Peptides and the blood-brain barrier: lipophilicity as a predictor of permeability

Eighteen peptides were examined for penetration across the blood-brain barrier (BBB) in rats. Iodinated peptides were injected via the carotid artery and 5 sec later the rats were decapitated. The results were expressed as a brain to blood ratio. The results showed that small amounts of most peptides enter the brain. The octanol coefficient, a measurement of lipophilicity, was a good predictor of penetration for most peptides. The low molecular weight, N-tyrosinated peptides (leucine-enkephalin, methionine enkephalin, N-Tyr-MIF-1, and N-Tyr-FMRF), that have been shown to be transported out of the brain by a saturable, carrier-mediated system, had much lower penetration rates than those predicted by their octanol coefficients. Molecular weight, percent of unbound peptide, total charge, net charge, and absolute charge were not good predictors of peptide penetration. Pretreatment of the rats with IP aluminum, which has been suggested to increase lipophilic permeability of the BBB, enhanced passage of 15 of the 18 peptides but not radioiodinated serum albumin or radioactive red blood cells. Thus, of the various physicochemical characteristics of peptides tested here, lipophilicity was most important in determining penetration of peptides across the BBB. However, the existence of one class of peptides that deviates from this trend (those of low molecular weight with an N-tyrosine) and the variability among the remaining peptides suggests that other, unidentified factors may be important in the prediction of peptide penetration across the BBB.

S-Nitrosoglutathione is a substrate for rat alcohol dehydrogenase class III isoenzyme

An enzyme isolated from rat liver cytosol (native molecular mass 78. 3 kDa; polypeptide molecular mass 42.5 kDa) is capable of catalysing the NADH/NADPH-dependent degradation of S-nitrosoglutathione (GSNO). The activity utilizes 1 mol of coenzyme per mol of GSNO processed. The isolated enzyme has, as well, several characteristics that are unique to alcohol dehydrogenase (ADH) class III isoenzyme: it is capable of catalysing the NAD+-dependent oxidations of octanol (insensitive to inhibition by 4-methylpyrazole), methylcrotyl alcohol (stimulated by added pentanoate) and 12-hydroxydodecanoic acid, and also the NADH/NADPH-dependent reduction of octanal. Methanol and ethanol oxidation activity is minimal. The enzyme has formaldehyde dehydrogenase activity in that it is capable of catalysing the NAD+/NADP+-dependent oxidation of S-hydroxymethylglutathione. Treatment with the arginine-specific reagent phenylglyoxal prevents the pentanoate stimulation of methylcrotyl alcohol oxidation and markedly diminishes the enzymic activity towards octanol, 12-hydroxydodecanoic acid and S-hydroxymethylglutathione; the capacity to catalyse GSNO degradation is also checked. Additionally, limited peptide sequencing indicates 100% correspondence with known ADH class III isoenzyme sequences. Kinetic studies demonstrate that GSNO is an exceptionally active substrate for this enzyme. S-Nitroso-N-acetylpenicillamine and S-nitrosated human serum albumin are not substrates; the activity towards S-nitrosated glutathione mono- and di-ethyl esters is minimal. Product analysis suggests that glutathione sulphinamide is the major stable product of enzymic GSNO processing, with minor yields of GSSG and NH3; GSH, hydroxylamine, nitrite, nitrate and nitric oxide accumulations are minimal. Inclusion of GSH in the reaction mix decreases the yield of the supposed glutathione sulphinamide in favor of GSSG and hydroxylamine.

Characterization of disease-associated single amino acid polymorphisms in terms of sequence and structure properties

In the present work, we use structural information to characterize a set of disease-associated single amino acid polymorphisms exhaustively. The analysis of different properties, such as substitution matrix elements, secondary structure, accessibility, free energies of transfer from water to octanol, amino acid volume, etc., suggests that many disease-causing mutations are associated with extreme changes in the value of parameters relating to protein stability. Overall, our results indicate that, while knowledge of protein structure clearly helps in understanding these mutations, a finer understanding can come only from a quantitative knowledge of protein stability and of the protein environment in the cell. Interestingly, use of evolutionary information from multiple sequence alignments can be used to increase our knowledge of disease-associated mutations.

Germination of penicillium paneum Conidia is regulated by 1-octen-3-ol, a volatile self-inhibitor

Penicillium paneum is an important contaminant of cereal grains which is able to grow at low temperature, low pH, high levels of carbon dioxide, and under acid conditions. P. paneum produces mycotoxins, which may be harmful to animals and humans. We found that conidia in dense suspensions showed poor germination, suggesting the presence of a self-inhibitor. A volatile compound(s) produced by these high-density conditions also inhibited mycelial growth of different species of fungi belonging to a variety of genera, suggesting a broad action range. The heat-stable compound was isolated by successive centrifugation of the supernatant obtained from spore suspensions with a density of 10(9) conidia ml(-1). By using static headspace analyses, two major peaks were distinguished, with the highest production of these metabolites after 22 h of incubation at 25 degrees C and shaking at 140 rpm. Gas chromatography coupled with mass spectra analysis revealed the compounds to be 3-octanone and 1-octen-3-ol. Notably, only the latter compound appeared to block the germination process at different developmental stages of the conidia (swelling and germ tube formation). In this study, 1-octen-3-ol influenced different developmental processes during the P. paneum life cycle, including induction of microcycle conidiation and inhibition of spore germination. Therefore, the compound can be considered a fungal hormone during fungal development.

Biotransformation of 8:2 fluorotelomer alcohol in soil and by soil bacteria isolates

The microbial transformation of 8:2 fluorotelomer alcohol (FTOH) to perfluorocarboxylic acids, including the globally detected perfluorooctanoic acid (PFOA), has recently been confirmed to occur in mixed bacteria cultures, activated sludge, and soil. However, little is known to date about the microbes involved in the transformation. In the present study, the effect of three carrier solvents (ethanol, octanol, and 1,4-dioxane), which may serve as carbon sources, on the aerobic degradation rate of 8:2 FTOH and metabolite distribution was evaluated both in a clay loam soil and in two pure soil bacterial cultures. Biodegradation pathways appeared similar regardless of the solvent; however, significant differences in 8:2 FTOH degradation rates were observed: 1,4-dioxane > ethanol > octanol. In the presence of 1,4-dioxane, which is not easily biodegraded, 8:2 FTOH degradation was the fastest With octanol, which is a structural analogue of 8:2 FTOH, the transformation was inhibited, but upon depletion of octanol, 8:2 FTOH was biodegraded. In the pure culture study, two soil bacterial strains, Pseudomonas species OCY4 and OCW4, enriched from soil using octanol as a sole carbon source, also transformed 8:2 FTOH without prior exposure or acclimation to 8:2 FTOH. Increased biomass resulting from octanol metabolism did increase 8:2 FTOH transformation rates; however, 8:2 FTOH could not support bacterial growth, indicating the transformation by pure cultures was via cometabolic processes.

Hydration and percutaneous absorption: I. Influence of hydration on alkanol permeation through hairless mouse skin

A method to study the influence of hydration on skin permeability where the skin is immersed in saline for up to 30 hr and under circumstances where a steady state rate of permeation can be established in several minutes is indicated. These circumstances allow multiple, sequential runs over a period where the permeability coefficients of some chemicals are gradually changing. It has been found that the permeabilities of water, methanol and ethanol are little affected by such hydration. However, there is a doubling of the permeability coefficients of butanol and hexanol during the first 10 hr of immersion. More hydrophobic alkanols seem to be less sensitive to the protracted aqueous conditioning. In general the results indicate that there are complex molecular structure-permeability relationships operating in skin. More specifically, the hydration effects are insightful with respect to developing barrier models for skin as they are further indications that different parallel diffusional paths are followed by polar and semi- and nonpolar species.

Biosynthesis of volatiles by the myxobacterium Myxococcus xanthus

The volatiles emitted from cell cultures of myxobacterium Myxococcus xanthus were collected by use of a closed-loop stripping apparatus (CLSA) and analyzed by GC-MS. Two new natural products, (S)-9-methyldecan-3-ol ((S)-1) and 9-methyldecan-3-one (2), were identified and synthesized, together with other aliphatic ketones and alcohols, and terpenes. Biosynthesis of the two main components (S)-1 and 2 was examined in feeding experiments carried out with the wild-type strain DK1622 and two mutant strains JD300 and DK11017, which are impaired in the degradation pathway from leucine to isovaleryl-SCoA. Isovaleryl-SCoA is used as a starter, followed by chain elongation with two malonate units. Subsequent use of methyl malonate and decarboxylation leads to (S)-1 and 2. Furthermore, 3,3-dimethylacrylic acid (DMAA) can be used by the mutant strain to form isovaleryl-SCoA, which corroborates recent data on the detection of a novel variety of the mevalonate pathway giving rise to isovaleryl-SCoA from HMGCoA.

The effect of halogenation on blood-brain barrier permeability of a novel peptide drug

The utility of a drug depends on its ability to reach appropriate receptors at the target tissue and remain metabolically stable to produce the desired effect. To improve central nervous system entry of the opioid analgesic [D-Pen2, L-Pen5, Phe6] Enkephalin (DPLPE-Phe), our research group synthesized analogs that had chloro, bromo, fluoro, and iodo halogens on the para positions of the phenylalanine-4 residue. This study reports on investigation of the effect of halogenation on stability, lipophilicity, and in vitro blood-brain barrier permeability of a novel enkephalin analog DPLPE-Phe. The stability of each halogenated DPLPE-Phe analog as well as the amidated and nonamidated parent peptide was tested in plasma and brain. All peptides tested had a half-time disappearance >300 min except for DPLPE-Phe-NH2, which was found to have a half-life of 30 min in plasma. Octanol/saline distribution studies indicated addition of halogens to DPLPE-Phe-OH significantly increased lipophilicity except for p-[F-Phe4]DPLPE-Phe-OH. p-[Cl-Phe4]DPLPE-Phe-OH exhibited the most pronounced increase in lipophilicity. Para-bromo and para-chloro halogen additions significantly enhanced in vitro blood-brain barrier permeability, providing evidence for improved delivery to the central nervous system.

Insect repellents: modulators of mosquito odorant receptor activity

Background

DEET, 2-undecanone (2-U), IR3535 and Picaridin are widely used as insect repellents to prevent interactions between humans and many arthropods including mosquitoes. Their molecular action has only recently been studied, yielding seemingly contradictory theories including odorant-dependent inhibitory and odorant-independent excitatory activities on insect olfactory sensory neurons (OSNs) and odorant receptor proteins (ORs).

Methodology/Principal Findings

Here we characterize the action of these repellents on two Aedes aegypti ORs, AaOR2 and AaOR8, individually co-expressed with the common co-receptor AaOR7 in Xenopus oocytes; these ORs are respectively activated by the odors indole (AaOR2) and (R)-(−)-1-octen3-ol (AaOR8), odorants used to locate oviposition sites and host animals. In the absence of odorants, DEET activates AaOR2 but not AaOR8, while 2-U activates AaOR8 but not AaOR2; IR3535 and Picaridin do not activate these ORs. In the presence of odors, DEET strongly inhibits AaOR8 but not AaOR2, while 2-U strongly inhibits AaOR2 but not AaOR8; IR3535 and Picaridin strongly inhibit both ORs.

Conclusions/Significance

These data demonstrate that repellents can act as olfactory agonists or antagonists, thus modulating OR activity, bringing concordance to conflicting models.

Penetration enhancers for human skin: mode of action of 2-pyrrolidone and dimethylformamide on partition and diffusion of model compounds water, n-alcohols, and caffeine

Penetration-enhancing solvents may modify diffusional routes through the stratum corneum and the partitioning of drugs into these pathways. To investigate the mechanisms of action of enhancers, steady-state fluxes were measured in vitro for polar methanol, nonpolar octanol, and an intermediate compound, caffeine, selected as model penetrants; human stratum corneum conditioned on both sides with water or accelerants (2-pyrrolidone or dimethylformamide solutions) was used. We determined partition, permeability, and apparent diffusion coefficients, and derived the standard free energy of transfer of the methylene group from water to stratum corneum (-423 cal mol-1); less negative values were obtained for transfer from 2-pyrrolidone solutions. We conclude that for these model compounds, and taking a fully hydrated membrane as a standard: (a) 2-pyrrolidone enhances permeation through the polar route of the skin by increasing the diffusivity, and reduces passage through the nonpolar route by decreasing diffusivity and partitioning, (b) dimethylformamide promotes polar route absorption by raising diffusivity and partitioning and reduces nonpolar absorption by decreasing both parameters, and (c) for caffeine, the markedly increased absorption (15-fold) caused by dimethylformamide is associated with damage to the membrane.

In vitro-in vivo extrapolation: estimation of human serum concentrations of chemicals equivalent to cytotoxic concentrations in vitro

In the present study an extrapolation model for estimating serum concentrations of chemicals equivalent to in vitro effective concentrations is developed and applied to median cytotoxic concentrations (EC(50)) determined in vitro. Nominal concentrations of a chemical in serum and in vitro are regarded as equivalent, if they result in the same aqueous concentration of the unbound form. The algorithm used is based on equilibrium distribution and requires albumin binding data, the octanol-water partition coefficient (K(ow)), and the albumin concentrations and lipid volume fractions in vitro and in serum. The chemicals studied cover wide ranges of cytotoxic potency (EC(50): 2.5-530,000 microM) and lipophilicity (logK(ow): -5 to 7). Their albumin binding characteristics have been determined by means of an in vitro cytotoxicity test as described previously. The equivalent serum concentrations of 19 of the 33 compounds investigated, having high protein binding and/or lipophilicity, were substantially higher than the EC(50)-values, by factors of 2.5-58. Prominent deviations between the equivalent nominal concentrations in serum and in vitro were largely restricted to chemicals with higher cytotoxic potency (EC(50)< or =1000 microM). The results suggest that estimates of equivalent serum concentrations based on in vitro data are robust for chemicals with low lipophilicity (logK(ow)< or =2) and low potency (EC(50)>1000 microM). With more potent chemicals or those with higher lipophilicity partitioning into lipids and/or binding to serum proteins have to be taken into account when estimating in vivo serum concentrations equivalent to in vitro effective concentrations.

The insect attractant 1-octen-3-ol is the natural ligand of bovine odorant-binding protein

Bovine odorant-binding protein (bOBP) is a dimeric lipocalin present in large amounts in the respiratory and olfactory nasal mucosa. The structure of bOBP refined at 2.0-A resolution revealed an elongated volume of electron density inside each buried cavity, indicating the presence of one (or several) naturally occurring copurified ligand(s) (Tegoni et al. (1996) Nat. Struct. Biol. 3, 863-867; Bianchet et al. (1996) Nat. Struct. Biol. 3, 934-939). In the present work, by combining mass spectrometry, x-ray crystallography (1.8-A resolution), and fluorescence, it has been unambiguously established that natural bOBP contains the racemic form of 1-octen-3-ol. This volatile substance is a typical component of bovine breath and in general of odorous body emanations of humans and animals. The compound 1-octen-3-ol is also an extremely potent olfactory attractant for many insect species, including some parasite vectors like Anopheles (Plasmodium) or Glossina (Trypanosoma). For the first time, a function can be assigned to an OBP, with a possible role of bOBP in the ecological relationships between bovine and insect species.

Multiple activities of insect repellents on odorant receptors in mosquitoes

Several lines of evidence suggest that insect repellent molecules reduce mosquito-host contacts by interacting with odorants and odorant receptors (ORs), thereby ultimately affecting olfactory-driven behaviours. We describe the molecular effects of 10 insect repellents and a pyrethroid insecticide with known repellent activity on two highly specific Aedes aegypti (Diptera: Culicidae) ORs, AaOR2 + AaOR7 and AaOR8 + AaOR7, exquisitely sensitive to key mosquito attractants indole and (R)-(-)-1-octen-3-ol, expressed in oocytes of Xenopus (Anura: Pipidae). Our study demonstrates that insect repellents can both inhibit odorant-evoked currents mediated by ORs and independently elicit currents in the absence of odorants. All of the repellents had effects on one or both ORs; most of these compounds were selective inhibitors and showed a high degree of specificity in their capacity to activate the two ORs. These results show that a range of insect repellents belonging to structurally diverse chemical classes modulate the function of mosquito ORs through multiple molecular mechanisms.

Functional expression of a bark beetle cytochrome P450 that hydroxylates myrcene to ipsdienol

The final steps in the pheromone-biosynthetic pathway of the pine engraver beetle, Ips pini (Say) (Coleoptera: Scolytidae) are unknown, but likely involve myrcene (7-methyl-3-methylene-1,6-octadiene) hydroxylation to produce the aggregation pheromone component, ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol). We have isolated a full-length I. pini cDNA encoding a cytochrome P450, CYP9T2. The recovered cDNA is 1.83kb and the open reading frame encodes a 532 amino acid protein. CYP9T2 is regulated by the same physiological factors that induce pheromone production. Quantitative real-time PCR experiments showed that feeding on host phloem induced CYP9T2 expression in males, but not females, and that basal expression levels are highest in male midguts, similar to other I. pini pheromone-biosynthetic genes. Microsomes prepared from Sf9 cells co-expressing baculoviral-mediated recombinant CYP9T2 and housefly (Musca domestica) NADPH-cytochrome P450 reductase converted myrcene to ipsdienol. The product identified by coupled GC-MS was mostly (4R)-(-)-ipsdienol, an important aggregation pheromone component for western North American I. pini. These results are consistent with CYP9T2 encoding a myrcene hydroxylase that functions near the end of the pheromone-biosynthetic pathway.

Identification of sites of incorporation in the nicotinic acetylcholine receptor of a photoactivatible general anesthetic

Most general anesthetics including long chain aliphatic alcohols act as noncompetitive antagonists of the nicotinic acetylcholine receptor (nAChR). To locate the sites of interaction of a long chain alcohol with the Torpedo nAChR, we have used the photoactivatible alcohol 3-[(3)H]azioctanol, which inhibits the nAChR and photoincorporates into nAChR subunits. At 1 and 275 microm, 3-[(3)H]azioctanol photoincorporated into nAChR subunits with increased incorporation in the alpha-subunit in the desensitized state. The incorporation into the alpha-subunit was mapped to two large proteolytic fragments. One fragment of approximately 20 kDa (alpha V8-20), containing the M1, M2, and M3 transmembrane segments, showed enhanced incorporation in the presence of agonist whereas the other of approximately 10 kDa (alpha V8-10), containing the M4 transmembrane segment, did not show agonist-induced incorporation of label. Within alpha V8-20, the primary site of incorporation was alpha Glu-262 at the C-terminal end of alpha M2, labeled preferentially in the desensitized state. The incorporation at alpha Glu-262 approached saturation between 1 microm, with approximately 6% labeled, and 275 microm, with approximately 30% labeled. Low level incorporation was seen in residues at the agonist binding site and the protein-lipid interface at approximately 1% of the levels in alpha Glu-262. Therefore, the primary binding site of 3-azioctanol is within the ion channel with additional lower affinity interactions within the agonist binding site and at the protein-lipid interface.

Intraspecific genotypic variability determines concentrations of key truffle volatiles

• Aroma variability in truffles has been attributed to maturation (Tuber borchii), linked to environmental factors (Tuber magnatum), but the involvement of genetic factors has been ignored. We investigated aroma variability in Tuber uncinatum, a species with wide distribution. Our aim was to assess aroma variability at different spatial scales (i.e. trees, countries) and to quantify how aroma was affected by genotype, fruiting body maturity, and geographical origin. • A volatile fingerprinting method was used to analyze the aroma of 223 T. uncinatum fruiting bodies from seven European countries. Maturity was estimated from spore melanization. Genotypic fingerprinting was performed by amplified fragment length polymorphism (AFLP). • Discriminant analysis revealed that, regardless of the geographical origin of the truffles, most of the aroma variability was caused by eight-carbon-containing volatiles (C8-VOCs). In an orchard of T. uncinatum, truffles producing different concentrations of C8-VOCs clustered around distinct host trees. This clustering was not associated with maturity, but was associated with fungal genotype. • These results indicate that the variation in C8-VOCs in truffles is most likely under genetic control. They exemplify that understanding the factors behind aroma variability requires a holistic approach. Furthermore, they also raise new questions regarding the ecological role of 1-octen-3-ol in truffles.

Biotransformation in double-phase systems: physiological responses of Pseudomonas putida DOT-T1E to a double phase made of aliphatic alcohols and biosynthesis of substituted catechols

Pseudomonas putida strain DOT-T1E is highly tolerant to organic solvents, with a logP(ow) (the logarithm of the partition coefficient of a solvent in a two-phase water-octanol system of > or =2.5. Solvent tolerant microorganisms can be exploited to develop double-phase (organic solvent and water) biotransformation systems in which toxic substrates or products are kept in the organic phase. We tested P. putida DOT-T1E tolerance to different aliphatic alcohols with a logP(ow) value between 2 and 4, such as decanol, nonanol, and octanol, which are potentially useful in biotransformations in double-phase systems in which compounds with a logP(ow) around 1.5 are produced. P. putida DOT-T1E responds to aliphatic alcohols as the second phase through cis-to-trans isomerization of unsaturated cis fatty acids and through efflux of these aliphatic alcohols via a series of pumps that also extrude aromatic hydrocarbons. These defense mechanisms allow P. putida DOT-T1E to survive well in the presence of high concentrations of the aliphatic alcohols, and growth with nonanol or decanol occurred at a high rate, whereas in the presence of an octanol double-phase growth was compromised. Our results support that the logP(ow) of aliphatic alcohols correlates with their toxic effects, as octanol (logP(ow) = 2.9) has more negative effects in P. putida cells than 1-nonanol (logP(ow) = 3.4) or 1-decanol (logP(ow) = 4). A P. putida DOT-T1E derivative bearing plasmid pWW0-xylE::Km transforms m-xylene (logP(ow) = 3.2) into 3-methylcatechol (logP(ow) = 1.8). The amount of 3-methylcatechol produced in an aliphatic alcohol/water bioreactor was 10- to 20-fold higher than in an aqueous medium, demonstrating the usefulness of double-phase systems for this particular biotransformation.

Percutaneous absorption of hair dyes: correlation with partition coefficients

A homologous series of hair dyes was selected for percutaneous absorption studies with excised human skin. The permeability constants obtained for the dyes were compared with octanol/water and skin membrane/water partition coefficients. The compounds examined were: p-phenylenediamine, o-phenylenediamine, 2-nitro-p-phenylenediamine, 2-amino-4-nitrophenol, 4-chloro-m-phenylenediamine, and 4-amino-2-nitrophenol. Skin absorption of the dyes was observed when they were applied in an aqueous solution. With one exception, the octanol/water partition coefficients were in the same rank order as the permeability constants. The determination of the partitioning of the hair dyes between water and either stratum corneum or epidermis was more complex. Preliminary stratum corneum/water partition studies resulted in values that were in the reverse order of skin permeation. When binding of the compounds to components of the membrane was saturated, the partition values more closely duplicated the rank order of permeability of the dyes. Prediction of percutaneous absorption of substances based on their partition coefficients may be confounded if these compounds are capable of binding to skin.

Altering the regioselectivity of cytochrome P450 CYP102A3 of Bacillus subtilis by using a new versatile assay system

A novel monooxygenase (CYP102A3) has been discovered within the Bacillus subtilis genome that reveals a similarity of 76 % to the well-known cytochrome P450 BM-3 of B. megaterium (CYP102A1). Both enzymes are natural fusion proteins consisting of a heme domain and a FAD/FMN-reductase domain. Because of their high turnover rates, these biocatalysts are of special interest for industrial applications, but show only limited regioselectivity. In this work, the regioselectivity of CYP102A3 was changed by directed evolution and protein design to hydroxylate substrates not only in different subterminal, but also to a high extent, in terminal carbon chain positions. To enable a high-throughput screening procedure, a very versatile assay was developed that is capable of discriminating between terminal and subterminal hydroxylation of carbon chains. A double mutant of CYP102A3 was obtained that produces 48 % octan-1-ol as the main product of the reaction.

Growth on octane alters the membrane lipid fatty acids of Pseudomonas oleovorans due to the induction of alkB and synthesis of octanol

Growth of Pseudomonas oleovorans GPo1, which contains the OCT plasmid, on octane results in changes in the membrane phospholipid fatty acid composition. These changes were not found for GPo12, an OCT-plasmid-cured variant of GPo1, during growth in the presence or absence of octane, implying the involvement of OCT-plasmid-encoded functions. When recombinant strain GPo12(pGEc47) carrying the alk genes from the OCT plasmid was grown on octane, the cells showed the same changes in fatty acid composition as those found for GPo1, indicating that such changes result from induction and expression of the alk genes. This finding was corroborated by inducing GPo12(pGEc47) with dicyclopropylketone (DCPK), a gratuitous inducer of the alk genes. Further experiments showed that the increase of the mean acyl chain length of fatty acids is related to the expression of alkB, which encodes a major integral membrane protein, while the formation of trans unsaturated fatty acids mainly results from the effects of 1-octanol, an octane oxidation product.

Volatiles mediating a plant-herbivore-natural enemy interaction in resistant and susceptible soybean cultivars

Several studies have shown that herbivore-induced plant volatiles act directly on herbivores and indirectly on their natural enemies. However, little is known about the effect of herbivore damage on resistant and susceptible plant cultivars and its effect on their natural enemies. Thus, the aim of this study was to evaluate the attraction of the herbivorous pentatomid bug Euschistus heros and its egg parasitoid Telenomus podisi to two resistant and one susceptible soybean cultivars with different types of damage (herbivory, herbivory+oviposition, and oviposition). In a Y-tube olfactometer, the parasitoids were attracted to herbivory and herbivory+oviposition damaged soybean plants when compared to undamaged soybean plants for the resistant cultivars, but did not show preference for the susceptible cultivar Silvânia in any of the damage treatments. The plant volatiles emitted by oviposition-damaged plants in the three cultivars did not attract the egg parasitoid. In four-arm-olfactometer bioassays, E. heros females did not show preference for odors of damaged or undamaged soybean plants of the three cultivars studied. The Principal Response Curves (PRC) analysis showed consistent variability over time in the chemical profile of volatiles between treatments for the resistant cultivar Dowling. The compounds that most contributed to the divergence between damaged soybean plants compared to undamaged plants were (E,E)-α-farnesene, methyl salicylate, (Z)-3-hexenyl acetate, and (E)-2-octen-1-ol.