An oxidized derivative of linoleic acid affects aldosterone secretion by adrenal cells in vitro.

Based on the clinical observation that humans with visceral adiposity have higher plasma aldosterone levels than controls, we postulated that endogenous fatty acids can be oxidized by the liver to form stimuli of the adrenal cortex. Although we could show that hepatocytes produced adrenal stimuli from linoleic acid in vitro, the yield was very small. To facilitate the elucidation of chemical structures, we incubated a large amount of linoleic acid with lipoxygenase, then treated the hydroperoxide with cysteine and iron. The major product of this process was 12,13-epoxy-9-keto-10-trans-octadecenoic acid. This epoxy-keto compound stimulated aldosterone production at concentrations from 0.5 to 15 microm. At higher concentrations, it was inhibitory. The epoxy-keto-octadecenoic acid exhibited the chromatographic characteristics of one product of the incubation of linoleic acid with hepatocytes. The results are consistent with the postulated conversion of linoleic acid to stimuli of aldosterone production. This may be a mechanistic link between visceral obesity and hypertension in humans.

Oxidized products of linoleic acid stimulate adrenal steroidogenesis.

Adrenal steroidogenesis is under complex control, and clinical observations suggest that not all regulators have been identified. We postulated that fatty acid oxidation products found in the diet or formed in the body could affect steroidogenesis. Linoleic acid is a prominent constituent of animal fat and is readily oxidized. We found that several products of linoleic acid oxidation affect production of aldosterone and corticosterone by isolated cells from rat adrenals. We characterized one linoleic acid derivative by gas chromatography/mass spectrometry. It is 12,13-epoxy-9-oxo-10(trans)-octadecenoic acid ("EKODE"). At concentrations between 1 and 30 microM, EKODE stimulated production of aldosterone by zona glomerulosa cells, but at concentrations above 50 microM, it was inhibitory. In zona fasciculata cells, EKODE stimulated corticosterone production at concentrations of 5 microM or greater, and there was no evidence of inhibition at high concentrations. Stimulation of steroidogenesis was observed after 15 min of incubation and continued for at least 2 hrs. The potential relevance of our findings to the hypertension of obesity is discussed.

Cultivar-dependent expression of a maize lipoxygenase responsive to seed infesting fungi.

Maize kernels are highly susceptible to Aspergillus spp. infection and aflatoxin (AF) contamination. Fatty acid signaling molecules appear to mediate the plant-fungal interaction by affecting the growth, development, and AF production of the fungus. In particular, fatty acid derivatives of the plant lipoxygenase (LOX) pathway are implicated in the Aspergillus spp.-seed interaction. The 9(S)-hydroperoxide derivative of linoleic acid promotes transcription of AF genes, whereas the 13(S)-hydroperoxide derivative decreases AF gene expression and production; both are sporulation factors. Our goal was to identify LOX genes responsive to Aspergillus spp. colonization and determine their specificities, 9(S)- or 13(S)-. Screening maize LOX expressed sequence tags (ESTs) identified one clone, cssap 92, which is highly expressed in Aspergillus spp.-infected seed susceptible to AF contamination and repressed in lines with resistance to AF contamination. The accumulation of cssap 92 transcript was similar during Fusarium spp. infection. The cDNA clone has 94% identity to the previously described L2 LOX gene from maize. Product-specificity analysis of the CSSAP 92 protein shows that it preferentially adds oxygen to carbon 9 of linoleic acid. Because 9(S)-hydroperoxy linoleic acid has been implicated as an aflatoxin-signaling molecule, it is possible that cssap 92 could be used as a biomarker that is indicative of AF resistance in maize lines.

Effect of 4-hydroxy-2(E)-nonenal on soybean lipoxygenase-1.

The oxidation of linoleic acid by soybean lipoxygenase-1 (LOX-1) was inhibited in a time-dependent manner by 4-hydroxy-2(E)-nonenal (HNE). Kinetic analysis indicated the effect was due to slow-binding inhibition conforming to an affinity labeling mechanism-based inhibition. After 25 min of preincubation of LOX-1 with and without HNE, Lineweaver-Burk reciprocal plots indicated mixed noncompetitive/competitive inhibition. Low concentrations of HNE influenced the electron paramagnetic resonance (EPR) signal of 13(S)-hydroperoxy-9(Z), 11 (E)-octadecadienoic acid (13-HPODE)-generated Fe3+-LOX-1 slightly, but higher concentrations completely eliminated the EPR signal indicating an active site hindered from access by 13-HPODE. HNE may compete for the active site of LOX-1 because its precursor, 4-hydroperoxy-(2E)-nonenal, is a product of LOX-1 oxidation of (3Z)-nonenal. Also, it was an attractive hypothesis to suggest that HNE may disrupt the active site by forming a Michael adduct with one or more of the three histidines that ligate the iron active site of LOX-1.

Method to produce 9(S)-hydroperoxides of linoleic and linolenic acids by maize lipoxygenase.

Seed from maize (corn) Zea mays provides a ready source of 9-lipoxygenase that oxidizes linoleic acid and linolenic acid into 9(S)-hydroperoxy-10(E),12(Z)-octadecadienoic acid and 9(S)-hydroperoxy-10(E),12(Z),15(Z)-octadecatrienoic acid, respectively. Corn seed has a very active hydroperoxide-decomposing enzyme, allene oxide synthase (AOS), which must be removed prior to oxidizing the fatty acid. A simple pH 4.5 treatment followed by centrifugation removes most of the AOS activity. Subsequent purification by ammonium sulfate fractional precipitation results in negligible improvement in 9-hydroperoxide formation. This facile alternative method of preparing 9-hydroperoxides has advantages over other commonly used plant lipoxygenases.

Genetic connection between fatty acid metabolism and sporulation in Aspergillus nidulans.

In the Ascomycete fungus Aspergillus nidulans, the ratio of conidia (asexual spores) to ascospores (sexual spores) is affected by linoleic acid moieties including endogenous sporogenic factors called psi factors. Deletion of odeA (Delta odeA), encoding a Delta-12 desaturase that converts oleic acid to linoleic acid, resulted in a strain depleted of polyunsaturated fatty acids (18:2 and 18:3) but increased in oleic acid (18:1) and total percent fatty acid content. Linoleic acid-derived psi factors were absent in this strain but oleic acid-derived psi factors were increased relative to wild type. The Delta odeA strain was reduced in conidial production and mycelial growth; these effects were most noticeable when cultures were grown at 26 degrees C in the dark. Under these environmental conditions, the Delta odeA strain was delayed in ascospore production but produced more ascospores than wild type over time. This suggests a role for oleic acid-derived psi factors in affecting the asexual to sexual spore ratio in A. nidulans. Fatty acid composition and spore development were also affected by veA, a gene previously shown to control light driven conidial and ascospore development. Taken together our results indicate an interaction between veA and odeA alleles for fatty acid metabolism and spore development in A. nidulans.

Effect of oleic and linoleic acids on the production of deep-fried odor in heated triolein and trilinolein.

To determine sources of desirable deep-fried flavor in frying oils, degradation products from heated triolein and trilinolein with 5-31% polar compounds representing low to high deterioration were evaluated by purge-trap gas chromatography-mass spectrometry-olfactometry. (E,E)-2,4-Decadienal, 2-heptenal, 2-octenal, 2,4-nonadienal, and 2,4-octadienal produced deep-fried odor at moderate-strong intensities in heated trilinolein. However, unexpected aldehydes-2,4-decadienal, 2,4-undecadienal, 2,4-nonadienal, and 2-octenal (all <15 ppm)-were produced in triolein heated for 6 h. These dienals possibly were produced by hydroperoxidation and/or hydroxylation followed by dehydration of 2-alkenals. The 2-alkenals were produced from thermal decomposition of hydroperoxides, epoxides, and keto and dimeric compounds produced during the heating of triolein. These aldehydes produced low intensities of deep-fried odor in triolein. This information helps to explain sources of the deep-fried flavor that is characteristic of high linoleic frying oils but which is only at low intensity levels in high oleic frying oils.

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.

A peanut seed lipoxygenase responsive to Aspergillus colonization.

Several lines of evidence have indicated that lipoxygenase enzymes (LOX) and their products, especially 9S- and 13S-hydroperoxy fatty acids, could play a role in the Aspergillus/seed interaction. Both hydroperoxides exhibit sporogenic effects on Aspergillus spp. (Calvo, A., Hinze, L., Gardner, H.W. and Keller, N.P. 1999. Appl. Environ. Microbiol. 65: 3668-3673) and differentially modulate aflatoxin pathway gene transcription (Burow, G.B., Nesbitt, T.C., Dunlap, J. and Keller, N.P. 1997. Mol. Plant-Microbe Interact. 10: 380-387). To examine the role of seed LOXs at the molecular level, a peanut (Arachis hypogaea L.) seed gene, PnLOX1, was cloned and characterized. Analysis of nucleotide sequence suggests that PnLOX1 encodes a predicted 98 kDa protein highly similar in sequence and biochemical properties to soybean LOX2. The full-length PnLOX1 cDNA was subcloned into an expression vector to determine the type(s) of hydroperoxide products the enzyme produces. Analysis of the oxidation products of PnLOX1 revealed that it produced a mixture of 30% 9S-HPODE (9S-hydroperoxy-10E, 12Z-octadecadienoic acid) and 70% 13S-HPODE (13S-hydroperoxy-9Z, 11E-octadecadienoic acid) at pH 7. PnLOX1 is an organ-specific gene which is constitutively expressed in immature cotyledons but is highly induced by methyl jasmonate, wounding and Aspergillus infections in mature cotyledons. Examination of HPODE production in infected cotyledons suggests PnLOX1 expression may lead to an increase in 9S-HPODE in the seed.

Sporogenic effect of polyunsaturated fatty acids on development of Aspergillus spp.

Aspergillus spp. are frequently occurring seed-colonizing fungi that complete their disease cycles through the development of asexual spores, which function as inocula, and through the formation of cleistothecia and sclerotia. We found that development of all three of these structures in Aspergillus nidulans, Aspergillus flavus, and Aspergillus parasiticus is affected by linoleic acid and light. The specific morphological effects of linoleic acid include induction of precocious and increased asexual spore development in A. flavus and A. parasiticus strains and altered sclerotium production in some A. flavus strains in which sclerotium production decreases in the light but increases in the dark. In A. nidulans, both asexual spore production and sexual spore production were altered by linoleic acid. Spore development was induced in all three species by hydroperoxylinoleic acids, which are linoleic acid derivatives that are produced during fungal colonization of seeds. The sporogenic effects of these linoleic compounds on A. nidulans are similar to the sporogenic effects of A. nidulans psi factor, an endogenous mixture of hydroxylinoleic acid moieties. Light treatments also significantly increased asexual spore production in all three species. The sporogenic effects of light, linoleic acid, and linoleic acid derivatives on A. nidulans required an intact veA gene. The sporogenic effects of light and linoleic acid on Aspergillus spp., as well as members of other fungal genera, suggest that these factors may be significant environmental signals for fungal development.

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

9-Hydroxy-traumatin, 9-hydroxy-12-oxo-10E-dodecenoic acid, was isolated as a product of 13S-hydroperoxy-9Z,11E-octadecadienoic acid as catalyzed by enzyme preparations of both soybean and alfalfa seedlings. This suggested that 9Z-traumatin, 12-oxo-9Z-dodecenoic acid, was being converted into 9-hydroxy-traumatin in an analogous manner to the previously identified enzymic conversion of 3Z-nonenal and 3Z-hexenal into 4-hydroxy-2E-nonenal and 4-hydroxy-2 E-hexenal, respectively. Other metabolites of 13S-hydroperoxy-9Z,11E-octadecadienoic acid were similar for both soybean and alfalfa seedling preparations, and they are briefly described.

Aspirin inhibition and acetylation of the plant cytochrome P450, allene oxide synthase, resembles that of animal prostaglandin endoperoxide H synthase.

The enzymatic reactions leading to octadecanoid lipid signaling intermediates in plants are similar to those of animals and are inhibited by nonsteroidal anti-inflammatory drugs (NSAIDs) such as salicylic acid and aspirin. In animals, NSAIDs inhibit the cyclooxygenase (COX) activity of prostaglandin endoperoxide H synthase, which ultimately blocks the formation of prostaglandins. In plants, NSAIDs block the formation of 12-oxo-phytodienoic acid and jasmonates, which are the equivalent signaling compounds. In this study we show that NSAIDs act as competitive inhibitors of allene oxide synthase (AOS), the cytochrome P450 that initiates plant oxylipin synthesis. We also show that aspirin causes the time-dependent inhibition and acetylation of AOS, which leads the irreversible inactivation of this enzyme. This inhibition and acetylation superficially resembles that observed for the inactivation of COX in animals. In AOS, aspirin acetylates three serine residues near the C-terminal region that appear to be highly conserved among AOS sequences from other plants but are not conserved among "classical" type P450s. The role of these serine residues is unclear. Unlike animal COX, where acetylation of a single serine residue within the substrate channel leads to inactivation of prostaglandin endoperoxide H synthase, the three serine residues in AOS are not thought to line the putative substrate channel. Thus, inhibition by aspirin may be by a different mechanism. It is possible that aspirin and related NSAIDs could inhibit other P450s that have motifs similar to AOS and consequently serve as potential biochemical targets for this class of drugs.

Mechanism of linoleic acid hydroperoxide reaction with alkali.

Treatment of (13S,9Z,11E)-13-hydroperoxy-9,11-octadecadienoic acid (13S-HPODE) with strong alkali resulted in the formation of about 75% of the corresponding hydroxy acid, (13S,9Z,11E)-13-hydroxy-9,11-octadecadienoic acid (13S-HODE), and the remaining 25% of products was a mixture of several oxidized fatty acids, the majority of which was formed from (9Z,11R,S,12S,R)-13-oxo-11,12-epoxy-9-octadecenoic acid by Favorskii rearrangement (Gardner, H.W., et al. (1993) Lipids 28, 487-495). In the present work, isotope experiments were completed in order to get further information about the initial steps of the alkali-promoted decomposition of 13S-HPODE. 1. Reaction of [hydroperoxy-18O2] 13S-HPODE with 5 M KOH resulted in the formation of [hydroxy-18O] 13S-HODE and [epoxy-18O](9Z,11R,S,12S,R)-13-oxo-11,12-epoxy-9-octadecenoi c acid; 2. treatment of a mixture of [U-14C] 13S-HODE and [hydroperoxy-18O2] 13S-HPODE with KOH and analysis of the reaction product by radio-TLC showed that 13S-HODE was stable under the reaction conditions and did not serve as precursor of other products; 3. reaction of a mixture of [U-14C] 13-oxo-9,11-octadecadienoic acid (13-OODE) and [hydroperoxy-18O2] 13S-HPODE with KOH resulted in the formation of [U-14C-epoxy-18O]99Z,11R,S,12S,R)-13-oxo-11,12-epoxy-9-octad ecenoic acid; 4. treatment of a mixture of [hydroperoxy-18O2] 13S-HPODE and [carboxyl-18O1] 13S-HPODE with KOH afforded (9Z,11R,S,12S,R)-13-oxo-11,12-epoxy-9-octadecenoic acid having an 18O-labeling pattern which was in agreement with its formation by intermolecular epoxidation. It was concluded that (9Z,11R,S,12S,R)-13-oxo-11,12-epoxy-9-octadecenoic acid is formed from 13S-HPODE by a sequence involving initial dehydration into the alpha, beta-unsaturated ketone, 13-OODE, followed by epoxidation of the delta 11 double bond of this compound by the peroxyl anion of a second molecule of 13S-HPODE. Rapid conversion of hydroperoxides by alkali appeared to require the presence of an alpha, beta-unsaturated ketone intermediate as an oxygen acceptor. This was supported by experiments with a saturated hydroperoxide, methyl 12-hydroperoxyoctadecanoate, which was found to be much more resistant to alkali-promoted conversion than 13S-HPODE.

Oxygenation of (3Z)-alkenal to (2E)-4-hydroxy-2-alkenal in soybean seed (Glycine max L.).

(3Z)-Alkenals, such as (3Z)-hexenal and (3Z)-nonenal, are produced from polyunsaturated fatty acids via lipoxygenase and hydroperoxide lyase catalysis, but in soybeans (Glycine max L.) (3Z)-alkenals have a fleeting existence. In this study it was shown that soybean seeds possess two pathways that metabolize (3Z)-alkenals. One is a soluble (3Z):(2E)-enal isomerase that transformed (3Z)-hexenal and (3Z)-nonenal into the corresponding (2E)-alkenals. The other was a membrane-bound system that converted (3Z)-hexenal and (3Z)-nonenal into (2E)-4-hydroxy-2-hexenal and (2E)-4-hydroxy-2-nonenal, respectively. The latter conversion was shown to absorb O2 with a pH optimum of 9.5. Little effect observed with lipoxygenase inhibitors suggested that oxidation was not catalyzed by lipoxygenase. Instead, a specific (3Z)-alkenal oxygenase was implicated in forming intermediate alkenal hydroperoxides. Hydroperoxide-dependent peroxygenase (epoxygenase) is known to reduce hydroperoxides to their corresponding hydroxides and is also known to be inhibited by hydrogen peroxide preincubation. Consequently, intermediate 4-hydroperoxy-2-alkenals could be observed after inhibiting hydroperoxide-dependent peroxygenase by preincubation with hydrogen peroxide. Because 4-hydroxy-2-alkenals are potent toxins, these compounds may be produced as nonvolatile plant defensive substances.

Characterization of a C-5,13-Cleaving Enzyme of 13(S)-Hydroperoxide of Linolenic Acid by Soybean Seed.

An activity was found in mature soybean seeds (Glycine max L. cv Century) that cleaved 13(S)-hydroperoxy-9(Z),11(E),15(Z)-octadecatrienoic acid (13S-HPOT) into 13-oxo-9(Z),11(E)-tridecadienoic acid and two isomeric pentenols, 2(Z)-penten-1-ol and 1-penten-3-ol. Isomeric pentene dimers were also produced and were presumably derived from the combination of two pentene radicals. 13(S)-Hydroperoxy-9(Z),11(E)-octadecadienoic acid (13S-HPOD) was, by contrast, a poor substrate. Activity with 13S-HPOT increased 24-fold under anaerobic conditions reminiscent of a similar anaerobic promoted reaction of 13S-HPOD catalyzed by lipoxygenase (LOX) in the presence of linoleic acid. However, prior to ion-exchange chromatography, cleavage activity did not require linoleic acid. After separation by gel filtration followed by ion-exchange chromatography, cleavage activity was lost but reappeared in the presence of either linoleic acid or dithiothreitol. Under these conditions cleavage activity was coincident with the activity of types 1 and 2 LOX. LOX inhibitors suppressed the cleavage reaction in a manner similar to inhibition of LOX activity. Heat-generated alkoxyl radicals derived from either 13S-HPOT or 13S-HPOD afforded similar products and yields of 13-oxo-9(Z),11(E)-tridecadienoic acid compared to the enzymic reaction. The product 1-penten-3-ol may be the precursor of the "raw-bean" volatile ethylvinylketone.

Allene Oxide Synthase and Allene Oxide Cyclase, Enzymes of the Jasmonic Acid Pathway, Localized in Glycine max Tissues.

Because jasmonic acid regulates a number of processes, including the expression of vegetative storage proteins in soybean (Glycine max L.) leaves, the relative activity of a specific portion of the jasmonic acid biosynthetic pathway in soybean tissues was examined. Allene oxide synthase and allene oxide cyclase were examined because they constitute a branch point leading specifically from 13(S)-hydroperoxy-9(Z), 11(E), 15(Z)-octadecatrienoic acid to 12-oxo-phytodienoic acid, the precursor of jasmonic acid. From growing plants, seed coats (hila plus testae) of green fruits (38 d post-anthesis) were most active, eliciting about 1.5 times greater activity on a per milligram of protein basis than the next most active tissue, which was the pericarp. Leaves from fruiting plants were only one-seventh as active as seed coats, and activities in both immature cotyledons and embryonic axes were very low. No activity was detected in any part of stored, mature seeds. After 72 h of germination of stored seeds, a small amount of activity, about 4% of that in immature seed coats, was found in the plumule-hypocotyl-root, and no activity was detected in the cotyledons. The high levels of jasmonic acid biosynthetic enzymes in soybean pericarp and seed coat suggest a role for jasmonic acid in the transfer of assimilate to seeds.

The major protein of guayule rubber particles is a cytochrome P450. Characterization based on cDNA cloning and spectroscopic analysis of the solubilized enzyme and its reaction products.

Guayule plants accumulate large quantities of rubber within parenchyma cells of their stembark tissues. This rubber is packed within discrete organelles called rubber particles composed primarily of a lipophilic, cis-polyisoprene core, small amounts of lipids, and several proteins, the most abundant of which is the M(r) 53,000 rubber particle protein (RPP). We have cloned and sequenced a full-length cDNA for RPP and show that it has 65% amino acid identity and 85% similarity to a cytochrome P450 known as allene oxide synthase (AOS), recently identified from flaxseed. RPP contains the same unusual heme-binding region and possesses a similar defective I-helix region as AOS, suggesting an equivalent biochemical function. Spectral analysis of solubilized RPP verifies it as a P450, and enzymatic assays reveal that it also metabolizes 13(S)-hydroperoxy-(9Z,11E)-octadecadienoic acid into the expected ketol fatty acids at rates comparable with flaxseed AOS. RPP is unusual in that it lacks the amino-terminal membrane anchor and the established organelle targeting sequences found on other conventional P450s. Together, these factors place RPP in the CYP74 family of P450s and establish it as the first P450 localized in rubber particles and the first eukaryotic P450 to be identified outside endoplasmic reticulum, mitochondria, or plastids.

Oxygenation of (3Z)-nonenal to (2E)-4-hydroxy-2-nonenal in the broad bean (Vicia faba L.).

Incubation of (3Z)-nonenal (NON) with the 269,000-g particle fraction of seed homogenate of the broad bean (Vicia faba L.) afforded (2E)-4-hydroxy-2-nonenal (HNE) as the principal product. One pathway of HNE formation consisted of initial oxygenation of NON into (2E)-4-hydroperoxy-2-nonenal (HPNE) by a novel (3Z)-alkenal oxygenase activity, followed by conversion of HPNE into HNE by a previously recognized hydroperoxide-dependent epoxygenase. The hydroperoxide intermediate was detected in coincubations of NON and oleic acid, in which experiments the HPNE generated from NON supported epoxygenase-catalyzed epoxidation of oleic acid into 9,10-epoxystearic acid. Furthermore, by using an enzyme preparation in which the epoxygenase had been inactivated by pretreatment with hydrogen peroxide it was possible to isolate and characterize racemic (4R,4S) HPNE following incubation of NON. Although the (3Z)-alkenal oxygenase resembled a lipoxygenase in its action, it was not inhibited by the lipoxygenase inhibitors, 5,8,11,14-eicosatetraynoic acid and nordihydroguaiaretic acid. In a second pathway, HNE was produced by rearrangement of 3,4-epoxynonenal, which was in turn formed from NON by a reaction catalyzed by hydroperoxide-dependent epoxygenase. Support for this pathway came from experiments in which 18O-labeled HNE was isolated following coincubation of NON and 13-18O-labeled linoleic acid 13-hydroperoxide. The existence of 3,4-epoxynonenal as a transient intermediate in HNE biosynthesis was further demonstrated by the isolation of 3,4-epoxynonenal (61% (4R)-configuration) as a trapping product in short time incubations interrupted by addition of sodium borohydride. The two pathways established for biosynthesis of HNE involved the hydroperoxide-reducing and the olefin-epoxidizing activities of hydroperoxide-dependent epoxygenase. In the absence of extraneous olefins and hydroperoxides the two pathways would be tightly coupled and follow the stoichiometry: 2NON + 1O2-->2HNE. It was also shown that the V. faba particle fraction catalyzed oxygenation of (3Z)-hexenal into (2E)-4-hydroxy-2-hexenal.

Lipoxygenase-derived aldehydes inhibit fungi pathogenic on soybean.

Several unsaturated aldehydes are produced from polyunsaturated fatty acids via the lipoxygenase pathway when soybean (Glycine max) plants are wounded mechanically or by pathogens. The effects of four of these aldehydes were examined on the growth of isolated fungal cultures ofColletotrichum truncatum, Rhizoctonia solani, andSclerotium rolfsii. (E)-2-Hexenal, (E)-2-nonenal, and (Z)-3-nonenal inhibited the growth ofR. solani andS. rolfsii at 35 µmol added per liter or greater when applied as volatiles, although higher levels were required for inhibition ofC. truncatum. (E)-4-Hydroxy-2-nonenal was the most inhibitory compound when applied directly in the growth medium, but it had the least effect as a volatile.