9-Hydroxy-traumatin, a new metabolite of the lipoxygenase pathway

Effect of a Topical Gel Based on Adelmidrol + Trans-Traumatic Acid in the Treatment of Diabetic Foot Ulcers: An Open-Label Study

BACKGROUND

Diabetic foot ulceration is a severe complication of diabetes characterized by chronic inflammation and impaired wound healing. This study aimed to evaluate the effect of a medical device gel based on adelmidrol + trans-traumatic acid in the healing process of diabetic foot ulcers.

METHODS

Thirty-seven diabetic patients with foot ulcers of mild/moderate grade were treated with the gel daily for 4 weeks on the affected area. The following parameters were evaluated at baseline and weekly: 1) wound area, measured by drawing a map of the ulcer and then calculated with photo editing software tools, and 2) clinical appearance of the ulcer, assessed by recording the presence/absence of dry/wet necrosis, infection, fibrin, neoepithelium, exudate, redness, and granulation tissue.

RESULTS

Topical treatment led to progressive healing of diabetic foot ulcers with a significant reduction of the wound area and an improvement in the clinical appearance of the ulcers. No treatment-related adverse events were observed.

CONCLUSIONS

The results of this open-label study show the potential benefits of adelmidrol + trans-traumatic acid topical administration to promote reepithelialization of diabetic foot ulcers. Further studies are needed to confirm the observed results.

Gene expression and metabolite analysis in barley inoculated with net blotch fungus and plant growth-promoting rhizobacteria

Net blotch, caused by the ascomycete Drechslera teres, can compromise barley production. Beneficial bacteria strains are of substantial interest as biological agents for plant protection in agriculture. Belonging to the genus Paraburkholderia, a bacterium, referred to as strain B25, has been identified as protective for barley against net blotch. The strain Paraburkholderia phytofirmans (strain PsJN), which has no effect on the pathogen's growth, has been used as control. In this study, the expression of target genes involved in cell wall-related processes, defense responses, carbohydrate and phenylpropanoid pathways was studied under various conditions (with or without pathogen and/or with or without bacterial strains) at different time-points (0-6-12-48 h). The results show that specific genes were subjected to a circadian regulation and that the expression of most of them increased in barley infected with D. teres and/or bacterized with the strain PsJN. On the contrary, a decreased gene expression was observed in the presence of strain B25. To complement and enrich the gene expression analysis, untargeted metabolomics was carried out on the same samples. The data obtained show an increase in the production of lipid compounds in barley in the presence of the pathogen. In addition, the presence of strain B25 leads to a decrease in the production of defense compounds in this crop. The results contribute to advance the knowledge on the mechanisms occurring at the onset of D. teres infection and in the presence of a biocontrol agent limiting the severity of net blotch in barley.

Lipoxygenase Activation in Peanut Seed Cultivars Resistant and Susceptible to Aspergillus parasiticus Colonization

Accumulative evidence indicates that the lipoxygenase (LOX) pathway plays a significant role in the Aspergillus-seed interaction, such as interfering with activities of endogenous fungal oxylipins or producing antimicrobial compounds and signaling molecules. In this study, we characterized the LOX pathway in peanut seed during Aspergillus parasiticus colonization in a model of two cultivars distinguished as resistant ('PI337394') and susceptible ('Florman INTA') to Aspergillus spp. infection and aflatoxin contamination. The LOX activity together with the content of LOX substrate and LOX products demonstrated the presence of a differential response mechanism to A. parasiticus infection between cultivars. Our findings suggest that this mechanism is under transcriptional control of previously identified (LOX 2 and LOX 3) and novel (LOX 4 and LOX 5) LOX genes. The results of this study support the role of these enzymes in defense during fungus infection in peanut seed.

Comparative transcriptome sequencing of tolerant rice introgression line and its parents in response to drought stress

BACKGROUND

Rice (Oryza sativa. L) is more sensitive to drought stress than other cereals, and large genotypic variation in drought tolerance (DT) exists within the cultivated rice gene pool and its wild relatives. Selective introgression of DT donor segments into a drought-sensitive (DS) elite recurrent parent by backcrossing is an effective way to improve drought stress tolerance in rice. To dissect the molecular mechanisms underlying DT in rice, deep transcriptome sequencing was used to investigate transcriptome differences among a DT introgression line H471, the DT donor P28, and the drought-sensitive, recurrent parent HHZ under drought stress.

RESULTS

The results revealed constitutively differential gene expression before stress and distinct global transcriptome reprogramming among the three genotypes under a time series of drought stress, consistent with their different genotypes and DT phenotypes. A set of genes with higher basal expression in both H471 and P28 compared with HHZ were functionally enriched in oxidoreductase and lyase activities, implying their positive role in intrinsic DT. Gene Ontology analysis indicated that common up-regulated genes in all three genotypes under mild drought stress were enriched in signaling transduction and transcription regulation. Meanwhile, diverse functional categories were characterized for the commonly drought-induced genes in response to severe drought stress. Further comparative transcriptome analysis between H471 and HHZ under drought stress found that introgression caused wide-range gene expression changes; most of the differentially expressed genes (DEGs) in H471 relative to HHZ under drought were beyond the identified introgressed regions, implying that introgression resulted in novel changes in expression. Co-expression analysis of these DEGs represented a complex regulatory network, including the jasmonic acid and gibberellin pathway, involved in drought stress tolerance in H471.

CONCLUSIONS

Comprehensive gene expression profiles revealed that genotype-specific drought induced genes and genes with higher expression in the DT genotype under normal and drought conditions contribute jointly to DT improvement. The molecular genetic pathways of drought stress tolerance uncovered in this study, as well as the DEGs co-localized with DT-related QTLs and introgressed intervals, will serve as useful resources for further functional dissection of the molecular mechanisms of drought stress response in rice.

A metabolic profiling strategy for the dissection of plant defense against fungal pathogens

Here we present a metabolic profiling strategy employing direct infusion Orbitrap mass spectrometry (MS) and gas chromatography-mass spectrometry (GC/MS) for the monitoring of soybean's (Glycine max L.) global metabolism regulation in response to Rhizoctonia solani infection in a time-course. Key elements in the approach are the construction of a comprehensive metabolite library for soybean, which accelerates the steps of metabolite identification and biological interpretation of results, and bioinformatics tools for the visualization and analysis of its metabolome. The study of metabolic networks revealed that infection results in the mobilization of carbohydrates, disturbance of the amino acid pool, and activation of isoflavonoid, α-linolenate, and phenylpropanoid biosynthetic pathways of the plant. Components of these pathways include phytoalexins, coumarins, flavonoids, signaling molecules, and hormones, many of which exhibit antioxidant properties and bioactivity helping the plant to counterattack the pathogen's invasion. Unraveling the biochemical mechanism operating during soybean-Rhizoctonia interaction, in addition to its significance towards the understanding of the plant's metabolism regulation under biotic stress, provides valuable insights with potential for applications in biotechnology, crop breeding, and agrochemical and food industries.

Molecular sequence variations of the lipoxygenase-2 gene in soybean

Soybean lipoxygenase genes comprise a multi-gene family, with the seed lipoxygenase isozymes LOX1, LOX2, and LOX3 present in soybean seeds. Among these, the LOX2 isozyme is primarily responsible for the "beany" flavor of most soybean seeds. The variety, Jinpumkong 2, having null alleles (lx1, lx2, and lx3) lacks the three seed lipoxygenases; so, sequence variations between the lipoxygenase-2 genes of Pureunkong (Lx2) and Jinpumkong 2 (lx2) cultivars were examined. One indel, four single nucleotide polymorphisms (SNPs), a 175-bp fragment in the 5'-flanking sequence, and a missense mutation within the coding region were found in Jinpumkong 2. The distribution of the sequence variations was investigated among 90 recombinant inbred lines (RILs) derived from a cross of Pureunkong × Jinpumkong 2 and in 480 germplasm accessions with various origins and maturity groups. Evidence for a genetic bottleneck was observed: the 175-bp fragment was rare in Glycine max, but present in the majority of the G. soja accessions. Furthermore, the 175-bp fragment was not detected in the 5' upstream region of the Lx2 gene on chromosome (Chr) 13 in Williams 82; instead, a similar 175-bp fragment was positioned in the homeologous region on Chr 15. The findings indicated that the novel fragment identified was originally present in the Lx2 region prior to the recent genome duplication in soybean, but became rare in the G. max gene pool. The missense mutation of the conserved histidine residue of the lx2 allele was developed into a single nucleotide-amplified polymorphism (SNAP) marker. The missense mutation showed a perfect correlation with the LOX2-lacking phenotype, so the SNAP marker is expected to facilitate breeding of soybean cultivars which lack the LOX2 isozyme.

C12 derivatives of the hydroperoxide lyase pathway are produced by product recycling through lipoxygenase-2 in Nicotiana attenuata leaves

In response to diverse stresses, the hydroperoxide lyase (HPL) pathway produces C(6) aldehydes and 12-oxo-(9Z )-dodecenoic acid ((9Z )-traumatin). Since the original characterization of (10E )-traumatin and traumatic acid, little has been added to our knowledge of the metabolism and fluxes associated with the conversion of (9Z )-traumatin into diverse products in response to wounding and herbivory. A liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method was developed to quantify C(12) derivatives of the HPL pathway and to determine their metabolism after wounding and simulated herbivory in Nicotiana attenuata leaves. Ninety-eight per cent of the (9Z )-traumatin produced was converted to 9-hydroxy-(10E )-traumatin (9-OH-traumatin); two-thirds by product recycling through lipoxygenase-2 (NaLOX2) activity and one-third by nonenzymatic oxidation. Thirty-eight per cent of the de novo produced 9-OH-traumatin was conjugated to glutathione, consistent with this oxylipin being a reactive electrophile species. 12-OH-(9Z )-dodecenoic and dodecenedioic acids also showed rapid increases after wounding and simulated herbivory and a role for C(12) derivatives as signals in these processes was consistent with their ability to elicit substantial changes in gene expression. These results underscore the importance of metabolite reflux through LOX2, an insight which creates new opportunities for a functional understanding of C(12) derivatives of the HPL pathway in the regulation of stress responses.

Hydroperoxide lyase cascade in pea seedlings: Non-volatile oxylipins and their age and stress dependent alterations

The profiles of non-volatile oxylipins of pea (Pisum sativum) seedlings were examined by gas chromatography-mass spectrometry after invitro incubation with α-linolenic acid. The 13-lipoxygenase/hydroperoxide lyase (HPL) products were predominant in the leaves, while the roots possess both 13- and 9-HPL products. Allene oxide synthase (AOS) and divinyl ether synthase (DES) products were not detected in the leaves or in the roots of any age. The HPL cascade produces a diversity of oxylipins, including the compounds (2E)-4-hydroxy-traumatic, (10E)-9,12-dihydroxy-10-dodecenoic and 9,12-dihydroxydodecanoic acids, as well as (2E)-4-hydroxy-2-nonenoic acid, which has not yet been detected in plants. Oxylipin patterns were altered by infection, water deficit, as well as by plant age. Infection caused the specific strong accumulation of azelaic (nonane-1,9-dioic) acid in the leaves. The azelaic acid content in the aged (14 and 18day-old) leaves was significantly higher than in the younger leaves. Water deficit induced the accumulation of (2E)-4-hydroxy-2-nonenoic acid and (2E)-traumatic acid in the roots. Results demonstrate that: (1) the HPL cascade is the predominant branch of the lipoxygenase pathway in pea seedlings; (2) the HPL products may have the regulatory role both in growth control and adaptation.

Genome-wide analysis of lipoxygenase gene family in Arabidopsis and rice

The enzymes called lipoxygenases (LOXs) can dioxygenate unsaturated fatty acids, which leads to lipoperoxidation of biological membranes. This process causes synthesis of signaling molecules and also leads to changes in cellular metabolism. LOXs are known to be involved in apoptotic (programmed cell death) pathway, and biotic and abiotic stress responses in plants. Here, the members of LOX gene family in Arabidopsis and rice are identified. The Arabidopsis and rice genomes encode 6 and 14 LOX proteins, respectively, and interestingly, with more LOX genes in rice. The rice LOXs are validated based on protein alignment studies. This is the first report wherein LOXs are identified in rice which may allow better understanding the initiation, progression and effects of apoptosis, and responses to bitoic and abiotic stresses and signaling cascades in plants.

Proteins modified by the lipid peroxidation aldehyde 9,12-dioxo-10(E)-dodecenoic acid in MCF7 breast cancer cells

The hydroperoxide of linoleic acid (13-HPODE) degrades to 9,12-dioxo-10(E)-dodecenoic acid (DODE), which readily modifies proteins. This study identified the major proteins in MCF7 cells modified by DODE. To reduce false positives, three methods were used to identify DODE-modified proteins. First, cells were treated with a synthetically biotinylated 13-HPODE (13-HPODE-biotin). Modified proteins were enriched by neutravidin affinity and identified by two-dimensional liquid chromatography--tandem mass spectrometry (2D LC-MS/MS). Second, cells were treated with native 13-HPODE. Protein carbonyls were biotinylated with an aldehyde reactive probe, and modified proteins were enriched by neutravidin affinity and identified by 2D LC-MS/MS. Third, using a newly developed DODE antibody, DODE-modified proteins were located by 2D sodium dodecyl sulfate--polyacrylamide gel electrophoresis and Western blot and identified by in-gel digestion and LC-MS/MS. Analysis of the proteins characterized by all three methods revealed a significant overlap and identified 32 primary proteins modified by DODE in MCF7 cells. These results demonstrated the feasibility for the cellular formation of DODE protein-carbonyl adducts that may be future indicators of oxidative stress.

The lipoxygenase gene family: a genomic fossil of shared polyploidy between Glycine max and Medicago truncatula

BACKGROUND

Soybean lipoxygenases (Lxs) play important roles in plant resistance and in conferring the distinct bean flavor. Lxs comprise a multi-gene family that includes GmLx1, GmLx2 and GmLx3, and many of these genes have been characterized. We were interested in investigating the relationship between the soybean lipoxygenase isozymes from an evolutionary perspective, since soybean has undergone two rounds of polyploidy. Here we report the tetrad genome structure of soybean Lx regions produced by ancient and recent polyploidy. Also, comparative genomics with Medicago truncatula was performed to estimate Lxs in the common ancestor of soybean and Medicago.

RESULTS

Two Lx regions in Medicago truncatula showing synteny with soybean were analyzed. Differential evolutionary rates between soybean and Medicago were observed and the median Ks values of Mt-Mt, Gm-Mt, and Gm-Gm paralogs were determined to be 0.75, 0.62, and 0.46, respectively. Thus the comparison of Gm-Mt paralogs (Ks = 0.62) and Gm-Mt orthologs (Ks = 0.45) supports the ancient duplication of Lx regions in the common ancestor prior to the Medicago-Glycine split. After speciation, no Lx regions generated by another polyploidy were identified in Medicago. Instead tandem duplication of Lx genes was observed. On the other hand, a lineage-specific duplication occurred in soybean resulting in two pairs of Lx regions. Each pair of soybean regions was co-orthologous to one Lx region in Medicago. A total of 34 Lx genes (15 MtLxs and 19 GmLxs) were divided into two groups by phylogenetic analysis. Our study shows that the Lx gene family evolved from two distinct Lx genes in the most recent common ancestor.

CONCLUSION

This study analyzed two pairs of Lx regions generated by two rounds of polyploidy in soybean. Each pair of soybean homeologous regions is co-orthologous to one region of Medicago, demonstrating the quartet structure of the soybean genome. Differential evolutionary rates between soybean and Medicago were observed; thus optimized rates of Ks per year should be applied for accurate estimation of coalescence times to each case of comparison: soybean-soybean, soybean-Medicago, or Medicago-Medicago. In conclusion, the soybean Lx gene family expanded by ancient polyploidy prior to taxon divergence, followed by a soybean- specific duplication and tandem duplications, respectively.

Purification and characterization of soluble Cichorium intybusVar. silvestre lipoxygenase

A water-soluble lipoxygenase enzyme (EC 1.13.11.12; LOX) occurring in the red cultivar produced in the geographical area of Chioggia (Italy) of Cichorium intybus var. silvestre was isolated and characterized. The molecular mass of the enzyme was estimated to be 74,000 Da by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration chromatography. The isoelectric point was pH 6.85. The optimum values of pH, ionic strength, and temperature, shown by isoresponse surface calculated by a randomized multilevel factorial design, were 7.58, 30 mM, and 38.5 degrees C, respectively. The enzyme showed high specificity toward linoleic acid, and the study of the variation of linoleic acid concentration between 30 and 300 microM, in the presence of Tween 20 at a concentration lower than the critical micelle concentration (0.01 v/v), resulted in a typical Michaelis-Mentem curve with KM and Vmax values of 1.49 x 10(-4) M and 2.049 microM min(-1) mg(-1), respectively. The biochemical properties, the kinetic parameters found, and the carotene-bleaching activity shown in aerobic conditions seem to indicate that the isolated enzyme is a lipoxygenase type III according to the indications given for soybean isoenzymes.

Hydroperoxide lyase and divinyl ether synthase

"Heterolytic" hydroperoxide lyase (HPL) and divinyl ether synthase (DES) are important enzymes of the plant lipoxygenase pathway. HPL cleaves fatty acid hydroperoxides into the aldehyde fragments. DES converts hydroperoxides into the divinyl ethers. The present paper is concerned with recent studies on HPL and DES including their occurrence, properties, mechanisms of action, the cloning of their cDNAs and physiological importance of the enzymes and their products.

Two distinct pathways of formation of 4-hydroxynonenal. Mechanisms of nonenzymatic transformation of the 9- and 13-hydroperoxides of linoleic acid to 4-hydroxyalkenals

The mechanism of formation of 4-hydroxy-2E-nonenal (4-HNE) has been a matter of debate since it was discovered as a major cytotoxic product of lipid peroxidation in 1980. Recent evidence points to 4-hydroperoxy-2E-nonenal (4-HPNE) as the immediate precursor of 4-HNE (Lee, S. H., and Blair, I. A. (2000) Chem. Res. Toxicol. 13, 698-702; Noordermeer, M. A., Feussner, I., Kolbe, A., Veldink, G. A., and Vliegenthart, J. F. G. (2000) Biochem. Biophys. Res. Commun. 277, 112-116), and a pathway via 9-hydroperoxylinoleic acid and 3Z-nonenal is recognized in plant extracts. Using the 9- and 13-hydroperoxides of linoleic acid as starting material, we find that two distinct mechanisms lead to the formation of 4-H(P)NE and the corresponding 4-hydro(pero)xyalkenal that retains the original carboxyl group (9-hydroperoxy-12-oxo-10E-dodecenoic acid). Chiral analysis revealed that 4-HPNE formed from 13S-hydroperoxy-9Z,11E-octadecadienoic acid (13S-HPODE) retains >90% S configuration, whereas it is nearly racemic from 9S-hydroperoxy-10E,12Z-octadecadienoic acid (9S-HPODE). 9-Hydroperoxy-12-oxo-10E-dodecenoic acid is >90% S when derived from 9S-HPODE and almost racemic from 13S-HPODE. Through analysis of intermediates and products, we provide evidence that (i) allylic hydrogen abstraction at C-8 of 13S-HPODE leads to a 10,13-dihydroperoxide that undergoes cleavage between C-9 and C-10 to give 4S-HPNE, whereas direct Hock cleavage of the 13S-HPODE gives 12-oxo-9Z-dodecenoic acid, which oxygenates to racemic 9-hydroperoxy-12-oxo-10E-dodecenoic acid; by contrast, (ii) 9S-HPODE cleaves directly to 3Z-nonenal as a precursor of racemic 4-HPNE, whereas allylic hydrogen abstraction at C-14 and oxygenation to a 9,12-dihydroperoxide leads to chiral 9S-hydroperoxy-12-oxo-10E-dodecenoic acid. Our results distinguish two major pathways to the formation of 4-HNE that should apply also to other fatty acid hydroperoxides. Slight ( approximately 10%) differences in the observed chiralities from those predicted in the above mechanisms suggest the existence of additional routes to the 4-hydroxyalkenals.

Aldehydic lipid peroxidation products derived from linoleic acid

Lipid peroxidation (LPO) processes observed in diseases connected with inflammation involve mainly linoleic acid. Its primary LPO products, 9-hydroperoxy-10,12-octadecadienoic acid (9-HPODE) and 13-hydroperoxy-9,11-octadecadienoic acid (13-HPODE), decompose in multistep degradation reactions. These reactions were investigated in model studies: decomposition of either 9-HPODE or 13-HPODE by Fe(2+) catalyzed air oxidation generates (with the exception of corresponding hydroxy and oxo derivatives) identical products in often nearly equal amounts, pointing to a common intermediate. Pairs of carbonyl compounds were recognized by reacting the oxidation mixtures with pentafluorobenzylhydroxylamine. Even if a pure lipid hydroperoxide is subjected to decomposition a great variety of products is generated, since primary products suffer further transformations. Therefore pure primarily decomposition products of HPODEs were exposed to stirring in air with or without addition of iron ions. Thus we observed that primary products containing the structural element R-CH=CH-CH=CH-CH=O add water and then they are cleaved by retroaldol reactions. 2,4-Decadienal is degraded in the absence of iron ions to 2-butenal, hexanal and 5-oxodecanal. Small amounts of buten-1,4-dial were also detected. Addition of m-chloroperbenzoic acid transforms 2,4-decadienal to 4-hydroxy-2-nonenal. 4,5-Epoxy-2-decenal, synthetically available by treatment of 2,4-decadienal with dimethyldioxirane, is hydrolyzed to 4,5-dihydroxy-2-decenal.

Oxygenation of (3Z)-alkenals to 4-hydroxy-(2E)-alkenals in plant extracts: a nonenzymatic process

There is large interest in 4-hydroxy-(2E)-alkenals because of their cytotoxicity in mammals. However, the biosynthetic pathway for these compounds has not been elucidated yet. In plants, 4-hydroxy-(2E)-alkenals were supposed to be derived by the subsequent actions of lipoxygenase and a peroxygenase on (3Z)-alkenals. The presence of 9-hydroxy-12-oxo-(10E)-dodecenoic acid (9-hydroxy-traumatin) in incubations of 12-oxo-(9Z)-dodecenoic acid (traumatin) in the absence of lipoxygenase or peroxygenase, has prompted us to reinvestigate its mode of formation. We show here that in vitro 9-hydroxy-traumatin, 4-hydroxy-(2E)-hexenal and 4-hydroxy-(2E)-nonenal, are formed in a nonenzymatic process. Furthermore, a novel product derived from traumatin was observed and identified as 11-hydroxy-12-oxo-(9Z)-dodecenoic acid. The results obtained here strongly suggest that the 4-hydroxy-(2E)-alkenals, observed in crude extracts of plants, are mainly due to autoxidation of (3Z)-hexenal, (3Z)-nonenal and traumatin. This may have implications for the in vivo existence and previously proposed physiological significance of these products in plants.

Biotransformation of linoleic acid by Clavibacter sp. ALA2: heterocyclic and heterobicyclic fatty acids

Clavibacter sp. ALA2 transformed linoleic acid into a variety of oxylipins. In previous work, three novel fatty acids were identified, (9Z)-12, 13, 17-trihydroxy-9-octadecenoic acid and two tetrahydrofuran-(di)hydroxy fatty acids. In this report, we confirm the structures of the tetrahydrofuran-(di)hydroxy fatty acids by nuclear magnetic resonance as (9Z)-12-hydroxy-13,16-epoxy-9-octadecenoic acid and (9Z)-7,12-dihydroxy-13,16-epoxy-9-octadecenoic acid. Three other products of the biotransformation were identified as novel heterobicyclic fatty acids, (9Z)-12,17;13, 17-diepoxy-9-octadecenoic acid, (9Z)-7-hydroxy-12,17;13,17-diepoxy-9-octadecenoic acid, and (9Z)-12,17;13,17-diepoxy-16-hydroxy-9-octadecenoic acid. Thus, Clavibacter ALA2 effectively oxidized linoleic acid at C-7, -12, -13, -16, and/or -17.

Synthesis of 9,12-dioxo-10(Z)-dodecenoic acid, a new fatty acid metabolite derived from 9-hydroperoxy-10,12-octadecadienoic acid in lentil seed (Lens culinaris Medik.)

The previously unknown linoleic acid peroxidation product 9,12-dioxo-10(Z)-decenoic acid (Z5) was detected in lentil seed flour (Lens culinaris Medik.) by electron impact mass spectrometry (EI-MS) after derivatization with pentafluorobenzyl-hydroxylamine-hydrochloride, methylation of acidic groups with diazomethane, and protection of hydroxylic groups with N-methyl-N-trimethylsilyl-trifluoroacetamide. The structure of the natural product was confirmed by synthesis of Z5, 9,12-dioxo-l0(E)-decenoic acid, and derivatives. EI-MS, nuclear magnetic resonance and gas chromatographic data of these compounds and synthetic intermediates are discussed.

Formation of a new class of oxylipins from N-acyl(ethanol)amines by the lipoxygenase pathway

N-Acylethanolamines (NAEs) constitute a new class of plant lipids and are thought to play a role in plant defense strategies against pathogens. In plant defense systems, oxylipins generated by the lipoxygenase pathway are important actors. To date, it is not known whether plants also use endogeneous oxylipins derived from NAEs in their defense reactions. We tested whether members of the NAE class can be converted by enzymes constituting this pathway, such as (soybean) lipoxygenase-1, (alfalfa) hydroperoxide lyase and (flax seed) allene oxide synthase. We found that both alpha-N-linolenoylethanolamine and gamma-N-linolenoylethanolamine (18:3), as well as alpha-N-linolenoylamine and gamma-N-linolenoylamine were converted into their (13S)-hydroperoxide derivatives by lipoxygenase. Interestingly, only the hydroperoxides of alpha-N-linolenoyl(ethanol)amines and their linoleic acid analogs (18:2) were suitable substrates for hydroperoxide lyase. Hexanal and (3Z)-hexenal were identified as volatile products of the 18:2 and 18:3 fatty acid (ethanol)amides, respectively. 12-Oxo-N-(9Z)-dodecenoyl(ethanol)amine was the nonvolatile hydrolysis product. Kinetic studies with lipoxygenase and hydroperoxide lyase revealed that the fatty acid ethanolamides were converted as readily or even better than the corresponding free fatty acids. Allene oxide synthase utilized all substrates, but was most active on (13S)-hydroperoxy-alpha-N-linolenoylethanolamine and the (13S)-hydroperoxide of linoleic acid and its ethanolamine derivative. alpha-Ketols and gamma-ketols were characterized as products. In addition, cyclized products, i.e. 12-oxo-N-phytodienoylamines, derived from (13S)-hydroperoxy-alpha-N-linolenoylamines were found. The results presented here show that, in principle, hydroperoxide NAEs can be formed in plants and subsequently converted into novel phytooxylipins.

Alfalfa contains substantial 9-hydroperoxide lyase activity and a 3Z:2E-enal isomerase

Fatty acid hydroperoxides formed by lipoxygenase can be cleaved by hydroperoxide lyase resulting in the formation of short-chain aldehydes and omega-oxo acids. Plant hydroperoxide lyases use 13- or 9-hydroperoxy linoleic and linolenic acid as substrates. Alfalfa (Medicago sativa L.) has been reported to contain a hydroperoxide lyase specific for 13-hydroperoxy linoleic and linolenic acid only. However, in addition to 13-hydroperoxide lyase activity we found substantial 9-hydroperoxide lyase activity in alfalfa seedlings as well. The specific activity for 9-hydroperoxy fatty acids was about 50% of the activity for the 13-isomers. Furthermore, alfalfa seedlings contain a 3Z:2E-enal isomerase that converts the 3Z-enal products to their 2E-enal isoforms.