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Showing papers on "Phytoalexin published in 2006"


Journal ArticleDOI
TL;DR: Chitosan (CHN), a deacetylated derivative of chitin, was shown to be efficient in promoting plant defense reactions and significantly reduced the infection of grapevine leaves by Botrytis cinerea and Plasmopara viticola, and in combination with CuSO(4) conferred protection against both pathogens.
Abstract: Aziz, A., Trotel-Aziz, P., Dhuicq, L., Jeandet, P., Couderchet, M., and Vernet, G. 2006. Chitosan oligomers and copper sulfate induce grapevine defense reactions and resistance to gray mold and downy mildew. Phytopathology 96:1188-1194. Chitosan (CHN), a deacetylated derivative of chitin, was shown to be efficient in promoting plant defense reactions. CHN oligomers of different molecular weight (MW) and degree of acetylation (DA) triggered an accumulation of phytoalexins, trans- and cis-resveratrol and their derivatives e-viniferin and piceid, in grapevine leaves. Highest phytoalexin production was achieved within 48 h of incubation with CHN at 200 µg/ml with an MW of 1,500 and a DA of 20% (CHN1.5/20), while oligomers with greater MW were less efficient, indicating that a specific MW threshold could be required for phytoalexin response. Treatment of grapevine leaves by highly active CHN1.5/20 also led to marked induction of chitinase and β-1,3-glucanase activities. CHN1.5/20 applied together with copper sulfate (CuSO4) strongly induced phytoalexin accumulation. CuSO4 alone, especially at low concentrations also elicited a substantial production of phytoalexins in grapevine leaves. Evidence is also provided that CHN1.5/20 significantly reduced the infection of grapevine leaves by Botrytis cinerea and Plasmopara viticola, and in combination with CuSO4 conferred protection against both pathogens.

220 citations


Journal ArticleDOI
TL;DR: This work shows that the chemically pure heptakis(2,6-di-O-methyl)-betaCD caused a dramatic extracellular accumulation of the phytoalexin resveratrol and changes in peroxidase activity and isoenzymatic pattern.
Abstract: In grapevine (Vitis vinifera L.), defense responses after microbial infection or treatment with elicitors involve accumulation of phytoalexins, oxidative burst, and the synthesis of pathogenesis-related proteins. Oligosaccharide fractions from fungal or algal cell walls efficiently induce the defense responses, but a detailed analysis of the elicitor−plant cell surface interaction at the molecular level is precluded by the lack of chemically pure oligosaccharide elicitors. A grapevine liquid cell culture system was used to examine the properties of cyclodextrins (CDs) as inducers of defense responses. This work shows that the chemically pure heptakis(2,6-di-O-methyl)-βCD caused a dramatic extracellular accumulation of the phytoalexin resveratrol and changes in peroxidase activity and isoenzymatic pattern. Other modified CDs tested on several grapevine cell lines resulted in different eliciting capacities of CDs and different sensibilities of the cell lines. The spent medium of elicited cultures was shown ...

138 citations


Journal ArticleDOI
TL;DR: The occurrence of phenalenone chromophores in phytoalexins of plants originally nonphototoxic suggests that these plants respond to pathogen attacks by biosynthesizing singlet oxygen photosensitizers able to use solar energy for defense.
Abstract: Plants defend themselves from pathogen infections or mechanical injury by a number of mechanisms, including the induced biosynthesis of antimicrobial secondary metabolites. These compounds, termed phytoalexins, represent a very economical way to counteract hazard, because the carbon and energy resources are diverted to phytoalexin synthesis only at the early period of attack and only at its site. The occurrence of phenalenone chromophores in phytoalexins of plants originally nonphototoxic suggests that these plants respond to pathogen attacks by biosynthesizing singlet oxygen photosensitizers able to use solar energy for defense. This concept may have implications for the development of novel crop protection strategies.

128 citations


Journal ArticleDOI
TL;DR: FA at nontoxic concentrations (i.e. below 10(-6) m) was able to induce the synthesis of phytoalexin, a classic delayed plant response to pathogen, and can act as an elicitor at nanomolar concentrations.
Abstract: Summary • Fusaric acid (FA) is a toxin produced by Fusarium species. Most studies on FA have reported toxic effects (for example, alteration of cell growth, mitochondrial activity and membrane permeability) at concentrations greater than 10−5 m. FA participates in fungal pathogenicity by decreasing plant cell viability. However, FA is also produced by nonpathogenic Fusarii, potential biocontrol agents of vascular wilt fusaria. The aim of this study was to determine whether FA, at nontoxic concentrations, could induce plant defence responses. • Nontoxic concentrations of FA were determined from cell-growth and O2-uptake measurements on suspensions of Arabidopsis thaliana cells. Ion flux variations were analysed from electrophysiological and pH measurements. H2O2 and cytosolic calcium were quantified by luminescence techniques. • FA at nontoxic concentrations (i.e. below 10−6 m) was able to induce the synthesis of phytoalexin, a classic delayed plant response to pathogen. FA could also induce rapid responses putatively involved in signal transduction, such as the production of reactive oxygen species, and an increase in cytosolic calcium and ion channel current modulations. • FA can thus act as an elicitor at nanomolar concentrations.

103 citations


Journal ArticleDOI
TL;DR: This treatment may offer the possibility of controlling both foliage and tuber blight and could have a major impact in reducing over-winter survival of P. infestans in tubers.
Abstract: The mechanism involved in systemic acquired resistance (SAR) can be non-specifically induced in susceptible plants. In response to pathogens, plants' natural defence mechanisms include the production of lignin and phytoalexins and the induction of plant enzymes. The aim of this research was to study the induction of SAR mediated by the chemical activator DL-3-aminobutyric acid (BABA) and the fungicide fosetyl-aluminium in potato cultivars with different levels of resistance against Phytophthora infestans (Mont) de Bary. To study the chemical induction of the resistance, the foliage of several potato cultivars was sprayed with BABA, fosetyl-aluminium or water (as a control treatment). After 3 days the foliage was inoculated with P. infestans. Seven days after inoculation, development of disease symptoms in the foliage was assessed. In postharvest tuber samples, evidence for enhancement of the defence response was evaluated by measuring the protein content of several hydrolytic enzymes as well as the phenol and phytoalexin content. The highest level of protection against late blight was observed when the chemicals were applied at early stages of crop development. An increase in resistance to late blight was also detected in tubers after harvest. There was also an increase in the protein level of beta-1,3-glucanase and aspartic protease as well as in the phenol and phytoalexin content of potato tuber discs obtained from postharvest tubers of treated plants. Thus the protective effect seemed to persist throughout the whole crop cycle. This treatment may offer the possibility of controlling both foliage and tuber blight and could have a major impact in reducing over-winter survival of P. infestans in tubers.

97 citations


Journal ArticleDOI
TL;DR: It can be suggested that resistance responses of Arabidopsis could be induced by the volatiles mostly independent on their reactivities and that a common signaling pathway unaffected by the reactivities of compound was activated by thevolatiles.

76 citations


Journal ArticleDOI
TL;DR: Neither resveratrol nor phenolic acids were found in the root mucilage; the prenylated stilbenes were restricted to the mucilage and were not found in other organs of the peanut plant.
Abstract: The peanut plant (Arachis hypogaea) is known to produce stilbene phytoalexins as a defensive response to fungal invasion; however, the distribution of phytoalexins among different organs of the peanut plant at early stages of growth under axenic conditions has not been studied. Axenic plants produced a stilbenoid, resveratrol, as well as soluble bound and free phenolic acids, including 4-methoxycinnamic acid, which is reported in peanuts for the first time. Neither resveratrol nor phenolic acids were found in the root mucilage; the prenylated stilbenes were restricted to the mucilage and were not found in other organs of the peanut plant. These findings may lead to a better understanding of the defensive role of peanut stilbenes and phenolic acids.

62 citations


Journal ArticleDOI
Shujun Liu1, Yuanlei Hu1, Xiaoli Wang1, Jin Zhong1, Zhongping Lin1 
TL;DR: Anticancer assay in HeLa cells revealed that apoptosis was induced by 200 microM of resveratrol extracted from transgenic lettuce, which was comparable to the amount in grape skin.
Abstract: Resveratrol (trans-3,5,4'-trihydroxystilbene) is a plant phytoalexin which has positive effects on human health. Stilbene synthase (STS) is a key enzyme involved in resveratrol biosynthesis. To construct a vector for STS expression in lettuce plant, a cDNA-encoding STS of Parthenocissus henryana was fused to the Cauliflower mosaic virus (CaMV) 35S promoter, and the bar gene was used as a selective marker gene. To increase the expression of STS, the expression cassette was flanked by MARs. In transgenic lettuce plants, an additional compound was identified as resveratrol by HPLC and ESI-MS. Quantitative analysis showed that the average content of resveratrol reached 56.40 +/- 5.52 microg/g leaf fresh weight, which was comparable to the amount in grape skin. Anticancer assay in HeLa cells revealed that apoptosis was induced by 200 microM of resveratrol extracted from transgenic lettuce.

60 citations


Journal ArticleDOI
TL;DR: The syntheses and antifungal activity of caulilexins A-C against the economically important pathogenic fungi Leptosphaeria maculans, Rhizoctonia solani and Sclerotinia sclerotiorum are reported, and the first synthesis of brassicanal C is reported.

60 citations


Journal ArticleDOI
TL;DR: It is indicated that accumulation of phenolics but not camalexin may be involved in resistance against bacterial pathogens used in this study, and a strong correlation was observed between the timing and extent of cell death and high levels of phenolic and lignin accumulation in cell-walls and cytoplasm of cells undergoing the HR.

54 citations


Journal ArticleDOI
TL;DR: Results indicate that CA is specifically recognized by rice and is a different type of elicitor from fungal cerebroside, indicating that bile acid induced defense responses in plants.
Abstract: When plants interact with certain pathogens, they protect themselves by generating various defense responses. These defense responses are induced by molecules called elicitors. Since long ago, composts fermented by animal feces have been used as a fertilizer in plant cultivation, and recently, have been known to provide suppression of plant disease. Therefore, we hypothesized that the compounds from animal feces may function as elicitors of plant defense responses. As a result of examination of our hypothesis, an elicitor of rice defense responses was isolated from human feces, and its structure was identified as cholic acid (CA), a primary bile acid in animals. Treatment of rice (Oryza sativa) leaves with CA induced the accumulation of antimicrobial compounds (phytoalexins), hypersensitive cell death, pathogenesis-related (PR) protein synthesis, and increased resistance to subsequent infection by virulent pathogens. CA induced these defense responses more rapidly than did fungal cerebroside, a sphingolipid elicitor isolated from the rice pathogenic fungus Magnaporthe grisea. Furthermore, fungal cerebroside induced both types of rice phytoalexins, phytocassanes and momilactones, whereas CA mainly induced phytocassanes, but not momilactones. In the structure-activity relationship analysis, the hydroxyl groups at C-7 and C-12, and the carboxyl group at C-24 of CA contributed to the elicitor activity. These results indicate that CA is specifically recognized by rice and is a different type of elicitor from fungal cerebroside. This report demonstrated that bile acid induced defense responses in plants.

Journal ArticleDOI
TL;DR: It is concluded that Gα mediates the stimulation of PLA2 by low elicitor concentrations and that the resulting peak of LPC initiates a transient efflux of vacuolar protons, generating an acidic peak of the cytoplasmic pH that causes the expression of enzymes of phytoalexin production independent of the hypersensitive response.
Abstract: The function of a Galpha protein in the elicitation of phytoalexin (benzophenanthridine) biosynthesis was characterized in cultured cells of California poppy (Eschscholzia californica). Both the decrease of Galpha content via antisense transformation and the expression of recombinant anti-Galpha single-chain antibodies strongly impaired the induction of alkaloid biosynthesis by low elicitor concentrations. All transgenic cell types were deficient in two elicitor-triggered early signal events: activation of phospholipase A2 (PLA2) and efflux of vacuolar protons. The lacking H+ efflux could be restored (1) by adding lysophosphatidylcholine (LPC), a product of PLA2 activity, to vacuoles in situ and (2) by exposing intact cells to isotonic, near-neutral HEPES buffers. The latter treatment induced alkaloid biosynthesis in the absence of elicitor and in Galpha-deficient cells. We conclude that Galpha mediates the stimulation of PLA2 by low elicitor concentrations and that the resulting peak of LPC initiates a transient efflux of vacuolar protons. In this way, an acidic peak of the cytoplasmic pH is generated that causes the expression of enzymes of phytoalexin production independent of the hypersensitive response.

Journal ArticleDOI
TL;DR: The isolation and structure of a phytoalexin, malvone A (2-methyl-3-methoxy-5,6-dihydroxy-1,4-naphthoquinone) is reported and showed water molecules were located in channels that run along the a-axis.

Journal ArticleDOI
TL;DR: Exposure to enriched CO 2 atmospheres can change inducible defensive responses in soybean against pathogens, and changes occurred in individual metabolites and were dependent on the cultivar resistance patterns.

Journal ArticleDOI
TL;DR: In the isolated hearts subjected to ischemia/reperfusion, the rats fed with modified tomato exhibited better cardiac performance, reduced myocardial infarct size and decreased number of apoptotic cardiomyocytes, and reduced oxidative stress compared to unmodified tomato or resveratrol alone indicating superior cardioprotective abilities of modified tomatoes.
Abstract: Tomato (Lycopersicon esculentum) is a vegetable rich in antioxidants, such as lycopene, lutein, and zeaxanthin. Their presence is responsible for the characteristic ability of this product to inhibit the formation of reactive oxygen species, including singlet oxygen. The grapes and wines derived from grapes also contain powerful antioxidants. The antioxidant effect is derived from the polyphenols such as resveratrol and proanthocyanidin. Resveratrol is phytoalexin that is synthesized via the activation of the gene, stilbene synthase (STS). We decided to determine if the introduction of this gene into Lycopersicon esculentum Mill could modify its antioxidant activity. Using Electronic Paramagnetic Resonance (EPR) spectroscopy, which permits the detection of antiradical activity, especially •OH (hydroxyl radical), we showed that the antioxidant activity of the products, into which the gene STS had been introduced, was almost double than that of natural products and that their activity was especially pronounced due to ripening. Moreover, resveratrol concentrations in modified tomatoes were much higher than that found in the individual fruit. In the isolated hearts subjected to ischemia/reperfusion, the rats fed with modified tomato exhibited better cardiac performance, reduced myocardial infarct size and decreased number of apoptotic cardiomyocytes, and reduced oxidative stress compared to unmodified tomato or resveratrol alone indicating superior cardioprotective abilities of modified tomatoes.

Journal ArticleDOI
TL;DR: It is shown that higher concentrations of ethanol induced a shift from apoptotic to necrotic cell death in human K562 cells, and that resveratrol, a grape-derived phytoalexin with known antioxidant and anti-inflammatory properties, inhibited or enhanced ethanol-induced apoptosis/necrosis depending on the treatment dosage.

Journal ArticleDOI
TL;DR: Results are promising with respect to the use of thiabendazole-containing pesticides as alternatives to currently used pesticides for control of esca in vines.

Journal ArticleDOI
TL;DR: Semi-quantitative RT-PCR revealed that the mRNA was expressed in all tissues tested and was not affected by CuCl2, jasmonic acid or UV treatment, and the enzyme also methylated flavonoids which have two adjacent hydroxyl groups in the B ring.
Abstract: A putative O-methyltransferase cDNA was cloned from UV-irradiated rice leaves based on an amino acid sequence reported as that of naringenin 7-O-methyltransferase, which is involved in the biosynthesis of a rice phytoalexin, sakuranetin. However, the recombinant protein (approximately 41 kDa) expressed in Escherichia coli showed not naringenin 7-O-methyltransferase activity but caffeic acid 3-O-methyltransferase activity. Semi-quantitative RT-PCR revealed that the mRNA was expressed in all tissues tested and was not affected by CuCl2, jasmonic acid or UV treatment. The enzyme also methylated flavonoids which have two adjacent hydroxyl groups in the B ring. © Pesticide Science Society of Japan

Journal ArticleDOI
TL;DR: Inorganic phosphate is discussed as a signal transmitter inducing part of the plant defense responses when inorganic phosphate was applied endogenously to pea tissues but phytoalexin production was not.
Abstract: When inorganic phosphate, a common and essential element for organisms, was applied endogenously, a rejection reaction and superoxide generation were induced in pea tissues but phytoalexin production was not. Phosphate-induced superoxide generation was sensitive to cycloheximide (CHX) and salicylhydroxamic acid (SHAM), indicating that part of the generation was dependent upon the expression of peroxidase gene(s). Peroxidases (POXs) are well known not only to scavenge hydrogen peroxide with phenolics but also to generate superoxide via NADH oxidation in the presence of p-coumaric acid and manganese ion. We cloned five pea POX cDNAs that are predicted to be located outside of the cells. The accumulation of five POX mRNAs, NTPase mRNA, and phenylalanine ammonia-lyase mRNA was measured by semiquantitative reverse transcription-polymerase chain reaction. The expression of the five POX genes was induced by a fungal elicitor. On the other hand, inorganic phosphate induced the accumulation of POX11, POX14, and POX21 mRNAs but not of POX13, POX29, and PsPAL1 mRNAs within 1–3 h after treatment of pea seedlings. In view of these findings, we discuss inorganic phosphate as a signal transmitter inducing part of the plant defense responses.

Journal ArticleDOI
TL;DR: This is the first report indicating that the stress-induced compound, 6,7-dimethoxycoumarin, isolated from P. digitatum-infected Valencia fruit confers resistance against the mycotoxigenic fungi A. parasiticus and F. verticillioides.

Journal ArticleDOI
TL;DR: The data suggests that elicitation of defense responses in the root alters metabolism in such a way that results in the modification of the architecture of bean roots.
Abstract: Phytoalexin accumulation is one of a myriad of plant defense responses; these responses can be elicited by pathogens or molecules such as oligogalacturonides (OGAs). Phytoalexin production has been considered a vital component of the resistance mechanisms that determine the outcome of many plant-microbe interactions. Besides inducing defense responses, OGAs have been shown to affect plant development, which normally is controlled by plant hormones, particularly auxin. In this work we measured phytoalexin accumulation in roots of bean (Phaseolus vulgaris L.) seedlings grown in the presence or absence of the auxin 3-naphtalenacetic acid (NAA) and treated with a decagalacturonide (OGA10). We found that OGA10 (0.01 mM) caused phytoalexin production and also inhibited main root elongation and the formation of secondary roots by ca. 33%. Expression of Cycb 2-2 was also inhibited, while pal and chs were highly expressed. The root growth inhibition was not overcome by the addition of a stimulatory concentration of auxin (NAA 0.1 µM). The data suggests that elicitation of defense responses in the root alters metabolism in such a way that results in the modification of the architecture of bean roots.

Journal ArticleDOI
TL;DR: To eliminate the risk of pathogen attack and activation of plants in the field, tissue cultures were initiated with the aim of producing cell suspension cultures and jasmonic acid was used as an elicitor to activate the resistance system of the plant, and to initiate the synthesis of defense compounds.

Journal Article
TL;DR: The biocontrol yeast Rhodotorula glutinis, isolate 21A, obtained from tomato fruit was used to control Penicillium digitatum, P. italicum and Botrytis cinerea on artificially wounded citrus fruit, revealing a fast colonization of the growing fungal mycelia by the yeast cells, but no sign of lytic activity on hyphae was observed.
Abstract: The biocontrol yeast Rhodotorula glutinis, isolate 21A, obtained from tomato fruit was used to control Penicillium digitatum, P. italicum and Botrytis cinerea on artificially wounded citrus fruit. Orange and satsuma mandarin fruit were treated with the biocontrol yeast, inoculated with the pathogens and stored for 7 days at 23 degrees C. On orange fruit the antagonist compared to the control reduced decay by 92.2, 88.4 and 96.2% for P. digitatum, P. italicum and B. cinerea, respectively. On satsuma mandarin fruit the same pathogens were inhibited by 96.2, 91.2 and 90.0%, respectively. Scanning electron microscope observations, focusing on the antagonist-pathogen interactions, revealed a fast colonization of the growing fungal mycelia by the yeast cells, but no sign of lytic activity on hyphae was observed. Moreover, the fruit accumulated the phytoalexins scoparone and scopoletin into artificial wounds previously treated by the yeast and either inoculated or uninoculated with the pathogen. The concentration of scoparone, which showed higher accumulation in fruit tissues, varied significantly in relation to the time lag between the application of the antagonist and the inoculation with the pathogen. In particular, the concentration of scoparone 4 days after application of the sole yeast was 69.0 microg x g(-1) fresh weight (FW), 6.3 times higher than in the uninoculated wounded tissues (11.0 microg x g(-1) FW). The phytoalexin accumulation was low (13.0 microg x g(-1)FW) applying the yeast jointly with P. digitatum into wounds, while it increased consistently (74.0 microg x g(-1)FW) when the antagonist was applied 24 h before the pathogen.

Journal ArticleDOI
TL;DR: The effects of AM fungi on the 3 groups of secondary metabolites are summarized and the species specificity in AM affected biosynthesis of alkaloids is shown.
Abstract: Mycorrhizal fungi form the most important mutualistic symbioses on earth with plants The most prevalent type of mycorrhizal fungi are the arbuscular mycorrhizal (AM) fungi Much research has shown that the development of AM fungi is correlated with plant secondary metabolism AM fungi can directly or indirectly affect plant secondary metabolic processes Secondary metabolites are classified into 3 groups, terpenoids, phenolics and alkaloids In this paper, we summarize the effects of AM fungi on the 3 groups of secondary metabolites The relationship between terpenoids and AM fungi have been well studied, and some research has explored interactive mechanisms at the molecular level Blumenin was first isolated and identified from mycorrhizal cereals, and its biosynthesis has been proven via the Glyceraldehyde 3_phosphate/ pyruvate pathway (MEP) by an isotopic labeling method Since then, the accumulation of blumenin induced by AM fungi and differences in blumenin levels among different kinds of AM fungi have been observed Studies on 1_deoxy_D_xylulose_5_phosphate synthase (DXS) and 1_deoxy_D_xylulose_5_phosphate reductoisomerase (DXR), two key enzymes in the biosynthesis of carotenoid metabolism via the MEP pathway, have found to increase the transcription of DXS and DXR in plants with AM fungi Moreover it was temporarily and spatially correlated with the accumulation of apocarotenoids Subsequently, two genes were identified: TC78589 encoding DXS2 which is highly expressed in roots inoculated with AM fungi, and TC77051 encoding mevalonate disphosphate decarboxylase, which is catalysed in the synthesis of terpenoids in the mevalonate pathway Although both genes separately encode enzymes in different pathways, an enhancement of carotenoid biosynthesis has been observed The interaction between phenolic compounds (such as phytoalexin, wall_bound phenol, flavonoids, isoflavonoids and their derivatives) and AM fungi also has been investigated intensively It has been shown that some flavonoids stimulated the spore germination and hyphal growth of AM fungi, and the contents of flavonoids increased before the infection of AM fungi Therefore some investigators hypothesized that flavonoids were a signal compound during the formation of AM fungi Afterward, increased levels of flavonoids were found after the formation of AM fungi which was related to specific species of AM fungi In addition, some experiments have indicated that the activity of peroxidase (POD), phenylalanine ammonia_lyase (PAL) and polyphenol oxidase (PPO) were significantly enhanced in AM plants In phenylpropamoid metabolism, there are two different signaling pathways in the accumulation of secondary metabolites induced by the mycorrhizal fungus: one is through the induction of PAL and chalcone synthase (CHS), and the other is through the suppression of isoflavone reductase (IFR)Although little research seldom has examined the relationship between alkaloids and AM fungi, a recent study has shown that the formation of AM is beneficial to the accumulation of alkaloids This study also showed the species specificity in AM affected biosynthesis of alkaloids

Journal ArticleDOI
TL;DR: In this paper, the authors examined phytoalexin production in florets of cauliflower (Brassica oleracea var. botrytis) under abiotic (UV light) elicitation.
Abstract: Our continuous search for phytoalexins from crucifers led us to examine phytoalexin production in florets of cauliflower (Brassica oleracea var. botrytis) under abiotic (UV light) elicitation. Four known (isalexin, S-(-)-spirobrassinin, 1-methoxybrassitin, brassicanal C) and three new (caulilexins A-C) phytoalexins were isolated. The syntheses and antifungal activity of caulilexins A-C against the economically important pathogenic fungi Leptosphaeria maculans, Rhizoctonia solani and Sclerotinia sclerotiorum, and the first synthesis of brassicanal C are reported.


01 Jan 2006
TL;DR: The interaction of a vesicular-arbuscular mycorrhizal fungus Glomus fasciculatum with a wilt-causing soil borne pathogen, Fusarium oxysporum, was studied in cowpea (Vigna unguiculata) as discussed by the authors.
Abstract: The interaction of a vesicular-arbuscular mycorrhizal fungus Glomus fasciculatum with a wilt-causing soil borne pathogen, Fusarium oxysporum, was studied in cowpea (Vigna unguiculata) It was found that pre-establishment by vesicular-arbuscular mycorrhizal fungus reduced the colonization of the pathogen and the severity of the disease, as determined by reduction in vascular discolouration index In mycorrhizal plants, the production of phytoalexin compounds was always higher than in the nonmycorrhizal plants There appeared to be a direct correlation between the concentration of the phytoalexins and the degree of mycorrhizal association Three different compounds with Rf values of 0·23 (I), 0·17 (II) and 0·11 (III) were obtained from mycorrhizal plants Similar compounds were also found to be induced by an abiotic elicitor CuSO4 The first compound was identified as an isoflavonoid, daidzein and the other two remain to be identified These compounds were checked for their antifungal activity in vitro The germination of conidial spores of Fusarium oxysporum was strongly inhibited by the compound III than the other two It is argued that the production of phytoalexin compounds in mycorrhizal plant could be one of the mechanisms imparting tolerance of the plants to wilt disease

Journal Article
TL;DR: Resveratrol is one of phytoalexin compounds in peanut seed, which can be elicited by slicing and inoculation with Aspergillus flavus, and the accumulation in resistant genotypes reached the maximum at 3d after inoculation, while in susceptible genotypes it reached the same level at 4d.
Abstract: Resveratrol is one of phytoalexin compounds in peanut seed,which can be elicited by slicing and inoculation with Aspergillus flavus.GC-MS analysis of resveratrol from resistant/susceptible peanut seeds after inoculation with Aspergillus flavus showed that the resistance to Aspergillus flavus invasion was related to their capacity to synthesize resveratrol.The accumulation of resveratrol in resistant genotypes reached the maximum at 3d after inoculation,whereas in susceptible genotypes it reached the same level at 4d.Cyclohexnomycin at a concentration of 100μg/mL caused a 93% decrease in total resveratrol production,while actinomycin D(100μg/mL) caused only a 10% decrease in resveratrol content.

Journal ArticleDOI
TL;DR: In this paper, the occurrence of phenalenone chromophores in phytoalexins of plants originally nonphototoxic suggests that these plants respond to pathogen attacks by biosynthesizing singlet oxygen photosensitizers able to use solar energy for defense.
Abstract: Plants defend themselves from pathogen infections or mechanical injury by a number of mechanisms, including the induced biosynthesis of antimicrobial secondary metabolites. These compounds, termed phytoalexins, represent a very economical way to counteract hazard, because the carbon and energy resources are diverted to phytoalexin synthesis only at the early period of attack and only at its site. The occurrence of phenalenone chromophores in phytoalexins of plants originally nonphototoxic suggests that these plants respond to pathogen attacks by biosynthesizing singlet oxygen photosensitizers able to use solar energy for defense. This concept may have implications for the development of novel crop protection strategies.