Interaction with and effects on the profile of proteins of Botrytis cinerea by C6 aldehydes

Inhibitory Mechanisms of trans-2-Hexenal on the Growth of Geotrichum citri-aurantii

Geotrichum citri-aurantii (G. citri-aurantii) is one of the most important postharvest pathogens leading to a postharvest loss of citrus by causing sour rot. In this study, the antifungal activity of trans-2-hexenal, a natural component of essential oil, against G. citri-aurantii was evaluated. Trans-2-hexenal treatment inhibited the mycelia growth of G. citri-aurantii with a minimum inhibitory concentration and minimum fungicidal concentration of trans-2-hexenal at 0.50 and 1.00 μL/mL, respectively. Moreover, trans-2-hexenal efficiently reduced the incidence of sour rot of Satsuma fruit inoculated with G. citri-aurantii. Ultrastructural observations and Fourier transform infrared (FT-IR) results showed that trans-2-hexenal treatment affected the cell wall and cell membrane instructions of G. citri-aurantii. The content of β-1,3-glucan was significantly decreased after trans-2-hexenal treatment, but the cell wall permeability was not changed. The decrease in lipid and ergosterol contents might be responsible for this antifungal activity. Several important genes, FKS1, ERG1, ERG7, and ERG11, showed decreasing expression levels after trans-2-hexenal treatment. Molecule-docking results also indicated that trans-2-hexenal could join with the protein of FKS1, ERG1, ERG7, and ERG11 to impact enzyme activities. These results demonstrated that trans-2-hexenal is a promising fungicide for controlling sour rot of harvested citrus fruit by damaging the membrane integrity of G. citri-aurantii.

Evaluation of sulfonated oxidized chitosan antifungal activity against Fusarium graminearum

Chitosan biomaterials are widely used in the biological area because of their broad-spectrum antibacterial activity. However, chitosan cannot be dissolved in a neutral solution, limiting its application in various fields seriously. In this study, water-soluble sulfonated oxidized chitosan (SOCS) with antifungal activity were prepared by oxidization and sulfonation. Its structure was clearly confirmed by spectroscopy data (FTIR, 1H NMR, ¹³C NMR) and elemental analysis. SEM images of OCS and SOCS revealed that there was a little curly and an irregular sheet-like morphologies on them which was attributed to the oxidation and sulfonation on CS. Moreover, the FTIR and NMR indicated that -OH on the CS was oxidized into -COOH on the OCS and -SO₃H groups on the SOCS. The EDS results of OCS and SOCS confirmed the presence of the oxygen element in OCS and the S element in SOCS. All studies confirmed the OCS and SOCS were synthesized successfully. Furthermore, the inhibitory activity of SOCS biocomposites against plant pathogenic fungi, (Fusarium graminearum), was investigated. The results showed that the SOCS have significant inhibitory effects on the mycelial growth of F. graminearum. The EC₅₀ value of SOCS against F. graminearum is 79.46 μg/mL. The research results presented above indicated that SOCS can be used as a candidate material for the control of plant pathogenic fungi, and can broaden the application of chitosan materials in plant protection and sustainable agriculture.Research highlightsSOCS showed better solubility in deionized water.The antifungal effect of SOCS dissolved in acetic acid was higher than that of CS dissolved in acetic acid.SOCS dissolved in water can cause an inhibitory effect on F. graminearum at lower concentrations.

Natural food flavour (E)-2-hexenal, a potential antifungal agent, induces mitochondria-mediated apoptosis in Aspergillus flavus conidia via a ROS-dependent pathway

Natural food flavour (E)-2-hexenal, a green leaf volatile, exhibits potent antifungal activity on Aspergillus flavus, but its antifungal mechanism has not been fully elucidated. In this study, we evaluated (E)-2-hexenal-induced apoptosis in A. flavus conidia and explored the underlying mechanisms of action. Evidence of apoptosis in A. flavus conidia were investigated by methods including fluorescent staining, flow cytometry, confocal laser scanning microscope, and spectral analysis. Results indicated that 4.0 μL/mL (minimum fungicidal concentration, MFC) of (E)-2-hexenal application induced early markers of apoptotic cell death in A. flavus conidia with a rate of 38.4% after 6 h exposure. Meanwhile, typical hallmarks of apoptosis, such as decreased mitochondrial membrane potential (MMP), activated metacaspase activity, fragmented DNA, mitochondrial permeability transition pore (MPTP) opening and cytochrome c (Cyt C) release from mitochondria to the cytosol were also confirmed. Furthermore, intracellular ATP levels were reduced by 63.3 ± 3.6% and reactive oxygen species (ROS) positive cells increased by 31.1 ± 3.1% during A. flavus apoptosis induced by (E)-2-hexenal. l-Cysteine (Cys), an antioxidant, could strongly block the excess ROS generation caused by (E)-2-hexenal, which correspondingly resulted in a significant inhibition of MPTP opening and decrease of apoptosis in A. flavus, indicating that ROS palys a pivotal role in (E)-2-hexenal-induced apoptosis. These results suggest that (E)-2-hexenal exerts its antifungal effect on A. flavus conidia via a ROS-dependent mitochondrial apoptotic pathway.

Trans-2-Hexenal-Based Antifungal Packaging to Extend the Shelf Life of Strawberries

Strawberries are valuable because of their nutritional value, but they are also highly perishable fruits. Fungal decay is the overriding factor that alters the overall quality of fresh strawberries. Because no hygienic treatments to reduce the initial microbial load are feasible, molds develop during postharvest when using conventional packaging. In this study, an antifungal packaging system for strawberries was developed to improve safety and quality. Trans-2-hexenal (HXAL), a natural compound in strawberries, was incorporated into the modified atmosphere packaging (MAP) systems. Zero, 100, and 250 µL of HXAL were included in cellulosic pads and were covered with a polyamide coating to control its release. The pads were placed on the bottom of plastic trays; an amount of250 g of strawberries was added, flow packed in micro-perforated PP bags, and stored at 4 °C for 14 days. Fungal infection was monitored during the storage period, and the optical and textural properties of the strawberries were measured at days 0 and 14. Analysis of the package headspace was conducted to check for the HXAL concentration. HXAL was partially retained in the fruits and was converted into hexyl acetate and 2-hexen-1-ol acetate, but this was only measurably present in the headspace of the active systems. Mold growth was fully inhibited in active packaging although the strawberries were softer and darker than those in the control packages. The active package was not as efficient if the fruits were stored under thermal-abuse conditions (15 and 22 °C).

Toxicity of Five Plant Volatiles to Adult and Egg Stages of Drosophila suzukii Matsumura (Diptera: Drosophilidae), the Spotted-Wing Drosophila

The environmental impact of methyl bromide (MB) has resulted in its phase out as an insecticidal fumigant except for critical use exempted categories. Consequently, there is an urgent need to develop an environmentally sustainable MB alternative fumigant. trans-Cinnamaldehyde (TC), benzaldehyde, allyl isothiocyanate (AITC), hexanal, and ethyl formate (EF) are naturally occurring plant volatiles with insecticidal properties. This study assessed the toxicity of these plant volatiles to adult and egg stages of the spotted-wing drosophila (SWD) (Drosophila suzukii Matsumura). The plant volatile treatments had a significant effect on adult SWD mortality. The descending order of toxicity to adult SWD was benzaldehyde > AITC > TC > hexanal > EF at a headspace concentration of 0.50 μL/L air for 24 h. All the volatiles, at a concentration of 4.00 μL/L air, significantly inhibited larval emergence from SWD eggs in artificial diet compared to the control. At a 0.50 μL/L air level, among the volatiles tested, only AITC exhibited 100% inhibition against larval emergence from SWD eggs in blueberry fruits after 24 h exposure. In summary, this study shows that all volatiles tested elicited varying degrees of toxicity toward SWD adults and eggs. However, AITC was the most efficacious volatile and the one with the greatest promise as a post-harvest fumigant for both adult and egg stages of SWD.

Hexanal Vapor Induced Resistance against Major Postharvest Pathogens of Banana (Musa acuminata L.)

Hexanal, a C-6 aldehyde has been implicated to have antimicrobial properties. Hence, this study was conducted to determine the antifungal activities of hexanal vapor against major postharvest pathogens of banana viz., Colletotrichum gloeosporioides and Lasiodiplodia theobromae. The pathogens were cultured in vitro and exposed to hexanal vapor at 600, 800, 1,000 and 1,200 ppm. Mycelial growth of both fungal pathogens were inhibited completely at 800 ppm and the incidence of anthracnose and stem-end rot diseases reduced by 75.2% and 80.2%, respectively. The activities of peroxidase, polyphenol oxidase, phenylalanine ammonia-lyase and glucanase had transiently increased in hexanal vapor treated banana by 5 to 7 days and declined thereafter. Postharvest treatment of banana with hexanal vapor resulted in phospholipase D inhibition and also resulted in cell wall thickening of the treated fruit, which impeded the penetration of the pathogenic spores. This was further confirmed by scanning electron micrographs. The defense-related protein intermediaries had increased in hexanal vapor treated banana fruit, which suggests induced resistance against C. gloeosporioides and L. theobromae, via., the phenylpropanoid pathway which plays a significant role in hindering the pathogen quiescence. Delayed ripening due to inhibition of phospholipase D enzyme, inhibition of mycelial growth and induced systemic resistance by defense enzymes collectively contributed to the postharvest disease reduction and extended shelf life of fruit.

Roles of plant volatiles in defence against microbial pathogens and microbial exploitation of volatiles

Plants emit a large variety of volatile organic compounds during infection by pathogenic microbes, including terpenes, aromatics, nitrogen-containing compounds, and fatty acid derivatives, as well as the volatile plant hormones, methyl jasmonate, and methyl salicylate. Given the general antimicrobial activity of plant volatiles and the timing of emission following infection, these compounds have often been assumed to function in defence against pathogens without much solid evidence. In this review, we critically evaluate current knowledge on the toxicity of volatiles to fungi, bacteria, and viruses and their role in plant resistance as well as how they act to induce systemic resistance in uninfected parts of the plant and in neighbouring plants. We also discuss how microbes can detoxify plant volatiles and exploit them as nutrients, attractants for insect vectors, and inducers of volatile emissions, which stimulate immune responses that make plants more susceptible to infection. Although much more is known about plant volatile-herbivore interactions, knowledge of volatile-microbe interactions is growing and it may eventually be possible to harness plant volatiles to reduce disease in agriculture and forestry. Future research in this field can be facilitated by making use of the analytical and molecular tools generated by the prolific research on plant-herbivore interactions.

( E)-2-Hexenal, as a Potential Natural Antifungal Compound, Inhibits Aspergillus flavus Spore Germination by Disrupting Mitochondrial Energy Metabolism

Fungal contamination imposes threats to agriculture and food production and human health. A method to safely and effectively restrict fungal contamination is still needed. Here, we report the effect and mode of action of ( E)-2-hexenal, one of the green leaf volatiles (GLVs), on the spore germination of Aspergillus flavus, which can contaminate a variety of crops. The EC₅₀ value, minimum inhibitory concentration (MIC), and minimum fungicidal concentration (MFC) of ( E)-2-hexenal were 0.26, 1.0, and 4.0 μL/mL, respectively. As observed by scanning electron microscopy (SEM), the surface morphology of A. flavus spores did not change after treatment with the MIC of ( E)-2-hexenal, but the spores were shrunken and depressed upon treatment with the MFC of ( E)-2-hexenal. The MIC and MFC of ( E)-2-hexenal induced evident phosphatidylserine (PS) externalization of A. flavus spores as detected by double staining with Annexin V-FITC and propidium iodide, indicating that early apoptosis was potentially induced. Furthermore, sublethal doses of ( E)-2-hexenal disturbed pyruvate metabolism and reduced the intracellular soluble protein content of A. flavus spores during the early stage of germination, and MIC treatment decreased acetyl-CoA and ATP contents by 65.7 ± 3.7% and 53.9 ± 4.0% ( P < 0.05), respectively. Additionally, the activity of mitochondrial dehydrogenases was dramatically inhibited by 23.8 ± 2.2% ( P < 0.05) at the MIC of ( E)-2-hexenal. Therefore, the disruption of mitochondrial energy metabolism and the induction of early apoptosis are involved in the mechanism of action of ( E)-2-hexenal against A. flavus spore germination.

Pre-harvest UV-C irradiation triggers VOCs accumulation with alteration of antioxidant enzymes and phytohormones in strawberry leaves

Recent studies have highlighted the biological and physiological effects of pre-harvest ultraviolet (UV)-C treatment on growing plants. However, little is known about the involvement of volatile organic compounds (VOCs) and their response to this treatment. In this study, strawberry plants were exposed to three different doses of UV-C radiation for seven weeks (a low dose: 9.6kJm^-2; a medium dose: 15kJm^-2; and a high-dose: 29.4kJm^-2). Changes in VOC profiles were investigated and an attempt was made to identify factors that may be involved in the regulation of these alterations. Principle compounds analysis revealed that VOC profiles of UV-C treated samples were significantly altered with 26 VOCs being the major contributors to segregation. Among them, 18 fatty acid-derived VOCs accumulated in plants that received high and medium dose of UV-C treatments with higher lipoxygenase and alcohol dehydrogenase activities. In treated samples, the activity of the antioxidant enzymes catalase and peroxidase was inhibited, resulting in a reduced antioxidant capacity and higher lipid peroxidation. Simultaneously, jasmonic acid level was 74% higher in the high-dose group while abscisic acid content was more than 12% lower in both the medium and high-dose UV-C treated samples. These results indicated that pre-harvest UV-C treatment stimulated the biosynthesis of fatty acid-derived VOCs in strawberry leaf tissue by upregulating the activity of enzymes of the LOX biosynthetic pathway and downregulating antioxidant enzyme activities. It is further suggested that the mechanisms underlying fatty acid-derived VOCs biosynthesis in UV-C treated strawberry leaves are associated with UV-C-induced changes in phytohormone profiles.

Effects of trans-2-hexenal on reproduction, growth and behaviour and efficacy against the pinewood nematode, Bursaphelenchus xylophilus

BACKGROUND

Bursaphelenchus xylophilus is a serious quarantined pest that causes severe damage and major economic losses to pine forests. Because of the adverse effects of some traditional nematicides on humans and the environment, the search for new plant toxicants against these nematodes has intensified. Nematicidal activity of trans-2-hexenal, which is a six-carbon aldehyde present in many plants, was tested against the nematode.

RESULTS

trans-2-Hexenal showed significant efficacy against B. xylophilus in a dose range of 349.5-699 g m^-3 by fumigation of pinewood logs. Additionally, it had significant nematicidal activity against different life stages of B. xylophilus in an in vitro test, with second-stage larvae (L2s) being the most sensitive, with an LC₅₀ value of 9.87 µg mL^-1 at 48 h. Egg hatch was also significantly inhibited. Further studies revealed that trans-2-hexenal inhibited the reproductive activity of B. xylophilus, with negative effects on reproduction rate and egg numbers. Moreover, trans-2-hexenal reduced the body length of B. xylophilus. Respiratory rate and thrashing behaviour of B. xylophilus also decreased following treatment with this compound.

CONCLUSION

trans-2-Hexenal had significant nematicidal activity against B. xylophilus, providing a basis for elucidation of the mode of action of trans-2-hexenal against plant-parasitic nematodes in future studies. © 2016 Society of Chemical Industry.

Antifungal Nanocomposites Inspired by Titanate Nanotubes for Complete Inactivation of Botrytis cinerea Isolated from Tomato Infection

Antifungal silver nanocomposites inspired by titanate nanotubes (AgTNTs) were successfully evaluated for the effective inactivation of the phytopathogenic fungus Botrytis cinerea within 20 min. One-dimensional H₂Ti₃O₇ nanotubes functionalized with silver nanoparticles (AgNPs) exhibit unique surface and antifungal properties for the photoinactivation of B. cinerea. Nanostructured titanates were synthesized by the eco-friendly, practical, microwave-induced, hydrothermal method followed by a highly monodispersive AgNP UV-photodeposition. Protonated nanotubes of ∼11 nm in diameter and four-layers displayed high surface areas, 300 m²/g, with a size functionalization of 5 nm for the AgNPs. UV-vis DRS and XPS allowed the characterization and/or quantification of surface reactive species and cytotoxic silver species such as Ag°, Ag⁺. The effective biocidal properties of the nanocomposites were confirmed by using the well-known Gram-negative bacteria Escherichia coli, and then proceeding to the effective inactivation of the phytopathogenic fungus under visible light. The photoassisted inactivation mechanism was examined by HAADF-STEM, HRTEM, and FESEM electronic microscopies. A plasmalemma invagination due to oxidative stress caused by reactive oxygen, silver cytotoxicity species, and AgTNT sharp morphology damage expands the conidia to induce the cell death. The impact of the eco-friendly inactivation is significant because of the ease with which it is carried out and the possibility of being performed in situ with plants like tomato and grapes, which are ranked among the most valuable agricultural products worldwide.

Green leaf volatiles: biosynthesis, biological functions and their applications in biotechnology

Plants have evolved numerous constitutive and inducible defence mechanisms to cope with biotic and abiotic stresses. These stresses induce the expression of various genes to activate defence-related pathways that result in the release of defence chemicals. One of these defence mechanisms is the oxylipin pathway, which produces jasmonates, divinylethers and green leaf volatiles (GLVs) through the peroxidation of polyunsaturated fatty acids (PUFAs). GLVs have recently emerged as key players in plant defence, plant-plant interactions and plant-insect interactions. Some GLVs inhibit the growth and propagation of plant pathogens, including bacteria, viruses and fungi. In certain cases, GLVs released from plants under herbivore attack can serve as aerial messengers to neighbouring plants and to attract parasitic or parasitoid enemies of the herbivores. The plants that perceive these volatile signals are primed and can then adapt in preparation for the upcoming challenges. Due to their 'green note' odour, GLVs impart aromas and flavours to many natural foods, such as vegetables and fruits, and therefore, they can be exploited in industrial biotechnology. The aim of this study was to review the progress and recent developments in research on the oxylipin pathway, with a specific focus on the biosynthesis and biological functions of GLVs and their applications in industrial biotechnology.

Green leaf volatiles: a plant's multifunctional weapon against herbivores and pathogens

Plants cannot avoid being attacked by an almost infinite number of microorganisms and insects. Consequently, they arm themselves with molecular weapons against their attackers. Plant defense responses are the result of a complex signaling network, in which the hormones jasmonic acid (JA), salicylic acid (SA) and ethylene (ET) are the usual suspects under the magnifying glass when researchers investigate host-pest interactions. However, Green Leaf Volatiles (GLVs), C₆ molecules, which are very quickly produced and/or emitted upon herbivory or pathogen infection by almost every green plant, also play an important role in plant defenses. GLVs are semiochemicals used by insects to find their food or their conspecifics. They have also been reported to be fundamental in indirect defenses and to have a direct effect on pests, but these are not the only roles of GLVs. These volatiles, being probably one of the fastest weapons exploited, are also able to directly elicit or prime plant defense responses. Moreover, GLVs, via crosstalk with phytohormones, mostly JA, can influence the outcome of the plant’s defense response against pathogens. For all these reasons GLVs should be considered as co-protagonists in the play between plants and their attackers.

Synthetic molecular mimics of naturally occurring cyclopentenones exhibit antifungal activity towards pathogenic fungi

The naturally occurring reactive electrophilic species 12-oxo-phytodienoic acid (12-oxo-PDA) is a potent antifungal agent, whereas the plant growth regulator jasmonic acid, which is synthesized from 12-oxo-PDA, is ineffective. To address what structural features of the molecule endow it with antifungal activity, we synthesized a series of molecular mimics of 12-oxo-PDA varying in the length of the alkyl chain at its C-4 ring position. The octyl analogue (4-octyl cyclopentenone) was the most effective at suppressing spore germination and subsequent mycelial growth of a range of fungal pathogens and was particularly effective against Cladosporium herbarum and Botrytis cinerea, with minimum fungicidal concentrations in the range 100–200 µM. Introduction of a carboxyl group to the end of the chain, mimicking natural fatty acids, markedly reduced antifungal efficacy. Electrolyte leakage, indicative of membrane perturbation, was evident in both C. herbarum and B. cinerea exposed to 4-octyl cyclopentenone. Lipid composition analysis of the fungal spores revealed that those species with a high oil content, namely Fusarium oxysporum and Alternaria brassicicola, were less sensitive to 4-octyl cyclopentenone. The comparable hydrophobicity of 4-octyl cyclopentenone and 12-oxo-PDA accounts for the similar spore suppression activity of these two compounds. The relative ease of synthesis of 4-octyl cyclopentenone makes it an attractive compound for potential use as an antifungal agent.

Volatile trans-2-hexenal, a soybean aldehyde, inhibits Aspergillus flavus growth and aflatoxin production in corn

Trans-2-hexenal, a volatile aldehyde, is produced by soybean (Glycine max [L.] Merr) and other plants via the lipoxygenase pathway. In vitro tests showed it significantly (P < 0.001) reduced Aspergillus flavus germinating conidial viability at 10 μM, with approximately 95% viability reduction observed at 20 μM. The viability of nongerminated conidia was not reduced. To test the effectiveness of this volatile to prevent fungal growth in stored corn, trans-2-hexenal was pumped intermittently into glass jars containing corn. Experiments were performed to determine the ability of 2 different pump cycle time-courses to prevent A. flavus growth on sterile corn (23% moisture). Intermittently (30-min pumping period) over 7 d, this volatile was pumped through 350 g of corn kernels inoculated with 1 mL of 3 × 10⁴ conidia of A. flavus. Controls consisted of (1) sterile corn, (2) corn inoculated with A. flavus with no pumped air, and (3) corn inoculated with A. flavus with intermittently pumped air. Aflatoxin B₁ (AFB₁), viability counts, and aldehyde concentration in the headspace were performed in each experiment. To determine whether an increased time period between volatile pumping would prevent A. flavus growth, a 2nd series of experiments were performed that were similar to the 1st series except that trans-2-hexenal (only) was pumped for a 30-min period every 12 h. Experiments were performed 3 times for each time course. Both experiments showed that intermittent pumping of volatile trans-2-hexenal significantly (P < 0.001) prevented A. flavus growth and aflatoxin B₁ production over a 7-d period.

PRACTICAL APPLICATION

Results from this study indicate that intermittent pumping of volatile trans-2-hexenal could be used to protect stored corn from A. flavus growth and aflatoxin contamination.

Effect of soybean volatile compounds on Aspergillus flavus growth and aflatoxin production

Soybean homogenates produced volatile compounds upon exposure to lipase. These induced volatiles were identified by SPME. Seventeen volatile compounds identified by SPME were chosen for determination of their ability to inhibit Aspergillus flavus growth and aflatoxin B(1) (AFB1) production in a solid media assay. These volatiles included aldehydes, alcohols, ketones, and furans. Of the tested compounds, the aldehydes showed the greatest inhibition of fungal growth and AFB1 production. These compounds inhibited up to 100% of the observed growth and AFB1 production as compared to the controls. The greatest activity by the aldehydes to disrupt growth was ranked as follows: 2,4 hexadienal > benzaldehyde > 2-octenal > (E)-2-heptenal > octanal > (E)-2-hexenal > nonanal > hexanal. The greatest activity by the aldehydes to reduce AFB1 was ranked as follows: (E)-2-hexenal > 2,4 hexadienal > (E)-2-heptenal > hexanal > nonanal. (E)-2-hexenal and (E)-2-heptenal were tested further in an A. flavus-inoculated corn kernel assay. Both compounds prevented colonization by A. flavus and eliminated AFB1 production when exposed to compound volumes < 10 muL as also shown in the solid media assay. The results suggest that soybeans react to lipase by production of potent antifungal volatiles.

Direct fungicidal activities of C6-aldehydes are important constituents for defense responses in Arabidopsis against Botrytis cinerea

C6-aldehydes, such as (Z)-3-hexenal, (E)-2-hexenal, and n-hexanal, are volatile compounds formed by hydroperoxide lyase (HPL) and found in most terrestrial plants. They are fungicidal and bactericidal compounds, and are also signaling compounds to induce defense responses in plants. Transgenic plants having overexpressed or suppressed HPL activity (SH or ASH, respectively) showed lower or higher susceptibility against a necrotrophic fungal pathogen, Botrytis cinerea. In this study, we examined whether the modulated susceptibility was accountable to the direct fungicidal activity or to the signaling potency of C6-aldehydes. When wild-type Arabidopsis leaves were inoculated with B. cinerea, HPL expression was upregulated, and concomitantly, the amounts of C6-aldehydes increased. Higher amounts of C6-aldehydes found in inoculated SH plants inhibited growth of B. cinerea in vitro, while lower amounts found in ASH plants caused no inhibitory effect on the fungi. Thus, it was suggested that direct fungicidal activity of C6-aldehydes accounted for the modulated susceptibility. With SH plants higher amounts of camalexin could be found, but with the ASH plants no difference from wild-type plants could be found. Surplus amounts of C6-aldehydes could induce formation of camalexin as signaling compounds; however, this was not the case with wild-type and ASH plants. Accordingly, it could be assumed that direct fungicidal activity of C6-aldehydes were prominently responsible to the defense against B. cinerea but their signaling roles could be little responsible if any.

Aspergillus niger metabolism of citrus furanocoumarin inhibitors of human cytochrome P450 3A4

Fungi metabolize polycyclic aromatic hydrocarbons by a number of detoxification processes, including the formation of sulfated and glycosidated conjugates. A class of aromatic compounds in grapefruit is the furanocoumarins (FCs), and their metabolism in humans is centrally involved in the "grapefruit/drug interactions." Thus far, the metabolism by fungi of the major FCs in grapefruit, including 6', 7'-epoxybergamottin (EB), 6', 7'-dihydroxybergamottin (DHB), and bergamottin (BM), has received little attention. In this study, Aspergillus niger was observed to convert EB into DHB and a novel water-soluble metabolite (WSM). Bergaptol (BT) and BM were also metabolized by A. niger to the WSM, which was identified as BT-5-sulfate using mass spectrometry, UV spectroscopy, chemical hydrolysis, and (1)H and (13)C nuclear magnetic resonance spectroscopy. Similarly, the fungus had a capability of metabolizing xanthotoxol (XT), a structural isomer of BT, to a sulfated analog of BT-5-sulfate, presumably XT-8-sulfate. A possible enzyme-catalyzed pathway for the grapefruit FC metabolism involving the cleavage of the geranyl group and the addition of a sulfate group is proposed.