Direct Defense Research Articles

Fungal secondary metabolite dynamics in fungus–grazer interactions: novel insights and unanswered questions

In response to fungivore grazing fungi are assumed to have evolved secondary metabolite-based defense mechanisms that harm and repel grazers, and hence provide a benefit to the metabolite producer. However, since research into the ecological meaning of highly diverse fungal secondary metabolites is still in its infancy, many central questions still remain. Which components of the enormous metabolite diversity of fungi act as direct chemical defense mechanisms against grazers? Is the proposed chemical defense of fungi induced by grazer attack? Which role do volatile compounds play in communicating noxiousness to grazers? What is the relative impact of grazers and that of interactions with competing microbes on the evolution of fungal secondary metabolism? Here, I briefly summarize and discuss the results of the very few studies that have tried to tackle some of these questions by (i) using secondary metabolite mutant fungi in controlled experiments with grazers, and by (ii) investigating fungal secondary metabolism as a flexible means to adapt to grazer-rich niches.

Insights into animal and plant lectins with antimicrobial activities.

Lectins are multivalent proteins with the ability to recognize and bind diverse carbohydrate structures. The glyco -binding and diverse molecular structures observed in these protein classes make them a large and heterogeneous group with a wide range of biological activities in microorganisms, animals and plants. Lectins from plants and animals are commonly used in direct defense against pathogens and in immune regulation. This review focuses on sources of animal and plant lectins, describing their functional classification and tridimensional structures, relating these properties with biotechnological purposes, including antimicrobial activities. In summary, this work focuses on structural-functional elucidation of diverse lectin groups, shedding some light on host-pathogen interactions; it also examines their emergence as biotechnological tools through gene manipulation and development of new drugs.

The effect of methyl salicylate on the induction of direct and indirect plant defense mechanisms in poplar (Populus × euramericana ‘Nanlin 895’)

The objective of this study was to investigate the effect of different concentrations of methyl salicylate (MeSA) on direct defense and indirect defense in poplar cuttings (Populus × euramericana ‘Nanlin 895’). Four defense-related enzyme activities, such as superoxide dismutase (SOD, EC1.15.1.1), oxydoreductases peroxidase (POD, EC1.11.1.7), catalase (CAT, EC1.11.1.6), and polyphenol oxidase (PPO, EC 1.14.18.1), were measured. The results showed that the SOD activities were induced by 1.0 and 10.0 mM MeSA and the POD activities were induced by MeSA. The CAT activity was induced at low concentrations of MeSA but was inhibited by high concentrations, and the PPO activity was affected by 0.1, 1.0, and 10.0 mM MeSA. Furthermore, the volatiles were detected using gas chromatography–mass spectrometry and gas chromatography. Twenty-one volatile compounds were tentatively identified in the emissions from plant leaves. Of these volatile compounds, (Z)-3-hexen-1-ol and cis-3-hexenyl acetate emissions were the highest. (Z)-3-Nonen-1-ol, (E)-2-hexen-1-ol, 1-octanol, (E,Z)-3,6-nonadien-1-ol, β-ionone, and hexadecanamide were six compounds that were only produced after treatment by 10.0 mM MeSA. These results showed that direct and indirect defense mechanisms in poplars were induced by MeSA.

NATO SeaSparrow Program: Cooperation Based on Trust

IntroductionThe purpose of this article is to analyze NATO's program for the development and production of ship-launched short-range missiles serving the direct defence of naval vessels, known as the NATO SeaSparrow Surface Missile System (NSSMS), in terms of the mechanisms that have allowed it to function for more than 45 years, involving twelve member nations.The author of this paper will also attempt to identify the so-called good practice, on which international cooperation programs in the development and production of weapons could be based, especially in the context of the concept of Smart Defense. The production and procurement of weapons, and thus technical upgrading of the armed forces, is of interest to both civilian and military communities. The discussion comes alive especially at the time of procurement (or just an intent) of expensive military equipment. Words of opposition and disapproval of the high cost of arms borne by the taxpayer often come in times of relative peace and subjectively perceived security. However, when the relations between countries are strained and continuation of their cooperation is called into question, the public looks much more favorably at dollars spent on the armed forces.Regardless of changing public opinion, one can assume it is correct to claim that, both now and in the future, states will continue to invest in defense, primarily in order to ensure the achievement of their own goals and national-and allied-interests. An old Latin adage, Si vis pacem para bellum, which can be interpreted as no one attacks the strong, is fitting here. The main challenge of shaping the future demand for weapons is the nature of the foreseeable risks. It is necessary, therefore, to develop the technology to deter and/or to combat and defeat these threats.According to a report prepared by the Stockholm International Peace Research Institute (SIPRI) the transfer of defense technologies in 2009-2013 was about 14% higher than in 2004-2008.1 In line with the ongoing trend for several years, most European countries have gradually reduced defense spending. Significant restrictions have also been noticed in the American defense budget. The primary factors affecting the size and nature of the production of weapons include:* A significant reduction of defense spending, as well as deference of the implementation of armaments' long-term acquisition and modernization programs in Europe and the United States in connection with the financial crisis; but it is worth noting that the difficulty of maintaining high spending on armaments is nothing new, especially in democratic countries where the authorities have to reckon with the opinions of voters.* A decrease in the demand for massive equipment in the absence of prospects for military conflict on a large scale, although there is more and more talk about the need to revise the forecasts of the security environment, especially in the context of the situation in Ukraine.* An increased demand for raising the efficiency of the technology, interoperability, situational awareness, and precision in asymmetric conflicts.* Shortening the time of the development cycle for equipment through the introduction of single-purpose technology in place of complex and expensive technologies requiring long years of research.2Taking into account the need to ensure effective defense of national and Allied interests with a simultaneous decrease in defense spending, NATO members have undertaken an initiative to prevent the negative effects of the occurring trends. Smart Defense is an initiative involving the development, acquisition, and maintenance of the ability of Allied forces on the basis of cooperation between member states. It is a consequence of the financial crisis of recent years, which has caused significant cuts in defense spending, thereby aggravating the disparities in defense investments between Europe and the United States. …

Protein profiling and tps23 induction in different maize lines in response to methyl jasmonate treatment and Diabrotica virgifera infestation

Plant responses to herbivore insects involve direct and indirect defense with the production of signal molecules including jasmonic acid (JA) and its derivatives (e.g. methyl jasmonate, MeJA). In maize (Zea mays), root feeding by Diabrotica virgifera larvae activates an indirect defense mechanism, through enthomopathogenic nematodes that are recruited after Terpene Synthase 23 (tps23) upregulation and (E)-β-caryophyllene root emission.In order to gain insight into the correlation between JA signaling and response to Diabrotica attack, we analyzed tps23 expression and protein profiles in maize roots in response to MeJA treatment and insect infestation. Similar to herbivore feeding, MeJA treatment was found to increase tps23 transcript accumulation, with consistent variations for both treatments in maize lines differing in (E)-β-caryophyllene production. Analysis of root protein profiles showed specific alterations leading to the identification of three proteins that were induced by MeJA treatment. We focused on a peroxidase-like protein (Px-like) showing that the corresponding transcripts accumulated in all tested lines.Results show that exogenous application of MeJA upregulates tps23 expression and specifically alters protein patterns in maize roots. Parallel effects on tps23 transcript accumulation were observed upon hormone exposure and insect infestation in different maize lines. In contrast, Px-like transcript profiling showed differences between treatments. These results support the possible involvement of MeJA in mediating the upregulation of tps23 in response to Diabrotica attack.

Citrus leaf volatiles response to ‘Candidatus Liberibacter asiaticus’ and to its insect vector Asian citrus psyllid

Author(s): Hijaz, Faraj; Killiny, Nabil | Abstract: Plant volatiles play an important role in defending plants against insects and pathogens attack. Released volatiles from insect-damaged plants may result in direct or indirect defense against insect, and volatile accumulation in pathogen-infected plants may inhibit the movement of the pathogens within plant tissues.n However, available information about the response of citrus leaf volatiles to Asian citrus psyllids (ACP) feeding and ‘Candidatus Liberibacter asiaticus’ (Clas) infection is limited.n Here we investigate the effect of ACP feeding, Clas infection, and simultaneous attack by ACP and Clas on the volatile content of Valencia leaves.n Leaf volatiles were extracted using hexane and analyzed with gas chromatography-mass spectrometry (GC-MS).n Eighteen out ofn twenty-seven detected volatiles were induced (2 to 10-folds) in ACP-infested plants.n On the other hand, only four volatiles were induced in Clas-infected plants (d-limonene, β-phelandrene, citronellal, and undecanl).n The abundance of latter compounds was induced 4-folds in Clas-infected plants, except for limonene, which was inducedn more than 20-folds.n In addition, citrus plants that were subjected ton a simultaneous attack by ACP and Clas reduced their volatiles production compared to those that experience an attack only by ACP.n Our results suggested that insect and pathogen attack not only changes the profile of plant released volatiles, but also influences the volatile contents of the attacked plants. The result of this study might contribute to better understanding of citrus response to ACP and Clas attacks and provide more information about the relation between stored and released volatiles.

Herbivore‐induced poplar cytochrome P450 enzymes of the CYP71 family convert aldoximes to nitriles which repel a generalist caterpillar

Numerous plant species emit volatile nitriles upon herbivory, but the biosynthesis as well as the relevance of these nitrogenous compounds in plant-insect interactions remains unknown. Populus trichocarpa has been shown to produce a complex blend of nitrogenous volatiles, including aldoximes and nitriles, after herbivore attack. The aldoximes were previously reported to be derived from amino acids by the action of cytochrome P450 enzymes of the CYP79 family. Here we show that nitriles are derived from aldoximes by another type of P450 enzyme in P.trichocarpa. First, feeding of deuterium-labeled phenylacetaldoxime to poplar leaves resulted in incorporation of the label into benzyl cyanide, demonstrating that poplar volatile nitriles are derived from aldoximes. Then two P450 enzymes, CYP71B40v3 and CYP71B41v2, were characterized that produce aliphatic and aromatic nitriles from their respective aldoxime precursors. Both possess typical P450 sequence motifs but do not require added NADPH or cytochrome P450 reductase for catalysis. Since both enzymes are expressed after feeding by gypsy moth caterpillars, they are likely to be involved in herbivore-induced volatile nitrile emission in P.trichocarpa. Olfactometer experiments showed that these volatile nitriles have a strong repellent activity against gypsy moth caterpillars, suggesting they play a role in induced direct defense against poplar herbivores.

Jasmonic acid enhances plant cyanogenesis and resistance to herbivory in lima bean.

Jasmonic acid (JA) is a natural plant hormone ubiquitously distributed in plants and centrally involved in the induction of direct and indirect plant defenses. Defenses up-regulated by this hormone include trichomes--a direct, mechanical defense--and alkaloids--a direct chemical defense--as well as two indirect chemical defenses: volatile organic compounds (VOCs) and extrafloral nectar (EFN). Plant cyanogenesis--the release of toxic hydrogen cyanide (HCN) from preformed cyanogenic precursors in fruits, leaves, and seeds of many plants--is recognized as a direct, constitutive plant defensive trait, and is among the most widely distributed of all direct chemical plant defenses. The cyanogenic system in plants is composed of three parameters: The cyanogenic potential (HCNp; concentration of cyanogenic precursors), β-glucosidase activity, and cyanogenic capacity (HCNc; release of gaseous hydrogen cyanide). Here, we demonstrated that experimental application of aqueous solutions of JA ranging from 0.001 to 1.0 mmol L(-1), as well as insect herbivory significantly enhanced HCNc via the induction of β-glucosidase activity in wild lima bean (Phaseolus lunatus L.). In choice feeding trials with JA induced and damaged leaves, adult Mexican bean beetles--natural herbivores of lima bean--rejected leaves with enhanced β-glucosidase activity and HCNc. Our findings suggest that jasmonic acid plays a critical role in regulating activity of β-glucosidases, which determines the rate of cyanogenesis, and thus mediates direct plant defense against herbivores.

Response of direct or priming defense against Botrytis cinerea to methyl jasmonate treatment at different concentrations in grape berries

This study was conducted to characterize the forms of disease resistance induced by methyl jasmonate (MeJA) in harvested grape berries and to evaluate the impact of the induced resistance on fruit quality. The results showed that MeJA treatment at concentrations from 10 to 100μmol/L could effectively induce disease resistance against Botrytis cinerea and reduce disease incidence in grape berries. The induced disease resistance was tightly associated with increased H2O2 generation, enhanced expression of the defense-related gene VvNPR1.1 and accumulation of stilbene phytoalexins such as tran-resveratrol and its oligomer (trans-)ε-viniferin. The expression of the defense-related gene and synthesis of phytoalexins in 10μmol/L MeJA-treated grape berries were only significantly enhanced upon inoculating the berries with B. cinerea, whereas the 50 or 100μmol/L of MeJA treatment directly induced these defense responses. Hence, we deduce that the low concentration of MeJA (10μmol/L) triggered a priming defense mechanism, while higher concentrations of MeJA (50 or 100μmol/L) directly activated defense responses, thus enhancing disease resistance in grape berries. Moreover, the primed grape berries maintained higher contents of soluble sugars and higher DPPH radical scavenging activity and reducing power compared with those expressing direct defense responses. These results indicate that priming of defense is a cost-effective strategy to protect harvested grape berries from B. cinerea infection in terms of minimizing quality loss.

Chemical alarm in the termite Termitogeton planus (Rhinotermitidae)

Effective defense is a common characteristic of insect societies. Indeed, the occurrence of specialized defenders, soldiers, has been the first step toward eusociality in several independent lineages, including termites. Among the multitude of defensive strategies used by termite soldiers, defense by chemicals plays a crucial role. It has evolved with complexity in advanced isopteran lineages, whose soldiers are equipped with a unique defensive organ, the frontal gland. Besides direct defense against predators, competitors, and pathogens, the chemicals emitted by soldiers from the frontal gland are used as signals of alarm. In this study, we investigated the chemical composition of the defensive secretion produced by soldiers of the termite Termitogeton planus (Isoptera: Rhinotermitidae), from West Papua, and the effects of this secretion on the behavior of termite groups. Detailed two-dimensional gas chromatography/mass spectrometry analyses of the soldier defensive secretion revealed the presence of four linear and nine monoterpene hydrocarbons. Soldier head extracts, as well as synthetic mixtures of the monoterpenes found in these extracts, elicited alarm behavior in both soldiers and pseudergates. Our results suggest that the alarm is not triggered by a single monoterpene from the defensive blend, but by a multi-component signal combining quantitatively major and minor compounds.

Relatedness of Neighboring Plants Alters the Expression of Indirect Defense Traits in an Extrafloral Nectary-Bearing Plant

Different degrees of genetic relatedness among plants living in close proximity create differences in resource allocation and change the expression of defense traits. I investigated the plasticity of defense traits in young Mallotus japonicus growing with half-siblings or non-siblings, and examined direct defense traits (trichome density, pellucid dot density, and total phenolic content) and indirect defense traits (number of extrafloral nectaries, volume of extrafloral nectar, and number of food bodies) on the leaves. The plants growing with non-siblings invested proportionally more in shoots at high root biomass. Most defense traits did not differ between the two conditions, but the volume of extrafloral nectar was significantly larger with non-siblings. Although trichome density was not correlated with total plant biomass, some relationships between defense and growth differed significantly between the conditions, indicating a trade-off between plant growth and the expression of each defense trait (representing defense allocation costs). The chemical defense traits (pellucid dot density, total phenolic compounds) were negatively correlated with total biomass in plants growing with half-siblings, but were significantly positively correlated with total biomass in plants growing with non-siblings. The indirect defense traits were significantly positively correlated with total biomass in plants growing with non-siblings. These results suggest that the relatedness of neighboring plants alters their defense strategy and defense allocation costs, and that the local genetic relatedness of plants may play an important role in plant–animal interactions.

Tobacco overexpressing β-ocimene induces direct and indirect responses against aphids in receiver tomato plants

In the last decade plant-to-plant communication has received an increasing attention, particularly for the role of Volatile Organic Compounds as possible elicitors of plant defense. The role of β-ocimene as an interspecific elicitor of plant defense has been recently assessed in multitrophic systems including different plant species (Solanaceae, Poaceae, legumes) and different pest species including chewer insects and phytophagous mites. Both chewer insects and phytophagous mites are known to elicit specific plant defensive pathways which are different (at least in part) from those elicited by sap feeders. The aim of this research was to fill this gap of knowledge and to assess the role of β-ocimene as an elicitor of plant defense against aphid pests, which are sap feeders.For this purpose we used as transgenic tobacco plant releasing an odour plume enriched in this compound as emitter and a tomato plant as receiver. We selected the aphid Macrosiphum euphorbiae and its natural enemy, the parasitoid Aphidius ervi, as the targets of plant induced defense.Tomato plant defense induced by β-ocimene was assessed by characterizing the aphid performance in terms of fixing behaviour, development and reproduction (direct plant defense) and the parasitoid performance in terms of attraction towards tomato plants (indirect plant defense). The characterization of tomato response to β-ocimene was completed by the identification of Volatile Organic Compounds as released by conditioned tomato plants.Tomato plants that were exposed to the volatiles of transgenic tobacco enriched in β-ocimene resulted in less suitable for the aphids in respect to control ones (direct defense). On tomato plants “elicited” by β-ocimene we recorded: a significant lower number of aphids settled; a significant lower number newborn nymphs; a significant lower weight of aphids feeding.In addition, tomato plants “elicited” by β-ocimene resulted became more attractive towards the parasitoid A. ervi than control ones.These results could be explained at least in part by examining the composition of the Volatile Organic Compounds released by tomato plants “elicited” by β-ocimene. Indeed, we found a significantly higher release of several compounds including methyl salicylate and cis-3-hexen-1-ol. These two compounds have been demonstrated to impair aphid development and reproduction and to be involved in the attraction of the aphid parasitoid A. ervi.By considering the ubiquity of β-ocimene and its ability to regulate the communication of plants belonging 30 to different species (if not families), we concluded that this compound is an ideal candidate for new 31 strategies of sustainable control of agricultural pests.

Synergistic effects of direct and indirect defences on herbivore egg survival in a wild crucifer.

Evolutionary theory of plant defences against herbivores predicts a trade-off between direct (anti-herbivore traits) and indirect defences (attraction of carnivores) when carnivore fitness is reduced. Such a trade-off is expected in plant species that kill herbivore eggs by exhibiting a hypersensitive response (HR)-like necrosis, which should then negatively affect carnivores. We used the black mustard (Brassica nigra) to investigate how this potentially lethal direct trait affects preferences and/or performances of specialist cabbage white butterflies (Pieris spp.), and their natural enemies, tiny egg parasitoid wasps (Trichogramma spp.). Both within and between black mustard populations, we observed variation in the expression of Pieris egg-induced HR. Butterfly eggs on plants with HR-like necrosis suffered lower hatching rates and higher parasitism than eggs that did not induce the trait. In addition, Trichogramma wasps were attracted to volatiles of egg-induced plants that also expressed HR, and this attraction depended on the Trichogramma strain used. Consequently, HR did not have a negative effect on egg parasitoid survival. We conclude that even within a system where plants deploy lethal direct defences, such defences may still act with indirect defences in a synergistic manner to reduce herbivore pressure.

Attracting mutualists and antagonists: plant trait variation explains the distribution of specialist floral herbivores and pollinators on crops and wild gourds.

• Floral traits play important roles in pollinator attraction and defense against floral herbivory. However, plants may experience trade-offs between conspicuousness to pollinators and herbivore attraction. Comparative studies provide an excellent framework to examine the role of multiple traits shaping mutualist and antagonist interactions.• To assess whether putative defensive and attractive traits predict species interactions, we grew 20 different Cucurbitaceae species and varieties in the field to measure interactions with pollinators and herbivores and in the greenhouse to assess trait variation. Cucurbits are characterized by the production of cucurbitacins, bitter nonvolatile terpenoids that are effective against generalist herbivores but can attract specialist beetles. We determined whether plant traits such as cucurbitacins predict herbivore resistance and pollinator attraction using an information-theoretic approach.• Mutualists and floral antagonists were attracted to the same cucurbit varieties once they flowered. However, rather than cucurbitacin concentration, we found that the size of the flower and volatile emissions of floral sesquiterpenoids explained both pollinator and floral herbivore visitation preference across cucurbit taxa. This pattern held across cucurbit taxa and within the Cucurbita genus.• Surprisingly, floral sesquiterpenoid volatiles, which are associated with direct defense, indirect defense, and attraction, rather than defense traits such as cucurbitacins, appeared to drive interactions with both pollinators and floral herbivores across cucurbit taxa. Identifying the relevant plant traits for attraction and deterrence is important in this economically valuable crop, particularly if pollinators and floral herbivores use the same plant traits as cues.

Generalist and sticky plant specialist predators suppress herbivores on a sticky plant

Glandular trichomes are conventionally viewed as a type of direct defense against herbivores that carry indirect costs associated with the exclusion of numerous predators. We tested the hypothesis that predators are ineffective on sticky plants using a predator that is adapted to sticky plants, the harpactorine assassin bug Pselliopus spinicollis Champion, and a common surrogate generalist predator in analogous studies, the coccinellid Hippodamia convergens Guerin. We tested their top–down effects on herbivores using sticky and non-sticky races of common madia plants (Asteraceae: Madia elegans) and their native herbivores, a noctuid moth (Noctuiidae: Heliothodes diminutiva Hodges) and an aphid (Aphididae: Uroleucon madia Swain). We report that both predators were effective at reducing herbivore abundances on sticky and non-sticky plants, with greater efficacy on sticky plants.

Elevated O₃ enhances the attraction of whitefly-infested tomato plants to Encarsia formosa.

We experimentally examined the effects of elevated O3 and whitefly herbivory on tomato volatiles, feeding and oviposition preferences of whiteflies and behavioural responses of Encarsia formosa to these emissions on two tomato genotypes, a wild-type (Wt) and a jasmonic acid (JA) defence-enhanced genotype (JA-OE, 35S). The O3 level and whitefly herbivory significantly increased the total amount of volatile organic compounds (VOCs), monoterpenes, green leaf volatiles (GLVs), and aldehyde volatiles produced by tomato plants. The 35S plants released higher amount of total VOCs and monoterpene volatiles than Wt plants under O3+herbivory treatments. The feeding and oviposition bioassays showed that control plants were preferred by adult whiteflies whereas the 35S plants were not preferred by whiteflies. In the Y-tube tests, O3+herbivory treatment genotypes were preferred by adult E. Formosa. The 35S plants were preferred by adult E. formosa under O3, herbivory and O3+herbivory treatments. Our results demonstrated that elevated O3 and whitefly herbivory significantly increased tomato volatiles, which attracted E. formosa and reduced whitefly feeding. The 35S plants had a higher resistance to B. tabaci than Wt plant. Such changes suggest that the direct and indirect defences of resistant genotypes, such as 35S, could strengthen as the atmospheric O3 concentration increases.

Role of castor plant phenolics on performance of its two herbivores and their impact on egg parasitoid behaviour

Plants are reported to reconfigure their metabolism and generate secondary metabolites as a defence response towards herbivore attack. In this study we aimed to evaluate the anti-nutritive and defensive properties of phenolic compounds that were enhanced in Castor, Ricinus communis L. plant due to herbivore damage. Through HPLC studies it was observed that damage caused by two pests, Achaea janata L. and Spodoptera litura F. on the castor plant resulted in quantitative enhancement of syringic, coumaric, cinnamic and vanillic acids. These phenolic compounds showed considerable impact on insect’s feeding and their toxic nature towards the herbivores was determined by estimating three detoxification mid-gut enzymes, glutathione-s-transferase, carboxyl esterase and β-glucosidase. In the ovipositional and orientation bioassays with the egg parasitoid Trichogramma chilonis Ishii, syringic and coumaric acids had shown good kairomonal activity, thus defining a new role of these chemicals in indirect plant defence. Thus, this study demonstrates a quantitative association between plant phenolic accumulation and the elevated reproductive performance of the herbivore natural enemies, by illustrating the role of plant phenolics in both the direct and indirect induced plant defences.

Insect herbivore‐associated organisms affect plant responses to herbivory

SummaryIn nature, plants interact with many organisms and need to integrate their responses to these diverse community members. Knowledge on plant–insect relationships has accumulated rapidly during the last decades. Yet most studies on direct or indirect defences of plants against herbivory have treated herbivores as individual stressors. However, herbivores often consist of communities themselves, comprising organisms such as parasites and symbionts, which may have important effects on the herbivore phenotype, and consequently on interactions of the herbivore with its food plant. Here, we review how herbivore‐associated organisms affect plant–herbivore interactions. Organisms associated with herbivores can directly affect how a plant interacts with their herbivorous hosts, by interfering with plant signal‐transduction pathways, repressing the expression of plant defence‐related genes, or altering plant secondary metabolism. In addition, herbivore‐associated organisms can also affect plant responses indirectly by their effect on the behaviour and physiology of their herbivore host. The changes in plant phenotype that arise from herbivore‐associated organisms may subsequently affect interactions with other community members, thereby impacting community dynamics. Furthermore, herbivore‐associated organisms may act as a hidden driving force of plant–herbivore coevolution. Therefore, to understand plant–herbivore interactions it is important to realize that every single herbivorous insect constitutes a community in itself.

Salicylhydroxamic acid (SHAM) negatively mediates tea herbivore-induced direct and indirect defense against the tea geometrid Ectropis obliqua.

We investigated the effect of the SHAM treatment of tea plants on their induced defense on a tea geometrid (TG), Ectropis obliqua Prout. Treatment of tea leaves with SHAM reduced the performance of TG and TG-elicited level of the lipoxygenase gene CsiLOX1 and the putative allene oxide synthase gene CsiAOS1. The release of wound-induced green leaf volatiles (GLVs) and the expression of the hydroperoxide lyase (HPL) gene CsiHPL1 were also reduced by SHAM treatment. The negative effect of SHAM dramatically reduced the total hebivore-induced plant volatiles (HIPVs) and the attractiveness to the parasitoid wasp Apanteles sp. These results indicated that SHAM may negatively mediate tea defense response against TG by modulating the wound-induced emission of GLVs, the expression of genes involved in oxylipin pathway, and the emission of other HIPV compounds that mediate direct and indirect defenses.

Plant volatiles and the environment.

Volatile organic compounds emitted by plants represent the largest part of biogenic volatile organic compounds (BVOCs) released into our atmosphere. Plant volatiles are formed through many biochemical pathways, constitutively and after stress induction. In recent years, our understanding of the functions of these molecules has made constant and rapid progress. From being considered in the past as a mere waste of carbon, BVOCs have now emerged as an essential element of an invisible language that is perceived and exploited by the plants' enemies, the enemies of plant enemies, and neighbouring plants. In addition, BVOCs have important functions in protecting plants from abiotic stresses. Recent advances in our understanding of the role of BVOC in direct and indirect defences are driving further attention to these emissions. This special issue gathers some of the latest and most original research that further expands our knowledge of BVOC. BVOC emissions and functions in (1) unexplored terrestrial (including the soil) and marine environments, (2) in changing climate conditions, and (3) under anthropic pressures, or (4) in complex trophic communities are comprehensively reviewed. Stepping up from scientific awareness, the presented information shows that the manipulation and exploitation of BVOC is a realistic and promising strategy for agricultural applications and biotechnological exploitations.