How rainfall, relative humidity and temperature influence volatile emissions from apple trees in situ

Developing Oak Buds Produce Volatile Emissions in Response to Herbivory by Freshly Hatched Caterpillars

Plant responses to damage by insectivorous herbivores are well-documented in mature leaves. The resulting herbivore-induced plant volatiles (HIPVs) protect the plant by attracting carnivorous arthropods and even some insectivorous vertebrates, to parasitize or consume the plant invaders. However, very little is known about plant production of HIPVs in developing buds, particularly when herbivorous insects are too small to be considered a prey item. It is additionally unclear whether plants respond differently to generalist and specialist chewing insects that overlap in distribution. Therefore, we compared HIPV production of Downy oak (Quercus pubescens Willd.) buds infested with freshly hatched caterpillars of Tortrix viridana (specialist) and Operophtera brumata (generalist), against uninfested buds. Of the compounds identified in both years of the experiment, we found that (Z)-hex-3-enyl acetate, (E)-β-ocimene, acetophenone, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), methyl salicylate, α-copaene, α-humulene, (E)-caryophyllene, and (E,E)-α-farnesene appeared to be higher in infested buds compared to controls. We found no difference in HIPV production between the specialist and the generalist herbivores. Production of HIPVs was also associated with leaf damage, with higher HIPV production in more severely attacked buds. Thus, our study shows that oak trees already start responding to insect herbivory before leaves are developed, by producing compounds similar to those found in damaged mature leaves. Future work should focus on how Downy oak may benefit from initiating alarm cues at a time when carnivorous arthropods and insectivorous vertebrates are unable to use herbivorous insects as host or food.

Drought induces moderate, diverse changes in the odour of grassland species

Plants react to drought stress with numerous changes including altered emissions of volatile organic compounds (VOC) from leaves, which provide protection against oxidative tissue damage and mediate numerous biotic interactions. Despite the share of grasslands in the terrestrial biosphere, their importance as carbon sinks and their contribution to global biodiversity, little is known about the influence of drought on VOC profiles of grassland species. Using coupled gas chromatography-mass spectrometry, we analysed the odorants emitted by 22 European grassland species exposed to an eight-week-lasting drought treatment (DT; 30% water holding capacity, WHC). We focused on the odorants emitted during the light phase from whole plant shoots in their vegetative stage. Emission rates were standardised to the dry weight of each shoot. Well-watered (WW) plants (70% WHC) served as control. Drought-induced significant changes included an increase in total emission rates of plant VOC in six and a decrease in three species. Diverging effects on the number of emitted VOC (chemical richness) or on the Shannon diversity of the VOC profiles were detected in 13 species. Biosynthetic pathways-targeted analyses revealed 13 species showing drought-induced higher emission rates of VOC from one, two, three, or four major biosynthetic pathways (lipoxygenase, shikimate, mevalonate and methylerythritol phosphate pathway), while six species exhibited reduced emission rates from one or two of these pathways. Similarity trees of odorant profiles and their drought-induced changes based on a biosynthetically informed distance metric did not match species phylogeny. However, a phylogenetic signal was detected for the amount of terpenoids released by the studied species under WW and DT conditions. A comparative analysis of emission rates of single compounds released by WW and DT plants revealed significant VOC profile dissimilarities in four species only. The moderate drought-induced changes in the odorant emissions of grassland species are discussed with respect to their impact on trophic interactions across the food web. (294 words).

The Influences of Rainfall Intensity and Timing on the Assemblage of Dung Beetles and the Rate of Dung Removal in an Alpine Meadow

Changes in precipitation patterns, including rainfall intensity and rainfall timing, have been extensively demonstrated to impact biological processes and associated ecosystem functions. However, less attention has been paid to the effects of rainfall intensity and rainfall timing on the assembly of detritivore communities and the decomposition rate of detritus such as animal dung. In a grazed alpine meadow on the eastern Qinghai-Tibet Plateau, we conducted a manipulative experiment involving two levels of rainfall intensity (heavy rainfall, 1000 mL/5 min; light rainfall, 100 mL/5 min) and five levels of rainfall timing (0, 2, 4, 24, and 48 h after yak dung deposition). The aim was to determine the effects of rainfall intensity, timing, and their interaction on the assemblage of dung beetles and dung removal rate during the early stage (i.e., 96 h after yak dung deposition) of dung decomposition. Light rainfall significantly increased species richness in the treatment of 48 h after dung pats were deposited. Heavy rainfall significantly decreased beetle abundance in both the 0 h and 48 h treatments while light rainfall had no effect on beetle abundance. Dung mass loss was significant lower in the 2 h treatment compared to other treatments regardless of rainfall intensity. The structural equation model further revealed that the species richness of dung beetles and dung mass loss were significantly affected by rainfall timing but not by rainfall intensity. However, no significant relationships were observed between any variables examined. These findings suggest that changes in precipitation patterns can influence both the structure of dung beetles and the rate of dung decomposition but may also decouple their relationship under a certain circumstance. Therefore, it is crucial to pay greater attention to fully understand local variability between the biological processes and ecosystem functions within a global climate change scenario.

Chemical variability of volatile concentrate from two Ipomoea L. species within a seasonal gradient

In the present study, are extracted volatile concentrate from Ipomoea asarifolia Poir. and Ipomoea setifera (Desr.) Roem. & Schult. in five-month seasonal gradient. The flowers were subjected to simultaneous distillation - extraction (SDE). The chemical composition of the volatile concentrate was determined by gas chromatography (CG/MS) and (CG-FID). Principal Component Analysis (PCA) and Hierarchical Clustering Analysis (HCA) were performed with the chemical constituents. It was observed that the chemical composition of I. asarifolia varied more with seasonality in relation to the species I. setifera. Furthermore, there is a possibility that germacrene D and α-copaene, the main components of the variation volatile of I. asarifolia and with higher concentrations in the rainy months, have ecological importance, attracting specific pollinators for the rainy season. This is the first study to report the chemical composition of the volatile compounds of I. asarifolia and I. setifera along a seasonal gradient.

Genetic-environment interactions and climatic variables effect on bean physical characteristics and chemical composition of Coffea arabica

BACKGROUND

The effects of the environment and genotype in the coffee bean chemical composition were studied using nine trials covering an altitudinal gradient [600-1100 m above sea level (a.s.l.)] with three genotypes of Coffea arabica in the northwest mountainous region of Vietnam. The impacts of the climatic conditions on bean physical characteristics and chemical composition were assessed.

RESULTS

We showed that the environment had a significant effect on the bean density and on all bean chemical compounds. The environment effect was stronger than the genotype and genotype-environment interaction effects for cafestol, kahweol, arachidic (C20:0), behenic acid (C22:0), 2,3-butanediol, 2-methyl-2-buten-1-ol, benzaldehyde, benzene ethanol, butyrolactone, decane, dodecane, ethanol, pentanoic acid, and phenylacetaldehyde bean content. A 2 °C increase in temperature had more influence on bean chemical compounds than a 100 mm increase in soil water content. Temperature was positively correlated with lipids and volatile compounds. With an innovative method using iterative moving averages, we showed that correlation of temperature, vapour pressure deficit (VPD) and rainfall with lipids and volatiles was higher between the 10th and 20th weeks after flowering highlighting this period as crucial for the synthesis of these chemicals. Genotype specific responses were evidenced and could be considered in future breeding programmes to maintain coffee beverage quality in the midst of climate change.

CONCLUSION

This first study of the effect of the genotype-environment interactions on chemical compounds enhances our understanding of the sensitivity of coffee quality to genotype environment interactions during bean development. This work addresses the growing concern of the effect of climate change on speciality crops and more specifically coffee. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Open field trials of food-grade gum in California and Oregon as a behavioral control for Drosophila suzukii Matsumura (Diptera: Drosophilidae)

The invasion of Drosophila suzukii, spotted-wing drosophila, across Europe and the US has led to economic losses for berry and cherry growers, and increased insecticide applications to protect fruit from damage. Commercial production relies heavily on unsustainable use of conventional toxic insecticides. Non-toxic insecticide strategies are necessary to alleviate the disadvantages and non-target impacts of toxic conventional insecticides and improve Integrated Pest Management (IPM). A novel food-grade gum deployed on dispenser pads (GUM dispensers) was evaluated to mitigate D. suzukii crop damage in five commercial crops and nine locations. Trials were conducted at a rate of 124 dispensers per hectare in cherry, wine grape, blueberry, raspberry, and blackberry in California and Oregon, USA during 2019 and 2020. The majority of trials with the food-grade gum resulted in a reduction of D. suzukii egg laying in susceptible fruit. In some cases, such damage was reduced by up to 78%. Overall, results from our meta-analysis showed highly significant differences between GUM treatments and the untreated control. Modeling simulations suggest a synergistic reduction of D. suzukii damage when used in combination with Spinosad (Entrust SC) insecticide. These data illustrate commercial value of this tool as a sustainable alternative to manage D. suzukii populations within a systems approach.

Dynamic environmental interactions shaped by vegetative plant volatiles

Covering: up to November 2022Plants shape terrestrial ecosystems through physical and chemical interactions. Plant-derived volatile organic compounds in particular influence the behavior and performance of other organisms. In this review, we discuss how vegetative plant volatiles derived from leaves, stems and roots are produced and released into the environment, how their production and release is modified by abiotic and biotic factors, and how they influence other organisms. Vegetative plant volatiles are derived from different biosynthesis and degradation pathways and are released via distinct routes. Both biosynthesis and release are regulated by other organisms as well as abiotic factors. In turn, vegetative plant volatiles modify the physiology and the behavior of a wide range of organisms, from microbes to mammals. Several concepts and frameworks can help to explain and predict the evolution and ecology of vegetative plant volatile emission patterns of specific pathways: multifunctionality of specialized metabolites, chemical communication displays and the information arms race, and volatile physiochemistry. We discuss how these frameworks can be leveraged to understand the evolution and expression patterns of vegetative plant volatiles. The multifaceted roles of vegetative plant volatiles provide fertile grounds to understand ecosystem dynamics and harness their power for sustainable agriculture.

Effect of the biosynthesis of the volatile compound phenylacetaldehyde on chloroplast modifications in tea (Camellia sinensis) plants

Plant volatile compounds have important physiological and ecological functions. Phenylacetaldehyde (PAld), a volatile phenylpropanoid/benzenoid, accumulates in the leaves of tea (Camellia sinensis) plants grown under continuous shading. This study was conducted to determine whether PAld production is correlated with light and to elucidate the physiological functions of PAld in tea plants. Specifically, the upstream mechanism modulating PAld biosynthesis in tea plants under different light conditions as well as the effects of PAld on chloroplast/chlorophyll were investigated. The biosynthesis of PAld was inhibited under light, whereas it was induced in darkness. The structural gene encoding aromatic amino acid aminotransferase 1 (CsAAAT1) was expressed at a high level in darkness, consistent with its importance for PAld accumulation. Additionally, the results of a transcriptional activation assay and an electrophoretic mobility shift assay indicated CsAAAT1 expression was slightly activated by phytochrome-interacting factor 3-2 (CsPIF3-2), which is a light-responsive transcription factor. Furthermore, PAld might promote the excitation of chlorophyll in dark-treated chloroplasts and mediate electron energy transfer in cells. However, the accumulated PAld can degrade chloroplasts and chlorophyll, with potentially detrimental effects on photosynthesis. Moreover, PAld biosynthesis is inhibited in tea leaves by red and blue light, thereby decreasing the adverse effects of PAld on chloroplasts during daytime. In conclusion, the regulated biosynthesis of PAld in tea plants under light and in darkness leads to chloroplast modifications. The results of this study have expanded our understanding of the biosynthesis and functions of volatile phenylpropanoids/benzenoids in tea leaves.

Volatile Profiling of Magnolia champaca Accessions by Gas Chromatography Mass Spectrometry Coupled with Chemometrics

Magnolia champaca (L.) Baill. ex Pierre of family Magnoliaceae, is a perennial tree with aromatic, ethnobotanical, and medicinal uses. The M. champaca leaf is reported to have a myriad of therapeutic activities, however, there are limited reports available on the chemical composition of the leaf essential oil of M. champaca. The present study explored the variation in the yield and chemical composition of leaf essential oil isolated from 52 accessions of M. champaca. Through hydrodistillation, essential oil yield was obtained, varied in the range of 0.06 ± 0.003% and 0.31 ± 0.015% (v/w) on a fresh weight basis. GC-MS analysis identified a total of 65 phytoconstituents accounting for 90.23 to 98.90% of the total oil. Sesquiterpene hydrocarbons (52.83 to 65.63%) constituted the major fraction followed by sesquiterpene alcohols (14.71 to 22.45%). The essential oils were found to be rich in β-elemene (6.64 to 38.80%), γ-muurolene (4.63 to 22.50%), and β-caryophyllene (1.10 to 20.74%). Chemometrics analyses such as PCA, PLS-DA, sPLS-DA, and cluster analyses such as hierarchical clustering, i.e., dendrogram and partitional clustering, i.e., K-means classified the essential oils of M. champaca populations into three different chemotypes: chemotype I (β-elemene), chemotype II (γ-muurolene) and chemotype III (β-caryophyllene). The chemical polymorphism analyzed in the studied populations would facilitate the selection of chemotypes with specific compounds. The chemotypes identified in the M. champaca populations could be developed as promising bio-resources for conservation and pharmaceutical application and further improvement of the taxa.

Elicitor-Induced VOC Emission by Grapevine Leaves: Characterisation in the Vineyard

The present study is aimed at determining whether leaf volatile organic compounds (VOCs) are good markers of the grapevine response to defence elicitors in the field. It was carried out in two distinct French vineyards (Burgundy and Bordeaux) over 3 years. The commercial elicitor Bastid^® (Syngenta, Saint-Sauveur, France) (COS-OGA) was first used to optimise the VOCs’ capture in the field; by bagging stems together with a stir bar sorptive extraction (SBSE) sensor. Three elicitors (Bastid^®, copper sulphate and methyl jasmonate) were assessed at three phenological stages of the grapevines by monitoring stilbene phytoalexins and VOCs. Stilbene production was low and variable between treatments and phenological stages. VOCs—particularly terpenes—were induced by all elicitors. However, the response profiles depended on the type of elicitor, the phenological stage and the vineyard, and no sole common VOC was found. The levels of VOC emissions discriminated between weak (Bastid^® and copper sulphate) and strong (methyl jasmonate) inducers. Ocimene isomers were constitutively present in the overall blends of the vineyards and increased by the elicitors’ treatments, whilst other VOCs were newly released throughout the growing seasons. Nonetheless, the plant development and climate factors undoubtedly influenced the release and profiles of the leaf VOCs.

Ozone Treatment Increases the Release of VOC from Barley, Which Modifies Seed Germination

Ozone is widely used to control pests in grain and has an impact on seed germination. The germination process involves multiple secondary metabolites, such as volatile organic compounds (VOCs), which are altered under ozone treatment. Here, an optimized solid-phase microextraction coupled with gas chromatography-mass spectrometry was implemented to explore changes in VOCs from barley seeds under ozone treatment. The data demonstrated that barley released both a greater variety and quantity of VOCs under oxidative stress. The number of alcohols and hydrocarbons gradually decreased, whereas aldehydes and organic acids markedly increased with increasing ozone treatment time. Acetic acid was identified as a potential ozone stress-specific marker. Furthermore, the dosage-dependent function of acetic acid on the germination of barley was verified, namely, a low dosage of acetic acid increased the germination and vice versa. This study provided new insights into how barley responds to ozone treatment and highlighted the role of acetic acid in seed germination.

GC-MS Metabolite and Transcriptome Analyses Reveal the Differences of Volatile Synthesis and Gene Expression Profiling between Two Apple Varieties

Aroma is a key quality attribute of apples, making major contributions to commercial value and consumer choice. However, the mechanism underlying molecular regulation of aroma formation genes and transcription factors remains poorly understood in apples. Here, we investigated the aroma volatile profiles of two apple varieties with distinctive flavors using headspace solid-phase microextraction (HS-SPME) combined with gas chromatography–mass spectrometry (GC-MS). A total of 35 volatile compounds were identified in Granny Smith and Jonagold apples. Aldehydes were the most abundant volatiles contributing to the aroma in Granny Smith apple while esters were the dominant volatile compounds in Jonagold apple. In order to know more about the expression levels of aroma-related genes involved in the metabolic pathways, transcriptome sequencing of these two different apple varieties was conducted utilizing the Illumina platform. In total, 94 differentially expressed genes (DEGs) were found in the fatty acid metabolism, amino acid metabolism, the mevalonate pathway and phenylpropanoid pathway. Furthermore, compared to the Granny Smith apple, the expression of multiple genes and transcription factors were upregulated in the Jonagold apple, which might play important roles in the synthesis of aroma volatile compounds. Our study contributes toward better understanding on the molecular mechanism of aroma synthesis in apples and provides a valuable reference for metabolic engineering and flavor improvement in the future.

The RIFM approach to evaluating Natural Complex Substances (NCS)

The Research Institute for Fragrance Materials, Inc. (RIFM) has evaluated safety data for fragrance materials for 55 years. The safety assessment of Natural Complex Substances (NCS) is similar to that of discrete fragrance materials; all of the same endpoints are evaluated. A series of decision trees, reflecting advances in risk assessment approaches of mixtures and toxicological methodologies, follows a tiered approach for each endpoint using a 4-step process with testing only as a last resort: 1) evaluate available data on NCS; 2) verify whether the Threshold of Toxicological Concern (TTC) can be applied; 3) verify whether the NCS risk assessment can be achieved on a component basis; and 4) determine whether data must be generated. Using in silico tools, RIFM examined NCS similarities based on the plant part, processing, and composition of materials across 81 plant families to address data gaps. Data generated from the Creme RIFM Aggregate Exposure Model for over 900 fragrance NCS demonstrate that dermal exposure is the primary route of human exposure for NCS fragrance uses. Over a third of materials are below the most conservative TTC limits. This process aims to provide a comprehensive Safety Assessment of NCS used as a fragrance ingredient.

Climate Change and Coffee Quality: Systematic Review on the Effects of Environmental and Management Variation on Secondary Metabolites and Sensory Attributes of Coffea arabica and Coffea canephora

Climate change is impacting crop performance and agricultural systems around the world with implications for farmers and consumers. We carried out a systematic review to synthesize evidence regarding the effects of environmental factors associated with climate change and management conditions associated with climate adaptation on the crop quality of a culturally-relevant perennial crop, coffee (Coffea arabica and Coffea canephora). Seventy-three articles were identified that addressed the study's research question including 42 articles on environmental factors, 20 articles on management conditions, and 11 articles on both. While variation was found between studies, findings highlight that coffee quality is vulnerable to changes in light exposure, altitude, water stress, temperature, carbon dioxide, and nutrient management. Both increases as well as decreases were found in secondary metabolites and sensory attributes that determine coffee quality in response to shifts in environmental and management conditions. The most consistent evidence identified through this systematic review includes the following two trends: (1) increased altitude is associated with improved sensory attributes of coffee and; (2) increased light exposure is associated with decreased sensory attributes of coffee. Research gaps were found regarding the effects of shifts in carbon dioxide, water stress, and temperature on the directionality (increase, decrease, or non-linear) of coffee quality and how this varies with location, elevation, and management conditions. This systematic review further identified the following research needs: (1) long-term studies that examine the interactive effects of multiple environmental factors and management conditions on coffee quality; (2) studies that examine the interaction between sensory attributes and secondary metabolites that determine coffee quality and; (3) studies on the feasibility of various climate-adaptation strategies for mitigating the effects of climate change on coffee quality. Evidence-based innovations are needed to mitigate climate impacts on coffee quality toward enhanced sustainability and resilience of the coffee sector from farm to cup.

Biogenic volatile organic compound emissions from leaves and fruits of apple and peach trees during fruit development

Biogenic volatile organic compounds (BVOCs) are widely involved in a variety of atmospheric chemical processes due to their high reactivity and species diversity. To date, however, research on BVOCs in agroecosystems, particularly fruit trees, remains scarce despite their large cultivation area and economic interest. BVOC emissions from different organs (leaf or fruit) of apple and peach trees were investigated throughout the stages of fruit development (FS, fruit swelling; FC, fruit coloration; FM, fruit maturity; and FP, fruit postharvest) using a proton-transfer-reaction mass spectrometer. Results indicated that methanol was the most abundant compound emitted by the leaf (apple tree leaf 492.5 ± 47.9 ng/(g·hr), peach tree leaf 938.8 ±  154.5 ng/(g·hr)), followed by acetic acid and green leaf volatiles. Beside the above three compounds, acetaldehyde had an important contribution to the emissions from the fruit. Overall, the total BVOCs (sum of eight compounds studied in this paper) emitted by both leaf and fruit gradually decreased along the fruit development, although the effect was significant only for the leaf. The leaf (2020.8 ±  258.8 ng/(g·hr)) was a stronger BVOC emitter than the fruit (146.0 ± 45.7 ng/(g·hr)) (P = 0.006), and there were no significant differences in total BVOC emission rates between apple and peach trees. These findings contribute to our understanding on BVOC emissions from different plant organs and provide important insights into the variation of BVOC emissions across different fruit developmental stages.

Phenological and Geographical Effects on Phenolic and Triterpenoid Content in Vaccinium vitis-idaea L. Leaves

Lingonberry leaves have been proposed as a potential raw material for nutraceutical products and functional food due to the richness of phenolic and triterpenic compounds. However, contents of these bioactive compounds tend to vary greatly with physiological, climatic, and edaphic conditions, resulting in lingonberry leaves’ nutritional-pharmaceutical quality changes. In this context, we examined the effects of seasonal and geographical factors on phenolic and triterpenoid contents in lingonberry leaves. Quantitative and qualitative differences between samples were determined using validated HPLC-PDA methods. A total of 43 bioactive compounds were found at a detectable level throughout the year in young and old lingonberry leaves, with the highest contents of most compounds observed in samples collected in autumn–first half of spring. This suggests the potential to exploit the continuous biosynthesis for a longer harvesting season. Considerable variations in phytochemical profiles of lingonberry leaves, obtained from 28 locations in Lithuania, were found. Correlation analyses revealed significant negative correlations between contents of particular constituents and sunshine duration, temperature, and precipitation, and positive correlation with air humidity, longitudes, and altitudes of collecting locations and macronutrients in soil. These results suggest that harsh weather is favorable for most identified compounds and it may be possible to achieve appropriate accumulation of secondary metabolites by adjusting edaphic conditions. Taken together, the accumulation of phenolics and triterpenoids in lingonberry leaves highly depends on phenological and geographical factors and the influence of both variables differ for the particular compounds due to different metabolic processes in response to stresses.

Behavior Matters-Future Need for Insect Studies on Odor-Mediated Host Plant Recognition with the Aim of Making Use of Allelochemicals for Plant Protection

Allelochemicals, chemical cues that, among other things, mediate insect-plant interactions, such as host plant recognition, have attracted notable interest as tools for ecological control of pest insects. Advances have recently been made in methods for sampling and analyzing volatile compounds and technology for tracking insects in their natural habitat. However, progress in odor-mediated behavioral bioassays of insects has been relatively slow. This perspective highlights this odor-mediated insect behavior, particularly in a natural setting and considering the whole behavioral sequence involved in the host location, which is the key to understanding the mechanisms underlying host plant recognition. There is thus a need to focus on elaborate behavioral bioassays in future studies, particularly if the goal is to use allelochemicals in pest control. Future directions for research are discussed.

Usage of Natural Volatile Organic Compounds as Biological Modulators of Disease

Plants produce a wide variety of natural volatile organic compounds (NVOCs), many of which are unique to each species. These compounds serve many purposes, such as fending off herbivores and adapting to changes in temperature and water supply. Interestingly, although NVOCs are synthesized to deter herbivores, many of these compounds have been found to possess several therapeutic qualities, such as promoting nerve stability, enhancing sleep, and suppressing hyperresponsiveness, in addition to acting as antioxidants and anti-inflammatory agents. Therefore, many NVOCs are promising drug candidates for disease treatment and prevention. Given their volatile nature, these compounds can be administered to patients through inhalation, which is often more comfortable and convenient than other administration routes. However, the development of NVOC-based drug candidates requires a careful evaluation of the molecular mechanisms that drive their therapeutic properties to avoid potential adverse effects. Furthermore, even compounds that appear generally safe might have toxic effects depending on their dose, and therefore their toxicological assessment is also critical. In order to enhance the usage of NVOCs this short review focuses not only on the biological activities and therapeutic mode of action of representative NVOCs but also their toxic effects.

Metabolomics and Molecular Approaches Reveal Drought Stress Tolerance in Plants

Metabolic regulation is the key mechanism implicated in plants maintaining cell osmotic potential under drought stress. Understanding drought stress tolerance in plants will have a significant impact on food security in the face of increasingly harsh climatic conditions. Plant primary and secondary metabolites and metabolic genes are key factors in drought tolerance through their involvement in diverse metabolic pathways. Physio-biochemical and molecular strategies involved in plant tolerance mechanisms could be exploited to increase plant survival under drought stress. This review summarizes the most updated findings on primary and secondary metabolites involved in drought stress. We also examine the application of useful metabolic genes and their molecular responses to drought tolerance in plants and discuss possible strategies to help plants to counteract unfavorable drought periods.

Great tits (Parus major) flexibly learn that herbivore-induced plant volatiles indicate prey location: An experimental evidence with two tree species

When searching for food, great tits (Parus major) can use herbivore-induced plant volatiles (HIPVs) as an indicator of arthropod presence. Their ability to detect HIPVs was shown to be learned, and not innate, yet the flexibility and generalization of learning remain unclear.We studied if, and if so how, naïve and trained great tits (Parus major) discriminate between herbivore-induced and noninduced saplings of Scotch elm (Ulmus glabra) and cattley guava (Psidium cattleyanum). We chemically analyzed the used plants and showed that their HIPVs differed significantly and overlapped only in a few compounds.Birds trained to discriminate between herbivore-induced and noninduced saplings preferred the herbivore-induced saplings of the plant species they were trained to. Naïve birds did not show any preferences. Our results indicate that the attraction of great tits to herbivore-induced plants is not innate, rather it is a skill that can be acquired through learning, one tree species at a time.We demonstrate that the ability to learn to associate HIPVs with food reward is flexible, expressed to both tested plant species, even if the plant species has not coevolved with the bird species (i.e., guava). Our results imply that the birds are not capable of generalizing HIPVs among tree species but suggest that they either learn to detect individual compounds or associate whole bouquets with food rewards.

Determination of geographical origin of concentrated apple juice through analysis of stable isotopic and mineral elemental fingerprints: preliminary results

BACKGROUND

With increasing attention being paid to food authenticity, the geographic origin of food has become a topic of interest for both consumers and producers. As far as we know, there are relatively few studies on the origin traceability of concentrated apple juice. The most commonly used methods of origin tracing research is by using stable isotopes and mineral elements technology, because these indicators are directly related to local geographical environment.

RESULTS

In this study, a discriminant model was established by determining the content of the stable isotopes (δ¹³ C, δ¹⁸ O) and 13 mineral elements (B, Mn, Co, Ni, Cu, Sr, V, Ba, Fe, Mg, Na, Ca and Cr) in concentrated apple juice. Linear discriminant analysis (LDA), principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were employed for regional classification of samples. After data conversion and correlation analysis, spatial and quantitative prediction models were established using multiple linear regressions. Finally, the experimental results showed that the eight key variables(δ ¹³ C, δ ¹⁸ O, B, Ca, Mg, Cu, Sr and Na) selected by the analysis can be used to further characterize the production area.

CONCLUSION

The results showed that the carbon and oxygen isotopes combined with certain mineral elements can be used to indicate the origin of concentrated apple juice. © 2020 Society of Chemical Industry.

Pre-Harvest and Post-Harvest Techniques for Plant Disease Detections

As the agriculture industry is growing fast, many efforts are introduced to ensure a high quality of produce. Diseases and defects found in plants and crops affect greatly the agriculture industry. Hence, many techniques and technologies have been developed to help solve or reduce the impact of plant diseases. Imagining analysis tools and gas sensors are becoming more frequently integrated into smart systems for plant disease detection. Many disease detection systems incorporate imaging analysis tools and VOC (Volatile Organic Compound) profiling techniques to detect early symptoms of diseases and defects of plants, fruits, and vegetative produce. These disease detection techniques can be further categorized into two main groups: preharvest disease detection and postharvest disease detection techniques. This paper aims to introduce the available disease detection techniques and to compare them with the latest innovative smart systems that feature visible imaging, hyperspectral imaging, and VOC profiling. In addition, this paper considers the efforts to automate imaging techniques to help accelerate the disease detection process. Different approaches are analyzed and compared in terms of work environment, automation, implementation, and accuracy of disease identification along with the future evolution perspective in this field.

Biopesticide Trunk Injection Into Apple Trees: A Proof of Concept for the Systemic Movement of Mint and Cinnamon Essential Oils

The use of conventional pesticides is debated because of their multiple potential adverse effects on non-target organisms, human health, pest resistance development and environmental contaminations. In this setting, this study focused on developing alternatives, such as trunk-injected essential oil (EO)-based biopesticides. We analysed the ecophysiology of apple trees (Malus domestica) following the injection of Cinnamomum cassia and Mentha spicata nanoemulsions in the tree's vascular system. Targeted and untargeted volatile organic compounds (VOCs) analyses were performed on leaf-contained and leaf-emitted VOCs and analysed through dynamic headspace-gas chromatography-mass spectrometry (DHS-GC-MS) and thermal desorption unit (TDU)-GC-MS. Our results showed that carvone, as a major constituent of the M. spicata EO, was contained in the leaves (mean concentrations ranging from 3.39 to 19.7 ng g_DW ^-1) and emitted at a constant rate of approximately 0.2 ng g_DW ^-1 h^-1. Trans-cinnamaldehyde, C. cassia's major component, accumulated in the leaves (mean concentrations of 83.46 and 350.54 ng g_DW ^-1) without being emitted. Furthermore, our results highlighted the increase in various VOCs following EO injection, both in terms of leaf-contained VOCs, such as methyl salicylate, and in terms of leaf-emitted VOCs, such as caryophyllene. Principal component analysis (PCA) highlighted differences in terms of VOC profiles. In addition, an analysis of similarity (ANOSIM) and permutational multivariate analysis of variance (PERMANOVA) revealed that the VOC profiles were significantly impacted by the treatment. Maximum yields of photosystem II (Fv/Fm) were within the range of 0.80-0.85, indicating that the trees remained healthy throughout the experiment. Our targeted analysis demonstrated the systemic translocation of EOs through the plant's vascular system. The untargeted analysis, on the other hand, highlighted the potential systemic acquired resistance (SAR) induction by these EOs. Lastly, C. cassia and M. spicata EOs did not appear phytotoxic to the treated trees, as demonstrated through chlorophyll fluorescence measurements. Hence, this work can be seen as a proof of concept for the use of trunk-injected EOs given the systemic translocation, increased production and release of biogenic VOCs (BVOCs) and absence of phytotoxicity. Further works should focus on the ecological impact of such treatments in orchards, as well as apple quality and production yields.

Comprehensive Evaluation of Healthcare Benefits of Different Forest Types: A Case Study in Shimen National Forest Park, China

Studies have shown that contact with nature plays a crucial role in the amelioration of human health. Forest therapy has recently received widespread attention as a novel and subsidiary treatment approach for stress recovery and health promotion. However, there is a lack of ample research on the comprehensive evaluation of the forest healthcare benefits. Moreover, it is not entirely clear what kind of forest types and seasons are suitable for forest therapy activities and how healthcare forests should be constructed and managed. From September 2019 to January 2020 and May to August 2020., five forest types of Phyllostachys edulis forest, subtropical evergreen broad-leaved forest, Liquidambar formosana forest, Cunninghamia lanceolata forest, coniferous and broad-leaved mixed forest and a forestless control group in Shimen National Forest Park, Guangzhou City, Guangdong Province, China were selected. Variations in the character of negative air ion concentration, air oxygen content, human comfort index and phytoncide relative content were analyzed. Principal component analysis and systematic clustering were used to construct forest comprehensive healthcare index and evaluation grade in order to assess the healthcare benefits of different forest types. In terms of negative air ion concentration, the subtropical evergreen broad-leaved forest was far ahead of the other forest types throughout the year, while the forestless control group was the worst. All stands reached the annual maximum in summer, followed by spring, autumn and winter. From the perspective of air oxygen content, summer > spring > autumn > winter, among them, all forest stands clearly exceeded the normal atmospheric oxygen content (20.9%) in the first three quarters. Moreover, the air oxygen content of coniferous and broad-leaved mixed forest was the highest in five forest types; the forestless control group was the lowest. Judging from the human comfort index, in the whole year, all forest types, including the forestless group, were at the comfortable level and above. However, the five forest types still differed greatly in diverse seasons, among which Phyllostachys edulis forest and subtropical evergreen broad-leaved forest were superior to Liquidambar formosana forest, Cunninghamia lanceolata forest, coniferous and broad-leaved mixed forest in spring and summer, while it was in reverse in autumn and winter. In view of the phytoncide relative content, the subtropical evergreen broad-leaved forest was the highest, followed by the Cunninghamia lanceolata forest. The relative content of phytoncide was released more in summer, second, by spring, autumn and winter. Furthermore, establishing forest comprehensive healthcare index (FCHI = 0.1NAICi + 0.35AOCi + 0.27HCIi + 0.28PRCi), according to the FCHI value, it was divided into five rating levels. Overall, the comprehensive healthcare index of the five forest stands distinctly outperformed the forestless control group in all seasons. In addition, the five forest types were at level I in spring and summer. From the comprehensive data of the whole year, the comprehensive healthcare index of the coniferous and broad-leaved mixed forest was the best, followed by the subtropical evergreen broad-leaved forest. The forest environment has a favorable influence on the human body and mind, so it is suggested that citizens go to the forest environment regularly for healthcare and physical and mental washing. In terms of the forest healthcare benefits, the best seasons for forest therapy in Shimen National Forest Park are spring and summer; autumn is suitable as well. When planning and constructing the forest therapy bases in Shimen National Forest Park in the future, coniferous and broad-leaved mixed forests should be allocated more in the stand transformation to promote forest healthcare benefits. Protecting and developing the landscape resources of the subtropical evergreen broad-leaved forests should be paid close attention, as well as making rational use of their health activity space.

Influence of Environmental Factors on the Genetic and Chemical Diversity of Brickellia veronicifolia Populations Growing in Fragmented Shrublands from Mexico

Brickellia veronicifolia is a native Asteraceae from Mexico that persists in fragmented habitats. This investigation reports the genetic and chemical diversity of B. veronicifolia. The diversity analysis based on iPBS markers showed an averaged Shannon index (S) of 0.3493, a Nei genetic diversity (h) of 0.2256, and a percentage of polymorphic loci average (P) of 80.7867%. The population structure obtained by AMOVA revealed that the highest variation found within populations was 94.58%. GC-MS profiling of six populations indicated that major volatiles were β–caryophyllene (11.63%), spathulenol (12.85%), caryophyllene oxide (13.98%), α–cadinol (7.04%), cubedol (6.72%) and tau-muurolol (4.81%). Mantel tests suggested a statistically significant relationship between minor volatiles and geographical distance (r = 0.6163; p = 0.0470; p ˂ 0.05). Likewise, major volatiles showed a significant correlation with the soil pH (r = 0.6862; p = 0.0230) and maximum temperature (r = 0.4999; p = 0.0280). Our study suggests that the variation and genetic divergence of B. veronicifolia has no relationship with climatic parameters, whereas the volatiles are probably influenced by environmental factors and not by the genotype per se. Based on the characteristics of B. veronicifolia, this plant could be considered as a candidate for restoring fragmented shrublands in Mexico.

Evaluation of Physiological Characteristics, Soluble Sugars, Organic Acids and Volatile Compounds in 'Orin' Apples (Malus domestica) at Different Ripening Stages

‘Orin’ is a popular apple cultivar, which has a yellow-green appearance, pleasant taste, and unique aroma. However, few studies on the fruit quality characteristics of ‘Orin’ apples have been reported before. In this study, changes of the physiological characteristics were measured at different ripening stages, and the soluble sugars and organic acids were determined by high-performance liquid chromatography (HPLC). Volatile compounds were identified using the headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). During the fruit ripening, the ‘Orin’ apple fruit weight, size, and total soluble solid were gradually increased by contrast with the titratable acidity, and the firmness decreased. The content of four soluble sugars reached the maximum at the 180 days after full bloom (DAFB) stage. Malic acid was measured as the most abundant organic acid in ‘Orin’ apples. Ethyl butyrate, hexyl propanoate, hexyl acetate and butyl acetate belonging to esters with high odor activity values (OAVs) could be responsible for the typical aroma of ‘Orin’ apples. The aim of this work was to provide information on the flavor characteristics of ‘Orin’ apples and promote this apple cultivar for marketing and processing in the future.

Identification and Functional Characterization of Tissue-Specific Terpene Synthases in Stevia rebaudiana

In addition to the well-known diterpenoid steviol glycosides, Stevia rebaudiana (Stevia) produces many labdane-type diterpenoids and a wide range of mono- and sesquiterpenoids. However, biosynthesis of mono- and sesquiterpenoids in Stevia remains unknown. Here we analyzed the extracts of Stevia leaves, flowers, stems, and roots by Gas Chromatography–Mass Spectrometry and putatively identified a total of 69 volatile organic compounds, most of which were terpenoids with considerably varied quantities among the four tissues of Stevia. Using Stevia transcriptomes, we identified and functionally characterized five terpene synthases (TPSs) that produced major mono- and sesquiterpenoids in Stevia. Transcript levels of these Stevia TPSs and levels of corresponding terpenoids correlated well in Stevia tissues. Particularly, the root-specific SrTPS4 and SrTPS5 catalyzed the formation of γ-curcumene/zingiberene/β-sesquiphellandrene and α-longipinene/β-himachalene/himachalol as multifunctional sesqui-TPSs, respectively. Most of the SrTPSs were highly responsive to various environmental stresses in a tissue-specific manner. Taken together, our results provide new insights into how Stevia produces diverse terpenoids to confer differential responses to various environmental factors in each tissue.

Deciphering the Biotic and Climatic Factors That Influence Floral Scents: A Systematic Review of Floral Volatile Emissions

Currently, a global analysis of the information available on the relative composition of the floral scents of a very diverse variety of plant species is missing. Such analysis may reveal general patterns on the distribution and dominance of the volatile compounds that form these mixtures, and may also allow measuring the effects of factors such as the phylogeny, pollination vectors, and climatic conditions on the floral scents of the species. To fill this gap, we compiled published data on the relative compositions and emission rates of volatile organic compounds (VOCs) in the floral scents of 305 plant species from 66 families. We also gathered information on the groups of pollinators that visited the flowers and the climatic conditions in the areas of distribution of these species. This information allowed us to characterize the occurrence and relative abundances of individual volatiles in floral scents and the effects of biotic and climatic factors on floral scent. The monoterpenes trans-β-ocimene and linalool and the benzenoid benzaldehyde were the most abundant floral VOCs, in both ubiquity and predominance in the floral blends. Floral VOC richness and relative composition were moderately preserved traits across the phylogeny. The reliance on different pollinator groups and the climate also had important effects on floral VOC richness, composition, and emission rates of the species. Our results support the hypothesis that key compounds or compounds originating from specific biosynthetic pathways mediate the attraction of the main pollinators. Our results also indicate a prevalence of monoterpenes in the floral blends of plants that grow in drier conditions, which could link with the fact that monoterpene emissions protect plants against oxidative stresses throughout drought periods and their emissions are enhanced under moderate drought stress. Sesquiterpenes, in turn, were positively correlated with mean annual temperature, supporting that sesquiterpene emissions are dominated mainly by ambient temperature. This study is the first to quantitatively summarise data on floral-scent emissions and provides new insights into the biotic and climatic factors that influence floral scents.

Chronic cement dust load induce novel damages in foliage and buds of Malus domestica

Cement industry-derived pollutants appear to play multiple roles in stimulating abiotic stress responses in plants. Cement dust deposition on agriculture fields can affect soils, photosynthesis, transpiration and respiration of plants. Here, we characterised the acute physiological responses of Malus × domestica leaves to different cement dust concentrations. The cement dust was sprinkled over plants daily for 2 months at 10 and 20 g/plant, with 0 g/plant serving as the control. Leaf physiological responses revealed significant increases in oxidative stress and antioxidant enzyme activity levels. Additionally, ascorbic acid, soluble sugar, free amino acid, and pigment levels decreased after exposure to cement dust. Macroscopic morphometric parameters, such as weight, dry matter content, and lengths and widths of leaves and buds, were significantly reduced in the cement-treated groups. A histological analysis of leaves and buds revealed decreased cellular areas, cellular damage, and abridged leaf thickness, while an ion leakage assay confirmed the negative effects on tissue integrity. These results provide evidence that cement dust is a hazardous pollutant that induces abiotic stress responses and has degradative effects on leaf health, pigment and biochemical metabolite levels, and anatomical features. Studies to determine the elemental residues of cement dust present in edible plant parts and the adverse impacts of their consumption on human health are strongly recommended.

Particle deposition and sensory drive

The mutualism between chemical cues emitted into the air and variations in how primates respond to them using olfaction has demonstrated aspects of species-specific adaptations. Building on this mutualism we can look at particle deposition as another means to understanding how various environments may have elicited biological changes that enable efficient communication. Research on particle movement and deposition within the nasal cavity is largely based on questions about health as it relates to drug delivery systems and overall olfactory function in modern humans. With increased access to 3D models and the use of computational fluid dynamic analysis, researchers have been able to simulate site-specific deposition, to determine what particles are making it through the nasal cavity to the main olfactory epithelium, which ultimately leads to processing in the olfactory bulb. Here we discuss particle deposition research, sensory drive and their potential applications to evolutionary anthropology.

Variation in Terpene Profiles of Thymus vulgaris in Water Deficit Stress Response

Thyme (Thymus spp.) volatiles predominantly consisting of monoterpenes and sesquiterpenes, serve as antimicrobial, antiseptic and antioxidant in phytomedicine. They also play a key role in plants as secondary metabolites via their potential role against herbivores, attracting pollinators and abiotic stress tolerance. Plant volatiles are affected by different environmental factors including drought. Here, the effect of prolonged water deficit stress on volatile composition was studied on the sensitive and tolerant thyme plant cultivars (T. vulgaris Var. Wagner and T. vulgaris Var. Varico3, respectively). Volatile sampling along with morpho–physiological parameters such as soil moisture, water potential, shoot dry weight, photosynthetic rate and water content measurements were performed on one-month-old plants subsequent to water withholding at 4-day intervals until the plants wilted. The tolerant and sensitive plants had clearly different responses at physiological and volatile levels. The most stress-induced changes on the plants’ physiological traits occurred in the photosynthetic rates, where the tolerant plants maintained their photosynthesis similar to the control ones until the 8th day of the drought stress period. While the analysis of the volatile compounds (VOCs) of the sensitive thyme plants displayed the same pattern for almost all of them, in the tolerant plants, the comparison of the pattern of changes in the tolerant plants revealed that the changes could be classified into three separate groups. Our experimental and theoretical studies totally revealed that the most determinant compounds involved in drought stress adaptation included α-phellandrene, O-cymene, γ-terpinene and β-caryophyelene. Overall, it can be concluded that in the sensitive plants trade-off between growth and defense, the tolerant ones simultaneously activate their stress response mechanism and continue their growth.

Discrimination of Cultivated Regions of Soybeans (Glycine max) Based on Multivariate Data Analysis of Volatile Metabolite Profiles

Soybean (Glycine max) is a major crop cultivated in various regions and consumed globally. The formation of volatile compounds in soybeans is influenced by the cultivar as well as environmental factors, such as the climate and soil in the cultivation areas. This study used gas chromatography-mass spectrometry (GC-MS) combined by headspace solid-phase microextraction (HS-SPME) to analyze the volatile compounds of soybeans cultivated in Korea, China, and North America. The multivariate data analysis of partial least square-discriminant analysis (PLS-DA), and hierarchical clustering analysis (HCA) were then applied to GC-MS data sets. The soybeans could be clearly discriminated according to their geographical origins on the PLS-DA score plot. In particular, 25 volatile compounds, including terpenes (limonene, myrcene), esters (ethyl hexanoate, butyl butanoate, butyl prop-2-enoate, butyl acetate, butyl propanoate), aldehydes (nonanal, heptanal, (E)-hex-2-enal, (E)-hept-2-enal, acetaldehyde) were main contributors to the discrimination of soybeans cultivated in China from those cultivated in other regions in the PLS-DA score plot. On the other hand, 15 volatile compounds, such as 2-ethylhexan-1-ol, 2,5-dimethylhexan-2-ol, octanal, and heptanal, were related to Korean soybeans located on the negative PLS 2 axis, whereas 12 volatile compounds, such as oct-1-en-3-ol, heptan-4-ol, butyl butanoate, and butyl acetate, were responsible for North American soybeans. However, the multivariate statistical analysis (PLS-DA) was not able to clearly distinguish soybeans cultivated in Korea, except for those from the Gyeonggi and Kyeongsangbuk provinces.

Rain downpours affect survival and development of insect herbivores: the specter of climate change?

Changes in the frequency, duration, and intensity of rainfall events are among the abiotic effects predicted under anthropogenic global warming. Heavy downpours may profoundly affect the development and survival of small organisms such as insects. Here, we examined direct (physically on the insects) and indirect (plant-mediated) effects of simulated downpours on the performance of caterpillars of two lepidopteran herbivores (Plutella xylostella and Pieris brassicae) feeding on black mustard (Brassica nigra) plants. Host plants were exposed to different rainfall regimes both before and while caterpillars were feeding on the plants in an attempt to separate direct and indirect (plant-mediated) effects of rainfall on insect survival and development. In two independent experiments, downpours were simulated as a single long (20 min) or as three short (5 min) daily events. Downpours had a strong negative direct effect on the survival of P. xylostella, but not on that of P. brassicae. Direct effects of downpours consistently increased development time of both herbivore species, whereas effects on body mass depended on herbivore species and downpour frequency. Caterpillar disturbance by rain and recorded microclimatic cooling by 5°C may explain extended immature development. Indirect, plant-mediated effects of downpours on the herbivores were generally small, despite the fact that sugar concentrations were reduced and herbivore induction of secondary metabolites (glucosinolates) was enhanced in plants exposed to rain. Changes in the frequency of precipitation events due to climate change may impact the survival and development of insect herbivores differentially. Broader effects of downpours on insects and other arthropods up the food chain could seriously impair and disrupt trophic interactions, ultimately destabilizing communities.

Rainfastness of Insecticides Used to Control Spotted-Wing Drosophila in Tart Cherry Production

Tart cherry production is challenged by precipitation events that may reduce crop protection against spotted-wing drosophila (Drosophila suzukii) (SWD). Due to SWD’s devastating impacts on yield, growers are often faced with the option of insecticide reapplication. Semi-field bioassays were used to assess simulated rainfall effects towards adult mortality, immature survival, and residue wash-off from different plant tissues for several compounds. Tart cherry shoots were treated with 0, 12.7 or 25.4 mm of simulated rainfall and infested with SWD for 5 days. Adult mortality was recorded 1, 3, and 5 days after shoots were infested, while immature stage individuals were counted 9 days after the first infestation day. All insecticides demonstrated higher adult mortality and lower immature survival compared with the untreated control at 0 mm of rainfall. Adult mortality and immature survival caused by phosmet, zeta-cypermethrin, and spinetoram were adversely affected by simulated rainfall. In all bioassays, acetamiprid was the least affected by simulated rainfall. Residue analysis demonstrated phosmet and spinetoram residues to be the most sensitive to wash-off. This study demonstrates different rainfall effects on SWD control for several compounds. This information may provide a basis for making an informed decision on whether reapplication is required.

In-Cold Exposure to Z-3-Hexenal Provides Protection Against Ongoing Cold Stress in Zea mays

Green leaf volatiles (GLVs), which have mostly been described as providers of protection against insect herbivory and necrotrophic pathogen infections, were recently shown to provide significant fortification against cold stress damage. It was further demonstrated that cold-damaged maize seedlings released a significant amount of GLVs, in particular, Z-3-hexenal (Z-3-HAL). Here, we report that the in-cold treatment of maize seedlings with Z-3-HAL significantly improved cold stress resistance. The transcripts for cold-protective genes were also significantly increased in the Z-3-HAL treated maize seedlings over those found in only cold stressed plants. Consequently, the maize seedlings treated with HAL during cold showed a significantly increased structural integrity, significantly less damage, and increased growth after cold stress, relative to the non-HAL treated maize seedlings. Together, these results demonstrate the protective effect of in-cold treatment with HAL against cold damage, and suggest that the perception of these compounds during cold episodes significantly improves resistance against this abiotic stress.

Linking monoterpenes and abiotic stress resistance in grapevines

Rising temperatures and ozone levels are among the most striking stressful phenomena of global climate changes, and they threaten plants that are unable to react rapidly and efficiently. Generic responses of plants to stresses include the production of excess reactive oxygen species (ROS). Excessive ROS accumulation can lead to extensive oxidation of important components such as nucleic acids, proteins and lipids which can further exacerbate ROS accumulation leading to programmed cell death. Although most studies on plant antioxidants have focused on non-volatile compounds, volatiles belonging to the isoprenoid family have been implicated in the protection against abiotic stresses, in particular thermal and oxidative stress whose frequency and extent is being exacerbated by ongoing global change and anthropogenic pollution. Historically, research has focused on isoprene, demonstrating that isoprene-emitting plants are more tolerant to ozone exposure and heat stress, reducing ROS accumulation. Yet, evidence is being compiled that shows other volatile isoprenoids may be involved in plant responses against abiotic stresses. Grapevines are not isoprene emitters but some varieties produce other volatile isoprenoids such as monoterpenes. We investigated photosynthesis and emission of volatile organic compounds upon heat stress in two Vitis vinifera cv. ‘Chardonnay’ clones differing only for a mutation in the DXS gene (2-C-methyl-D-erythritol 4-phosphate (MEP) pathway), regulating volatile isoprenoid biosynthesis. We showed that the mutation led to a strong increase in monoterpene emission upon heat stress. At the same time, maximum photochemical quantum yield (Fv/Fm ratio) of PSII was affected by the stress in the non-emitting clone while the monoterpene emitter showed a significant resilience, thus indicating a possible antioxidant role of monoterpenes in grapevine. Future mechanistic studies should focus on unveiling the actual mechanism responsible for such findings.

Identification and functional characterization of three new terpene synthase genes involved in chemical defense and abiotic stresses in Santalum album

BACKGROUND

It is well known that aromatic essential oils extracted from the heartwood of Santalum album L. have wide economic value. However, little is known about the role of terpenoids in response to various adverse environmental stresses as other plants do in the form of signals during plant-environment interactions.

RESULTS

In this study, trace amounts of volatiles consisting of α-santalene, epi-β-santalene, β-santalene, α-santalol, β-santalol, (E)-α-bergamotene, (E)-β-farnesene and β-bisabolene were found in the leaves of mature S. album trees. We identified more than 40 candidate terpene synthase (TPS) unigenes by mining publicly-available RNA-seq data and characterized the enzymes encoded by three cDNAs: one mono-TPS catalyzes the formation of mostly α-terpineol, and two multifunctional sesqui-TPSs, one of which produces (E)-α-bergamotene and sesquisabinene as major products and another which catalyzes the formation of (E)-β-farnesene, (E)-nerolidol and (E,E)-farnesol as main products. Metabolite signatures and gene expression studies confirmed that santalol content is closely related with santalene synthase (SaSSY) transcripts in heartwood, which is key enzyme responsible for santalol biosynthesis. However, the expression of three new SaTPS genes differed significantly from SaSSY in the essential oil-producing heartwood. Increased activities of antioxidant enzymes, superoxide dismutase, catalase, peroxidase and ascorbate peroxidase, were detected in different tissues of S. album plants after applying 1 mM methyl jasmonate (MeJA) and 1 mM salicylic acid (SA), or exposure to 4°C, 38°C and high light intensity. MeJA and SA dramatically induced the expression of SaTPS1 and SaTPS2 in leaves. SaTPS1 to 3 transcripts were differentially activated among different tissues under adverse temperature and light stresses. In contrast, almost all SaSSY transcripts decreased in response to these environmental stresses, unlike SaTPS1 to 3.

CONCLUSIONS

Multifunctional enzymes were biochemically characterized, including one chloroplastic mono-TPS and two cytosolic sesqui-TPSs in sandalwood. Our results suggest the ecological importance of these three new SaTPS genes in defensive response to biotic attack and abiotic stresses in S. album.

Green leaf volatiles protect maize (Zea mays) seedlings against damage from cold stress

Although considerable evidence has accumulated on the defensive activity of plant volatile organic compounds against pathogens and insect herbivores, less is known about the significance of volatile organic compounds emitted by plants under abiotic stress. Here, we report that green leaf volatiles (GLVs), which were previously shown to prime plant defences against insect herbivore attack, also protect plants against cold stress (4 °C). We show that the expression levels of several cold stress-related genes are significantly up-regulated in maize (Zea mays) seedlings treated with physiological concentrations of the GLV, (Z)-3-hexen-1-yl acetate (Z-3-HAC), and that seedlings primed with Z-3-HAC exhibit increased growth and reduced damage after cold stress relative to unprimed seedlings. Together, these data demonstrate the protective and priming effect of GLVs against cold stress and suggest an activity of GLVs beyond the activation of typical plant defence responses against herbivores and pathogens.

Phytochemical variation in treetops: causes and consequences for tree-insect herbivore interactions

The interaction of plants and their herbivorous opponents has shaped the evolution of an intricate network of defences and counter-defences for millions of years. The result is an astounding diversity of phytochemicals and plant strategies to fight and survive. Trees are specifically challenged to resist the plethora of abiotic and biotic stresses due to their dimension and longevity. Here, we review the recent literature on the consequences of phytochemical variation in trees on insect-tree-herbivore interactions. We discuss the importance of genotypic and phenotypic variation in tree defence against insects and suggest some molecular mechanisms that might bring about phytochemical diversity in crowns of individual trees.

Design of an Attractant for Empoasca onukii (Hemiptera: Cicadellidae) Based on the Volatile Components of Fresh Tea Leaves

The tea leafhopper, Empoasca onukii Matsuda, is a serious pest of the tea plant. E. onukii prefers to inhabit vigorously growing tender tea leaves. The host selection of E. onukii adults may be associated with plant volatile compounds (VOCs). We sought to identify potentially attractive VOCs from tea leaves at three different ages and test the behavioral responses of E. onukii adults to synthetic VOC blends in the laboratory and field to aid in developing an E. onukii adult attractant. In darkness, the fresh or mature tea leaves of less than 1-mo old could attract more leafhoppers than the mature branches (MB) that had many older leaves (leaf age >1 mo). Volatile analysis showed that the VOC composition of the fresh leaves was the same as that of the mature leaves, but linalool and indole were not at detectable levels in VOCs from the MB. Moreover, the mass ratio differed for each common volatile in the three types of tea leaves. When under competition with volatiles from the MB, the leafhoppers showed no significant tropism to each single volatile but could be attracted by the synthetic volatile blend imitating the fresh leaves. With the removal of some volatile components, the effective synthetic volatile blend was mixed with (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate, and linalool at a mass ratio of 0.6:23:12.6. These three volatiles may be the key components for the host selection of E. onukii adults and could be used as an attractant in tea gardens.

An Alcohol Dehydrogenase Gene from Synechocystis sp. Confers Salt Tolerance in Transgenic Tobacco

Synechocystis salt-responsive gene 1 (sysr1) was engineered for expression in higher plants, and gene construction was stably incorporated into tobacco plants. We investigated the role of Sysr1 [a member of the alcohol dehydrogenase (ADH) superfamily] by examining the salt tolerance of sysr1-overexpressing (sysr1-OX) tobacco plants using quantitative real-time polymerase chain reactions, gas chromatography-mass spectrometry, and bioassays. The sysr1-OX plants exhibited considerably increased ADH activity and tolerance to salt stress conditions. Additionally, the expression levels of several stress-responsive genes were upregulated. Moreover, airborne signals from salt-stressed sysr1-OX plants triggered salinity tolerance in neighboring wild-type (WT) plants. Therefore, Sysr1 enhanced the interconversion of aldehydes to alcohols, and this occurrence might affect the quality of green leaf volatiles (GLVs) in sysr1-OX plants. Actually, the Z-3-hexenol level was approximately twofold higher in sysr1-OX plants than in WT plants within 1-2 h of wounding. Furthermore, analyses of WT plants treated with vaporized GLVs indicated that Z-3-hexenol was a stronger inducer of stress-related gene expression and salt tolerance than E-2-hexenal. The results of the study suggested that increased C6 alcohol (Z-3-hexenol) induced the expression of resistance genes, thereby enhancing salt tolerance of transgenic plants. Our results revealed a role for ADH in salinity stress responses, and the results provided a genetic engineering strategy that could improve the salt tolerance of crops.

Diel rhythms in the volatile emission of apple and grape foliage

This study investigated the diel emission of volatile organic compounds (VOCs) from intact apple (Malus x domestica Borkh., cv. Golden Delicious) and grape (Vitis vinifera L., cv. Pinot Noir) foliage. Volatiles were monitored continuously for 48 h by proton transfer reaction - time of flight - mass spectrometry (PTR-ToF-MS). In addition, volatiles were collected by closed-loop-stripping-analysis (CLSA) and characterized by gas chromatography-mass spectrometry (GC-MS) after 1 h and again 24 and 48 h later. Fourteen and ten volatiles were characterized by GC-MS in apple and grape, respectively. The majority of these were terpenes, followed by green leaf volatiles, and aromatic compounds. The PTR-ToF-MS identified 10 additional compounds and established their diel emission rhythms. The most abundant volatiles displaying a diel rhythm included methanol and dimethyl sulfide in both plants, acetone in grape, and mono-, homo- and sesquiterpenes in apple. The majority of volatiles were released from both plants during the photophase; whereas methanol, CO₂, methyl-butenol and benzeneacetaldehyde were released at significantly higher levels during the scotophase. Acetaldehyde, ethanol, and some green leaf volatiles showed distinct emission bursts in both plants following the daily light switch-off. These new results obtained with a combined analytical approach broaden our understanding of the rhythms of constitutive volatile release from two important horticultural crops. In particular, diel emission of sulfur and nitrogen-containing volatiles are reported here for the first time in these two crops.

Biochemistry of Apple Aroma: A Review

Flavour is a key quality attribute of apples defined by volatile aroma compounds. Biosynthesis of aroma compounds involves metabolic pathways in which the main precursors are fatty and amino acids, and the main products are aldehydes, alcohols and esters. Some enzymes are crucial in the production of volatile compounds, such as lipoxygenase, alcohol dehydrogenase, and alcohol acyltransferase. Composition and concentration of volatiles in apples may be altered by pre- and postharvest factors that cause a decline in apple flavour. Addition of biosynthetic precursors of volatile compounds may be a strategy to promote aroma production in apples. The present manuscript compiles information regarding the biosynthesis of volatile aroma compounds, including metabolic pathways, enzymes and substrates involved, factors that may affect their production and also includes a wide number of studies focused on the addition of biosynthetic precursors in their production.