Testing the optimal defence hypothesis for two indirect defences: extrafloral nectar and volatile organic compounds

Many plants respond to herbivory with an increased production of extrafloral nectar (EFN) and/or volatile organic compounds (VOCs) to attract predatory arthropods as an indirect defensive strategy. In this study, we tested whether these two indirect defences fit the optimal defence hypothesis (ODH), which predicts the within-plant allocation of anti-herbivore defences according to trade-offs between growth and defence. Using jasmonic acid-induced plants of Phaseolus lunatus and Ricinus communis, we tested whether the within-plant distribution pattern of these two indirect defences reflects the fitness value of the respective plant parts. Furthermore, we quantified photosynthetic rates and followed the within-plant transport of assimilates with (13)C labelling experiments. EFN secretion and VOC emission were highest in younger leaves. Moreover, the photosynthetic rate increased with leaf age, and pulse-labelling experiments suggested transport of carbon to younger leaves. Our results demonstrate that the ODH can explain the within-plant allocation pattern of both indirect defences studied.     

Plant-mediated effects in the Brassicaceae on the performance and behaviour of parasitoids

Direct and indirect plant defences are well studied, particularly in the Brassicaceae. Glucosinolates (GS) are secondary plant compounds characteristic in this plant family. They play an important role in defence against herbivores and pathogens. Insect herbivores that are specialists on brassicaceous plant species have evolved adaptations to excrete or detoxify GS. Other insect herbivores may even sequester GS and employ them as defence against their own antagonists, such as predators. Moreover, high levels of GS in the food plants of non-sequestering herbivores can negatively affect the growth and survival of their parasitoids. In addition to allelochemicals, plants produce volatile chemicals when damaged by herbivores. These herbivore induced plant volatiles (HIPV) have been demonstrated to play an important role in foraging behaviour of insect parasitoids. In addition, biosynthetic pathways involved in the production of HIPV are being unraveled using the model plant Arabidopsis thialiana. However, the majority of studies investigating the attractiveness of HIPV to parasitoids are based on experiments mainly using crop plant species in which defence traits may have changed through artificial selection. Field studies with both cultivated and wild crucifers, the latter in which defence traits are intact, are necessary to reveal the relative importance of direct and indirect plant defence strategies on parasitoid and plant fitness. Future research should also consider the potential conflict between direct and indirect plant defences when studying the evolution of plant defences against insect herbivory.     

Ecological functions of volatile organic compounds in aquatic systems

In terrestrial ecosystems, volatile organic compounds (VOCs) are widely acknowledged as an important group of infochemicals. They play a major role in pollinator attraction by terrestrial plants and as insect pheromones. Furthermore, they are the mediating agent of so-called 'tritrophic interactions'. When plants are attacked by herbivorous insects, volatile signal substances are emitted, which act as attractants for parasitoids that kill the herbivores, thereby protecting the plant from herbivory. Despite the generally acknowledged importance of VOCs in terrestrial chemical ecology, their functions in aquatic food webs are largely unknown. VOCs produced by algae and cyanobacteria are a major concern in water processing, since aquatic primary producers are the reason for regularly encountered taste and odour problems in drinking water. Only very recently, research in aquatic chemical ecology has started to investigate possible ecological functions for the production of VOCs by algae and cyanobacteria. Volatile aldehydes released by wounded cells of marine planktonic diatoms seem to act as defensive compounds against herbivorous copepods on the population level. Just recently, it was found that VOCs released from benthic algae and cyanobacteria can be utilised as food and/or habitat finding cues by aquatic invertebrates such as freshwater gastropods and nematodes. Here, I review concepts and recent experimental studies on the ecological functions of such VOCs in aquatic ecosystems. Understanding the factors that lead to the liberation of volatile compounds is an essential prerequisite to properly assessing their ecological functions. It appears that (similar to terrestrial plant-herbivore interactions) VOCs can also play a steering role for both attraction and defence in aquatic ecosystems.     

Health risk assessment of volatile organic compounds in urban areas

The atmosphere is the first medium containing hazardous compounds entering the living environment. Metropolitan areas contain many industrial complex areas with high emissions of volatile organic compounds (VOCs), and consequently also large-scale exposure groups. As respiration is the most important part of the human exposure pathway, the atmosphere should be treated with greater importance than other media. It is therefore very important to monitor the emission of hazardous air pollutants (HAPs) and measure the concentration of VOCs in the atmosphere of such areas. It is essential to establish basic measures in order to protect public health as part of overall national safety management. This study utilized the national air pollution monitoring network data from Seoul, Incheon, and Gyeonggi, and investigated the differences in risk levels for humans considering various factors of the receptors, including gender and age. A total of 13 VOCs were categorized into carcinogens and noncarcinogens for risk assessment. The carcinogens 1,3-butadiene and benzene demonstrated a high level of cancer risk, ranging between 10^?4 and 10^?6, respectively. Noncarcinogens did not exceed Hazard Quotient (HQ) 1 in any area. The results will serve as important references for managing urban air environments and setting air quality standards.     

Biofiltration of a mixture of volatile organic compounds on granular activated carbon

The performance of a biofilter packed with Active Carbon (AC) was evaluated. The effluent (alcohol, ketones, esters, aromatic and chlorinated compounds) treated was a representative mixture of most common industrial emissions. To achieve a better knowledge of multicomponent adsorption mechanisms, and to underline the interest of inoculating AC, a control abiotic humidified filter had been operated in the same conditions as the biofilter. For a load of 110 g VOC m(-3) AC h(-1), after 55 days of operation, the removal efficiency was higher in the biotic than in the abiotic filter (85% vs 55%, respectively). Moreover, in the biofilter, at steady state, the elimination of all compounds was almost complete except for chlorinated compounds and p-xylene (removal efficiency of 25% and 64%, respectively). The microbial colonization of AC involved a decrease of the adsorption sites accessibility and enhanced the treatment of VOCs (volatile organic compounds) having a lower affinity for activated carbon. Moreover, while aromatic compounds and MIBK were eliminated along the overall height of the biofilter, pollutants with reduced affinity for AC, such as methanol, acetone, and halogenated compounds were only treated on the second half of the reactor. Thus, the affinity for activated carbon was an important parameter controlling the biodegradation process. Nevertheless, the use of AC as packing material in biofilters treating complex mixtures of VOCs is limited. Actually, similar removal efficiency could be reached, in the same conditions, for a biofilter packed with granular peat. Furthermore, for the biofilter packed with AC, the column height necessary to remove biodegradable compounds, with reduced affinity for the support, was important.     

The effects of herbivore-induced plant volatiles on interactions between plants and flower-visiting insects

Plants are faced with a trade-off between on the one hand growth, development and reproduction and on the other hand defence against environmental stresses. Yet, research on insect-plant interactions has addressed plant-pollinator interactions and plant-attacker interactions separately. Plants have evolved a high diversity of constitutive and induced responses to attack, including the systemic emission of herbivore-induced plant volatiles (HIPVs). The effect of HIPVs on the behaviour of carnivorous insects has received ample attention for leaf-feeding (folivorous) species and their parasitoids and predators. Here, we review whether and to what extent HIPVs affect the interaction of plants in the flowering stage with mutualistic and antagonistic insects. Whereas the role of flower volatiles in the interactions between plants and insect pollinators has received increased attention over the last decade, studies addressing both HIPVs and pollinator behaviour are rare, despite the fact that in a number of plant species herbivory is known to affect flower traits, including size, nectar secretion and composition. In addition, folivory and florivory can also result in significant changes in flower volatile emission and in most systems investigated, pollinator visitation decreased, although exceptions have been found. Negative effects of HIPVs on pollinator visitation rates likely exert negative selection pressure on HIPV emission. The systemic nature of herbivore-induced plant responses and the behavioural responses of antagonistic and mutualistic insects, requires the study of volatile emission of entire plants in the flowering stage. We conclude that approaches to integrate the study of plant defences and pollination are essential to advance plant biology, in particular in the context of the trade-off between defence and growth/reproduction.     

Effects of aphid herbivory on volatile organic compounds of Artemisia annua and Chrysanthemum morifolium

We showed the effect of aphid infesting on the volatile organic compounds (VOCs) emitted by the infested Artemisia annua and Chrysanthemum morifolium cultivar ‘Nan nong hong feng’ plants by using headspace solid-phase microextraction (HS-SPME) method combined with gas chromatography mass spectrometry (GC–MS). In olfactometer bioassay experiment, aphids showed a preference for the odour of both healthy and infested chrysanthemum, while we found an opposite result in A. annua. Aphids tend to healthy plants compared with the infested, and the phenomenon became obvious with time. Different extracts were tested with the healthy plants and aphid infested plants. Eucalyptol, β-caryophyllene, (E)-β-farnesene, and germacrene D were released as the major constituents in both species. After aphid infesting, we observed a great increase in artemisia ketone and (E)-β-farnesene and a decrease in germacrene D in A. annua; comparatively, eucalyptol, isoborneol and β-caryophyllene increased in chrysanthemum. Combined with the GC–MS data and olfactometer bioassay results we concluded that (E)-β-farnesene and artemisia ketone emitted from A. annua might act as a potential volatile compound to resist aphids, and the two compounds would be useful for future ecological control of aphid in chrysanthemum cultivation.     

受害兴安落叶松挥发物混合物对林间昆虫的诱集

植株释放的挥发物能够调节寄主、害虫及天敌三者关系,是植物与害虫协同进化的产物。兴安落叶松挥发物种类虽已确定,但这些物质,特别是受害植株所释放的挥发物对林间昆虫的影响尚不清楚。本研究在3种林龄林分内设置携带受害兴安落叶松枝叶挥发物的诱捕器以考察其对林间昆虫的影响。结果表明挥发物混合物对昆虫诱集效果良好,特别是对天牛类及叶甲类。林龄并未对挥发物的引诱效果造成显著影响,可能与本研究年龄组的划分标准有关。文章指出应将诱集昆虫群落进一步细化,并对关键种或类群进行电生理方面的深入探讨。本文也指出了受害兴安落叶松挥发物混合物发展为植物源农药的前景。     

Production and effects of volatile organic compounds during interspecific interactions

Competition between mycelia of saprotrophic cord-forming basidiomycetes occurs both within dead woody resources and in the soil-litter interface, and involves a variety of antagonistic mechanisms including the production of volatile organic compounds (VOCs). The antagonistic potential of VOC profiles from interactions in wood blocks and in soil microcosms was assessed using shared headspace experiments, and the profile of VOCs emitted over the course of interactions elucidated using solid phase microextraction (SPME) with gas chromatography-mass spectrometry (GC–MS). Quantitative and qualitative changes in VOC production occurred in interactions compared to self-pairing controls, with different VOC profiles from fungi growing in wood blocks compared to soil trays. There were both stimulatory and inhibitory effects of VOCs on target mycelial extension rate, hyphal coverage and fractal dimension. VOC-mediated effects were greater in self-pairing controls compared to interactions, and differed depending on the substratum in which the VOC-producing fungi were growing.     

The biochemistry of homoterpenes--common constituents of floral and herbivore-induced plant volatile bouquets

Volatile organic compounds emitted by plants mediate a variety of interactions between plants and other organisms. The irregular acyclic homoterpenes, 4,8-dimethylnona-1,3,7-triene (DMNT) and 4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT), are among the most widespread volatiles produced by angiosperms with emissions from flowers and from vegetative tissues upon herbivore feeding. Special attention has been placed on the role of homoterpenes in attracting parasitoids and predators of herbivores and has sparked interest in engineering homoterpene formation to improve biological pest control. The biosynthesis of DMNT and TMTT proceeds in two enzymatic steps: the formation of the tertiary C₁₅-, and C₂₀-alcohols, (E)-nerolidol and (E,E)-geranyl linalool, respectively, catalyzed by terpene synthases, and the subsequent oxidative degradation of both alcohols by a single cytochrome P450 monooxygenase (P450). In Arabidopsis thaliana, the herbivore-induced biosynthesis of TMTT is catalyzed by the concerted activities of the (E,E)-geranyllinalool synthase, AtGES, and CYP82G1, a P450 of the so far uncharacterized plant CYP82 family. TMTT formation is in part controlled at the level of AtGES expression. Co-expression of AtGES with CYP82G1 at wound sites allows for an efficient conversion of the alcohol intermediate. The identified homoterpene biosynthesis genes in Arabidopsis and related genes from other plant species provide tools to engineer homoterpene formation and to address questions of the regulation and specific activities of homoterpenes in plant-herbivore interactions.     

Polycyclic aromatic hydrocarbons and volatile organic compounds in biochar and biochar‐amended soil: a review

Residual pollutants including polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), and carbon (aceous) nanoparticles are inevitably generated during the pyrolysis of waste biomass and remain on the solid coproduct called biochar. Such pollutants could have adverse effects on the plant growth as well as microbial community in soil. Although biochar has been proposed as a ‘carbon negative strategy’ to mitigate the greenhouse gas emissions, the impacts of its application with respect to long‐term persistence and bioavailability of hazardous components are not clear. Moreover, the co‐occurrence of low molecular weight VOCs with PAHs in biochar may exert further phytotoxic effects. This review describes the basic need to unravel key mechanisms driving the storage vs. emission of these organics and the dynamics between the sorbent (biochar) and soil microbes. Moreover, there is an urgent need for standardized methods for quantitative analysis of PAHs and VOCs in biochar under environmentally relevant conditions. This review is also extended to cover current research gaps including the influence of biochar application on the short‐ and long‐term fate of PAHs and VOCs and the proper control tactics for biochar quality and associated risk.     

大花栀子植物挥发物成分测定及其日变化分析

为探究大花栀子植物挥发物成分组成及其一天内早、中、晚的差异,采用热脱附气质联用技术对其进行香气成分的分析。结果表明:全天从其花朵中共鉴定出62种成分,主要为萜烯类、酯类、醇类物质,且不同时间其成分差异显著,如早、中、晚3个时间段,β-蒎烯相对含量分别为1.93%、1.69%、8.81%,顺式-β-罗勒烯分别为28.22%、4.35%、16.47%。3-蒈烯(3.45%)、异丁子香酚(0.21%)等只在早上检出;月桂烯(0.38%)、伞花烃(2.46%)等只在晚上检出;芳樟醇、金合欢烯等在早上和午间两个时间段相对含量较高,而在晚上却未检测出。从植物VOCs角度结合其日变化动态,为大花栀子园林配置及其综合开发利用提供理论依据。     

Source analysis and health risk-assessment of ambient volatile organic compounds in automobile manufacturing processes

Abstract

The sources and process-specific emission of volatile organic compounds (VOCs) from an automobile manufacturing plant in Beijing, China were explored and monitored to assess the health risk from VOCs to workers of the automobile manufacturing plant. Eleven VOCs were detected in the air samples collected from the 12 working posts of five workshops of the automobile manufacturing plant using a meteorological chromatographic analytical method. The health risks exposed to VOCs were assessed using the probabilistic risk-assessment method, and the sensitivity and uncertainty analysis were conducted using the Monte Carlo simulation method. The results showed that VOCs mainly originated from the use and volatilization of chemical raw materials. The total carcinogenic risks were large owing to the high concentrations of benzene and ethylbenzene in various processes, suggesting a definite risk. The total non-carcinogenic risk in the paint shop was the highest, and the topcoat post, mixing paint post and basecoat post contributed to more than 70% of the total risk of this workshop. Exposure duration and concentration of VOCs had a greater impact on the health risk. These research findings may provide scientific basis for policy toward improving the health status of workers in automobile manufacturing enterprise in China.     

Exploiting volatile organic compounds in crop protection: A systematic review of 1-octen-3-ol and 3-octanone

The 21st century has brought new challenges to the agri-food industry due to population growth, global warming, and greater public awareness of environmental issues. Ensuring global food security for future generations is crucial. However, pests, weeds, and diseases still significantly contribute to crop losses, and the availability of effective conventional synthetic pesticides is decreasing. To address this, new and diverse pest management tools are needed. One pest management tool showing potential for invertebrate pest management is the exploitation of volatile organic compounds (VOCs)—in particular, the compounds 1-octen-3-ol and 3-octanone. This review aims to explore the extent to which 1-octen-3-ol and 3-octanone show potential in the future management of invertebrate crop and animal pests. A significant increase in the rate of publication of literature on the use of 1-octen-3-ol and 3-octanone in crop protection since 2018 is identified by this review, therefore, showing the potential importance of these compounds for use in future pest management. This review also identifies key interactions between naturally occurring biosynthesised 1-octen-3-ol and 3-octanone, and a range of invertebrate targets. Many of these interactions with key crop pests are sourced from the taxonomic families Lamiaceae, Fabaceae, and Trichomaceae. However, analysis of the practical application of these sources in an integrated pest management programme identifies clear limitations with the use of naturally occurring biosynthesised 1-octen-3-ol and 3-octanone. Rather, future focus should be placed on the development and exploitation of synthesised nature identical 1-octen-3-ol and 3-octanone for use as a biopesticide product. Overall, 1-octen-3-ol and 3-octanone show potential for exploitation in future crop protection, being abundant in source and diversity of invertebrate interactions. However, their use as a naturally occurring biosynthesised chemical is likely not practical for direct implementation in crop protection. Rather, focus should be placed on the development and exploitation of synthesised nature identical variants of these compounds for use as a biopesticide.     

In situ modification of herbivore-induced plant odors: a novel approach to study the attractiveness of volatile organic compounds to parasitic wasps

Many parasitic wasps (parasitoids) exploit volatile organic compounds (VOCs) emitted by herbivore-infested plants in order to locate their hosts, but it remains largely unknown which specific compounds within the volatile blends elicit the attractiveness to parasitoids. One way of studying the importance of specific VOCs is to test the attractiveness of odor blends from which certain compounds have been emitted. We used this approach by testing the attraction of naive and experienced females of the two parasitoids Cotesia marginiventris and Microplitis rufiventris to partially altered volatile blends of maize seedlings (Zea mays var. Delprim) infested with Spodoptera littoralis larvae. Adsorbing filter tubes containing carbotrap-C or silica were installed in a four-arm olfactometer between the odor source vessels and the arms of the olfactometer. The blends breaking through were tested for chemical composition and attractiveness to the wasps. Carbotrap-C adsorbed most of the sesquiterpenes, but the breakthrough blend remained attractive to naive C. marginiventris females. Silica adsorbed only some of the more polar VOCs, but this essentially eliminated all attractiveness to naive C. marginiventris, implying that among the adsorbed compounds there are some that play key roles in the attraction. Unlike C. marginiventris, M. rufiventris was still attracted to the latter blend, showing that parasitoids with a comparable biology may employ different strategies in their use of plant-provided cues to locate hosts. Results from similar experiments with modified odor blends of caterpillar-infested cowpea (Vigna unguiculata) indicate that key VOCs in different plant species vary greatly in quality and/or quantity. Finally, experienced wasps were more strongly attracted to a specific blend after they perceived the blend while ovipositing in a host. Considering the high number of distinct adsorbing materials available today, this in situ modification of complex volatile blends provides a new and promising approach pinpointing on key attractants within these blends. Advantages and disadvantages compared to other approaches are discussed.     

A study on volatile organic compounds (VOCs) produced by tropical ascomycetous yeasts

As a part of a program aiming at the selection of strains which might be of interest as sources of natural flavouring molecules, the production of volatile organic compounds (VOCs) by 98 ascomycetous yeast strains (representative of 40 species belonging to 12 genera) isolated from tropical environments was investigated. Volatiles produced were sampled by means of headspace solid-phase microextraction (SPME) and the compounds were analysed and identified by gas chromatography–mass spectroscopy (GC–MS). The VOCs produced were found to be alcohols (amyl alcohol and isoamyl alcohol), aldehydes (2-methyl-2-hexenal and 2-isopropyl-5-methyl-2-hexenal) and esters (ethyl isobutyrate, isobutyl acetate, isoamyl acetate, 2-methylbutyl acetate, ethyl isovalerate, isoamyl propionate and phenylmethyl acetate). Differences in VOC profiles were used to cluster the yeast strains into 25 VOC phenotypes. The different frequency of VOC phenotypes in three specific habitats was correlated to the divergent environmental conditions, possibly affecting the selection of specific yeasts. From a biotechnological viewpoint, this study reveals the potentiality of ascomycetous yeasts isolated from tropical environments as a promising source of VOCs relevant in food and fragrance industry. This revised version was published online in June 2006 with corrections to the Cover Date.     

Induced production of extrafloral nectar in intact lima bean plants in response to volatiles from spider mite-infested conspecific plants as a possible indirect defense against spider mites

We found that intact lima bean plants increased the secretion of extrafloral nectar (EFN) after exposure to Tetranychus urticae-induced plant volatiles. Predatory mites, Phytoseiulus persimilis, dispersed more slowly from an exposed intact plant than from a control plant (plant exposed to volatiles from intact conspecific). The predators also dispersed more slowly from those plants that were provided with extra EFN than from untreated plants. We further show that EFN was a potential alternative food source for P. persimilis. From these results, we concluded that increased EFN was involved in the slow dispersal of P. persimilis from the plants exposed to herbivore-induced plant volatiles. Our data suggest that the increase of EFN in an HIPV-exposed intact plant could be an induced indirect defense against spider mites.     

Probabilistic health risk of volatile organic compounds (VOCs): Comparison among different commuting modes in Guangzhou,China

Probabilistic risk assessment was conducted to evaluate health risks caused by eight volatile organic compounds (VOCs) (benzene, toluene, xylene, ethylbenzene, styrene, formaldehyde, acetaldehyde, and acrolein) in five commuting modes (car, air-conditioned bus, non-air-conditioned bus, subway, and bicycle) in Guangzhou. Monte Carlo method and the contribution to variance method were applied to obtain the more scientific evaluation results and the more influential variables. The results revealed that the carcinogenic risk of air-conditioned bus and car were the highest, followed by bicycle, non-air-conditioned bus, and subway. The probability of the risk exceeding 10^?6 was approximately 90%, 62%, 62%, 91%, and 92%, respectively. Moreover, the noncarcinogenic risk of air-conditioned bus and car were the highest, followed by non-air-conditioned bus, bicycle, and subway. It indicated that subway, non-air-conditioned bus, and bicycle are better commuting choices for city dwellers to reduce health risks and alleviate traffic pressure. Formaldehyde, benzene, and acrolein contribute to a significant proportion in health risk and should be the prior controlled organic pollutants. Sensitivity analysis suggests that exposure time is the most influential parameter for carcinogenic and noncarcinogenic risk, followed by concentrations of VOCs in air and exposure duration.