Synthesis Of Volatile Organic Compounds Research Articles

Isoprene emission dynamics in Chaetoceros curvisetus: Insights from transcriptome analysis under light/dark cycles

Isoprene from marine emissions significantly influences the atmospheric oxidative capacity and secondary pollutants in the marine boundary layer. While marine algae are recognized as primary contributors to marine emissions of isoprene, the long-term and dark-phase isoprene production from these organisms remains underexplored, potentially lead to inaccuracies in estimating marine isoprene emissions. In this study, we conducted a time series investigation of isoprene emission from Chaetoceros curvisetus with a growth cycle duration of 19 days and examined the influence of environmental factors. Our findings revealed that C. curvisetus emits isoprene during its whole growth cycle, with peak emissions (2.82 × 10−11 μmol cells−1 h−1) recorded in the stationary phase. Under nitrogen, light and temperature stress, significant release of isoprene is found. During both the light and dark phases, isoprene emission was observed with comparable intensities. Transcriptome analysis showed that 41 differentially expressed transcripts were involved in the synthesis of volatile organic compounds. Notably, downregulation of genes associated with pyruvate synthesis in the glycolysis pathway suggests its importance for dark isoprene release. The study also highlighted downregulation of isopentenyl phosphate kinase and Gene Ontology enrichment in organelles housing mevalonate (MVA) pathways, suggesting that exchange involving the transport of intermediate metabolites between MVA and methylerythritol phosphate (MEP) pathway may contribute to the released isoprene in dark phase. Furthermore, the synthesis of substrates and downstream products is related to the dark release of isoprene. In conclusion, our study illuminates the pivotal roles of substrate availability, interplay between MVA and MEP pathways, and glycolysis pathway in governing isoprene emissions under light/dark cycles.

Technological affinity index for interaction between lactic acid bacteria and Saccharomyces cerevisiae strains to modulate the fruity and floreal aroma of Catarratto wines

Microbial interactions during the fermentation process influence the sensory characteristics of wines. Alongside alcoholic fermentation, malolactic fermentation also plays a crucial role in determining the aromatic traits of wines. The time (t), rate (m) and volatile organic compounds (VOCs) of malolactic fermentation are linked to the interaction between yeasts and lactic acid bacteria. The study investigated the interactions between Lactiplantibacillus plantarum or Oenococcus oeni with Saccharomyces cerevisiae by using the Technological Affinity Index (TAIndex). The co-inoculation of L. plantarum/S. cerevisiae resulted in a higher TAIndex than the co-inoculation of O. oeni/S. cerevisiae conditions. A low TAIndex led to increased aromaticity of the wines. The time and rate of malolactic fermentation have a strong impact on the synthesis of VOCs with a high olfactory impact. Therefore, knowledge of the TAIndex could play a decisive role in improving winemaking planning to produce wines with higher fruit and floral perceptions.

Examination of internal metabolome and VOCs profile of brewery yeast and their mutants producing beer with improved aroma

Volatile organic compounds (VOCs) are metabolites pivotal in determining the aroma of various products. A well-known VOC producer of industrial importance is Saccharomyces cerevisiae, partially responsible for flavor of beers and wines. We identified VOCs in beers produced by yeast strains characterized by improved aroma obtained in UV-induced mutagenesis. We observed significant increase in concentration of compounds in strains: 1214uv16 (2-phenylethyl acetate, 2- phenylethanol), 1214uv31 (2-ethyl henxan-1-ol), 1214uv33 (ethyl decanoate, caryophyllene). We observed decrease in production of 2-phenyethyl acetate in strain 1214uv33. Analysis of intracellular metabolites based on 1H NMR revealed that intracellular phenylalanine concentration was not changed in strains producing more phenylalanine related VOCs (1214uv16 and 1214uv33), so regulation of this pathway seems to be more sophisticated than is currently assumed. Metabolome analysis surprisingly showed the presence of 3-hydroxyisobutyrate, a product of valine degradation, which is considered to be absent in S. cerevisiae. Our results show that our knowledge of yeast metabolism including VOC production has gaps regarding synthesis pathways for individual metabolites and regulation mechanisms. Detailed analysis of 1214uv16 and 1214uv33 may enhance our knowledge of the regulatory mechanisms of VOC synthesis in yeast, and analysis of strain 1214uv31 may reveal the pathway of 2-ethyl henxan-1-ol biosynthesis.

Molecular Regulatory Mechanisms Affecting Fruit Aroma.

Aroma, an important quality characteristic of plant fruits, is produced by volatile organic compounds (VOCs), mainly terpenes, aldehydes, alcohols, esters, ketones, and other secondary metabolites, in plant cells. There are significant differences in the VOC profile of various fruits. The main pathways involved in the synthesis of VOCs are the terpenoid, phenylalanine, and fatty acid biosynthesis pathways, which involve several key enzyme-encoding genes, transcription factors (TFs), and epigenetic factors. This paper reviews the main synthetic pathways of the main volatile components in fruit, summarizes studies on the regulation of aroma formation by key genes and TFs, summarizes the factors affecting the fruit aroma formation, describes relevant studies on the improvement of fruit flavor quality, and finally proposes potential challenges and prospects for future research directions. This study provides a theoretical basis for the further precise control of fruit aroma quality and variety improvement.

The Potential of Fecal Volatile Organic Compound Analysis for the Early Diagnosis of Late-Onset Sepsis in Preterm Infants: A Narrative Review.

Early diagnosis and treatment of late-onset sepsis (LOS) is crucial for survival, but challenging. Intestinal microbiota and metabolome alterations precede the clinical onset of LOS, and the preterm gut is considered an important source of bacterial pathogens. Fecal volatile organic compounds (VOCs), formed by physiologic and pathophysiologic metabolic processes in the preterm gut, reflect a complex interplay between the human host, the environment, and microbiota. Disease-associated fecal VOCs can be detected with an array of devices with various potential for the development of a point-of-care test (POCT) for preclinical LOS detection. While characteristic VOCs for common LOS pathogens have been described, their VOC profiles often overlap with other pathogens due to similarities in metabolic pathways, hampering the construction of species-specific profiles. Clinical studies have, however, successfully discriminated LOS patients from healthy individuals using fecal VOC analysis with the highest predictive value for Gram-negative pathogens. This review discusses the current advancements in the development of a non-invasive fecal VOC-based POCT for early diagnosis of LOS, which may potentially provide opportunities for early intervention and targeted treatment and could improve clinical neonatal outcomes. Identification of confounding variables impacting VOC synthesis, selection of an optimal detection device, and development of standardized sampling protocols will allow for the development of a novel POCT in the near future.

Role of Volatile Organic Compounds Produced by Kosakonia cowanii Cp1 during Competitive Colonization Interaction against Pectobacterium aroidearum SM2.

The competitive colonization of bacteria on similar ecological niches has a significant impact during their establishment. The synthesis speeds of different chemical classes of molecules during early competitive colonization can reduce the number of competitors through metabolic effects. In this work, we demonstrate for the first time that Kosakonia cowanii Cp1 previously isolated from the seeds of Capsicum pubescens R. P. produced volatile organic compounds (VOCs) during competitive colonization against Pectobacterium aroidearum SM2, affecting soft rot symptoms in serrano chili (Capsicum annuum L.). The pathogen P. aroidearum SM2 was isolated from the fruits of C. annuum var. Serrano with soft rot symptoms. The genome of the SM2 strain carries a 5,037,920 bp chromosome with 51.46% G + C content and 4925 predicted protein-coding genes. It presents 12 genes encoding plant-cell-wall-degrading enzymes (PCDEWs), 139 genes involved in five types of secretion systems, and 16 genes related to invasion motility. Pathogenic essays showed soft rot symptoms in the fruits of C. annuum L., Solanum lycopersicum, and Physalis philadelphica and the tubers of Solanum tuberosum. During the growth phases of K. cowanii Cp1, a mix of VOCs was identified by means of HS-SPME-GC-MS. Of these compounds, 2,5-dimethyl-pyrazine showed bactericidal effects and synergy with acetoin during the competitive colonization of K. cowanii Cp1 to completely reduce soft rot symptoms. This work provides novel evidence grounding a better understanding of bacterial interactions during competitive colonization on plant tissue, where VOC synthesis is essential and has a high potential capacity to control pathogenic microorganisms in agricultural systems.

Volatile Organic Compounds Produced by Kosakonia cowanii Cp1 Isolated from the Seeds of Capsicum pubescens R & P Possess Antifungal Activity.

The Kosakonia cowanii Cp1 strain was isolated from seeds of Capsicum pubescens R. & P. cultivated in Michoacan, Mexico. Genetic and ecological role analyses were conducted for better characterization. The results show that genome has a length of 4.7 Mbp with 56.22% G + C and an IncF plasmid of 128 Kbp with 52.51% G + C. Furthermore, pathogenicity test revealed nonpathogenic traits confirmed by the absence of specific virulence-related genes. Interestingly, when fungal inhibitory essays were carried out, the bacterial synthesis of volatile organic compounds (VOCs) with antifungal activity showed that Sclerotinia sp. and Rhizoctonia solani were inhibited by 87.45% and 77.24%, respectively. Meanwhile, Sclerotium rolfsii, Alternaria alternata, and Colletotrichum gloeosporioides demonstrated a mean radial growth inhibition of 52.79%, 40.82%, and 55.40%, respectively. The lowest inhibition was by Fusarium oxysporum, with 10.64%. The VOCs' characterization by headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS) revealed 65 potential compounds. Some of the compounds identified with high relative abundance were ketones (22.47%), represented by 2-butanone, 3-hydroxy (13.52%), and alcohols (23.5%), represented by ethanol (5.56%) and 1-butanol-3-methyl (4.83%). Our findings revealed, for the first time, that K. cowanii Cp1 associated with C. pubescens seeds possesses potential traits indicating that it could serve as an effective biocontrol.

Insights Into the MYB-Related Transcription Factors Involved in Regulating Floral Aroma Synthesis in Sweet Osmanthus.

As an important member of the MYB transcription factor (TF) family, the MYB-related TFs play multiple roles in regulating the synthesis of secondary metabolites and developmental processes, as well as in response to numerous biotic and abiotic stressors in plants. However, little is known regarding their roles in regulating the formation of floral volatile organic compounds (VOCs). In this study, we conducted a genome-wide analysis of MYB-related proteins in sweet osmanthus; 212 OfMYB-related TFs were divided into three distinct subgroups based on the phylogenetic analysis. Additionally, we found that the expansion of the OfMYB-related genes occurred primarily through segmental duplication events, and purifying selection occurred in all duplicated gene pairs. RNA-seq data revealed that the OfMYB-related genes were widely expressed in different organs of sweet osmanthus, and some showed flower organ/development stage-preferential expression patterns. Here, three OfMYB-related genes (OfMYB1R70/114/201), which were expressed nuclearly in floral organs, were found to be significantly involved in regulating the synthesis of floral VOCs. Only, OfMYB1R201 had transcriptional activity, thus implying that this gene participates in regulating the expression of VOC synthesis related genes. Remarkably, the transient expression results suggested that OfMYB1R70, OfMYB1R114, and OfMYB1R201 are involved in the regulation of VOC synthesis; OfMYB1R114 and OfMYB1R70 are involved in accelerating β-ionone formation. In contrast, OfMYB1R201 decreases the synthesis of β-ionone. Our results deepen our knowledge of the functions of MYB-related TFs and provide critical candidate genes for the floral aroma breeding of sweet osmanthus in the future.

Peach fruit PpNAC1 activates PpFAD3-1 transcription to provide ω-3 fatty acids for the synthesis of short-chain flavor volatiles.

Volatile organic compounds (VOCs) derived from fatty acids are major contributors to fruit flavor and affect human preferences. The ω-3 fatty acid linolenic acid 3 (18:3) serves as an important precursor for synthesis of (E)-2-hexenal and (Z)-3-hexenol. These short-chain C6 VOCs provide unique fresh notes in multiple fruit species. Metabolic engineering to improve fruit aroma requires knowledge of the regulation of fatty acid-derived VOCs. Here, we determined that ripe fruit-specific expression of PpFAD3-1 contributes to 18:3 synthesis in peach fruit. However, no significant increases in (E)-2-hexenal and (Z)-3-hexenol were detected after overexpressing PpFAD3-1. Interestingly, overexpressing the PpNAC1 transcription factor increased the content of 18:3 and enhanced the production of its derived volatiles. Moreover, induced expression of genes responsible for downstream VOC synthesis was observed for transgenic tomato fruit overexpressing PpNAC1, but not for transgenic fruit overexpressing PpFAD3-1. Electrophoretic mobility shift and ChIP-Seq assays showed that PpNAC1 activated PpFAD3-1 expression via binding to its promoter. Therefore, PpNAC1 plays an important role in modulating fatty acid flux to produce fruit flavor-related VOCs. In addition to PpNAC1, PpFAD3-1 expression was also associated with epigenetic modifications during peach fruit ripening. Taken together, our results provide new insights into the molecular mechanisms regulating biosynthesis of fatty acid and short-chain VOCs in fruit.

Biogenic volatile organic compounds in the grapevine response to pathogens, beneficial microorganisms, resistance inducers, and abiotic factors.

The synthesis of volatile organic compounds (VOCs) in plants is triggered in response to external stimuli, and these compounds can migrate to distal tissues and neighbouring receivers. Although grapevine VOCs responsible for wine aroma and plant-insect communications are well characterized, functional properties of VOCs produced in response to phytopathogens, beneficial microorganisms, resistance inducers, and abiotic factors have been less studied. In this review, we focused on the emission patterns and potential biological functions of VOCs produced by grapevines in response to stimuli. Specific grapevine VOCs are emitted in response to the exogenous stimulus, suggesting their precise involvement in plant defence response. VOCs with inhibitory activities against pathogens and responsible for plant resistance induction are reported, and some of them can also be used as biomarkers of grapevine resistance. Likewise, VOCs produced in response to beneficial microorganisms and environmental factors are possible mediators of grapevine-microbe communications and abiotic stress tolerance. Although further functional studies may improve our knowledge, the existing literature suggests that VOCs have an underestimated potential application as pathogen inhibitors, resistance inducers against biotic or abiotic stresses, signalling molecules, membrane stabilizers, and modulators of reactive oxygen species. VOC patterns could also be used to screen for resistant traits or to monitor the plant physiological status.

Effects of modified atmosphere and sugar immersion on physiology and quality of fresh-cut 'Braeburn' apples

Fresh-cut fruits are highly perishable and show a short shelf life. Therefore, storage in sugar syrup is commercially used to delay undesirable metabolic changes and to prevent browning. Investigations on the effects of syrup application on volatile organic compounds (VOCs), important for the consumers’ acceptance, are rare. It is, however, known that low O2 availability, as found in fruit slices after immersion, may result in the formation of unwanted off-odour. This negatively affects the sensory quality of fresh-cuts. In the present study, fresh-cut 'Braeburn' apples were comparatively stored in air, in three modified atmospheres (O2: 10, 5 and approx. 0 %; CO2: 10, 15 and 20 %) or in sugar syrup (20 % sugar content). Relevant quality, physiological and microbiological parameters were evaluated on days 3, 6 and 10 of storage. Particular focus was laid on the evaluation of VOC emission to indicate biosynthetic responses that affect aroma-relevant VOCs. Atmospheric storage of apple slices, among others, increased the emission of ethyl acetate, which may create off-odour and negatively affects the customers’ acceptance. In contrast, syrup-immersion of apple slices resulted in a pronounced loss of aroma but prevented the occurrence of off-odour. The results indicated metabolic changes, which were independent of O2 availability. High CO2 or VOCs concentrations in the fruit tissue may inhibit esterification or may induce a feedback inhibition of VOC synthesis.

Aroma profile of two commercial truffle species from Yunnan and Sichuan, China: inter- and intraspecific variability and shared key compounds

Aroma is central to the worldwide success of truffles as gourmet food and the high prices paid for these edible mushrooms. In this study, volatile organic compounds (VOCs) from fruiting bodies of two Chinese truffles of commercial relevance, Tuber indicum and Tuber pseudohimalayense, were analyzed using headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). We aimed to characterize the aroma profile and determine whether it would be influenced by provenance and stage of maturation. We thus collected and analyzed young, middle mature and mature fruiting bodies of each species from different locations in Yunnan and Sichuan provinces, located in southwestern China. Overall, 76 VOCs were identified, belonging to different chemical classes, i.e. alcohols and phenols, aldehydes and ketones, benzenes and methoxy compounds, hydrocarbons and amines. A large number of volatiles identified in T. indicum and T. pseudohimalayense are reported here for the first time for these truffles. While more than 50% of identified VOCs were produced by both truffle species, considerable differences were present in the aroma profiles of fruiting bodies collected at various maturation stages, revealing a dynamic pattern in the biosynthesis of VOCs. Furthermore, truffles of different provenance had distinct proportions of volatile constituents, suggesting that, besides genetic factors, edaphic and microclimatic conditions influence the synthesis of VOCs in a complex manner.

Dynamic histone acetylation in floral volatile synthesis and emission in petunia flowers.

Biosynthesis of secondary metabolites relies on primary metabolic pathways to provide precursors, energy, and cofactors, thus requiring coordinated regulation of primary and secondary metabolic networks. However, to date, it remains largely unknown how this coordination is achieved. Using Petunia hybrida flowers, which emit high levels of phenylpropanoid/benzenoid volatile organic compounds (VOCs), we uncovered genome-wide dynamic deposition of histone H3 lysine 9 acetylation (H3K9ac) during anthesis as an underlying mechanism to coordinate primary and secondary metabolic networks. The observed epigenome reprogramming is accompanied by transcriptional activation at gene loci involved in primary metabolic pathways that provide precursor phenylalanine, as well as secondary metabolic pathways to produce volatile compounds. We also observed transcriptional repression among genes involved in alternative phenylpropanoid branches that compete for metabolic precursors. We show that GNAT family histone acetyltransferase(s) (HATs) are required for the expression of genes involved in VOC biosynthesis and emission, by using chemical inhibitors of HATs, and by knocking down a specific HAT gene, ELP3, through transient RNAi. Together, our study supports that regulatory mechanisms at chromatin level may play an essential role in activating primary and secondary metabolic pathways to regulate VOC synthesis in petunia flowers.

Cuticle thickness affects dynamics of volatile emission from petunia flowers.

The plant cuticle is the final barrier for volatile organic compounds (VOCs) to cross for release to the atmosphere, yet its role in the emission process is poorly understood. Here, using a combination of reverse-genetic and chemical approaches, we demonstrate that the cuticle imposes substantial resistance to VOC mass transfer, acting as a sink/concentrator for VOCs and hence protecting cells from the potentially toxic internal accumulation of these hydrophobic compounds. Reduction in cuticle thickness has differential effects on individual VOCs depending on their volatility, and leads to their internal cellular redistribution, a shift in mass transfer resistance sources and altered VOC synthesis. These results reveal that the cuticle is not simply a passive diffusion barrier for VOCs to cross, but plays the aforementioned complex roles in the emission process as an integral member of the overall VOC network.

Effects of Shading on the Synthesis of Volatile Organic Compounds in ‘Marselan’ Grape Berries (Vitis vinifera L.)

Effects of Shading on the Synthesis of Volatile Organic Compounds in ‘Marselan’ Grape Berries (Vitis vinifera L.)

Similitudes and differences between two closely related Ficus species in the synthesis by the ostiole of odors attracting their host-specific pollinators: A transcriptomic based investigation

Flower odor is often essential for attracting pollinators, and this is especially true for species-specific mutualism such as the one between Ficus species and their pollinating wasps. Receptive figs emit a stage and species specific odor composed of a mix of volatile organic compounds (VOC) that is attractive to their pollinators. Histological studies suggest that the ostiolar bracts are the main locus of fig floral VOC synthesis. To confirm a major role of the ostiole in VOC synthesis, detect the genes involved in VOC synthesis and analyze differences between closely related species, we compare the transcriptomes of pre-receptive and receptive figs of two closely related species, F. hirta and F. triloba. The two species presented similar numbers of expressed genes and similar annotation, classification results, and their up-regulated unigenes belonged to similar biosynthetic pathways. However, phenylpropanoid and terpene synthesis were the main enriched VOC pathways in receptive figs of F. hirta while terpene and jasmonate synthesis were the main enriched VOC pathways in F. triloba. The shift in gene expression between pre-receptive and receptive figs was much more marked in the ostiolar bracts than in the flowers of F. hirta, and in the fig wall, confirming an important role of the ostiole in receptive fig odor emission. Only one unigene directly involved in VOC synthesis presented signatures of positive selection, further supporting that the source of interspecific receptive fig odor differentiation is based on gene regulation rather than on gene differentiation. Regulation based receptive fig odor differentiation between species suggests a potential for rapid evolution of this interspecific barrier.

Influence of mineral substances on the synthesis of volatile organic compounds by Pleurotus ostreatus in the process of solid phase cultivation

Mineral substances play an important role in ensuring high-grade growth and high organoleptic quality of the fruit bodies of basidiomycetes. In the process of solid-phase cultivation of the mushroom Pleurotus ostreatus (Jacq.: Fr.) Kumm. the lignocellulosic substrates were enriched with mineral additives of calcium, iron and selenium. Their influence on the synthesis of volatile aroma compounds was investigated by the methods of sensory profile analysis and ultraviolet spectroscopy. Mineral additives in the form of CaCl2, FeSO2•7H2O and Na2SeO3 salts were added to the substrate (sunflower husk, barley straw) before sterilization in concentrations that correspond to the physiological needs of the mushrooms. When carrying out a sensory profile analysis of dried fruit bodies, the following attributes of the flavor were determined: mushroom, woody, sweet, herbaceous, fish, meat, floral, earthy, acidic, putrescent. The conducted profile analysis showed an unequal dependence of the effect of mineral additives for each of the P. ostreatus strains. For IBK-549 and IBK-1535, an increase in the intensity of mushroom notes of aroma was observed with the addition of calcium and selenium to the husks, and for IBK-551, this was observed with the addition of iron and selenium to both substrates. The volatile aroma compounds were extracted with hexane at boiling point for 30 minutes. Absorption spectra were recorded in the wavelength range 200–330 nm. The examined extracts had light absorption maxima at 200–210 and 260–300 nm, which is typical for solutions of unsaturated compounds that have non-conjugated double bonds, saturated and unsaturated aldehydes and ketones. Additions of iron to the substrates increased the intensity of light absorption in comparison with the control. Additions of selenium selectively influenced different strains, and calcium ions did not significantly affect the change in the intensity of light absorption, and therefore the synthesis of volatile compounds by mushrooms. The level of synthesis of aroma-forming substances was higher when cultivating fungi on sunflower husks than on barley straw. This was confirmed both by the obtained aroma profiles and by the recorded absorption spectra of all examined strains. The study showed the possibility of influencing the organoleptic qualities of P. ostreatus fruiting bodies during solid-phase cultivation by supplementing the composition of lignocellulosic substrates with various mineral additives.

Exploration and Exploitation of the Yeast Volatilome

Background: Volatile organic compounds (VOCs) are small molecular mass substances, which exhibit high-vapor pressures, low boiling points, and lipophilic character. VOCs are produced by all organisms including eukaryotic microbes like yeast, whose volatile metabolites are for centuries exploited for examples as flavors in bread, beer, and wine. Notably, while the applications of VOCs are many, the knowledge on their biochemical synthesis is still limited. Objective: We review here the current information of yeast volatile metabolites and techniques to further explore the VOC landscape made possible by improvements of the analytical possibilities, regarding sampling frequency, identification, and quantification and the development to computationally interpret (high-throughput) data. Especially possibilities for online and even real-time analysis should trigger new experimental approaches that elucidate the biochemistry as well as the regulation of VOC synthesis. Baker’s yeast is here the organism of choice as the genetic inventory can be linked to VOC formation and with this in hand improved applications can be envisaged. The physical, chemical or biological properties make many VOCs interesting targets for different industrial sectors while their natural function as semiochemicals or in defense mechanisms can be exploited to engineer synthetic microbial communities or to develop new antibiotics. Conclusion: VOCs produced by microbes including yeast are a chemical diverse group of compounds with highly different applications. The new analytical techniques briefly summarized here will enable the use of VOCs in even broader applications including human health monitoring and bioprocess control. We envisage a bright future for VOC research and for the resulting applications Keywords: Gas chromatography, ion mobility spectrometry, metabolic pathway inference, metabolism, Saccharomyces cerevisiae, VOC, volatile organic compounds, yeast.

The Relationship between CmADHs and the Diversity of Volatile Organic Compounds of Three Aroma Types of Melon (Cucumis melo).

Alcohol dehydrogenase (ADH) plays an important role in aroma volatile compounds synthesis of plants. In this paper, we tried to explore the relationship between CmADHs and the volatile organic compounds (VOCs) in oriental melon. Three different aroma types of melon were used as materials. The principle component analysis of three types of melon fruit was conducted. We also measured the CmADHs expression level and enzymatic activities of ADH and alcohol acyl-transferase (AAT) on different stages of fruit ripening. An incubation experiment was carried out to investigate the effect of substrates and inhibitor (4-MP, 4-methylpyrazole) on CmADHs expression, ADH activity, and the main compounds of oriental melon. The results illustrated that ethyl acetate, hexyl acetate (E,Z)-3,6-nonadien-1-ol and 2-ethyl-2hexen-1-ol were the four principal volatile compounds of these three types of melon. AAT activity was increasing with fruit ripening, and the AAT activity in CH were the highest, whereas ADH activity peaked on 32 DAP, 2 days before maturation, and the ADH activity in CB and CG were higher than that in CH. The expression pattern of 11 CmADH genes from 24 to 36 day after pollination (DAP) was found to vary in three melon varieties. CmADH4 was only expressed in CG and the expression levels of CmADH3 and CmADH12 in CH and CB were much higher than that in CG, and they both peaked 2 days before fruit ripening. Ethanol and 4-MP decreased the reductase activity of ADH, the expression of most CmADHs and ethyl acetate or hexyl acetate contents of CB, except for 0.1 mM 4-MP, while aldehyde improved the two acetate ester contents. In addition, we found a positive correlation between the expression of CmADH3 and CmADH12 and the key volatile compound of CB. The relationship between CmADHs and VOCs synthesis of oriental melon was discussed.

Temporal changes in fungal communities from buckwheat seeds and their effects on seed germination and seedling secondary metabolism

Seed-associated fungal communities affect multiple parameters of seed quality at all stages of production, from seed development to post-harvest storage and germination. We therefore investigated the diversity and dynamics of fungal communities in the seeds of common buckwheat (Fagopyrum esculentum) and Tartary buckwheat (F. tataricum) from harvest to 1 y of storage. Fungal populations in seeds were relatively stable, comprised mainly of field fungi. Incidence of fungi was most likely determined by fungal interspecies direct interactions, as well as by their synthesis of volatile organic compounds. Most prominent antagonistic interactions were seen for two plant pathogens, Alternaria alternata on Botrytis cinerea. Detrimental effects of the fungi on seed germination and seedling development were related to fungal extracellular enzyme activity, and in particular to amylase, cellulase and, polyphenol oxidase. Polyphenol and tannin concentrations in buckwheat seedlings were related to fungal growth rate and intensity of fungal cellulase activity, respectively, which suggests that physical penetration of the fungi through the host tissues is probably the stimulus for the activation of plant defence reactions in these seedlings.