in terms of the level of a nutrient required to avoid deficiency, or the amount required to have an effect on biomarkers and functional indicators of nutrient intake, or the level of a nutrient which prevents disease. Functional biomarkers of n-3 PUFA include plasma, platelet and erythrocyte phospholipid-n-3 PUFA levels. Plasma triacylglycerol concentrations represent a functional indicator of n-3 PUFA because n-3 PUFA exert a consistent hypotriacylglycerolaemic effect which is dose-dependent and persistent. In terms of disease status, epidemiological studies have demonstrated that the incidence of CHD is inversely associated with consumption of n-3 PUFA. Despite the health benefits of n-3 PUFA, the mean daily intake falls far short of most of the recommendations. Increasing fish intake is the most obvious way to increase n-3 PUFA intake. However, a large percentage (up to 65) of the population do not eat fish. Thus, there is a need for alternative sources of n-3 PUFA, such as functional foods, whose unique fatty acid composition could fortify staple foods thereby promoting optimal levels of n-3 PUFA intake.