Mass spectral characterization of fatty acid amides from alfalfa trichomes and their deterrence against the potato leafhopper

A homologous series of N-(3-methylbutyl)amides of normal saturated C14, C15, C16, C17 and C18 fatty acids were identified as major components of glandular trichome extracts from Medicago sativa G98A, an alfalfa genotype resistant to the potato leafhopper, Empoasca fabae. A second homologous series of N-(2-methylpropyl)amides of C14 through C18 normal fatty acids were minor components. Saturated free fatty acids C12, C13, C14, C15, C16, C17 and C18 were present in trace amounts, as was the N-(3-methylbutyl)amide of linoleic acid (C18:2). N-(3-methylbutyl)amides and N-(2-methylpropyl)amides of C14 through C18 fatty acids, along with the N-(3-methylbutyl)amide of linoleic acid, were synthesized and bioassayed for leafhopper deterrence by applying the compounds to the surface of a sachet containing an artificial diet. Leafhoppers were then offered a two-way choice between diet surfaces treated with the synthetic amides or an untreated control. N-(3-methylbutyl)amides and N-(2-methylpropyl)amides of C14 through C18 fatty acids did not deter leafhopper settling in a dose-dependent fashion. In contrast, when tested singly, N-(3-methylbutyl)amide of linoleic acid exhibited dose-dependent deterrence against leafhopper settling. Fatty acid amides localized in alfalfa glandular trichomes likely contribute to leafhopper resistance.     

Novel diterpenoids and hydrocarbons in the Dufour gland of the ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae)

Chemical constituents contained in the Dufour gland of the ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae) were characterized. Three terpenes, beta-springene, a homo-beta-springene, and a homo-geranyllinalool constitute approximately 37% of the gland components, with the remaining 63% all being hydrocarbons. The hydrocarbons consist of a homologous series of n-alkanes (n-C21 to n-C31), a trace amount of 3-methyl C23, a homologous series of internally methyl-branched alkanes (11-methyl C23 to 13-methyl C35), one dimethylalkane (13,17-dimethyl C33), a homologous series of monoenes (C(25:1) to C(37:1)) with the double bonds located at Delta9, Delta13 and Delta15 for alkenes of carbon number 25 to 31 and at Delta13 and Delta15 for carbon numbers 33 to 37 and three homologous dienes in very low amounts with carbon numbers of 31, 32, and 33. The terpenoid and hydrocarbon composition of the Dufour gland was similar in virgin and mated females. However, in contrast to the hydrocarbons, the amount of beta-springene and homo-geranyllinalool increased significantly with time after adult emergence from the cocoon. Although many hydrocarbons in the Dufour gland are the same as those on the cuticle of this species [Howard and Baker, Arch. Insect Biochem. Physiol. 53:1-18 (2003)], substantial differences also occur. Of particular note is the chain length of alkenes and location of the double bonds: cuticular alkenes have a chain length of C23 to C29 and double bond locations at Delta5, Delta7, and Delta9, whereas the Dufour gland alkenes contains a greater range of carbon numbers and have no Delta5 or Delta7 alkenes. The Dufour gland contains only one of the long-chain dimethylalkanes found on the cuticle. Also, no terpenoids are found on the cuticle, and the Dufour gland contains none of the secondary wax esters that are major components on the cuticle. GC-MS analysis of lipids carried in the hemolymph of H. hebetor indicated that all hydrocarbons found on both the cuticle and in the Dufour gland are present, as are some of the wax esters. However, none of the terpenoids were detected in the hemolymph. This suggests that the hydrocarbons are synthesized in other tissues or cells, probably by oenocytes, and differentially partitioned between the cuticle and the Dufour gland. The terpenoids are most likely synthesized within the Dufour gland. Analysis of surface lipids from eggs laid within 18 h indicated that no diterpenoids were present. Rather, the lipids present on the eggs were n-alkanes, monomethylalkanes, alkenes, and secondary alcohol wax esters. This composition did not reflect that of the Dufour gland, hence eggs are not being coated with Dufour gland components during oviposition.     

Analyses of barley spike mutant waxes identify alkenes, cyclopropanes and internally branched alkanes with dominating isomers at carbon 9

About 15% of the epidermal wax on Hordeum vulgare cv. Bonus barley spikes is n-alkanes. Longer homologues are greatly reduced in the eceriferum mutants, cer-a(6), cer-e(8), cer-n(26), cer-n(53), cer-n(985), cer-x(60), cer-yc(135) and cer-yl(187). Simultaneously hydrocarbons accounting for only traces in the wild-type become prominent in the mutants, although their chain-length distributions remain unchanged. Accordingly several new hydrocarbon series were identified. The two major ones were C(23)-C(35)cis monoenoic alkenes (the major 9-ene isomer was part of a homologous series including 11, 13 and 15-enes), and the novel C(27)-C(31) cyclopropanes (the ring carbons of major isomers were 9,10 and 11,12 with lesser amounts of 13,14). Three minor series included 2- and 3-methylalkanes plus C(25)-C(33) internally branched alkanes (methyls on carbons 9, 11, 13, 15 or 17; shorter homologues dominated by the 9 isomer, longer homologues by 11, 13 or 15 isomers). Acyl chains destined for spike waxes are synthesized via acyl and polyketide elongase systems plus associated reductive and decarbonylative/decarboxylative enzyme systems. Both elongation systems are defective in synthesizing C(32) acyl chains in all nine mutants. The similarities in the position of the chemical groups (primarily on carbon 9, secondarily on carbon 11) of the alkenes, cyclopropanes and internally branched methyl alkanes imply an origin from a common, hitherto unrecognized associated pathway in barley, designated the enoic pathway. The elongation system leading to the enoic derived hydrocarbons differs from the known elongation systems by inclusion of a mechanism for introducing a double bond.     

Structure and molecular species composition of three homologous series of alpha-mycolic acids from Mycobacterium spp

Three homologous series of alpha-mycolic acids (dicyclopropanoyl acids, monocyclopropanoyl monoenoic acids and dienoic acids) from 16 rapidly growing and 14 slowly growing mycobacteria were separated by argentation thin-layer chromatography and analysed by gas chromatography/mass spectrometry of their trimethylsilyl ether derivatives. Mycobacterial species were separated into five groups. Strains of group A contained similar amounts of even and odd carbon-numbered dienoic acids, with a methyl branch on the odd acids and a C24-alpha-unit, as typified by Mycobacterium fortuitum and M. chitae. Group B strains possessed similar amounts of even carbon-numbered dicyclopropanoyl alpha-mycolic acids and odd carbon-numbered unsaturated acids with C22- and C24-alpha-units, as found in M. phlei and M. diernhoferi. Group C strains contained mainly even carbon-numbered dicyclopropanoyl acids with C22- and C24-alpha-units, as shown by M. vaccae and M. aurum. Group D strains possessed mainly odd carbon-numbered dienoic acids with a methyl branch and a C24-alpha-unit, as seen in M. triviale and M. nonchromogenicum. Group E strains had mainly even carbon-numbered dicyclopropanoyl acids with C24- or C26-alpha-units, as found in M. avium and M. tuberculosis. Many rapidly growing mycobacteria also produced alpha'-mycolic acids which were shorter in the length of the main carbon chain but whose alpha-units were the same as those in alpha-mycolic acids from the same species. These alpha'-mycolic acids had either one or two double bonds and showed variations in both their unsaturation and overall size, which may be useful in taxonomic studies.     

Very long chain alkylresorcinols accumulate in the intracuticular wax of rye (Secale cereale L.) leaves near the tissue surface

Alkylresorcinols (ARs) are bioactive compounds occurring in many members of the Poaceae, likely at or near the surface of various organs. Here, we investigated AR localization within the cuticular wax layers of rye (Secale cereale) leaves. The total wax mixture from both sides of the leaves was found to contain primary alcohols (71%), alkyl esters (11%), aldehydes (5%), and small amounts (<3%) of alkanes, steroids, secondary alcohols, fatty acids and unknowns. A homologous series of ARs (3%) was identified by GC-MS and comparison with a synthetic standard of nonadecylresorcinol. The alkyl side chains of the wax ARs contained odd numbers of carbons ranging from C19 to C27, with a prevalence of C21, C23 and C25. Waxes from both sides of the leaf, analyzed separately in a second experiment, comprised the same compound classes in similar relative amounts and with similar homolog patterns. Finally, the epicuticular and intracuticular wax layers were sampled separately from the abaxial side of the leaf. While ARs accounted for 2% of the intracuticular wax, they were not detectable in the epicuticular wax. The intracuticular wax was also slightly enriched in steroids, whereas the epicuticular layer contained more primary alcohols. All other wax constituents were distributed evenly between both wax layers.     

Laetiporic acids, a family of non-carotenoid polyene pigments from fruit-bodies and liquid cultures of Laetiporus sulphureus (Polyporales, Fungi)

The non-isoprenoid polyene laetiporic acid A, recently described from fruit-bodies of the wood-rotting fungus Laetiporus sulphureus, was found to be the major orange pigment also in mycelium grown in liquid culture. Its formation was variable, ranging from 0.1 to 6.7 mg/g dry weight in three strains, all of which were identified as L. sulphureus by ITS rDNA sequence analysis. A second pigment, 2-dehydro-3-deoxylaetiporic acid A, is also described and fully characterized by NMR spectroscopy. Two further minor pigments, laetiporic acids B and C, were produced in liquid culture. These resemble laetiporic acid A but are enlarged by two and four carbon atoms, respectively, resulting in chromophores with 11 or 12 instead of 10 conjugated double bonds as described for laetiporic acid A. Since fruit-bodies of L. sulphureus are edible, laetiporic acids might hold potential as food colourants.     

Synthesis of four isomers of parinaric acid

A simple and reliable method for synthesizing four isomers of parinaric acid from alpha-linolenic acid (ALA) in high yields is described. The methylene-interrupted, cis triene system (1,4,7-octatriene) of ALA and common to other naturally occurring polyunsaturated fatty acids was transformed to a conjugated tetraene system (1,3,5,7-octatetraene). The synthesis involves bromination of ALA using 0.l M Br(2) in a saturated solution of NaBr in methanol, esterification of the fatty acid dibromides, double dehydrobromination by 1,8-diazabicyclo[5.4.0]undec-7-ene and saponification of the conjugated esters to a mixture of free conjugated acids. Addition of one molecule of bromine to the 12,13-double bond of ALA and subsequent dehydrobromination produces alpha-parinaric acid (9Z,11E,13E,15Z-octadecatetraenoic acid); addition of Br(2) to the 9,10-double bond or 15,16-double bond and then dehydrobromination and rearrangement yields 9E,11E,13E,15Z-octadecatetraenoic or 9E,11E,13E,15Z-octadecatetraenoic acids, respectively. The mixture of parinaric acid isomers is obtained in 65% yield, and the isomers can be purified by preparative HPLC; alternatively, the isomers can be converted by base catalyzed cis-trans isomerization (or by treatment with I(2)) to exclusively beta-parinaric acid (9E,11E,13E,15E-octadecatetraenoic acid). The various parinaric acid isomers were characterized by (1)H NMR, (13)C NMR, UV, GLC, HPLC and mass spectrometry.     

Applications of chromic acid-celite columns to lipid analysis. Location of double bond position in submicro- and microgram amounts of methyl octadecenoates.

A procedure for locating the double bond position in a series of methyl octadecenoates is detailed. Submicrogram or microgram amounts of substrate dissolved in CS₂ are brought in contact with a very small column of chromic acid on Celite, and the oxidation products (car?ylic acids) are eluted, converted to methyl esters, and resolved by gas-liquid chromatography. Beside the acids resulting from scission of the double bond, acids containing one less carbon atom arise from oxidation of the allylic carbons on both sides of the double bond so that pairs of peaks appear on the chromatogram. All positions from Δ3 to Δ17 were located successfully. The Δ2 position failed to oxidize.     

Regiospecific oxygenation of alkenones in the benthic haptophyte Chrysotila lamellosa Anand HAP 17

Two groups of previously unidentified C37-C39 epoxyalkenones and alkenediones were detected in late stationary phase cultures of the haptophyte microalga Chrysotila lamellosa. The formation of these compounds is attributed to the involvement of enzymatic processes acting specifically on the C-21 or C-22 allylic carbon and the omega15 double bond of methyl and ethyl alkenones respectively. Thus, the epoxyalkenones appear to be derivatives of alkenones where the omega15 double bond is oxidized to the epoxide. These epoxyalkenones disappear as the cells age to be replaced by a series of alkenediones. The structures of these compounds indicate that they are derivatives of methyl and ethyl alkenones with an additional carbonyl group on the C-21 or C-22 carbon respectively and without the omega15 double bond. We propose that these compounds are formed by an initial regiospecific lipoxygenase-catalyzed peroxidation of methyl and ethyl alkenones on their C-21 or C-22 allylic carbon, respectively. Lipohydroperoxidase-catalyzed homolytic cleavage of the O-O bond could then result in the formation of conjugated ketones which may then undergo a saturation reaction to form the diketones identified. This work demonstrates that alkenones can be degraded by enzymatic reactions in senescent cells, and by implication this could also occur in the natural environment.     

Seasonal and within-plant gradients in the intramolecular carbon isotopic composition of amino acids of Spartina alterniflora

Autotrophy and heterotrophy create different patterns of carbon flux through the central metabolic pathway. One consequence of these different fluxes is that the α-carboxyl carbon of amino acids is derived from different carbon sources and has a different isotopic composition under autotrophic and heterotrophic conditions. In Spartina alterniflora, a C4 grass and a common and ecologically important component of coastal ecosystems, the isotopic composition of bulk acid hydrolyzable carbon and total amino acid carboxyl carbon were compared over a seasonal cycle. The isotopic composition of plants varied significantly between aboveground and below ground tissues, and the δ¹³C of both hydrolyzable organic carbon and total amino acid carboxyl carbon showed significant variation among seasons. The isotopic heterogeneity within amino acids was used to infer seasonal changes in source/sink relationships for amino acid carbon among plant organs. Comparison of the intramolecular isotope data for Spartina and C3 freshwater marsh plants indicates that the patterns and processes inferred for Spartina are not unique to this taxon.     

Mechanistic characterization of omega-3 desaturation in the green alga Chlorella vulgaris

alpha-Linolenic acid (ALA, 9(Z),12(Z),15(Z)-octadecatrienoic acid) derivatives are important plant lipids which play a critical key role in cold tolerance. The final steps of ALA biosynthesis feature a series of regio- and stereoselective dehydrogenation reactions which are catalyzed by a set of enzymes known as fatty acid desaturases. In conjunction with ongoing research into the structural biology of these remarkable catalysts, we have examined the mechanism of double bond introduction at C15,16 as it occurs in a model photosynthetic organism, Chlorella vulgaris. The individual deuterium kinetic isotope effects associated with the C-H bond cleavages at C-15 and C-16 of a thialinoleoyl analogue were measured via competition experiments using appropriately deuterium-labelled 7-thia substrates. A large kinetic isotope effect (KIE) (k(H)/k(D)=10.2+/-2.8) was observed for the C-H bond-breaking step at C-15 while the C-H bond cleavage at C-16 was found to be relatively insensitive to deuterium substitution (k(H)/k(D)=0.8+/-0.2). These results point to C-15 as the site of initial oxidation in omega-3 desaturation and imply that the Chlorella and corresponding plant systems share a common active site architecture.     

Antioxidant dehydrotocopherols as a new chemical character of Stemona species

From the roots of various Stemona species four new dehydrotocopherols (chromenols) were isolated and their structures and stereochemistry elucidated by spectroscopic methods. The double bond between C-3 and C-4 proved to be a typical chemical character of the genus found in most of the species. Various C-methylations of the aromatic ring reflect differences in methyltransferase activities and agreed with the current species delimitations showing an exclusive accumulation of dehydro-delta-tocopherol for the Stemona tuberosa group, whereas different provenances of Stemona curtisii were characterized by dehydro-gamma-tocopherol accompanied by small amounts of dehydro-alpha-tocopherol. From Stemona collinsae all four tocopherols were isolated with a clear preponderance of dehydro-delta-tocopherol accompanied by smaller amounts of the rare dehydro-beta-tocopherol. Stemona burkillii and a group of unidentified species showed a weak accumulation trend towards dehydro-alpha-tocopherol, whereas Stemona cochinchinensis and especially Stemona kerrii clearly differed by a preponderance of chromanol derivatives. In Stemona cf. pierrei no tocopherols could be detected at all. Based on TLC tests and microplate assays with the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH*) the antioxidant capacities of all chromenol derivatives were comparable with that of alpha-tocopherol showing no significant differences among each other, except for a more rapid kinetic behaviour of the 5,7,8-methylated dehydro-alpha-tocopherol.     

Identification of the cuticular lipid composition of the Western Flower Thrips Frankliniella occidentalis

The Western Flower Thrips Frankliniella occidentalis effectively resists many insecticides, but it can be controlled by the use of bioinsecticides such as entomopathogenic fungi. The epicuticular chemistry of these insects is therefore of great interest, and accordingly, the cuticular lipid composition of F. occidentalis was analysed. It was found that the cuticular lipids of both the adult and larval stages of F. occidentalis consist of two groups of compounds--hydrocarbons and free fatty acids. The same hydrocarbon pattern was found in both adults and larvae, with the exception of n-hentriacontane, which was detected only in adult insects. The following homologous series were identified: n-alkanes from C-25 to C-29 (31) with the marked dominance of odd numbers of carbon atoms, 3-methylalkanes with 26 and 28 carbon atoms, and branched monomethylalkanes (branched at C-9, -11, -13 and -15) with 26, 28 and 30 carbon atoms. The chemical composition of the free fatty acids consists of two homologous series: saturated (C(14:0), C(16:0), C(18:0)) and unsaturated fatty acids (C(16:1) and C(18:1)). This analysis confirmed the lack of potential inhibitors of entomopathogenic fungi in the cuticular lipids of this insect species.     

Characterization of mycolic acids from the pathogen Rhodococcus equi by tandem mass spectrometry with electrospray ionization

We describe a simple tandem mass spectrometric approach toward structural characterization of mycolic acids, the long-chain α-alkyl-β-hydroxy fatty acids unique to mycobacteria and related taxa. On collisionally activated dissociation in a linear ion trap or tandem quadrupole mass spectrometer, the [M−H]⁻ ions of mycolic acid generated by electrospray ionization undergo dissociation to eliminate the meroaldehyde residue, leading to formation of carboxylate anions containing α-alkyl chains. The structural information from these fragment ions affords structural assignment of the mycolic acids, including the lengths of the meromycolate chain and the α-branch. This study revealed that the mycolic acids isolated from pathogenic Rhodococcus equi 103 contained a series of homologous ions having C₃₀ to C₅₀ chain with 0–2 double bonds. The α-branch ranged from C₁₀ to C₁₈ with 0 to 1 double bond, in which 16:0 and 14:0 are the most prominent, whereas the meromycolate chain ranged from C₁₄ to C₃₄ with 0 to 2 double bonds. The major molecular species consisted of more than 3 isomers that differ by the lengths of the α-branch or meromycolate chain, and up to 10 isobaric isomers were identified for some minor ions. We also employed tandem quadrupole mass spectrometry with precursor ion and neutral loss scans for profiling mycolic acid with specific structure in mixtures. The tandem spectra obtained from precursor ion scans of m/z 255 (16:0-carboxylate anion) and m/z 227 (14:0-carboxylate anion) may provide a simple specific means for classification of Rhodococci species, whereas tandem spectra from neutral loss of meroaldehyde residue scans provided a simple approach to reveal the mycolic acid molecules with specific meromycolate chain in mixtures.     

Biological activity of trisporoids and trisporoid analogues in Mucor mucedo (-)

In the course of their sexual interactions, zygomycete fungi communicate via an elaborate series of carotene-derived compounds, namely trisporic acid and its biosynthetic progenitors. A novel building-block strategy allowed the systematic generation of structurally modified trisporoids along with putative early biosynthetic precursors for physiological tests. The impact of discrete structural elements was documented by the ability of individual compounds to induce sexually committed hyphae in Mucor mucedo. The activity screening contributed to establish general structure-function relationships for trisporoid action. Most crucial for activity were the dimension of the longer side chain, the polarity of functional groups at C(4) and C(13), and the number of conjugated double bonds in the side chain. The presence of an oxygen substituent at the cyclohexene ring is not essential for function. The overall biological activity apparently results from the combination of the various structural elements.     

Assimilation and biosynthesis of lipids in Arctic Calanus species based on feeding experiments with a C labelled diatom

The dominant Arctic Ocean and North Atlantic copepods Calanus hyperboreus, Calanus glacialis, and Calanus finmarchicus were collected in the Greenland Sea and fed ¹³C labelled diatom Thalassiosira weissflogii to follow the transfer and assimilation of carbon, lipid, and individual fatty acids and alcohols. The diatom was grown with ¹³C for 3 to 5 days and fed then to the copepods. During the feeding period of 14 days, total carbon increased in the copepodite stages V of C. hyperboreus and C. finmarchicus, whereas carbon remained almost constant in C. glacialis females. However, total lipid increased in all species and stages. Highest lipid accumulation occurred in C. hyperboreus in which nearly all lipids were exchanged already after 11 days of feeding. In the other species lipid accumulation made up between 22% (C. finmarchicus) and 45% of total lipid (C. glacialis). The proportion of wax esters was high ranging from 76% of total lipid in C. glacialis to 92% in C. finmarchicus. The fatty acid composition of the alga was dominated by 16:1(n-7), 16:0, 20:5(n-3), and 22:6(n-3). The composition of the copepods was similar because of feeding already on diatoms in the field. In addition, the monounsaturated fatty acids and alcohols, 20:1(n-9) and 22:1(n-11), were major components of the copepod lipids. During the feeding period the highest ¹³C labelling was always found in the C₁₆ polyunsaturated fatty acids and in the 16:1(n-7) alcohol. Because these components occurred only in trace amounts in the copepods they totally originated from the diet explaining the high labelling. It is noteworthy that the 16:1(n-7) alcohol originated only from the corresponding dietary and not from the abundant internal fatty acid. The long-chain monounsaturated fatty acids and alcohols, 20:1(n-9) and 22:1(n-11), are not existent in phytoplankton and have to be produced de novo. They were less labelled in the smaller species but highly ¹³C enriched in C. hyperboreus. Although dietary fatty acids were generally retained by the copepods it seems that fatty acids or even lipids were selectively accumulated and turned over due to bodily requirements, and thus, essential polyunsaturated fatty acids were preferentially retained. During feeding mixing, accumulation, and exchange of internal and dietary fatty acids and alcohols occurred as well as utilisation of lipids from both sources for metabolic requirements. The differences in lipid assimilation fit to the different life strategies of the copepods.     

Fatty acid content of the dorsal muscle—an indicator of fat quality in freshwater fish

In 56 samples of freshwater fish, most were low in fat, ≤ 5% of dry weight (D.W.), and the sum of all fatty acids (ΣFA) was about 2% of D.W. Trout, whitefish, and grayling had the highest content of the long-chained FA. of ω3 type, EPA and DHA (1·7–2·6% of D.W.). Two large, low-fat pikes with ΣFA of about12–3% of D.W. and a medium-fat whitefish had the highest ω3/ω6 ratios, 8–9, whereas the fattiest fishes, eels from two lakes and the Baltic (ΣFA =17–26% of D.W.) had lower ω3/ω6 ratios, 1·1–1·8 (ω3 and ω6 FA are two important series of FA). The results indicate that ΣA controls the content of saturated FA (SAFA) and monounsaturated FA (MUFA), whereas the polyunsaturated FA (PUFA) was independent of ΣFA after a break point of about 10%ΣFA of D.W. The P/S ratio (PUFA/SAFA) and the PUFA/ΣFA ratio decreased with increased ΣFA, whereas the ω3/ω6 ratio showed no clear correlation to ΣFA. The difference in fatty acid patterns lay between low-fat and high-fat fishes, rather than between marine and freshwater fishes. The variation, both within and between species of the separate FA is small in fish with similar ΣFA content. Also, low-fat and medium-fat fishes tend to be more dietarily favourable than high-fat fishes, when considering the latest criteria for high nutritional value to humans. Abbreviations used in the text: FA, fatty acids; ΣFA, sum of all FA; AA, arachidonic acid (20 : 4ω6); EPA, eicosapentaenoic acid (20 : 5ω3); DHA, docosahexaenoic acid (22 : 6ω3); SAFA, saturated fatty acids; MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids; D.W., dry weight; F.W. fresh weight; CV, coefficient of variation; ω3 FA, series of PUFA with the first double bond located at carbon number 3; ω6 FA, series of PUFA with the first double bond located at carbon number 6. The fatty acids are described by three numbers, x:ywz, where x=number of carbon atoms, y=number of double bonds, and z=position of the first double bond counted from the methyl end of the molecule.     

(n-7) and (n-9) cis-Monounsaturated fatty acid contents of 12 Brassica species

cis-Vaccenic acid or cis-11-octadecenoic acid, a C18:1 (n-7) isomer of oleic acid (C18:1 (n-9)) has been found in several oilseeds. It is synthesized from palmitic acid (C16:0) via production of C16:1 (n-7) by a Delta9 desaturase and elongation by an elongase giving C18:1 (n-7). In this study, the fatty acid composition of 12 Brassica species was analyzed by GC-FID and confirmed by GC-MS. All species contained C18:1 (n-7), C20:1 (n-7) and C22:1 (n-7) fatty acid isomers, suggesting that C18:1 (n-7) was elongated. The levels of these fatty acids varied according to the species. C18:1(n-7)) represented from 0.4% to 3.3% of the total relative fatty acid contents of the seeds. The contents of C20:1(n-7) and C22:1(n-7) levels were lower than C18:1(n-7) contents; the relative fatty acid composition varied from 0.02% to 1.3% and from below the limit of detection to 1.3% for C20:1 (n-7) and C22:1 (n-7), respectively. The ratios of (n-7)/(n-9) ranged from 2.8% to 16.7%, 0.6% to 29.5% and 0% to 2.6% for C18:1, C20:1 and C22:2, respectively. Using statistical similarities or differences of the C18:1 (n-7)/(n-9) ratios for chemotaxonomy, the surveyed species could be arranged into three groups. The first group would include Brassica napus, B. rapa, and B. tournefortii with Eruca sativa branching only related to B. napus. The second group would include B. tournefortii, Raphanus sativus and Sinapis alba. The last group would include B. juncea, B. carinata and B. nigra with no similarity/relationship between them and between the other species. Results suggested that the level of C20:1 (n-7) influenced the levels of all monounsaturated fatty acids with chain length higher than 20 carbons. On the other hand, palmitoleic acid (C16:1) levels, C16:1 being the parent of all (n-7) fatty acids, had no statistically significant correlation with the content of any of the fatty acids of the (n-7) or (n-9) family.     

Cuticular hydrocarbons and wax esters of the ectoparasitoid Habrobracon hebetor: Ontogenetic,reproductive, and nutritional effects

Hydrocarbon and wax ester components of cuticular lipids of the braconid parasitoid Habrobracon hebetor Say reared at 25 degrees C on larvae of a pyralid moth have been identified by GC-MS and analyzed with respect to adult age, mating status, and diet. The hydrocarbons range in carbon number from C(21) to C(45) and consist of a homologous series of n-alkanes, 11-, 13-, and 15-methyl alkanes, 13,17-dimethyl alkanes, and Z-5, Z-7, and Z-9-alkenes. The wax esters found in the cuticular lipid fraction are a series of homologous compounds with the acid portion being short chain, unbranched, even carbon number acids from C(8) to C(20) (predominately C(8) to C(16)). The alcohol portions of the esters are secondary alcohols with carbon number from C(22) to C(25) (predominately C(23) and C(25)) with the hydroxyl function located at C(6), C(7), C(8), and C(9). Gender, age, and nutritional states were significant factors for variation in several of the individual esters, but mating status did not affect wax ester composition. Ontogenetic examinations indicated that prepupal, and early pupal cuticular lipids contain only hydrocarbons. Low levels of wax esters are detectable in late stage pupae, and somewhat greater quantities of wax esters are present on newly eclosed adults. When pharate adults emerge from the cocoon, however, their cuticular lipids consist of approximately equal amounts of hydrocarbons and wax esters, and 6d post emergence from the cocoon, wax esters are the predominant lipid component.