Structure-activity relationship of volatile compounds that induce defense-related genes in maize seedlings

Volatile organic compounds mediate plant-to-plant communication, and plants receiving volatile cues can acquire greater defenses against attackers. It has been expected that volatiles are received by factors that eventually lead to the induction of defense-related gene expression; however, the nature of these factors remain unclear. Structure-activity relationship analysis of gene expression induction by volatiles should provide insights into the nature of these factors. We conducted a structure-activity relationship study using maize seedlings and (Z)-3-hexen-1-yl acetate (Z3HAC) as the lead compound. The acid portion of Z3HAC was not essential, and (Z)-3-hexen-1-ol (Z3HOL), which is formed after the hydrolysis of Z3HAC, is likely the structure essential for the upregulation of the genes. The double bond of Z3HOL is essential; however, its geometry is indistinguishable. Strict specificity was detected regarding the length of the methylene chain on the α- and ω-sides of the double bond, and therefore, the 3-hexen-1-ol structure was found to be the ultimate structure. This finding provides insight into the nature of the factors that interact with a volatile compound and subsequently activate signaling pathways, leading to the upregulation of a subset of defense genes.

6-(7-Nitro-2,1,3-benzoxadiazol-4-ylthio) Hexanol Inhibits Proliferation and Induces Apoptosis of Endometriosis by Regulating Glutathione S-Transferase Mu Class 4

Endometriosis is a chronic disease associated with a disrupted oxidative balance and chronic inflammation. In this study, we investigated the role of glutathione S-transferase Mu class 4 (GSTM4) in endometriosis and determined whether 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio) hexanol (NBDHEX) regulates GSTM4 expression to affect cellular functions and oxidative stress. GSTM4 expression was detected by immunohistochemistry in endometrium from 15 endometriosis patients and 15 healthy controls. Western blotting was used to detect the expression of GSTM4, proliferating cell nuclear antigen (PCNA), matrix metalloproteinase-9 (MMP-9), Survivin, B-cell lymphoma-extra-large (Bcl-XL), Bax, kelch-like ECH-associated protein 1 (Keap1), and nuclear factor-erythroid 2-related factor 2 (Nrf2) in primary endometrial stromal cells with endometriosis (EESC) and normal endometrial stromal cells (NESC). The effects of NBDHEX on cell proliferation, migration, and invasion were evaluated using Cell Counting Kit-8 (CCK8) and Transwell assays. Apoptosis was detected by flow cytometry. The expression of GSTM4 was significantly increased in endometrium from endometriosis patients. Upon NBDHEX treatment, ESC exhibited reduced proliferation, migration and invasion abilities, and increased apoptosis. NBDHEX decreased the expression of endometriosis prognostic markers (PCNA and MMP-9) and anti-apoptotic proteins (Survivin and Bcl-xl), while it increased the expression of the apoptotic protein Bax. It had no effect on Keap1 expression, and it decreased the expression of Nrf2. The effect of siRNA-mediated knockdown of GSTM4 was similar to that of suppressing GSTM4 expression with NBDHEX treatment. These results indicate that GSTM4 is highly expressed in endometriosis and its expression is inhibited by NBDHEX. Decreased expression of GSTM4 inhibits cell growth, migration, and invasion, and negatively regulates Nrf2 to affect oxidative stress-induced apoptosis. Our results suggest that GSTM4 may play a role in ameliorating the progression of endometriosis. NBDHEX may have therapeutic potential in the treatment of endometriosis.

CML8 and GAD4 function in (Z)-3-hexenol-mediated defense by regulating γ-aminobutyric acid accumulation in Arabidopsis

(Z)-3-hexenol, a small gaseous molecule, is produced in plants under biotic stress and induces defense responses in neighboring plants. However, little is known about how (Z)-3-hexenol induces plant defense-related signaling. In this study, we uncovered how (Z)-3-hexenol treatment enhances plant resistance to insect attacks by increasing γ-aminobutyric acid (GABA) contents in Arabidopsis leaves. First, (Z)-3-hexenol increases the intracellular content of calcium as secondary messenger in Arabidopsis leaf mesophyll cells. Both intracellular and extracellular calcium stores regulate changes in calcium content. Then, CML8 and GAD4 transmit calcium signaling to affect (Z)-3-hexenol induced GABA content and plant resistance. Herein, CML8 interaction with GAD4 was examined via yeast two-hybrid assays, firefly luciferase complementation imaging, and GST pull-down assays. These results indicate that (Z)-3-hexenol treatment increased the GABA contents in Arabidopsis leaves based on CML8 and GAD4, thus increasing plant resistance to the insect Plutella xylostella. This study revealed the mechanism of activating plant insect defense induced by (Z)-3-hexenol, which guides the study of volatiles as biological pest control.

Trimethylamine N-oxide promotes hyperlipidemia acute pancreatitis via inflammatory response

Trimethylamine N-oxide (TMAO), a metabolite of gut microbiota, is involved in the regulation of lipid metabolism and inflammatory response; however, the role of TMAO in hyperlipidemia acute pancreatitis (HAP) is not clear. In this study, HAP mice were used as an animal model to explore the effects and possible mechanism of TMAO on HAP, which may provide new ideas for the treatment of HAP. Results found that the levels of triglycerides, total cholesterol, low-density lipoprotein cholesterol, nonestesterified fatty acid, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, α-amylase, TMAO, and flavin-containing monooxygenase 3 were significantly increased, the levels of high-density lipoprotein cholesterol and insulin were significantly decreased, and there was an obvious pancreatic injury and inflammatory response in the model group. The choline analogue 3,3-dimethyl-1-butanol (DMB) treatment reversed the changes of serum biochemical parameters, alleviated the pancreatic tissue injury, and reduced the levels of inflammatory cytokines. Further studies of toll-like receptor (TLR)/p-glycoprotein 65 (p65) pathway found that the expressions of TLR2, TLR4, and p-p65/p65 in the model group were significantly increased, which was more obvious after Escherichia coli (Migula) Castellani & Chalmers treatment, while activation of the TLR/p65 pathway was inhibited by DMB. The results indicated that TMAO promotes HAP by promoting inflammatory response through TLR/p65 signaling pathway, suggesting that TMAO may be a potential target of HAP.

Maternal 3,3-Dimethyl-1-Butanol Therapy Protects Adult Male Rat Offspring against Hypertension Programmed by Perinatal TCDD Exposure

Maternal exposure to environmental pollutants affects fetal development, which can result in hypertension in adulthood. Gut microbiota-derived metabolite trimethylamine (TMA), trimethylamine-N-oxide (TMAO), and short chain fatty acids (SCFAs) have been associated with hypertension. We tested a hypothesis that maternal 3,3-Dimethyl-1-butanol (DMB, a TMA inhibitor) therapy prevents 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure-induced hypertension in adult offspring relevant to alterations of gut microbiota-derived metabolites, the mediation of aryl hydrocarbon receptor (AHR) signaling, and the renin-angiotensin system (RAS). Pregnant Sprague-Dawley rats were given weekly oral dose of TCDD 200 ng/kg for four doses (T), 1% DMB in drinking water (D), TCDD + DMB (TD), or vehicle (C) in pregnancy and lactation periods. Male progeny (n = 8/group) were sacrificed at the age of 12 weeks. Perinatal TCDD exposure caused hypertension in adult male offspring coinciding with reduced α-diversity, increased the Firmicutes to Bacteroidetes ratio, less abundant beneficial bacteria, impaired SCFA receptors' expression, the activation of AHR signaling, and the aberrant activation of the RAS. Treatment with DMB during pregnancy and lactation rescued hypertension induced by perinatal TCDD exposure. This was accompanied by reshaping gut microbiota, mediating TMA-TMAO metabolic pathway, increasing acetic acid and its receptors, and restoring the AHR and RAS pathway. Our data provide new insights into the therapeutic potential of DMB, a microbiome-based metabolite treatment, for the prevention of hypertension of developmental origins.

Therapeutic Potential of TLR8 Agonist GS-9688 (Selgantolimod) in Chronic Hepatitis B: Remodeling of Antiviral and Regulatory Mediators

BACKGROUND AND AIMS

GS-9688 (selgantolimod) is a toll-like receptor 8 agonist in clinical development for the treatment of chronic hepatitis B (CHB). Antiviral activity of GS-9688 has previously been evaluated in vitro in HBV-infected hepatocytes and in vivo in the woodchuck model of CHB. Here we evaluated the potential of GS-9688 to boost responses contributing to viral control and to modulate regulatory mediators.

APPROACH AND RESULTS

We characterized the effect of GS-9688 on immune cell subsets in vitro in peripheral blood mononuclear cells of healthy controls and patients with CHB. GS-9688 activated dendritic cells and mononuclear phagocytes to produce IL-12 and other immunomodulatory mediators, inducing a comparable cytokine profile in healthy controls and patients with CHB. GS-9688 increased the frequency of activated natural killer (NK) cells, mucosal-associated invariant T cells, CD4+ follicular helper T cells, and, in about 50% of patients, HBV-specific CD8+ T cells expressing interferon-γ. Moreover, in vitro stimulation with GS-9688 induced NK-cell expression of interferon-γ and TNF-α, and promoted hepatocyte lysis. We also assessed whether GS-9688 inhibited immunosuppressive cell subsets that might enhance antiviral efficacy. Stimulation with GS-9688 reduced the frequency of CD4+ regulatory T cells and monocytic myeloid-derived suppressor cells (MDSCs). Residual MDSCs expressed higher levels of negative immune regulators, galectin-9 and programmed death-ligand 1. Conversely, GS-9688 induced an expansion of immunoregulatory TNF-related apoptosis-inducing ligand+ NK cells and degranulation of arginase-I+ polymorphonuclear MDSCs.

CONCLUSIONS

GS-9688 induces cytokines in human peripheral blood mononuclear cells that are able to activate antiviral effector function by multiple immune mediators (HBV-specific CD8+ T cells, CD4+ follicular helper T cells, NK cells, and mucosal-associated invariant T cells). Although reducing the frequency of some immunoregulatory subsets, it enhances the immunosuppressive potential of others, highlighting potential biomarkers and immunotherapeutic targets to optimize the antiviral efficacy of GS-9688.

3,3-Dimethyl-1-butanol attenuates cardiac remodeling in pressure-overload-induced heart failure mice

Trimethylamine N-oxide (TMAO) is closely related to cardiovascular diseases, particularly heart failure (HF). Recent studies shows that 3,3-dimethyl-1-butanol (DMB) can reduce plasma TMAO levels. However, the role of DMB in overload-induced HF is not well understood. In this research study, we explored the effects and the underlying mechanisms of DMB in overload-induced HF. Aortic banding (AB) surgery was performed in C57BL6/J mice to induce HF, and a subset group of mice underwent a sham operation. After surgery, the mice were fed with a normal diet and given water supplemented with or without 1% DMB for 6 weeks. Cardiac function, plasma TMAO level, cardiac hypertrophy and fibrosis, expression of inflammatory, electrophysiological studies and signaling pathway were analyzed at the sixth week after AB surgery. DMB reduced TMAO levels in overload-induced HF mice. Adverse cardiac structural remodeling, such as cardiac hypertrophy, fibrosis and inflammation, was elevated in overload-induced HF mice. Susceptibility to ventricular arrhythmia also significantly increased in overload-induced HF mice. However, these changes were prevented by DMB treatment. DMB attenuated all of these changes by reducing plasma TMAO levels, hence negatively inhibiting the p65 NF-κB signaling pathway and TGF-β1/Smad3 signaling pathway. DMB plays an important role in attenuating the development of cardiac structural remodeling and electrical remodeling in overload-induced HF mice. This may be attributed to the p65 NF-κB signaling pathway and TGF-β1/Smad3 signaling pathway inhibition.

Molecular basis for potentiation of Cx36 gap junction channel conductance by n-alcohols and general anesthetics

In our recent study, we have demonstrated that short carbon chain n-alcohols (up to octanol) stimulated while long carbon chain n-alcohols inhibited the conductance of connexin (Cx) 36 (Cx36) gap junction (GJ) channels. In contrast, GJ channels composed of other types of Cxs all were inhibited by n-alcohols independent of their carbon chain length. To identify the putative structural domains of Cx36, responsible for the dual effect of n-alcohols, we performed structural modeling of Cx36 protein docking with hexanol and isoflurane that stimulated as well as nonanol and carbenoxolone that inhibited the conductance of Cx36 GJs and revealed their multiple common docking sites and a single pocket accessible only to hexanol and isoflurane. The pocket is located in the vicinity of three unique cysteine residues, namely C264 in the fourth, and C92 and C87 in the second transmembrane domain of the neighboring Cx36 subunits. To examine the hypothesis that disulphide bonding might be involved in the stimulatory effect of hexanol and isoflurane, we generated cysteine substitutions in Cx36 and demonstrated by a dual whole-cell patch-clamp technique that in HeLa (human cervix carcinoma cell line) and N2A (mouse neuroblastoma cell line) cells these mutations reversed the stimulatory effect of hexanol and isoflurane to inhibitory one, typical of other Cxs that lack respective cysteines and a specific docking pocket for these compounds. Our findings suggest that the stimulatory effect of hexanol and isoflurane on Cx36 GJ conductance could be achieved by re-shuffling of the inter-subunit disulphide bond between C264 and C92 to the intra-subunit one between C264 and C87.

Spatial differences in (Z)-3-hexen-1-ol production preferentially reduces Spodoptera litura larva attack on the young leaves of Nicotiana benthamiana

Plants synthesize specialized metabolites which possess extremely important ecological functions including direct defense, indirect defense, and signaling. The optimal defense theory (ODT) proposes that defensive metabolites are preferentially allocated to the tissues with high fitness value or in locations that are easily injured. In our present study, using the model plant Nicotiana benthamiana, we found that direct defense of N. benthamiana against Spodoptera litura (Fabricius) larvae showed spatial differences in the sites producing defensive chemicals. The upper leaves possessed significantly stronger direct defense ability than the middle and lower leaves. Interestingly, the strong defense ability of the upper leaves was not due to occurrences of well-known defensive metabolites such as nicotine and chlorogenic acid. After damage, the middle and lower leaves emitted higher amounts of (Z)-3-hexen-1-ol than the upper leaves, which could both attract larvae and significantly increase the amount of middle and lower leaf eaten by the larvae. The spatial difference in (Z)-3-hexen-1-ol emission may be due to spatial differences in expression of lipoxygenase (NbLOX2), which is responsible for the formation and emission of (Z)-3-hexen-1-ol. This study provided new insight into ODT, showing that plants effectively protect easily injured tissues through reduction in concentration of herbivore-feeding stimulant in the tissues.

New strategies for the use of Linum usitatissimum cell factories for the production of bioactive compounds

In this work, suspension-cultured cells of Linum usitatissimum L. were used to evaluate the effect of two types of cyclodextrins, β-glucan and (Z)-3-hexenol separately or in combination on phytosterol and tocopherol production. Suspension-cultured cells of L. usitatissimum were able to produce high levels of phytosterols in the presence of 50 mM methylated-β-cyclodextrins (1325.96 ± 107.06 μg g dry weight(-1)) separately or in combination with β-glucan (1278.57 ± 190.10 μg g dry weight(-1)) or (Z)-3-hexenol (1507.88 ± 173.02 μg g dry weight(-1)), being cyclodextrins able to increase both the secretion and accumulation of phytosterols in the spent medium, whereas β-glucan and (Z)-3-hexenol themselves only increased its intracellular accumulation. Moreover, the phytosterol values found in the presence of hydroxypropylated-β-cyclodextrins were lower than those found in the presence of methylated-β-cyclodextrins in all cases studied. However, the results showed that the presence of methylated-β-cyclodextrins did not increase the tocopherols production and only an increase in tocopherol levels was observed when cells were elicited with 50 mM hydroxypropylated-β-cyclodextrins in combination with β-glucan (174 μg g dry weight(-1)) or (Z)-3-hexenol (257 μg g dry weight(-1)). Since the levels of tocopherol produced in the combined treatment were higher than the sum of the individual treatments, a synergistic effect between both elicitors was assumed. To sum up, flax cell cultures elicited with cyclodextrins alone or in combination with β-glucan or (Z)-3-hexenol were able produce phytosterols and tocopherols, and therefore, these elicited suspension-cultured cells of L. usitatissimum can provide an alternative system, which is at the same time more sustainable, economical and ecological for their production.

Identification of leaf volatiles from olive (Olea europaea) and their possible role in the ovipositional preferences of olive fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae)

The olive fly, Bactrocera oleae (Rossi), is a monophagous pest that displays an oviposition preference among cultivars of olive (Olea europaea L.). To clarify the oviposition preference, the olive leaf volatiles of three olive cultivars (Cobrançosa, Madural and Verdeal Transmontana) were assessed by headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC/MS) at six different periods of olive fruit maturation and degrees of infestation. A total of 39 volatiles were identified, mainly esters and alcohols, with a minor percentage of aldehydes, ketones and terpenic compounds, including sesquiterpenes. At sampling dates with higher degrees of infestation, cv. Cobrançosa had, simultaneously, significantly lower infestation degrees and higher volatile amounts than the other two cultivars, with a probable deterrent effect for oviposition. The green leaf volatiles (GLVs) (Z)-3-hexen-1-ol and (Z)-3-hexen-1-ol acetate) were the main compounds identified in all cultivars, together with toluene. The abundance of GLVs decreased significantly throughout maturation, without significant differences among cultivars, while toluene showed a general increase and positive correlation with olive fly infestation levels. The results obtained could broaden our understanding of the roles of various types and amounts of olive volatiles in the environment, especially in olive fly host selection and cultivar preference.

Influence of two different alcohols in the esterification of fatty acids over layered zinc stearate/palmitate

In this work, esterification of fatty acids (oleic, linoleic and stearic acid) with a commercial zinc carboxylate (a layered compound formed by simultaneous intercalation of stearate and palmitate anions) was performed. Kinetic modeling using a quasi-homogeneous approach successfully fitted experimental data at different molar ratio of fatty acids/alcohols (1-butanol and 1-hexanol) and temperature. An apparent first-order reaction related to all reactants was found and activation energy of 66 kJ/mol was reported. The catalyst showed to be unique, as it can be easily recovered like a heterogeneous catalysts behaving like ionic liquids. In addition, this catalyst demonstrated a peculiar behavior, because higher reactivity was observed with the increase in the alcohols chain length compared to the authors' previous work using ethanol.

Effect of Selected Volatiles on Two Stored Pests: The Fungus Fusarium verticillioides and the Maize Weevil Sithophilus zeamais

New agronomic practices and technology enabled Argentina a larger production of cereal grains, reaching a harvest yield of 26.5 million metric tons of maize, of which, about 40% was exported. However, much of the maize production is lost annually by the attack of fungi and insects (2.6 million tons). In this study, the antifungal effect of selected volatiles on Fusarium verticillioides, its mycotoxin production, and the repellent and insecticidal activities against the weevill Sithophilus zeamais, an insect vector of F. verticillioides, were evaluated. The compounds tested were (2E)-2-hexenal, (2E)-2-nonenal, (2E,6Z)-2,6-nonadienal, 1-pentanol, 1-hexanol, 1-butanol, 3-methyl-1-butanol, pentanal, 2-decanone, and 3-decanone, which occur in the blend of volatile compounds emitted by various cereal grains. The most active antifungals were the aldehydes (2E)-2-nonenal, (2E)-2-hexenal, and (2E,6Z)-2,6-nonadienal (minimum inhibitory concentration values of <0.03, 0.06, and 0.06 mM, respectively). The occurrence of fumonisin B1 also was prevented because these compounds completely inhibited fungal growth. The best insecticidal fumigant activities against the maize weevil were shown by 2-decanone and 3-decanone (lethal concentration ≤ 54.6 μL/L (<0.28 mM)). Although, all tested compounds showed repellent activity against S. zeamais at a concentration of 4 μL/L, (2E,6Z)-2,6-nonadienal was the most active repellent compound. These results demonstrate the potential of (2E,6Z)-2,6-nonadienal to be used as a natural alternative to synthetic pesticides on F. verticillioides and S. zeamais.

Orco mediates olfactory behaviors and winged morph differentiation induced by alarm pheromone in the grain aphid, Sitobion avenae

Olfaction is crucial for short distance host location and pheromone detection by insects. Complexes of olfactory receptors (ORs) are composed of odor-specific ORs and OR co-receptors (Orco). Orcos are widely co-expressed with odor-specific ORs and are conserved across insect taxa. A number of Orco orthologs have been studied to date, although none has been identified in cereal aphids. In this study, an Orco gene ortholog was cloned from the grain aphid, Sitobion avenae, and named "SaveOrco"; RNA interference (RNAi) reduced the expression of SaveOrco to 34.11% in aphids, resulting in weaker EAG (electroantennogram) responses to plant volatiles (Z-3-hexene-1-ol; methyl salicylate, MeSA) and aphid alarm pheromone (E-β-farnesene, EBF). Aphid wing differentiation induced by EBF was investigated in both RNAi treated and untreated aphids. EBF induced production of winged aphids in both pre-natal and post-natal periods in untreated aphids, but no such induction was observed in the RNAi-treated aphids. We conclude that SaveOrco is crucial for the aphid's response to pheromones and other volatiles, and is involved in wing differentiation triggered by EBF.

Effects of Pheromone Release Rate and Trap Placement on Trapping of Agrilus planipennis (Coleoptera: Buprestidae) in Canada

The emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a devastating insect pest in its introduced range. A trapping system that increases trap catches or detection rates in low-density populations would be beneficial for survey programs. Five trapping experiments were conducted to investigate factors influencing capture rates of male beetles on dark green traps baited with the A. planipennis pheromone, (3Z)-dodecen-12-olide ((3Z)-lactone), plus the green leaf volatile, (3Z)-hexenol. Low doses (0.001-1.0 mg) of (3Z)-lactone + (3Z)-hexenol did not consistently increase captures of male A. planipennis. In other experiments, mean captures of males were significantly higher on traps baited with a moderate dose (3.0 mg/septum) of (3Z)-lactone + (3Z)-hexenol, compared with lower doses (0.001, 0.1, and 1.0 mg) or (3Z)-hexenol alone. Next, we demonstrated that addition of (3Z)-lactone to traps baited with (3Z)-hexenol resulted in significantly greater increases in male captures when pairs of traps were placed on the same tree, than when traps were placed on adjacent trees. Moreover, significantly more A. planipennis were captured on pheromone-baited traps placed in the southern versus northern aspect of the crown. These results highlight the importance of experimental set-up for elucidating lure treatment effects and also suggests the (3Z)-lactone may be more active at close range. Our findings increase our understanding of the pheromone ecology of this species and lend support toward the use of dark green traps baited with 3.0 mg (3Z)-lactone + (3Z)-hexenol deployed in the south aspect of the canopy for detection programs for this insect.

Early transcriptome analyses of Z-3-Hexenol-treated zea mays revealed distinct transcriptional networks and anti-herbivore defense potential of green leaf volatiles

Green leaf volatiles (GLV), which are rapidly emitted by plants in response to insect herbivore damage, are now established as volatile defense signals. Receiving plants utilize these molecules to prime their defenses and respond faster and stronger when actually attacked. To further characterize the biological activity of these compounds we performed a microarray analysis of global gene expression. The focus of this project was to identify early transcriptional events elicited by Z-3-hexenol (Z-3-HOL) as our model GLV in maize (Zea mays) seedlings. The microarray results confirmed previous studies on Z-3-HOL -induced gene expression but also provided novel information about the complexity of Z-3-HOL -induced transcriptional networks. Besides identifying a distinct set of genes involved in direct and indirect defenses we also found significant expression of genes involved in transcriptional regulation, Ca(2+)-and lipid-related signaling, and cell wall reinforcement. By comparing these results with those obtained by treatment of maize seedlings with insect elicitors we found a high degree of correlation between the two expression profiles at this early time point, in particular for those genes related to defense. We further analyzed defense gene expression induced by other volatile defense signals and found Z-3-HOL to be significantly more active than methyl jasmonate, methyl salicylate, and ethylene. The data presented herein provides important information on early genetic networks that are activated by Z-3-HOL and demonstrates the effectiveness of this compound in the regulation of typical plant defenses against insect herbivores in maize.

Effect of nine plant volatiles in the field on the sex pheromones of Leguminivora glycinivorella

Attraction of the soybean pod borer, Leguminivora glycinivorella (Matsumura), an economically important pest of soybean, to nine plant volatiles, alone or combined with two kinds of synthetic sex pheromone, ((E,E)-8,10-dodecadienyl acetate (EE8,10-12:Ac), or a blend of EE8,10-12:Ac and (E)-10-dodecenyl acetate in a 10:1 ratio), was evaluated in field trapping experiments in a soybean field in Harbin, China. By themselves, the plant volatiles (dose) linalool (0.1 mg), (Z)-3-hexenyl acetate (0.1 mg), and geraniol (0.1 mg, 1.0 mg) were weakly attractive to L. glycinivorella males, but significantly reduced mean catches when higher doses were combined with pheromones. Conversely, (E)-2-hexenal, benzaldehyde, and phenylacetaldehyde were not attractive to L. glycinivorella males at any dose tested, but significantly increased mean catch when certain doses were combined with the binary pheromone blend. Other plant volatiles, such as (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate, and (E)-2-hexenyl acetate, were unattractive on their own, but significantly reduced mean catch of L. glycinivorella males when certain doses were combined with the pheromones. These results suggest that efficacy of pheromone-baited traps for survey and monitoring of L. glycinivorella male moths may be enhanced by the addition of specific plant volatiles and that the relative dose is critical.

Environmental and seasonal influences on red raspberry flavour volatiles and identification of quantitative trait loci (QTL) and candidate genes

Raspberry volatiles are important for perceptions of sensory quality, mould resistance and some have nutraceutical activities. Twelve raspberry character volatiles were quantified, 11 of them in fruit from two seasons, from plants from the Glen Moy × Latham mapping population growing in both open field and under cover (polytunnels). Effects of season and environment were examined for their impact on the content of α-ionone, α-ionol, β-ionone, β-damascenone, linalool, geraniol, benzyl alcohol, (Z)-3-hexenol, acetoin, acetic and hexanoic acids, whilst raspberry ketone was measured in one season. A significant variation was observed in fruit volatiles in all progeny between seasons and method of cultivation. Quantitative trait loci were determined and mapped to six of the seven linkage groups, as were candidate genes in the volatiles pathways.

Testing for phytochemical synergism: arthropod community responses to induced plant volatile blends across crops

Using herbivore-induced plant volatiles (HIPVs) to attract specific natural enemies in the field has proven challenging, partly because of a poor understanding of: (i) which compound(s) to manipulate to attract specific taxa, and (ii) the ecological conditions over which HIPVs are effective. To address these issues, we quantified the response of a complex arthropod community to three common HIPVs (methyl salicylate, cis-3-hexen-1-ol, and phenylethyl alcohol) as individual compounds and equal part blends in corn and soybean fields. Of 119 arthropod taxa surveyed, we found significant responses by four species in corn fields (2 parasitoids, 1 herbivore, and 1 detritivore) and 16 in soybean fields (8 parasitoids, 3 predators, 4 herbivores, and 1 detritivore), with both attractive and repellent effects of the HIPVs observed. For example, tachinid flies were highly attracted to cis-3-hexen-1-ol (ca. 3-fold increase), but repelled by methyl salicylate (ca. 60 % decrease). Surprisingly, we found very few cases in which HIPVs acted synergistically; only two arthropod groups (ichneumonid wasps and phorid flies) were more attracted by a blend of the HIPVs than by the individual compounds composing the blend. Crop type, however, had a strong impact on the strength of arthropod responses to HIPVs. A few arthropod species were broadly affected across both crops (i.e., the herbivore Halticus bractatus was repelled by most of our treatments, regardless of crop background), but overall more arthropod groups responded to HIPVs released in soybean fields compared with corn. This was true despite the fact that taxa responding to HIPVs were present and abundant in both systems, suggesting that crop-based outcomes were likely driven by the plant matrix rather than mere differences in taxonomic composition of the arthropod community in corn vs. soybean fields. As a whole, these results suggest that: (i) repellent effects of HIPVs on natural enemies of herbivorous insects can be observed as frequently as attractive effects; (ii) odor blends may be no more effective than single-compound lures for some taxa; and (iii) crop background alters the magnitude of attraction to HIPVs, depending on the species being targeted.

Attraction of Agrilus planipennis (Coleoptera: Buprestidae) to a volatile pheromone: effects of release rate, host volatile, and trap placement

Attraction of emerald ash borer, Agrilus planipennis Fairmaire, to a volatile pheromone was demonstrated in three field experiments using baited green sticky traps. A dose-response curve was generated for male A. planipennis to increasing release rates of (3Z)-dodecen-12-olide ((3Z)-lactone) in combination with the green leaf volatile, (3Z)-hexenol. Only the lowest release rate (<2.50 μg/d) of (3Z)-lactone significantly increased captures of male A. planipennis, as compared with traps baited with (3Z)-hexenol alone. Effect of trap height, (3Z)-lactone, and (3Z)-hexenol and their interactions on the trap capture of A. planipennis was determined in a factorial experiment. Number of males per trap was significantly and positively affected by (3Z)-lactone, (3Z)-hexenol, and trap height whereas number of females per trap was affected by trap height only; none of the interactions were significant. As predicted, the greatest mean catch of males was in traps baited with (3Z)-lactone and (3Z)-hexenol placed high in the canopy. Electroantennogram tests on the bark volatile, 7-epi-sesquithujene, demonstrated the ability of male and female A. planipennis antennae to detect and respond to this compound, particularly the (+)-7-epi-sesquithujene isomer. Results from an olfactometer bioassay and field testing did not demonstrate attraction of either males or females to (+)-7-epi-sesquithujene. These data increase our understanding of the pheromone ecology of the invasive emerald ash borer, provide further confirmation of the behavioral activity of the female-produced lactone pheromone, and should increase the ability to detect A. planipennis infestations where they are present.

Transcriptional analysis of Arabidopsis thaliana response to lima bean volatiles

BACKGROUND

Exposure of plants to herbivore-induced plant volatiles (HIPVs) alters their resistance to herbivores. However, the whole-genome transcriptional responses of treated plants remain unknown, and the signal pathways that produce HIPVs are also unclear.

METHODOLOGY/PRINCIPAL FINDINGS

Time course patterns of the gene expression of Arabidopsis thaliana exposed to Lima bean volatiles were examined using Affymetrix ATH1 genome arrays. Results showed that A. thaliana received and responded to leafminer-induced volatiles from Lima beans through up-regulation of genes related to the ethylene (ET) and jasmonic acid pathways. Time course analysis revealed strong and partly qualitative differences in the responses between exposure at 24 and that at 48 h. Further experiments using either A. thaliana ET mutant ein2-1 or A. thaliana jasmonic acid mutant coi1-2 indicated that both pathways are involved in the volatile response process but that the ET pathway is indispensable for detecting volatiles. Moreover, transcriptional comparisons showed that plant responses to larval feeding do not merely magnify the volatile response process. Finally, (Z)-3-hexen-ol, ocimene, (3E)-4,8-dimethyl-1,3,7-nonatriene, and (3E,7E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene triggered responses in A. thaliana similar to those induced by the entire suite of Lima bean volatiles after 24 and 48 h.

CONCLUSIONS/SIGNIFICANCE

This study shows that the transcriptional responses of plants to HIPVs become stronger as treatment time increases and that ET signals are critical during this process.

Influence of trap color and host volatiles on capture of the emerald ash borer (Coleoptera: Buprestidae)

Field trapping assays were conducted in 2009 and 2010 throughout western Michigan, to evaluate lures for adult emerald ash borer, A. planipennis Fairmaire (Coleoptera: Buprestidae). Several ash tree volatiles were tested on purple prism traps in 2009, and a dark green prism trap in 2010. In 2009, six bark oil distillate lure treatments were tested against manuka oil lures (used in 2008 by USDA APHIS PPQ emerald ash borer cooperative program). Purple traps baited with 80/20 (manuka/phoebe oil) significantly increased beetle catch compared with traps baited with manuka oil alone. In 2010 we monitored emerald ash borer attraction to dark green traps baited with six lure combinations of 80/20 (manuka/phoebe), manuka oil, and (3Z)-hexenol. Traps baited with manuka oil and (3Z)-hexenol caught significantly more male and total count insects than traps baited with manuka oil alone. Traps baited with manuka oil and (3Z)-hexenol did not catch more beetles when compared with traps baited with (3Z)-hexenol alone. When compared with unbaited green traps our results show that (3Z)-hexenol improved male catch significantly in only one of three field experiments using dark green traps. Dark green traps caught a high number of A. planipennis when unbaited while (3Z)-hexenol was seen to have a minimal (nonsignificant) trap catch effect at several different release rates. We hypothesize that the previously reported kairomonal attractancy of (3Z)-hexenol (for males) on light green traps is not as obvious here because of improved male attractancy to the darker green trap.

Comparison of male and female emerald ash borer (Coleoptera: Buprestidae) responses to phoebe oil and (Z)-3-hexenol lures in light green prism traps

We conducted trapping experiments for the emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) in Michigan, U.S.A., and Ontario, Canada, to compare unbaited light green sticky prism traps with traps baited with phoebe oil, (Z)-3-hexenol (Z3-6:OH), or blends of other green leaf volatiles (GLVs) with Z3-6:OH. Traps were placed in the lower canopy of ash trees (Fraxinus spp.). Catches with Z3-6:OH-baited traps showed a significant male bias and these traps caught significantly more males than the unbaited controls at both sites. They were also superior to phoebe oil-baited traps and those baited with GLV blends. Catches with phoebe oil showed a significant female bias but there was no difference in the number of females captured between traps baited with phoebe oil or Z3-6:OH lures. Catches were analyzed at regular time intervals to examine the response of A. planipennis to the lures over the course of the flight season. Z3-6:OH-baited traps consistently caught more males than the controls at each interval throughout the flight season. Catches of females with Z3-6:OH and phoebe oil were significantly better than the controls early in the flight season but declined to control levels by midseason. Our results suggest that Z3-6:OH-baited green traps placed in the ash canopy would be a superior lure for detecting and monitoring A. planipennis throughout the flight season.

"Green odor" inhalation by stressed rat dams reduces behavioral and neuroendocrine signs of prenatal stress in the offspring

Chronic maternal stress during pregnancy results in the "prenatally stressed" offspring displaying behavioral and neuroendocrine alterations that persist into adulthood. We investigated how inhalation of green odor (a mixture of equal amounts of trans-2-hexenal and cis-3-hexenol) by stressed dams might alter certain indices of prenatal stress in their offspring. These indices were depression-like behavior (increased immobility time in the forced-swim test) and acute restraint stress-induced changes in hypothalamo-pituitary-adrenocortical (HPA) axis activity [plasma corticosterone (CORT) and ACTH levels and the number of Fos-immunoreactive cells in the hypothalamic paraventricular nucleus (an index of neuronal activity)]. Pregnant rats were exposed to restraint stress for 60 min/day for 10 days (gestational days 10-19). The prenatally stressed offspring exhibited significant increases in depression-like behavior and in restraint stress-induced ACTH, CORT, and Fos responses, unless their dam had been exposed to green odor. The behavioral effect of the odor was also seen in offspring that were fostered by unstressed dams. The results obtained in the dams themselves were as follows. In vehicle-exposed stressed dams, but not in green odor-exposed ones, total body and adrenal weights were significantly decreased or increased, respectively. Depression-like behavior was not observed in the vehicle-exposed stressed dams themselves. Green odor inhalation prevented the impairment of maternal behavior induced by restraint stress. Thus, exposure of dams to stress may affect both the fetal brain and fetal HPA axis, and also maternal behavior, leading to altered behavioral and neuroendocrine responses in the offspring. Such effects may be prevented by the stressed dams inhaling green odor.

Representation of a mixture of pheromone and host plant odor by antennal lobe projection neurons of the silkmoth Bombyx mori

Pheromone-source orientation behavior can be modified by coexisting plant volatiles. Some host plant volatiles enhance the pheromonal responses of olfactory receptor neurons and increase the sensitivity of orientation behavior in the Lepidoptera species. Although many electrophysiological studies have focused on the pheromonal response of olfactory interneurons, the response to the mixture of pheromone and plant odor is not yet known. Using the silkmoth, Bombyx mori, we investigated the physiology of interneurons in the antennal lobe (AL), the primary olfactory center in the insect brain, in response to a mixture of the primary pheromone component bombykol and cis-3-hexen-1-ol, a mulberry leaf volatile. Application of the mixture enhanced the pheromonal responses of projection neurons innervating the macroglomerular complex in the AL. In contrast, the mixture of pheromone and cis-3-hexen-1-ol had little influence on the responses of projection neurons innervating the ordinary glomeruli whereas other plant odors dynamically modified the response. Together this suggests moths can process plant odor information under conditions of simultaneous exposure to sex pheromone.

Differential electroantennogram response of females and males of two parasitoid species to host-related green leaf volatiles and inducible compounds

Parasitoids employ different types of host-related volatile signals for foraging and host-location. Host-related volatile signals can be plant-based, originate from the herbivore host or produced from an interaction between herbivores and their plant host. In order to investigate potential sex- and species-related differences in the antennal response of parasitoids to different host-related volatiles, we compared the electroantennogram (EAG) responses of both sexes of the specialist parasitoid, Microplitis croceipes (Cresson), and the generalist, Cotesia marginiventris (Cresson), to varying doses of selected plant-based host-related volatiles: two green leaf volatiles (cis-3-hexenol and hexanal) and three inducible compounds (cis-3-hexenyl acetate, linalool, and (E,E)-alpha-farnesene). Mating had no significant effect on EAG response. Females of both species showed significantly greater EAG responses than conspecific males to green leaf volatiles, which are released immediately after initiation of herbivore feeding damage. In contrast, males showed greater responses than conspecific females to inducible compounds released much later after initial damage. Cotesia marginiventris females and males showed greater EAG responses than counterpart M. croceipes to the tested compounds at various doses, suggesting that the generalist parasitoid shows greater antennal sensitivity than the specialist to the tested host-plant volatiles. These results are discussed in relation to the possible roles of green leaf volatiles and inducible compounds in the ecology of female and male parasitoids.

Aspergillus volatiles regulate aflatoxin synthesis and asexual sporulation in Aspergillus parasiticus

Aspergillus parasiticus is one primary source of aflatoxin contamination in economically important crops. To prevent the potential health and economic impacts of aflatoxin contamination, our goal is to develop practical strategies to reduce aflatoxin synthesis on susceptible crops. One focus is to identify biological and environmental factors that regulate aflatoxin synthesis and to manipulate these factors to control aflatoxin biosynthesis in the field or during crop storage. In the current study, we analyzed the effects of aspergillus volatiles on growth, development, aflatoxin biosynthesis, and promoter activity in the filamentous fungus A. parasiticus. When colonies of Aspergillus nidulans and A. parasiticus were incubated in the same growth chamber, we observed a significant reduction in aflatoxin synthesis and asexual sporulation by A. parasiticus. Analysis of the headspace gases demonstrated that A. nidulans produced much larger quantities of 2-buten-1-ol (CA) and 2-ethyl-1-hexanol (EH) than A. parasiticus. In its pure form, EH inhibited growth and increased aflatoxin accumulation in A. parasiticus at all doses tested; EH also stimulated aflatoxin transcript accumulation. In contrast, CA exerted dose-dependent up-regulatory or down-regulatory effects on aflatoxin accumulation, conidiation, and aflatoxin transcript accumulation. Experiments with reporter strains carrying nor-1 promoter deletions and mutations suggested that the differential effects of CA were mediated through separate regulatory regions in the nor-1 promoter. The potential efficacy of CA as a tool for analysis of transcriptional regulation of aflatoxin biosynthesis is discussed. We also identify a novel, rapid, and reliable method to assess norsolorinic acid accumulation in solid culture using a Chroma Meter CR-300 apparatus.

Methyl salicylate, identified as primary odorant of a specific receptor neuron type, inhibits oviposition by the moth Mamestra brassicae L. (Lepidoptera, noctuidae)

The cabbage moth, Mamestra brassicae L. (Lepidoptera, Noctuidae), is a polyphagous species that is often choosing plants of Brassica as hosts for oviposition. In the search for biologically relevant odorants used by these moths, gas chromatography linked to electrophysiological recordings from single receptor neurons (RNs) has been employed, resulting in classification of distinct types of neurons. This study presents specific olfactory RNs responding to methyl salicylate (MeS) as primary odorant and showing a weak response to methyl benzoate, the 2 aromatic compounds occurring together in several plant species. In 2 cases, the neuron was colocated with another RN type responding to 6 green leaf volatiles: 1-hexanol, (3Z)-hexen-1-ol, (2E)-hexen-1-ol, (3Z)-hexenyl acetate, (2Z)-hexen-1-ol, and an unidentified compound. Whereas the specific RNs detected the minor amounts of MeS in some plants, the compound was not found by gas chromatography linked to mass spectrometry in intact plants, but it was found after herbivore attack. The behavioral effect of MeS was studied in outdoor test arenas with Brassica napus and artificial plants. These experiments indicated that mated M. brassicae females avoid plants with dispensers emitting MeS. As it is induced by caterpillar feeding, this compound may mediate a message to mated M. brassicae females that the plant is already occupied.

Myzus persicae is Arrested More by Blends Than by Individual Compounds Elevated in Headspace of PLRV-Infected Potato

Volatiles from potato plants (Solanum tuberosum L.) infected with Potato leaf roll virus (PLRV) attract and arrest the principal vector of PLRV, the green peach aphid, Myzus persicae (Sulzer), more strongly than volatiles from non-infected plants. The total concentration of volatiles detectable in the headspace of PLRV-infected plants is greater than that in the headspace of non-infected controls, and the relative composition is altered. To determine the basis of the aphid response to PLRV-infection-induced volatiles from potato, behavioral bioassays were conducted. We measured arrestment of aphids by individual components, by synthetic blends of these, and by a naturally occurring blend by using an emigration rate bioassay, and quantified observations of the behavior of individual aphids. The components tested were those elevated at least twofold in response to PLRV infection. Before conducting the behavioral bioassays, electroantennograms confirmed the electrophysiological responses of aphids to the components of the blend. For bioassays, individual compounds or blends were tested by applying them in solution to paper strips at concentrations designed to mimic those present in the headspace of the plants. All bioassays were conducted by placing aphids on fine-mesh screening positioned above treated paper strips. Arrestment was measured by placing groups of 30 aphids directly over the treated strips and counting the number moving away at 10-min intervals for 50 min. Among the individual compounds tested, only beta-pinene was a mild arrestant. The other compounds did not elicit significant changes in arrestment or behavior at a range of physiologically relevant concentrations. In contrast, synthetic blends that mimicked the concentration and composition present in headspace of PLRV-infected potato plants arrested aphids significantly more strongly than blends mimicking volatiles from the headspace of non-infected plants. The naturally occurring blend collected from headspace of PLRV-infected plants also arrested M. persicae more strongly than the blend collected from headspace of non-infected plants. Aphid behavior was quantified by directly observing individual aphids and recording their activities during a 5-min period on screening above strips treated with test materials. Few differences in time budgets were observed among aphids exposed to individual components, but synthetic blends and trapped headspace volatiles from PLRV-infected plants resulted in significantly less time spent walking by aphids than synthetic blends and trapped headspace from non-infected controls. Our results indicate that arrestment of M. persicae by PLRV-infected plants requires the blend of volatile organic compounds released by these plants and is not produced in response to a single compound.

"Green odor" inhalation reduces the skin-barrier disruption induced by chronic restraint stress in rats: physiological and histological examinations

We investigated whether inhalation of green odor (a mixture of equal amounts of trans-2-hexenal and cis-3-hexenol) prevents the skin-barrier disruption induced by chronic restraint stress in rats. To this end, transepidermal water loss (TEWL) was measured as an index of the disruption of skin-barrier function, whereas light- and electron-microscope examinations were performed to observe histological changes in the skin of the stressed animals. In addition, the effects on TEWL induced by chronic administration of a glucocorticoid, dexamethasone (DEX), were examined. Chronic restraint stress (8 h per day for 14 days) increased TEWL (vehicle + stress group). This effect (and the chronic stress-induced increase in adrenal weight) was prevented in rats that inhaled green odor at the beginning of each day's restraint (2 h each day for 14 days; green odor + stress group). Electron-microscope studies revealed that rats in the green odor + stress group possessed sufficient intercorneocyte lipids to create an effective skin barrier, although these had apparently been decreased in the vehicle + stress group. Daily administration of DEX for 14 days increased TEWL. The present results suggest that chronic stress-induced disruption of the skin barrier in rats can be reduced or prevented by green odor (possibly at least in part through an inhibitory effect on the stress-induced activation of the hypothalamo-pituitary-adrenocortical axis).

Dose-Dependent Nonassociative Olfactory Learning in a Fly

Olfactory sensory stimulation induces a fast-phase arrest response (FPA-R) of the blowfly heart activity that has been described as a sensitive tool for testing insect reactivity to odor perception. We analyzed FPA-R occurrence to repeated olfactory stimulation with low and high 1-hexanol concentrations that are behaviorally attractant and repellent, respectively, in the blowfly. FPA-R occurrence diminished and ceased with repeated presentations of low and medium odor concentrations, according to dynamics inversely related to odor doses. On the other hand, repeated stimulation with higher odor concentrations induced persistent FPA-Rs. Sensory input amplitude to repeated presentations of singly tested odor concentrations did not change throughout stimulation sessions. A spontaneous restoration of FPA-R to olfactory stimulation was recorded 30 min after cessation of FPA-R to a previous olfactory stimulation session. However, a prompt restoration of FPA-R to olfactory stimulation after cessation of FPA-R was obtained following mechano-taste stimulation of labellar sensilla. Our findings show that the FPA-R habituates to olfactory sensory stimulation with low and medium odor concentrations according to dynamics inversely related to odor intensities. On the other hand, the FPA-R does not habituate to higher odor concentrations. Therefore, flies learn to disregard nonaversive odor information, but they cannot ignore iterative detection of a repellent volatile.

Subunit-dependent modulation of the 5-hydroxytryptamine type 3 receptor open-close equilibrium by n-alcohols

5-Hydroxytryptamine (5-HT, serotonin) type 3 (5-HT(3)) receptors belong to the alcohol-sensitive superfamily of Cys-loop ligand-gated ion channels, and they are thought to play an important role in alcoholism. Alcohols with small molecular volumes increase the amplitude of currents evoked by low 5-HT concentrations and shift the 5-HT concentration-response curve for 5-HT(3) receptor activation leftward, indicative of increased receptor sensitivity to agonist. This action is significantly smaller when currents are mediated by heteromeric 5-HT(3AB) receptors compared with homomeric 5-HT(3A) receptors. In this study, we used the highly inefficacious 5-HT(3) receptor agonist dopamine to determine whether this difference between 5-HT(3A) and 5-HT(3AB) receptors reflects differential alcohol modulation of agonist binding affinity or channel gating efficacy. Human recombinant 5-HT(3A) and 5-HT(3AB) receptors were expressed in Xenopus oocytes, and currents were measured in the absence and presence of alcohols using the two-electrode voltage-clamp technique. Modulation by alcohols of peak currents elicited by maximally activating concentrations of dopamine was alcohol concentration-dependent. Potentiation by smaller alcohols was consistently significantly greater in 5-HT(3A) than in 5-HT(3AB) receptors, whereas inhibition by larger alcohols was not. A representative small (butanol) and large (octanol) alcohol failed to alter the EC(50) value for channel activation by dopamine. We conclude that the presence of the 5-HT(3B) subunit in 5-HT(3AB) receptors significantly reduces the enhancement of gating efficacy by small alcohols without altering the inhibitory actions of large alcohols.

Phase partition of gaseous hexane and surface hydrophobicity of Fusarium solani when grown in liquid and solid media with hexanol and hexane

The filamentous fungus, Fusarium solani, was grown in liquid and solid culture with glucose, glycerol, 1-hexanol and n-hexane. The partition coefficient with gaseous hexane (HPC) in the biomass was lower when grown in liquid medium with 1-hexanol (0.4) than with glycerol (0.8) or glucose (1) The HPC for surface growth were 0.2 for 1-hexanol, 0.5 for glycerol, 0.6 for glucose, and 0.2 for F. solani biomass obtained from a biofilter fed with gaseous n-hexane. These values show a 200-fold increase in n-hexane solubility when compared to water (HPC = 42). Lower HPC values can be partially explained by increased lipid accumulation with 1-hexanol, 10.5% (w/w) than with glycerol (8.5% w/w) or glucose (7.1% w/w). The diameter of the hyphae diminished from 3 microm to 2 microm when F. solani was grown on solid media with gaseous n-hexane thereby doubling the surface area for gaseous substrate exchange. The surface hydrophobicity of the mycelia increased consistently with more hydrophobic substrates and the contact angle of a drop of water on the mycelial mat was 113 degrees when grown on n-hexane as compared to 75 degrees with glucose. The fungus thus adapts to hydrophobic conditions and these changes may explain the higher uptake of gaseous hydrophobic substances by fungi in biofilters.

Differential effects of volatile anesthetics on M3 muscarinic receptor coupling to the Galphaq heterotrimeric G protein

BACKGROUND

Halothane inhibits airway smooth muscle contraction in part by inhibiting the functional coupling between muscarinic receptors and one of its cognate heterotrimeric G proteins, Galphaq. Based on previous studies indicating a more potent effect of halothane and sevoflurane on airway smooth muscle contraction compared with isoflurane, the current study hypothesized that at anesthetic concentrations of 2 minimum alveolar concentration (MAC) or less, halothane and sevoflurane but not isoflurane inhibit acetylcholine-promoted Galphaq guanosine nucleotide exchange.

METHODS

Galphaq guanosine nucleotide exchange was measured in crude membranes prepared from COS-7 cells transiently coexpressing the human M3 muscarinic receptor and human Galphaq. A radioactive, nonhydrolyzable analog of guanosine-5'-triphosphate, [35S]GTPgammaS, was used as a reporter for nucleotide exchange at Galphaq.

RESULTS

Acetylcholine caused a concentration-dependent increase in Galphaq [35S]GTPgammaS-GDP exchange. Neither anesthetic affected constitutive Galphaq [35S]GTPgammaS-GDP exchange in the absence of acetylcholine. Conversely, each anesthetic caused a concentration-dependent and reversible inhibition of Galphaq [35S]GTPgammaS-GDP exchange when promoted by acetylcholine. At concentrations of 3 MAC or less, the effect of halothane and sevoflurane were significantly greater than that of isoflurane, with only a minimal inhibition by isoflurane observed at 2 MAC.

CONCLUSION

The differential effects of volatile anesthetics on acetylcholine-promoted guanosine nucleotide exchange at Galphaq are consistent with the apparent more potent direct effect of halothane and sevoflurane compared with isoflurane on muscarinic receptor-mediated contraction of isolated airway smooth muscle. These differential effects also suggest a mode of anesthetic action that could be due to anesthetic-protein interactions and not simply anesthetic accumulation in the lipid membrane.

Chirality in anesthesia II: stereoselective modulation of ion channel function by secondary alcohol enantiomers

Chirality has been proposed as a means for distinguishing relevant from irrelevant molecular targets of action, but the sensitivity and specificity of this test is unknown for volatile anesthetics. We applied enantiomers of two chiral anesthetic alcohols (2-butanol and 2-pentanol) that are enantioselective for the minimum alveolar concentration (MAC) preventing movement in 50% of animals and one (2-hexanol) that was not to frog oocytes. Each oocyte expressed one of three anesthetic-sensitive ion channels: a Twik-related-spinal cord K+ (TRESK) channel, a gamma-amino butyric acid type A (GABA(A)) receptor and an N-methyl-d-aspartate (NMDA) receptor. Using voltage-clamp techniques, we found that 2-butanol was not enantioselective for any channel (e.g., 16 mM 2-butanol R(-) and S(-) enantiomers decreased current through an NMDA receptors by 44% +/- 3% [mean +/- se] and 37% +/- 4%, respectively); 2-pentanol was enantioselective for one channel (the GABA(A) receptor, the enantiomers increasing current by 277% +/- 20% and 141% +/- 30%); 2-hexanol was enantioselective for both GABA(A) and NMDA receptors (e.g., decreasing current through the NMDA receptor by 19% +/- 3% and 43% +/- 5%). We calculated the sensitivity and specificity of chirality as a test of anesthetic relevance under two scenarios: 1) all three channels were relevant mediators of MAC and 2) no channel was a mediator of MAC. These sensitivities and specificities were poor because there is no consistent correspondence between receptor and whole animal results. We recommend that enantioselectivity not be used as a test of relevance for inhaled anesthetic targets.

Unusual hydrophobic linker region of beta-glucosidase (BGLII) from Thermoascus aurantiacus is required for hyper-activation by organic solvents

A gene encoding a putative beta-glucosidase was isolated from Thermoascus aurantiacus IFO9748 and designated as bgl2. The recombinant enzyme showed beta-glucosidase activity when p-nitrophenyl-beta-glucose (pNP-Glc) was used as substrate. We also found that the enzyme activity was increased in the presence of organic solvents. An addition of 20 % (v/v) 1-octanol resulted in 54-fold higher activity of pNP-Glc hydrolysis, and transglycosylation activity was also found to be activated. The results of tryptophan fluorescence spectral analysis revealed the changes in the tertiary structure of the enzyme in the presence of 1-hexanol that may cause increased enzyme activity. BGLII has a distinctive hydrophobic linker region between N- and C-terminal domains. A chimeric enzyme in which the linker region was substituted by the corresponding region of another beta-glucosidase failed to be activated by organic solvents, suggesting that the hydrophobic linker region may act as a molecular switch in BGLII.

Sites in TM2 and 3 are critical for alcohol-induced conformational changes in GABA receptors

Abstract gamma-Aminobutyric acid type A (GABA(A)) receptors are molecular targets for alcohols. Previous work suggests that S270 and A291 residues in the transmembrane (TM) 2 and 3 domains of the GABA(A) receptor alpha subunit are components of an alcohol-binding pocket, and S270I and A291W mutants abolished ethanol potentiation. Our results showed that A295C and F296C residues in the TM3 of the GABA(A) receptor alpha1 subunit are accessible to hexylmethanethiosulfonate (HMTS) in the alcohol-bound state, but not in the resting state. Thus, the A295C and F296C sites become water-accessible as a result of alcohol-induced conformational changes. If S270 or A291 residues are sites of alcohol binding, then S270I or A291W mutations should prevent alcohol-induced conformational movements within the TM3 domain. To investigate this question, the accessibility of HMTS reagent to double mutants (A291W/A295C, A291W/F296C, S270I/A295C or S270I/F296C) in the presence of ethanol or hexanol was tested. The A291W or S270I mutations markedly reduced the accessibility of HMTS to all the double mutants in the ethanol-bound state, and to S270I/F296C, A291W/A295C and A291W/F296C double mutants in the hexanol-bound state, suggesting that the A291 or S270 residues are critical sites for alcohol binding and alcohol-induced conformational changes.

Effects of (Z)-3-hexenol, a major component of green odor, on anxiety-related behavior of the mouse in an elevated plus-maze test and biogenic amines and their metabolites in the brain

In the present study, the effect of (Z)-3-hexenol, one of the main constituent of green odor, on the anxiety-related behavior of mouse and the content of 5-hydroxytryptamine (5-HT), dopamine and their metabolites in the brain were investigated. Evaluation of anxiety-related animal behavior was performed by measuring the percent of time spent on the open arms and the percent of open-arm entries as conventional anxiety indices. The number of times displaying risk-assessment from a closed arm was also measured as an ethological anxiety index. Diazepam, an anxiolytic agent, enhanced the percent of time spent on the open arms and the percent of open-arm entries. The number of times displaying risk-assessment was not affected by diazepam in the present study. The percent of time on the open arms were depressed, and the number of times displaying risk-assessment were stimulated by 1-(3-trifluoromethylphenyl)piperazine (TFMPP), indicating that TFMPP acts as an anxiogenic agent. (Z)-3-Hexenol revealed anxiolytic activity and increased the percent of time spent on the open arms and decreased the number of times displaying risk-assessment. In the neurochemical study, diazepam had no effect on the content of 5-HT and its metabolite in the brain cortex or hippocampus. On the other hand, TFMPP inhibited the 5-HT turnover rate accompanied by the elevation of the 5-HT content and reduction of the 5-HIAA content in the brain cortex and hippocampus. (Z)-3-Hexenol significantly increased the 5-HT content without affecting the 5-HIAA content or the 5-HT turnover rate in the brain cortex or hippocampus. Changes in serotonergic activity in the cortex and hippocampus were suggested to be involved in the anxiolytic effect of (Z)-3-hexenol observed in the elevated plus-maze test.

Plant–Plant Signaling: Ethylene Synergizes Volatile Emission In Zea mays Induced by Exposure to (Z)-3-Hexen-1-ol

Leaf alcohol (Z)-3-hexen-1-ol (Z-3-ol) is emitted by green plants upon mechanical damage. Exposure of intact maize plants to Z-3-ol induces the emission of a volatile blend that is typically released after caterpillar feeding and attracts natural enemies of the herbivores [herbivore-induced volatile organic compounds (HI-VOC)]. Thus, it has been suggested that Z-3-ol might have a function in indirect plant defense mediating plant-plant signaling and intraplant information transfer. Here, we demonstrate that HI-VOC induction by Z-3-ol is synergized by the phytohormone ethylene. Exposure to Z-3-ol at doses of 100 and 250 nmol induced HI-VOC emission in intact maize plants. HI-VOC emissions increased by 2.5-fold when ethylene was added. The effect of ethylene was more pronounced (5.1- to 6.6-fold) when only total sesquiterpene release was considered. In contrast, ethylene alone had no inductive effect but rather decreased the emission of the constitutive maize volatile linalool. We suggest that ethylene plays a synergistic role in plant-plant signaling mediated by green leaf volatiles.

The involvement of volatile infochemicals from spider mites and from food-plants in prey location of the generalist predatory mite Neoseiulus californicus

We investigated volatile infochemicals possibly involved in location of the generalist predatory mite Neoseiulus californicus to plants infested with spider mites in a Y-tube olfactometer. The predators significantly preferred volatiles from lima bean leaves infested with Tetranychus urticae to uninfested lima bean leaves. Likewise, they were attracted to volatiles from artificially damaged lima bean leaves and those from T. urticae plus their visible products. Significantly more predators chose infested lima bean leaves from which T. urticae plus their visible products had been removed than artificially damaged leaves, T. urticae, and their visible products. These results suggest that N. californicus is capable of exploiting a variety of volatile infochemicals originating from their prey, from the prey-foodplants themselves, and from the complex of the prey and the host plants (e.g., herbivore-induced volatiles). We also investigated predator response to some of the synthetic samples identified as volatile components emitted from T. urticae-infested lima bean leaves and/or artificially damaged lima bean leaves. The predators were attracted to each of the five synthetic volatile components: linalool, methyl salicylate, (Z)-3-hexen-1-ol, (E)-2-hexenal, and (Z)-3-hexenyl acetate. The role of each volatile compound in prey-searching behavior is discussed.

The lipid/protein interface as xenobiotic target site

High-resolution X-ray diffraction structures of integral membrane proteins have revealed various binding modes of lipids, but current spectroscopic studies still use uniform macroscopic binding constants to describe lipid binding. The Adair approach employing microscopic lipid-binding constants has previously been taken to explain the enhancement of agonist binding to the nicotinic acetylcholine receptor by general anaesthetics in terms of the competitive displacement of essential lipid activator molecules [Walcher S, Altschuh J & Sandermann H (2001) J. Biol. Chem.276, 42191-42195]. This approach was extended to tadpole narcosis induced by alcohols. A single class, or two different classes of lipid activator binding sites, are considered. Microscopic lipid and inhibitor binding constants are derived and allow a close fit to dose-response curves of tadpole narcosis on the basis of a preferential displacement of more loosely bound essential lipid activator molecules. This study illustrates the potential of the Adair approach to resolve protein-bound lipid populations.

(Z)-3-Hexenol induces defense genes and downstream metabolites in maize

In response to insect feeding, corn plants (Zea mays cv. Delprim) release elevated levels of volatile organic compounds (VOCs), including the C(6)-volatile (Z)-3-hexenol. The level of mRNA accumulation for a series of defense genes was monitored in response to application of (Z)-3-hexenol (50 nmol) to undamaged plants. The induction of transcripts for hpl (hydroperoxide lyase), fps (farnesyl pyrophosphate synthase), pal (phenylalanine ammonia-lyase), lox (lipoxygenase), igl (indole-3-glycerol phosphate lyase) and mpi (maize proteinase inhibitor) were compared with metabolites generated from the respective pathways. While headspace VOC analysis showed an increase in (Z)-3-hexenyl acetate and methyl salicylate with lox and pal induction, respectively, MPI accumulation was not observed with an increase in mpi transcripts. Moreover, (Z)-3-hexenol treatment did not elevate sesquiterpene emissions or activate fps transcription. Chemical labeling and bioassay experiments established that exogenous (Z)-3-hexenol can be taken up and converted to a less active acetylated form. These data indicate that (Z)-3-hexenol can serve as a signaling molecule that triggers defense responses in maize and can rapidly be turned over in planta.

Functional and Structural Analysis of the GABAA Receptor α1 Subunit during Channel Gating and Alcohol Modulation

The substituted cysteine accessibility method has proven useful for investigating structural changes of the gamma-aminobutyric acid type A (GABA(A)) receptor during channel gating and allosteric modulation. In the present study, the surface accessibility and reaction rate of propyl- and hexyl-methanethiosulfonate to cysteine residues introduced into the third transmembrane segment of the GABA(A) receptor alpha(1) subunit were examined. GABA-induced currents in Xenopus oocytes expressing wild type and cysteine mutant GABA(A) receptors were recorded before and after application of methanethiosulfonate (MTS) reagents in the resting, GABA- or alcohol-bound (ethanol or hexanol) states. Our results indicate that a water-filled cavity exists around the Ala(291) and Tyr(294) residues of the third transmembrane segment, in agreement with previous results. Furthermore, our data indicate that a conformational change produced by alcohols (200 mM ethanol or 0.5 mM hexanol) exposure induces the water cavity around the A291C and Y294C residues to extend deeper, causing the A295C and F296C residues to become accessible to the MTS reagents. In addition, exposure of the A291C, Y294C, F296C, and V297C mutants to MTS reagents in the presence of GABA had significant effects on their GABA-induced currents, indicating that the water cavity around A291C and Y294C residues expanded to F296C and V297C by a structural movement caused by GABA binding. Our data show that GABA(A) receptor is a dynamic protein during alcohol modulation and channel gating.

Dynamics of glass-forming liquids. VIII. Dielectric signature of probe rotation and bulk dynamics in branched alkanes

We have measured the dielectric relaxation of several glass forming branched alkanes with very low dielectric loss in the frequency range 50 Hz-20 kHz. The molecular liquids of this study are 3-methylpentane, 3-methylheptane, 4-methylheptane, 2,3-dimethylpentane, and 2,4,6-trimethylheptane. All liquids display asymmetric loss peaks typical of supercooled liquids and slow beta relaxations of similar amplitudes. As an unusual feature, deliberate doping with 2-ethyl-1-hexanol, 5-methyl-2-hexanol, 2-methyl-1-butanol, 1-propanol, or 2-methyltetrahydrofuran at the 1 wt % level generates additional relaxation peaks at frequencies below those of the alpha relaxation. The relaxation times of these sub-alpha-peaks increase systematically with the size of the dopant molecules. Because these features are spectrally separate from the bulk dynamics, the rotational behavior and effective dipole moments of the probes can be studied in detail. For the alcohol guest molecules, the large relative rotational time scales and small effective dipole moments are indicative of hydrogen bonded clusters instead of individual molecules.

Endocochlear potential and endolymphatic K+ changes induced by gap junction blockers

OBJECTIVE

To examine the effects of gap junction blockers on the endocochlear potential (EP) and endolymphatic potassium concentration ([K(+)](e)).

MATERIAL AND METHODS

The EP and [K(+)](e) were monitored using double-barreled ion-selective microelectrodes in the second turn of the guinea pig cochlea during perilymphatic perfusion.

RESULTS

When the perilymphatic scalae of the cochlea were perfused with artificial perilymph containing 10 mM n-heptanol the EP was decreased by -8.8+/-1.4 mV (n=10), and this was accompanied by a decline in the [K(+)](e) of -6.7+/-2.1 mM (n=6). Perilymphatic application of 10 mM hexanol also produced declines in both the EP and [K(+)](e). In control studies, perilymphatic perfusion with 10 mM ethanol showed no remarkable changes in either the EP or [K(+)](e). Anoxia during perfusion with heptanol resulted in the generation of a negative EP, similar to the situation in controls.

CONCLUSIONS

A decline in the EP together with a lowering of [K(+)](e) induced by long-chain n-alkanols, which act as gap junction blockers, may be explained by an interruption in potassium ion transport related to a gap junction dysfunction.

Anesthetics inhibit acetylcholine-promoted guanine nucleotide exchange of heterotrimeric G proteins of airway smooth muscle

BACKGROUND

Anesthetics inhibit airway smooth muscle contraction in part by a direct effect on the smooth muscle cell. This study tested the hypothesis that the anesthetics halothane and hexanol, which both relax airway smooth muscle in vitro, inhibit acetylcholine-promoted nucleotide exchange at the alpha subunit of the Gq/11 heterotrimeric G protein (Galphaq/11; i.e., they inhibit muscarinic receptor-Galphaq/11 coupling).

METHODS

The effect of halothane (0.38 +/- 0.02 mm) and hexanol (10 mm) on basal and acetylcholine-stimulated Galphaq/11 guanosine nucleotide exchange was determined in membranes prepared from porcine tracheal smooth muscle. The nonhydrolyzable, radioactive form of guanosine-5'-triphosphate, [S]GTPgammaS, was used as the reporter for Galphaq/11 subunit dissociation from the membrane to soluble fraction, which was immunoprecipitated with rabbit polyclonal anti-Galphaq/11 antiserum.

RESULTS

Acetylcholine caused a significant time- and concentration-dependent increase in the magnitude of Galphaq/11 nucleotide exchange compared with basal values (i.e., without acetylcholine), reaching a maximal difference at 100 microm (35.9 +/-2.9 vs. 9.8 +/-1.2 fmol/mg protein, respectively). Whereas neither anesthetic had an effect on basal Galphaq/11 nucleotide exchange, both halothane and hexanol significantly inhibited the increase in Galphaq/11 nucleotide exchange produced by 30 microm acetylcholine (by 59% and 68%, respectively).

CONCLUSIONS

Halothane and hexanol interact with the receptor-heterotrimeric G-protein complex in a manner that prevents acetylcholine-promoted exchange of guanosine-5(')-triphosphate for guanosine-5'-diphosphate at Galphaq/11. These data are consistent with the ability of anesthetics to interfere with cellular processes mediated by heterotrimeric G proteins in many cells, including effects on muscarinic receptor-G-protein regulation of airway smooth muscle contraction.

Host plant volatiles synergize response to sex pheromone in codling moth, Cydia pomonella

Plant volatile compounds synergize attraction of codling moth males Cydia pomonella to sex pheromone (E,E)-8,10-dodecadien-1-ol (codlemone). Several apple volatiles, known to elicit a strong antennal response, were tested in a wind tunnel. Two-component blends of 1 pg/min codlemone and 100 pg/min of either racemic linalool, (E)-beta-farnesene, or (Z)-3-hexen-1-ol attracted significantly more males to the source than codlemone alone (60, 58, 56, and 37%, respectively). In comparison, a blend of codlemone and a known pheromone synergist, dodecanol, attracted 56% of the males tested. Blends of pheromone and plant volatiles in a 1:100 ratio attracted more males than 1:1 or 1:10,000 blends. Adding two or four of the most active plant compounds to codlemone did not enhance attraction over blends of codlemone plus single-plant compounds. Of the test compounds, only farnesol was attractive by itself; at a release rate of 10,000 pg/min, 16% of the males arrived at the source. However, attraction to a 1:10,000 blend of codlemone and farnesol (42%) was not significantly different from attraction to codlemone alone (37%). In contrast, a codlemone mimic, (E)-10-dodecadien-1-ol, which attracted 2% males by itself, had a strong antagonistic effect when blended in a 1:10,000 ratio with codlemone.

Macrokinetic analysis of blockade of NMDA-gated currents by substituted alcohols, alkanes and ethers

Volatile hydrocarbon based CNS depressants including short chain alcohols and anesthetics act, in part, by inhibition of the excitatory effect of glutamate at the NMDA receptor. While effects of several of these volatile agents on NMDA-gated currents have been demonstrated, there has been no direct comparison of different chemical classes of CNS depressant drugs on NMDA-gated currents. Here, whole-cell voltage clamp measurements of currents gated by 100 microM NMDA from cultured cerebrocortical neurons were examined in the presence of varying concentrations of the alcohols ethanol and hexanol, the halogenated alcohol trichloroethanol, the halogenated alkane halothane and the halogenated ethers isoflurane and sevoflurane. All drugs tested showed concentration-dependent inhibition of NMDA-gated currents with anesthetic concentrations of each agent producing approximately 30% inhibition of the NMDA-gated current. A rapid-translation perfusion system was used to study the onset and offset kinetics of each of the volatile agents. Onset kinetics for the CNS depressants was similar with tau values near 100 ms. Offset kinetics was more variable with tau ranging from 88.2 ms for ethanol to 221.4 ms for trichloroethanol. These data indicate that a wide variety of volatile hydrocarbon based CNS depressants produce a similar inhibition of NMDA-gated currents and that the kinetics for these agents are inconsistent with an open channel block.

TtgV bound to a complex operator site represses transcription of the promoter for the multidrug and solvent extrusion TtgGHI pump

The TtgGHI efflux pump of Pseudomonas putida extrudes a variety of antibiotics and solvents. We show that the ttgGHI operon is transcribed in vitro and in vivo from a single promoter and not from two overlapping promoters as previously proposed. The expression of this promoter is controlled by the TtgV repressor, whose operator expands through four helical turns that overlap the -10 region of the promoter. We also show that TtgV is released from its operator on binding of effectors such as aliphatic alcohols. Mutational analysis of the ttgGHI promoter revealed that substitutions at -13, -12, and -8 yielded promoters that were unable to drive transcription whereas certain mutations at -9, -11, and -6 to -3 increased expression in vivo. The cause of the increased expression was either a decrease in the affinity of the TtgV protein for its operator or an increase in the affinity of RNA polymerase for the mutant promoters.

The effects of hexanol on Galpha(i) subunits of heterotrimeric G proteins

Alcohols and other anesthetics interfere with the function of a variety of systems regulated by guanosine triphosphate (GTP)-binding proteins (G proteins). We examined the effect of hexanol on the activity of the alpha subunit (Galpha(i1)) of heterotrimeric G proteins. The GTP hydrolysis activity of recombinant Galpha(i1) was 0.029 mole Pi. mole Galpha(i1)(-1) x min(-1) and was inhibited by hexanol at concentrations larger than 10 mM, with a 50% inhibitory concentration of 22 mM. Circular dichroism spectroscopy revealed that hexanol decreased the denaturation temperature of Galpha(i1) from 47.2 degrees C to 42.5 degrees C without altering its secondary structure at 10 degrees C. Hexanol (30 mM) reduced the amount of monomeric Galpha(i1) in solution measured by size-exclusion chromatography, indicating that hexanol caused protein aggregation. However, the rate of GTPgammaS binding to Galpha(i) immunoprecipitated from airway smooth muscle membranes was not affected by 30 mM hexanol. Excluding the apparent inhibition of recombinant Galpha(i1) resulting from aggregation-induced artifact, we found no evidence that the hexanol-induced inhibition of receptor-activated Galpha(i)-coupled pathways in intact airway smooth muscle resulted from direct inhibition of the intrinsic rate of [(35)S]GTPgammaS binding to Galpha(i).

IMPLICATIONS

Although the alpha subunit of heterotrimeric G proteins is a potential target of anesthetics, we found no evidence that hexanol affects the ability of the Galpha(i) subunit to bind or hydrolyze guanosine triphosphate, either in purified subunits or in subunits derived from smooth muscle cell membranes. This finding implies that this is not a mechanism by which hexanol interferes with receptor-G protein function.