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Yield losses of crops due to plant pathogens are a major threat in all agricultural systems. In view of environmental issues and legislative limitations for chemical crop protection products, the need to design new environmentally friendly disease management strategies has gained interest. Despite the unique capability of green leaf volatiles (GLVs) to suppress a broad spectrum of plant pathogens, their capacity to control the potato late-blight-causing agent Phytophthora infestans has not been well studied. This study addresses the potential role of the GLV Z-3-hexenyl acetate (Z-3- HAC) in decreasing the severity of late blight and the underlying gene-based evidence leading to this effect. Nine-week-old potato plants (Solanum tuberosum L.) were exposed to Z-3-HAC before they were inoculated with P. infestans genotypes at different time points. These pre-exposed potato plants exhibited slower disease development after infection with the highly pathogenic genotype of P. infestans (EU-13-A2) over time. Qualitative assessment showed that the exposed, infected plants possessed significantly lower sporulation intensity and disease severity compared to the control plants. Hypersensitive response (HR)-like symptoms were observed on the treated leaves when inoculated with different pathogen genotypes. No HR-like lesions were detected on the untreated leaves after infection. It was shown that the transcript levels of several defense-related genes, especially those that are involved in reactive oxygen species (ROS) production pathways were significantly expressed in plants at 48 and 72 h postexposure to the Z-3-HAC. The current work provides evidence on the role of Z-3-HAC in the increased protection of potato plants against late blight through plant immunity and offers new opportunities for the sustainable control of potato diseases. [ABSTRACT FROM AUTHOR]

Tef (Eragrostis tef), a staple crop that originated in the Horn of Africa, has been introduced to multiple countries over the last several decades. Crop cultivation in new geographic regions raises questions regarding the molecular basis for biotic stress responses. In this study, we aimed to classify the insect abundance on tef crop in Israel, and to elucidate its chemical and physical defense mechanisms in response to insect feeding. To discover the main pests of tef in the Mediterranean climate, we conducted an insect field survey on three selected accessions named RTC-144, RTC-405, and RTC-406, and discovered that the most abundant insect order is Hemiptera. We compared the differences in Rhopalosiphum padi (Hemiptera; Aphididae) aphid performance, preference, and feeding behavior between the three accessions. While the number of aphid progeny was lower on RTC-406 than on the other two, the aphid olfactory assay indicated that the aphids tended to be repelled from the RTC-144 accession. To highlight the variation in defense responses, we investigated the physical and chemical mechanisms. As a physical barrier, the density of non-granular trichomes was evaluated, in which a higher number of trichomes on the RTC-406 than on the other accessions was observed. This was negatively correlated with aphid performance. To determine chemical responses, the volatile and central metabolite profiles were measured upon aphid attack for 4 days. The volatile analysis exposed a rich and dynamic metabolic profile, and the central metabolism profile indicated that tef plants adjust their sugars and organic and amino acid levels. Overall, we found that the tef plants possess similar defense responses as other Poaceae family species, while the non-volatile deterrent compounds are yet to be characterized. A transcriptomic time-series analysis of a selected accession RTC-144 infested with aphids revealed a massive alteration of genes related to specialized metabolism that potentially synthesize non-volatile toxic compounds. This is the first report to reveal the variation in the defense mechanisms of tef plants. These findings can facilitate the discovery of insect-resistance genes leading to enhanced yield in tef and other cereal crops.

The activation and priming of plant defense upon perception of green leaf volatiles (GLVs) have often been reported. However, information as to which metabolic pathways in plants are affected by GLVs remains elusive. We report the production of reactive oxygen species in the tip of young wheat leaves followed by activation of antioxidant-related enzyme activity. In this study, we aimed to uncover metabolic signatures upon exposure to the GLV Z-3-hexenyl acetate (Z-3-HAC). By using an untargeted metabolomics approach, we observed changes in the phenylpropanoid pathways which yield metabolites that are involved in many anti-oxidative processes. Furthermore, exposure to GLV, followed by infection with Fusarium graminearum (Fg), induced significantly greater changes in the phenylpropanoid pathway compared to a sole Z-3-HAC treatment. Fragmentation of a selection of metabolites, which are significantly more upregulated in the Z-3-HAC + Fg treatment, showed D-glucose to be present as a substructure. This suggests that Z-3-HAC induces early glycosylation processes in plants. Additionally, we identified the presence of hexenyl diglycosides, which indicates that aerial Z-3-HAC is metabolized in the leaves by glycosyltransferases. Together these data indicate that GLV Z-3-HAC is taken up by leaves and incites oxidative stress. This subsequently results in the modulation of the phenylpropanoid pathway and an induction of glycosylation processes.

Tef (Eragrostis tef), a staple crop that originated in the Horn of Africa, has been introduced to multiple countries over the last several decades. Crop cultivation in new geographic regions raises questions regarding the molecular basis for biotic stress responses. In this study, we aimed to classify the insect abundance on tef crop in Israel, and to elucidate its chemical and physical defense mechanisms in response to insect feeding. To discover the main pests of tef in the Mediterranean climate, we conducted an insect field survey on three selected accessions named RTC-144, RTC-405, and RTC-406, and discovered that the most abundant insect order is Hemiptera. We compared the differences in Rhopalosiphum padi (Hemiptera; Aphididae) aphid performance, preference, and feeding behavior between the three accessions. While the number of aphid progeny was lower on RTC-406 than on the other two, the aphid olfactory assay indicated that the aphids tended to be repelled from the RTC-144 accession. To highlight the variation in defense responses, we investigated the physical and chemical mechanisms. As a physical barrier, the density of non-granular trichomes was evaluated, in which a higher number of trichomes on the RTC-406 than on the other accessions was observed. This was negatively correlated with aphid performance. To determine chemical responses, the volatile and central metabolite profiles were measured upon aphid attack for 4 days. The volatile analysis exposed a rich and dynamic metabolic profile, and the central metabolism profile indicated that tef plants adjust their sugars and organic and amino acid levels. Overall, we found that the tef plants possess similar defense responses as other Poaceae family species, while the non-volatile deterrent compounds are yet to be characterized. A transcriptomic time-series analysis of a selected accession RTC-144 infested with aphids revealed a massive alteration of genes related to specialized metabolism that potentially synthesize non-volatile toxic compounds. This is the first report to reveal the variation in the defense mechanisms of tef plants. These findings can facilitate the discovery of insect-resistance genes leading to enhanced yield in tef and other cereal crops. [ABSTRACT FROM AUTHOR]

The activation and priming of plant defense upon perception of green leaf volatiles (GLVs) have often been reported. However, information as to which metabolic pathways in plants are affected by GLVs remains elusive. We report the production of reactive oxygen species in the tip of young wheat leaves followed by activation of antioxidant-related enzyme activity. In this study, we aimed to uncover metabolic signatures upon exposure to the GLV Z-3-hexenyl acetate (Z-3-HAC). By using an untargeted metabolomics approach, we observed changes in the phenylpropanoid pathways which yield metabolites that are involved in many anti-oxidative processes. Furthermore, exposure to GLV, followed by infection with Fusarium graminearum (Fg), induced significantly greater changes in the phenylpropanoid pathway compared to a sole Z-3-HAC treatment. Fragmentation of a selection of metabolites, which are significantly more upregulated in the Z-3-HAC + Fg treatment, showed D-glucose to be present as a substructure. This suggests that Z-3-HAC induces early glycosylation processes in plants. Additionally, we identified the presence of hexenyl diglycosides, which indicates that aerial Z-3-HAC is metabolized in the leaves by glycosyltransferases. Together these data indicate that GLV Z-3-HAC is taken up by leaves and incites oxidative stress. This subsequently results in the modulation of the phenylpropanoid pathway and an induction of glycosylation processes. [ABSTRACT FROM AUTHOR]

Green leaf volatile (GLV) organic compounds, released from vegetation, act as plants' multifunctional weapon and are known to be a source of secondary organic aerosols (SOAs). In the present study, the mechanism of oxidation reaction of methyl salicylate (MeSa), a known GLV, by OH radical has been investigated by means of density functional theory (DFT). Canonical transition state (CTST) and Rice‐Ramsperger‐Kassel‐Marcus theories (RRKM) with Wigner and Eckart tunneling correction were applied to calculate the transition pressure, the total rate constant, and the individual rate constants for every channel of this oxidation reaction of MeSa with OH radical. The calculated overall bimolecular rate constant with Eckart tunneling correction for the title reaction is 1.18×109 and 1.01×109 L mol−1s−1 at Mn15‐L/aug‐cc‐pVTZ and MN15‐L/MG3S levels of theory in the gas phase at 298 K which is comparable to the experimental reported value of 6.66×109 L mol−1s−1, indicating that the results of MN15‐L/aug‐cc‐pVTZ level of theory is more accurate. Investigation of transition pressure and fall‐off curve of unimolecular channels at proposed mechanism for oxidation reaction of MeSa revealed that the TST breaks down slightly to estimate the high pressure limit of reaction rate and the reaction become second order (bimolecular reaction). Furthermore, the atmospheric lifetime of MeSa is about 2.95 and 3.44 days calculated at those two levels of theory, respectively, which indicates that MeSa can be considered as a medium‐lifetime organic volatile compound. [ABSTRACT FROM AUTHOR]

Yield losses of crops due to plant pathogens are a major threat in all agricultural systems. In view of environmental issues and legislative limitations for chemical crop protection products, the need to design new environmentally friendly disease management strategies has gained interest. Despite the unique capability of green leaf volatiles (GLVs) to suppress a broad spectrum of plant pathogens, their capacity to control the potato late-blight-causing agent Phytophthora infestans has not been well studied. This study addresses the potential role of the GLV Z-3-hexenyl acetate (Z-3-HAC) in decreasing the severity of late blight and the underlying gene-based evidence leading to this effect. Nine-week-old potato plants (Solanum tuberosum L.) were exposed to Z-3-HAC before they were inoculated with P. infestans genotypes at different time points. These pre-exposed potato plants exhibited slower disease development after infection with the highly pathogenic genotype of P. infestans (EU-13-A2) over time. Qualitative assessment showed that the exposed, infected plants possessed significantly lower sporulation intensity and disease severity compared to the control plants. Hypersensitive response (HR)-like symptoms were observed on the treated leaves when inoculated with different pathogen genotypes. No HR-like lesions were detected on the untreated leaves after infection. It was shown that the transcript levels of several defense-related genes, especially those that are involved in reactive oxygen species (ROS) production pathways were significantly expressed in plants at 48 and 72 h postexposure to the Z-3-HAC. The current work provides evidence on the role of Z-3-HAC in the increased protection of potato plants against late blight through plant immunity and offers new opportunities for the sustainable control of potato diseases.

To forage nonrandomly, animals must discriminate among food items. Foods differ in look, smell and taste, providing cues for foragers with appropriate senses. Irrespective of the sensory modality, however, foragers can only use cues effectively if they can detect sensory signals above background noise. Recent evidence shows that foraging mammalian herbivores can detect plant odours, but their capacity to select preferred plants in a noisy olfactory background is unknown. Using choice trials, we tested whether the African elephant, Loxodonta africana , uses plant odour as a salient cue despite increasingly complex and challenging background odours. We first established their preference for familiar plant species. We then tested their capacity to discriminate and select preferred plants based on odour alone. We found that elephants successfully chose preferred species even when presented with complex background odours from nonpreferred plants mimicking multispecies vegetation patches. Elephants also succeeded despite our attempt to mask distinguishing odours with large amounts of a synthetic green leaf volatile. GC–MS analysis confirmed that volatile organic compound profiles differed between plant species. In demonstrating that elephants exploit plant odours even when the signal from preferred plants is embedded in sensory noise of background odours, we provide crucial behavioural evidence that olfaction provides an efficient mechanism for selective, nonrandom foraging. Whether mammalian herbivores recognize novel odours, for example from newly invading plant species, or when air pollution degrades odours of familiar plants, needs investigating. Accounting for the capacity of mammalian herbivores to use plant odour cues will improve models of both their foraging behaviour and the ecosystem impacts of their foraging. • Elephants choose preferred plants using odour cues alone. • Odour cues are useful even when mixed with odours from other plants. • An abundant green leaf volatile fails to mask odour cues of preferred plants. • Olfaction probably plays a key role in efficient foraging by mammalian herbivores. [ABSTRACT FROM AUTHOR]

Green plants emit green leaf volatiles (GLVs) as a general damage response. These compounds act as signals for the emitter plant, neighboring plants, and even for insects in the ecosystem. However, when oral secretions from certain caterpillars are applied to wounded leaves, GLV emissions are significantly decreased or modified. We examined four caterpillar species representing two lepidopteran families for their capacity to decrease GLV emissions from Zea mays leaf tissue. We also investigated the source of the GLV modifying components in the alimentary tract of the various caterpillars. In Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae), Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), and Manduca sexta (Linnaeus) (Lepidoptera: Sphingidae), we found three distinct mechanisms to modify GLV emission: a heat-stable compound in the gut, a heat-labile enzyme in salivary gland homogenate (previously described in Bombyx mori (Linnaeus) (Lepidoptera: Bombycidae), and an isomerase in the salivary gland homogenate, which catalyzes the conversion of (Z)-3-hexenal to (E)-2-hexenal (previously described in M. sexta). These mechanisms employed by caterpillars to suppress or modify GLV emission suggest a counteraction against the induced indirect volatile defenses of a plant and provides further insights into the ecological functions of GLVs. [ABSTRACT FROM AUTHOR]

In plants, lipoxygenases (LOXs) play a crucial role in biotic and abiotic stresses. In our previous study, five 13-LOX genes of oriental melon were regulated by abiotic stress but it is unclear whether the 9-LOX is involved in biotic and abiotic stresses. The promoter analysis revealed that CmLOX09 (type of 9-LOX) has hormone elements, signal substances, and stress elements. We analyzed the expression of CmLOX09 and its downstream genes—CmHPL and CmAOS—in the leaves of four-leaf stage seedlings of the oriental melon cultivar “Yumeiren” under wound, hormone, and signal substances. CmLOX09, CmHPL, and CmAOS were all induced by wounding. CmLOX09 was induced by auxin (indole acetic acid, IAA) and gibberellins (GA3); however, CmHPL and CmAOS showed differential responses to IAA and GA3. CmLOX09, CmHPL, and CmAOS were all induced by hydrogen peroxide (H2O2) and methyl jasmonate (MeJA), while being inhibited by abscisic acid (ABA) and salicylic acid (SA). CmLOX09, CmHPL, and CmAOS were all induced by the powdery mildew pathogen Podosphaera xanthii. The content of 2-hexynol and 2-hexenal in leaves after MeJA treatment was significantly higher than that in the control. After infection with P. xanthii, the diseased leaves of the oriental melon were divided into four levels—levels 1, 2, 3, and 4. The content of jasmonic acid (JA) in the leaves of levels 1 and 3 was significantly higher than that in the level 0 leaves. In summary, the results suggested that CmLOX09 might play a positive role in the response to MeJA through the hydroperoxide lyase (HPL) pathway to produce C6 alcohols and aldehydes, and in the response to P. xanthii through the allene oxide synthase (AOS) pathway to form JA. [ABSTRACT FROM AUTHOR]

Green leaf volatiles (GLVs), which include C6 aldehydes, alcohols, and their esters, are emitted by damaged plants and are, therefore, thought to be involved in stress responses. However, the effects of GLVs on gene expression are not fully understood. Thus, the aim of the present study was to analyze the early transcriptional responses of Arabidopsis to the major GLVs--(Z)-3-hexenal, (Z)-3-hexenol, (E)-2-hexenal, and (Z)-3-hexenyl acetate--using comprehensive microarray gene expression analysis. All of the GLVs induced changes in gene expression, and (Z)-3-hexenal, (Z)-3-hexenol, and (Z)-3-hexenyl acetate commonly triggered the expression of defense-related genes, whereas (E)-2-hexenal mainly induced genes responsible for responding to abiotic stress, such as heat and oxidative stress. These results suggest that GLVs can function as airborne infochemicals that regulate the rapid expression of defense response-related genes and that GLVs might play a physiological role as self-made damage-associated molecular patterns (DAMPs) in damaged leaves. [ABSTRACT FROM AUTHOR]

In contrast to many biotic stresses that plants face, feeding by herbivores produces unique mechanical and chemical signatures. Plants have evolved effective systems to recognise these mechanical stimuli and chemical elicitors at the plasma membrane (PM), where this recognition generates ion fluxes, including an influx of Ca2+ that elicits cellular Ca2+ signalling, production of reactive oxygen species (ROS), and variation in transmembrane potential. These signalling events also function in propagation of long-distance signals (Ca2+ waves, ROS waves, and electrical signals), which contribute to rapid, systemic induction of defence responses. Recent studies have identified several candidate channels or transporters that likely produce these ion fluxes at the PM. Here, we describe the important roles of these channels/transporters in transduction or transmission of herbivory-induced early signalling events, long-distance signals, and jasmonic acid and green leaf volatile signalling in plants. [ABSTRACT FROM AUTHOR]

In Citrus species chromosome doubling naturally occurs in somatic embryos and doubled diploid plants often show better adaptation to adverse environmental condition. To understand the molecular determinants of stress acclimation, we examined the response to water deficit in diploid (2×VL) and doubled diploid (4×VL) seedlings of Volkamer lemon ( Citrus limonia Osb.) assessing the profile of constitutive volatile organic compound (VOC) in control and stressed conditions. Physiological parameters and leaf volatile compound profiles were measured during water deficit and 24 h after rehydration of plants to field capacity. Net photosynthesis and stomatal conductance were reduced in water stressed leaves, with no significant differences between 2×VL and 4×VL plants. Malondialdehyde concentration, a marker of lipid peroxidation of cellular membranes, was significantly more higher in stressed 2×VL leaves than in 4×VL. The blend of constitutive VOC was different in control leaves being oxygenated monoterpenoids more abundant in 2×VL leaves, and monoterpenoids more abundant in 4×VL leaves. Water deficit did not stimulate biosynthesis of terpenoids, whereas accumulation of trans-2 hexenal, a green leaf volatile (GLV) synthesized after membrane denaturation, was observed in stressed leaves of 2×VL leaves, but not in 4×VL leaves. Semiquantitative PCR showed an increase of the expression of HPL , the gene encoding for hydroperoxidase lyase which catalyzes 2-hexenal formation, only in 2×VL plants. The expression of the putative dehydration transcription factor DREB2A was also observed only in 2×VL water stressed plants. This work shows that level of ploidy may alter constitutive content of GLV by Citrus, therefore likely affecting plants capacity of protection and interaction with other organisms. Whereas diploid and double diploid plants showed similar physiological responses to water deficit, a biochemical marker indicated that membranes of double diploid leaves were more resistant to the stress. These results provide intriguing insights into the regulation of terpenoids and oxylipins pathways as a function of polyploidization in a non-model plant species. [ABSTRACT FROM AUTHOR]

Main conclusion: Punica granatum has a noticeable adaptation to drought stress. The levels of the green leaf volatile trans-2-hexenal increased in response to drought stress suggesting a possible role of this compound in drought stress response in pomegranate. Punica granatum (L.) is a highly valued fruit crop for its health-promoting effects and it is mainly cultivated in semi-arid areas. Thus, understanding the response mechanisms to drought stress is of great importance. In the present research, a metabolomics analysis was performed to evaluate the effects of drought stress on volatile organic compounds extracted from the leaves of pomegranate plants grown under water shortage conditions. The time course experiment (7 days of water deprivation and 24-h recovery) consisted of three treatments (control, drought stress, and rehydration of drought-stressed plants). Plant weights were recorded and control plants were irrigated daily at pot capacity to provide the lost water. Fraction of transpirable soil water has been evaluated as indicator of soil water availability in stressed plants. The levels of proline, hydrogen peroxide and lipid peroxidation as well as of the photosynthetic parameters such as photosynthesis rate ( A), stomatal conductance ( g), photosynthetic efficiency of photosystem II, and photochemical quenching were monitored after the imposition of drought stress and recovery as markers of plant stress. Constitutive carbon volatile components were analyzed in the leaf of control and drought-stressed leaves using Head Space Solid Phase Micro Extraction sampling coupled with Gas Chromatography Mass Spectrometry. A total of 12 volatile compounds were found in pomegranate leaf profiles, mainly aldehydes, alcohols, and organic acids. Among them, the trans-2-hexenal showed a significant increase in water-stressed and recovered leaves respect to the well-watered ones. These data evidence a possible role of the oxylipin pathway in the response to water stress in pomegranate plants. [ABSTRACT FROM AUTHOR]

Green leaf volatiles (GLVs) are C6-aliphatic aldehydes/alcohols/acetates, and biosynthesized from the central precursor fatty acid 13-hydroperoxides by 13-hydroperoxide lyases (HPLs) in various plant species. While GLVs have been implicated as defense compounds in plants, GLVs give characteristic grassy note to a bouquet of aroma in green tea, which is manufactured from young leaves of Camellia sinensis . Here we identify three HPL- related genes from C. sinensis via RNA-Sequencing (RNA-Seq) in silico , and functionally characterized a candidate gene, CYP74B24 , as a gene encoding tea HPL. Recombinant CYP74B24 protein heterologously expressed in Escherichia coli specifically produced ( Z )-3-hexenal from 13-HPOT with the optimal pH 6.0 in vitro . CYP74B24 gene was expressed throughout the aerial organs in a rather constitutive manner and further induced by mechanical wounding. Constitutive expression of CYP74B24 gene in intact tea leaves might account for low but substantial and constitutive formation of a subset of GLVs, some of which are stored as glycosides. Our results not only provide novel insights into the biological roles that GLVs play in tea plants, but also serve as basis for the improvement of aroma quality in tea manufacturing processes. [ABSTRACT FROM AUTHOR]

Secondary organic aerosol (SOA) plays integral roles in climate and human health, yet there remains a limited understanding of the mechanisms that lead to its formation and ultimate fate, as evidenced by a disparity between modeled atmospheric SOA loadings and field measurements. This disparity highlights the need for a more accurate representation of the molecular-level interactions between SOA sources and oxidative pathways. Due to the paucity of detailed chemical data for most SOA precursors of atmospheric relevance, models generally predict SOA loadings using structure activity relationships generalized to classes of SOA precursors. However, the kinetics and SOA forming potential of molecules are nuanced by seemingly minor structural differences in parent molecules that may be neglected in models. Laboratory chamber studies were used to measure SOA yields and rate constants for the ozonolysis of several linear, cyclic and oxygenated C 5 –C 7 alkenes whose molecular structure vary in the site of unsaturation and/or the presence/position of functional groups and that represent atmospherically relevant classes of molecules. For the alkenes studied in this work, we found greater SOA yields for cyclic compounds compared to their linear analogs. For 1-alkenes, SOA yield increased with carbon number but was also dependent on the position of the double bond (internal vs terminal). Both the identity and position of oxygenated functional groups influenced SOA yield and kinetics through steric and electronic effects. Additionally, terminal alkenes generally resulted in a greater SOA yield than analogous internal alkenes, indicating that the position of the double bond in alkenes plays an important role in its atmospheric fate. Herein, we demonstrate the nuanced behavior of these ozonolysis reactions and discuss relationships between parent compound molecular structure and SOA yield and kinetics. [ABSTRACT FROM AUTHOR]

Green leaf volatiles (GLVs), the products of the hydroperoxide lyase (HPL) branch of the oxylipin pathway, play important roles in plant defense responses to both insect pests and pathogens. However, little is known about the role of GLVs in the defense responses of rice to the white-backed planthopper (WBPH, Sogatella furcifera (Horváth)). Here, we found that the rice HPL gene OsHPL3 was upregulated in response to infestation by WBPH adults and nymphs. Using an Agrobacterium-mediated transformation system, we obtained two homozygous lines with an antisense expression vector of OsHPL3 (as- hpl) and a single insertion that reduced the gene's expression by 48.31-52.56 %. Biochemical assays revealed that as- hpl lines had lower wound-induced GLV levels, mainly ( Z)-3-hexenal, ( Z)-3-hexen-1-ol, and ( E)-2-hexenal, but higher JA levels, compared to wild-type (WT) plants. Biological assays showed that WBPH adult females and nymphs preferred to settle and/or oviposit on WT plants, where they survived better than on as- hpl plants. In addition, both male and female WBPH nymphs fed on as- hpl plants performed less well: they developed more slowly, and pairs subsequently laid fewer eggs compared to pairs fed on WT plants. The enhanced resistance of as- hpl plants to WBPH infestation mainly correlated with lower levels of GLVs, especially ( Z)-3-hexenal. Collectively, these results indicated that WBPH infestation may enhance the susceptibility of rice by inducing the release of ( Z)-3-hexenal. [ABSTRACT FROM AUTHOR]

Green leaf volatiles (GLVs) are a group of biogenic volatile organic compounds (BVOCs) released into the atmosphere by vegetation. BVOCs produce secondary organic aerosol (SOA) via gas-phase reactions, but little is known of their aqueous-phase oxidation as a source of SOA. GLVs can partition into atmospheric water phases, e.g., fog, mist, dew or rain, and be oxidized by hydroxyl radicals (˙OH). These reactions in the liquid phase also lead to products that have higher molecular weights, increased polarity, and lower vapor pressures, ultimately forming SOA after evaporation of the droplet. To examine this process, we investigated the aqueous, ˙OH-mediated oxidation of methyl jasmonate (MeJa) and methyl salicylate (MeSa), two GLVs that produce aqueous-phase SOA. High performance liquid chromatography/electrospray ionization mass spectrometry (HPLC-ESI-MS) was used to monitor product formation. The oxidation products identified exhibit higher molecular mass than their parent GLV due to either dimerization or the addition of oxygen and hydroxyl functional groups. The proposed structures of potential products are based on mechanistic considerations combined with the HPLC/ESI-MS data. Based on the structures, the vapor pressure and the Henry's law constant were estimated with multiple methods (SPARC, SIMPOL, MPBPVP, Bond and Group Estimations). The estimated vapor pressures of the products identified are significantly (up to 7 orders of magnitude) lower than those of the associated parent compounds, and therefore, the GLV oxidation products may remain as SOA after evaporation of the water droplet. The contribution of the identified oxidation products to SOA formation is estimated based on measured HPLC-ESI/MS responses relative to previous aqueous SOA mass yield measurements. [ABSTRACT FROM AUTHOR]

Background Previously it has been shown that mechanical wounding, salinity and heat activated a 46 kDa and 44 kDa mitogen-activated protein kinases (MAPKs) in forage related grasses. Forage and turf related grasses are utilized in diverse environments where they are routinely subjected to herbicides and exposed to fire and volatiles after cutting, however very little is known concerning the perception or molecular responses to these different stresses or compounds. Results In the model grass species Lolium temulentum (Lt), a 46 kDa mitogen-activated protein kinase (MAPK) was activated in the leaves within 5 min and a 44 kDa MAPK 15 min after exposure to green leaf volatiles released from grass clippings. When the tips of leaves of Lt plants were scorched by fire, the 46 kDa MAPK and 44 kDa MAPK were rapidly activated within 5 min and 20 min respectively in the treated leaf, and 15 min systemically in an adjacent untreated tiller after exposure to fire. Nonanoic acid (pelargonic acid), a component in herbicides used on grasses, activated a 46 kDa MAPK in the treated leaves within 5 min of exposure and 15 min in systemic tissues. At concentrations normally used in the herbicides, nonanoic acid was found to only weakly activate the 44 kDa MAPK after an hour in treated leaves, but strongly activated it in the systemic tillers 30 min after treatment. Acetic acid, HCl and NaOH also were found to activate these MAPKs in treated tillers. Conclusion The rapid activation of these MAPKs to a wide range of stress stimuli, suggest that these MAPKs play a role in the perception and response to these stresses and compounds. The activation of the MAPK by green leaf volatiles indicates a role for these compounds in wound signaling in grasses. [ABSTRACT FROM AUTHOR]

Optimization of male moth trapping rates in sex pheromone-baited traps plays akey role in managing Plutella xylostella (L.). We investigated various ways to increase the attractiveness of pheromone-baited traps to P. xylostella in canola agroecosystems in AB, Canada. Factors tested included pheromone blend and dose, addition of a green leaf volatile to the pheromone at different times during the season, lure type, trap color, and height. The industry standard dose of 100 µg of pheromone (four-component blend) per lure (ConTech Enterprises Inc., Delta, British Columbia [BC], Canada) captured the most moths in the two lure types tested. Traps baited with pheromone released from gray rubber septa captured more males than those baited with red rubber septa. Traps baited with lures in which Z11-16: Ac is the main component attracted significantly more moths than those in which Z11-16: Ald is the main component. The addition of the green leaf volatile, (Z)-3-hexenyl acetate, to pheromone at a range of doses, did not increase moth capture at any point during the canola growing season. Unpainted white traps captured significantly more male moths than pheromone-baited traps that were painted yellow. Trap height had no significant effect on moth capture. Recommendations for monitoring P. xylostella in canola agroecosystems of western Canada include using a pheromone blend with Z11-16: Ac as the main component released from gray rubber septa at a dose of 100 µg. [ABSTRACT FROM AUTHOR]

Most crop pests find a suitable host through chemical cues released from plants, but little is known about the odorscape encountered by host-seeking gravid females under natural, outdoor conditions. In this field study, the volatile organic compound (VOC) composition of maize ( Zea mays, L.), a host for the European corn borer (ECB) ( Ostrinia nubilalis Hüb.) was characterized during the oviposition flight and compared with a forest odorscape. VOCs from maize fields and the forest atmosphere were collected by solid phase microextraction and characterized by gas chromatography-mass spectrometry. The electroantennographic (EAG) response of female ECB antennae to candidate VOCs was tested. Analyses revealed clear differences between the maize field and the forest odorscapes, mainly composed of ubiquitous VOCs but in specific ratios. The maize field odorscape is more complex than the forest odorscape for maize found 18 VOCs but only eight in the forest. Both biotopes shared seven VOCs-green leaf volatiles (GLV), monoterpènes (MT) and homoterpenes. In addition, we found in the forest a distinctive sesquiterpene (SQT) identified as isoledene. The highest EAG responses were elicited by two GLVs and a MT shared by the two biotopes. SQT elicited weak EAG responses, except β-farnesene, only found in the maize field odorscape. Our results suggest that the two biotopes produce specific chemical signatures that insects may use as host cues. To the best of our knowledge this paper is the first report on the maize odorscapes under field conditions. The putative role of the VOCs in host plant detection and selection is discussed. [ABSTRACT FROM AUTHOR]

We studied the influence of synthetic ( E)-2-hexenal on the abundance of Telenominae aiming to attract parasitoids and enhance stink bug egg parasitism in treated areas. We conducted experiments in 2006, 2007 and 2008 soybean seasons with two short-term (one week) and one long-term (seven weeks) experiment, respectively. We evaluated the abundance of parasitoids with yellow sticky traps and estimated the incidence and intensity of parasitism with sentinel eggs of Euschistus heros Fabricius (Hemiptera: Pentatomidae) or with tulle bags, enclosing laboratory pregnant E. heros as an egg source. In short-term experiments, there was increased abundance of Trissolcus spp. (Hymenoptera: Platygastridae: Telenominae) in treated areas, associated with greater intensity of parasitism. In long-term experiments, treatment with ( E)-2-hexenal did not influence the abundance of Telenominae or parasitism levels, but increased egg predation. Applications of ( E)-2-hexenal can be used to increase recruitment of Trissolcus spp. in the early flowering stages of soybean and also to attract other natural enemies, but do not increase egg parasitism. [ABSTRACT FROM AUTHOR]

Lipoxygenases (LOXs) are non-heme iron-containing enzymes that catalyse the dioxygenation of polyunsaturated fatty acids. The resulting hydroperoxides are further metabolized into biologically active oxylipins including jasmonic acid and green leaf volatiles (GLV) such as C6-aldehydes and C6-alcohols. LOXs are also known to play a decisive role in the production of volatiles that influence the flavour and aroma of fruits and vegetables. To obtain an overview of the inventory of the apple LOX gene family, the published Golden Delicious genome was mined for LOX coding sequences. In total, 23 putative functional LOX genes were identified and used for the construction of a phylogenetic tree. Two sub-trees were found which differentiate the LOX sequences into type 1- and type 2-LOXs. Their chromosomal locations were assigned to the predicted chromosomes of the assembled Golden Delicious genome sequence. Single LOX genes as well as clusters consisting of up to four genes were detected on apple chromosomes 2, 4, 5, 6, 7, 9, 11, 12, 13 and 16. LOX gene clusters on chromosomes 2 and 7, and on 4 and 12, respectively, indicated duplicated genome regions with high homology, which supports previous hypotheses of an ancient genome-wide duplication event in Malus. By using a PCR-based strategy, eight genes belonging to both type 1- and type 2-LOXs with altogether 30 full-length sequences were cloned. Several putative LOX alleles were detected within the same and among different apple cultivars. Two parental genetic maps available for ‘Discovery’ and ‘Prima’ were used for a quantitative trait locus (QTL) mapping experiment of apple volatile compounds known to be produced by the LOX biosynthetic pathway. The QTL detection resulted in a total number of 15 QTLs for eight volatiles (esters and the aldehyde hexanal) which were located on chromosomes 2, 7, 9 and 12 determined in silico as carriers of at least one LOX gene. To examine the putative roles of apple LOX genes in fruit volatile production, the spatial and temporal expression patterns were analysed by RT-PCR-based transcription analyses of apple leaf and fruit tissues. Two genes, MdLOX1a and MdLOX5e, were identified as candidate genes to be involved in fruit aroma volatile production in apple. The genetic association of QTLs found for the GLV hexanal at the top of chromosome 7, three clustered MdLOX5 genes with a putative 13-LOX function and published apple aphid resistance factors located all in the same region of chromosome 7 indicate that a lipoxygenase action might be involved in Malus aphid resistance reactions. [ABSTRACT FROM AUTHOR]

From an herbivore's first bite, plants release herbivory-induced plant volatiles (HIPVs) which can attract enemies of herbivores. However, other animals and competing plants can intercept HIPVs for their own use, and it remains unclear whether HIPVs serve as an indirect defense by increasing fitness for the emitting plant. In a 2-year field study, HIPV-emitting N. attenuata plants produced twice as many buds and flowers as HIPV-silenced plants, but only when native Geocoris spp. predators reduced herbivore loads (by 50%) on HIPV-emitters. In concert with HIPVs, plants also employ antidigestive trypsin protease inhibitors (TPIs), but TPI-producing plants were not fitter than TPI-silenced plants. TPIs weakened a specialist herbivore's behavioral evasive responses to simulated Geocoris spp. attack, indicating that TPIs function against specialists by enhancing indirect defense.

By comparing wild-type and transgenic tobacco plants in a natural ecosystem, researchers have confirmed that the indirect defence mechanisms employed by plants to fend off herbivorous insects can increase Darwinian fitness.

• The 100 μmol L-1 (E)-2-hexenal reduced disease severity caused by B. cinerea in kiwifruit. • (E)-2-hexenal contributed to the tolerance against B. cinerea in kiwifruit. • Transcriptomic analysis revealed upregulated pattern recognition receptor genes and MPK3 in kiwifruit. • Jasmonic acid and flavonoid contents were increased by (E)-2-hexenal fumigation. (E)-2-Hexenal is a reactive electrophile species released by green plants upon herbivory or pathogenic infection and induces various defense responses. In this study, (E)-2-hexenal was used as a natural alternative to artificial fumigants to prevent postharvest pathogenic infection of the 'Haegeum' kiwifruit (Actinidia chinensis). Integrated transcriptome-metabolome analyses were performed to investigate its effect on the induction of plant defense responses. When kiwifruit was fumigated with 100 μ mol L-1 (E)-2-hexenal for 24 h at 20 °C and then inoculated with fungal pathogen Botrytis cinerea , the disease severity, as assessed by necrotic lesion size and B. cinerea biomass, was reduced compared to the control, distilled water-treated fruit. (E)-2-Hexenal treatment also led to upregulated expression of genes encoding pattern recognition receptors, signal transducer proteins, and pathogenesis-related proteins, including chitinase. Furthermore, treatment led to increased jasmonic acid and flavonoid biosynthesis. (E)-2-Hexenal fumigation therefore enhanced the resistance of kiwifruit to B. cinerea infection, presumably by facilitating the signaling network from pathogen recognition to defense gene expression and enabling the accumulation of secondary metabolites, such as flavonoids. The present study not only suggests an optimal concentration of (E)-2-hexenal fumigation for controlling postharvest disease of kiwifruit, but also broadens our understanding of the underlying molecular mechanism by which (E)-2-hexenal enhances plant resistance. [ABSTRACT FROM AUTHOR]

Abstract: Previous studies suggest that the sensitivity of leaf mitochondrial respiration and the pool of soluble sugars to water stress could influence the response of leaf isoprene emission to drought by affecting the availability of extra-chloroplastic carbon for isoprene synthesis. We measured rates of isoprene emission and CO2 exchange, and the concentration of nonstructural carbohydrates in leaves of Quercus pubescens Willd. seedlings subjected to either normal watering (control plants, C) or drought (droughted plants, D). Stopping of watering caused predawn leaf water potential (Ψ pd) to decline between −2.3 and −5.1MPa among D plants, whereas Ψ pd remained higher than −0.45MPa in C plants. Isoprene emission (I s), net CO2 assimilation (A n) and dark mitochondrial respiration (R d) decreased with increasing water deficit, with declines in these variables relative to the respective means of C plants being A n > I s > R d. This resulted in positive pairwise correlations between the three variables. The concentration of nonstructural carbohydrates did not change between treatments, but the concentration of soluble sugars increased and that of starch decreased in D plants as compared with C plants. As a consequence, there was a negative correlation between I s and the concentration of soluble sugars, which supports a limited use of cytosolic sugars in sustaining isoprene synthesis at high to severe water stress. Our data also indicate that competition between I s and R d for the same carbon substrates had little importance for isoprene emission at high to severe water stress, as compared to the overall constraint on isoprene metabolism probably imposed by the shortage of photosynthetic carbon, energy and reducing equivalents. [Copyright &y& Elsevier]

Abstract: Following a promising preliminary study concerning sugar beet leaves valorization and to fulfill the high demand in natural C6-aldehydes flavors, an efficient biocatalytic reaction was developed to synthesize (2E)-hexenal at large scale. As major product of the lipoxygenase enzyme, 13-HPOT was converted by sugar beet hydroperoxide lyase extracted from leaves or expressed by recombinant Escherichia coli strains. With the adaptation of a fed-batch substrate addition and a continuous extraction of volatiles, 3.46mM and 1.37mM of C6-aldehydes were produced with the native hydroperoxide lyase at respectively 2 and 100L scale. Furthermore, higher molar productivity of green leaf volatiles was reached with recombinant hydroperoxide lyase (5.5mM at 2L scale) while no others side products from the lipoxygenase pathway were formed. Once purified, these natural aromas are suitable for food and beverage preparations, perfumes or cosmetic products. [Copyright &y& Elsevier]

Diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is one of the most serious pests of Brassicaceae crops worldwide. Electrophysiological and behavioral responses of P. xylostella to green leaf volatiles (GLVs) alone or together with its female sex pheromone were investigated in laboratory and field. GLVs 1-hexanol and (Z)-3-hexen-l-ol elicited strong electroan- tennographic responses from unmated male and female P. xylostella, whereas (Z)-3-hexenyl acetate only produced a relatively weak response. The behavioral responses of unmated moths to GLVs were fiarther tested in Y-tube olfactometer experiments. (E)-2-Hexenal, (Z)-3-hexen-l-ol, and (Z)-3- hexenyl acetate induced attraction of males, reaching up to 50%, significantly higher than the response to the unbaited control arm. In field experiments conducted in 2008 and 2009, significantly more moths were captured in traps baited with synthetic sex pheromone with either (Z)-3-hexenyl acetate alone or a blend of (Z)-3-hexenyl acetate, (Z)-3-hexen-l-ol, and (E)-2-hexenal compared with sex pher- omone alone and other blend mixtures. These results demonstrated that GLVs could be used to enhance the attraction of P. xylostella males to sex pheromone-baited traps. [ABSTRACT FROM AUTHOR]

Abstract: Odour perception is controlled by environmental and genetic influences. Most people can discriminate over 10,000 different odours, but the molecular basis of this ability is poorly understood. Little is known about which odorant receptors (ORs) detect what odour compounds, and additional research is required to gain knowledge of why detection thresholds for some odorants vary 1000-fold, or more, across people. The primary purpose of this paper is to describe a research strategy for investigating the genetic basis of human odour perception. Background information on human olfaction, human genetics and the associated research approaches is presented. This is followed by a case study on cis-3-hexen-1-ol, a compound which contributes to the ‘green leaf’ odour (and flavour) in fruit, vegetables and wine. Odour detection threshold data for 48 participants were obtained using the rating R-index methodology. The ability to perceive cis-3-hexen-1-ol odour was tested for association with genetic variability on a genome-wide scale by microarray probe genotyping. A group of significant SNPs on chromosome 6 around the SNP rs9295791 was identified and these localise with a cluster of OR genes which could potentially be involved in perception of cis-3-hexen-1-ol. Further steps required to identify genes and alleles that encode the different ability to perceive cis-3-hexen-1-ol are outlined. [Copyright &y& Elsevier]

Herbivore-induced plant volatiles (HIPVs) emitted from lima bean leaves infested with the two-spotted spider mites Tetranychus urticae strongly attract the predatory mites Neoseiulus californicus. Among these HIPVs, methyl salicylate and linalool can attract the predators. Three green-leaf volatiles (GLVs) of (Z)-3-hexen-1-ol, (Z)-3- hexenyl acetate and (E)-2-hexenal, found in the odor blends from T. urticae-infested leaves and physically damaged leaves, can also attract the predators. To search for a strong predator attractant, the olfactory responses of N. californicus to each synthetic compound or their combinations were investigated in a Y-tube olfactometer. When presented a choice between a mixture of the five compounds (i.e. the two HIPVs and the three GLVs) and T. urticae-infested leaves, N. californicus did not discriminate between these odor sources. The same trend was observed when either a mixture of the two HIPVs or methyl salicylate vs. T. urticae-infested leaves were compared. In contrast, the predators preferred T. urticae- infested leaves to linalool, each of the three GLVs, or a mixture of the three GLVs. These results indicated that methyl salicylate is a strong predator attractant, and its potential attractiveness almost equaled that of the blend of HIPVs from T. urticae-infested leaves. [ABSTRACT FROM AUTHOR]

The influence of two synthetic plant volatiles on the number of male Helicoverpa armigera (Hübner 1808) (Lepidoptera: Noctuidae) caught in sex pheromone-baited traps was studied in field plots in Australia. Phenylacetaldehyde and ( Z)-3-hexenyl acetate were combined with synthetic sex pheromone in traps. Generally, most males were captured in traps baited with pheromone alone and more males were captured by the mixture containing ( Z)-3 hexenyl acetate than that containing phenylacetaldehyde. At the three concentrations studied, neither volatile synergised the activity of the pheromone. Traps baited with the plant volatiles alone caught very few moths of either sex. [ABSTRACT FROM AUTHOR]

Green-leaf volatiles are commonly emitted from mechanically and herbivore-damaged plants. Derived from the lipoxygenase pathway, these compounds may serve as attractants to predators and parasitoids of herbivores, prevent the spread of bacteria and fungi, and induce several important plant defense pathways. In Arabidopsis thaliana, the major volatile released upon mechanical wounding of the leaves is the GLV ester, ( Z)-3-hexen-1-yl acetate. We have characterized a member of the BAHD acyltransferase gene family At3g03480 which catalyzes the formation of ( Z)-3-hexen-1-yl acetate from acetyl-CoA and ( Z)-3-hexen-1-ol. The encoded acetyl CoA:( Z)-3-hexen-1-ol acetyltransferase (CHAT) has the ability to accept several medium-chain-length aliphatic and benzyl-derived alcohols, but has highest catalytic efficiency with ( Z)-3-hexen-1-ol. The highest expression of CHAT occurs in the leaves and stems. Upon mechanical damage, the ( Z)-3-hexen-1-yl acetate emission peaked after 5 min and declined to pre-damage levels after 90 min. However, CHAT gene transcript levels increased much more slowly with the highest levels detected between 3 and 6 h after wounding. An increase in CHAT enzyme activity in vitro followed the transcript increase, with levels peaking between 10 and 12 h after wounding. Plants expressing either an RNAi cassette for the CHAT gene or plants harboring a T-DNA insertion in the CHAT coding region had greatly reduced ( Z)-3-hexen-1-yl acetate emission, showing that the CHAT enzyme is responsible for the in planta production of this ester. [ABSTRACT FROM AUTHOR]