Showing papers on "Phytoalexin published in 2011"

Resistance to hemi-biotrophic F. graminearum infection is associated with coordinated and ordered expression of diverse defense signaling pathways.

Abstract: Fusarium species cause serious diseases in cereal staple food crops such as wheat and maize. Currently, the mechanisms underlying resistance to Fusarium-caused diseases are still largely unknown. In the present study, we employed a combined proteomic and transcriptomic approach to investigate wheat genes responding to F. graminearum infection that causes Fusarium head blight (FHB). We found a total of 163 genes and 37 proteins that were induced by infection. These genes and proteins were associated with signaling pathways mediated by salicylic acid (SA), jasmonic acid (JA), ethylene (ET), calcium ions, phosphatidic acid (PA), as well as with reactive oxygen species (ROS) production and scavenging, antimicrobial compound synthesis, detoxification, and cell wall fortification. We compared the time-course expression profiles between FHB-resistant Wangshuibai plants and susceptible Meh0106 mutant plants of a selected set of genes that are critical to the plants' resistance and defense reactions. A biphasic phenomenon was observed during the first 24 h after inoculation (hai) in the resistant plants. The SA and Ca2+ signaling pathways were activated within 6 hai followed by the JA mediated defense signaling activated around 12 hai. ET signaling was activated between these two phases. Genes for PA and ROS synthesis were induced during the SA and JA phases, respectively. The delayed activation of the SA defense pathway in the mutant was associated with its susceptibility. After F. graminearum infection, the endogenous contents of SA and JA in Wangshuibai and the mutant changed in a manner similar to the investigated genes corresponding to the individual pathways. A few genes for resistance-related cell modification and phytoalexin production were also identified. This study provided important clues for designing strategies to curb diseases caused by Fusarium.

Cytokinins Mediate Resistance against Pseudomonas syringae in Tobacco through Increased Antimicrobial Phytoalexin Synthesis Independent of Salicylic Acid Signaling

Abstract: Cytokinins are phytohormones that are involved in various regulatory processes throughout plant development, but they are also produced by pathogens and known to modulate plant immunity A novel transgenic approach enabling autoregulated cytokinin synthesis in response to pathogen infection showed that cytokinins mediate enhanced resistance against the virulent hemibiotrophic pathogen Pseudomonas syringae pv tabaci This was confirmed by two additional independent transgenic approaches to increase endogenous cytokinin production and by exogenous supply of adenine- and phenylurea-derived cytokinins The cytokinin-mediated resistance strongly correlated with an increased level of bactericidal activities and up-regulated synthesis of the two major antimicrobial phytoalexins in tobacco (Nicotiana tabacum), scopoletin and capsidiol The key role of these phytoalexins in the underlying mechanism was functionally proven by the finding that scopoletin and capsidiol substitute in planta for the cytokinin signal: phytoalexin pretreatment increased resistance against P syringae In contrast to a cytokinin defense mechanism in Arabidopsis (Arabidopsis thaliana) based on salicylic acid-dependent transcriptional control, the cytokinin-mediated resistance in tobacco is essentially independent from salicylic acid and differs in pathogen specificity It is also independent of jasmonate levels, reactive oxygen species, and high sugar resistance The novel function of cytokinins in the primary defense response of solanaceous plant species is rather mediated through a high phytoalexin-pathogen ratio in the early phase of infection, which efficiently restricts pathogen growth The implications of this mechanism for the coevolution of host plants and cytokinin-producing pathogens and the practical application in agriculture are discussed

The Phytoalexin Resveratrol Regulates the Initiation of Hypersensitive Cell Death in Vitis Cell

Abstract: Resveratrol is a major phytoalexin produced by plants in response to various stresses and promotes disease resistance. The resistance of North American grapevine Vitis rupestris is correlated with a hypersensitive reaction (HR), while susceptible European Vitis vinifera cv. ‘Pinot Noir’ does not exhibit HR, but expresses basal defence. We have shown previously that in cell lines derived from the two Vitis species, the bacterial effector Harpin induced a rapid and sensitive accumulation of stilbene synthase (StSy) transcripts, followed by massive cell death in V. rupestris. In the present work, we analysed the function of the phytoalexin resveratrol, the product of StSy. We found that cv. ‘Pinot Noir’ accumulated low resveratrol and its glycoside trans-piceid, whereas V. rupestris produced massive trans-resveratrol and the toxic oxidative d-viniferin, indicating that the preferred metabolitism of resveratrol plays role in Vitis resistance. Cellular responses to resveratrol included rapid alkalinisation, accumulation of pathogenesis-related protein 5( PR5) transcripts, oxidative burst, actin bundling, and cell death. Microtubule disruption and induction of StSy were triggered by Harpin, but not by resveratrol. Whereas most responses proceeded with different amplitude for the two cell lines, the accumulation of resveratrol, and the competence for resveratrol-induced oxidative burst differed in quality. The data lead to a model, where resveratrol, in addition to its classical role as antimicrobial phytoalexin, represents an important regulator for initiation of HR-related cell death.

Biological activity of peanut (Arachis hypogaea) phytoalexins and selected natural and synthetic Stilbenoids.

Abstract: The peanut plant (Arachis hypogaea L.), when infected by a microbial pathogen, is capable of producing stilbene-derived compounds that are considered antifungal phytoalexins. In addition, the potential health benefits of other stilbenoids from peanuts, including resveratrol and pterostilbene, have been acknowledged by several investigators. Despite considerable progress in peanut research, relatively little is known about the biological activity of the stilbenoid phytoalexins. This study investigated the activities of some of these compounds in a broad spectrum of biological assays. Since peanut stilbenoids appear to play roles in plant defense mechanisms, they were evaluated for their effects on economically important plant pathogenic fungi of the genera Colletotrichum, Botrytis, Fusarium, and Phomopsis. We further investigated these peanut phytoalexins, together with some related natural and synthetic stilbenoids (a total of 24 compounds) in a panel of bioassays to determine their anti-inflammatory, cytotoxic, and antioxidant activities in mammalian cells. Several of these compounds were also evaluated as mammalian opioid receptor competitive antagonists. Assays for adult mosquito and larvae toxicity were also performed. The results of these studies reveal that peanut stilbenoids, as well as related natural and synthetic stilbene derivatives, display a diverse range of biological activities.

Prunus domestica Pathogenesis-Related Protein-5 Activates the Defense Response Pathway and Enhances the Resistance to Fungal Infection

Abstract: Pathogenesis-related protein-5 (PR-5) has been implicated in plant disease resistance and its antifungal activity has been demonstrated in some fruit species. However, their roles, especially their interactions with the other defense responses in plant cells, are still not fully understood. In this study, we have cloned and characterized a new PR-5 cDNA named PdPR5-1 from the European plum (Prunus domestica). Expression of PdPR5-1 was studied in different cultivars varying in resistance to the brown rot disease caused by the necrotrophic fungus Monilinia fructicola. In addition transgenic Arabidopsis, ectopically expressing PdPR5-1 was used to study its role in other plant defense responses after fungal infection. We show that the resistant cultivars exhibited much higher levels of transcripts than the susceptible cultivars during fruit ripening. However, significant rise in the transcript levels after infection with M. fructicola was observed in the susceptible cultivars too. Transgenic Arabidopsis plants exhibited more resistance to Alternaria brassicicola. Further, there was a significant increase in the transcripts of genes involved in the phenylpropanoid biosynthesis pathway such as phenylalanine ammonia-lyase (PAL) and phytoalexin (camalexin) pathway leading to an increase in camalexin content after fungal infection. Our results show that PdPR5-1 gene, in addition to its anti-fungal properties, has a possible role in activating other defense pathways, including phytoalexin production.

Cell wall integrity and high osmolarity glycerol pathways are required for adaptation of Alternaria brassicicola to cell wall stress caused by brassicaceous indolic phytoalexins.

Abstract: Camalexin, the characteristic phytoalexin of Arabidopsis thaliana, inhibits growth of the fungal necrotroph Alternaria brassicicola. This plant metabolite probably exerts its antifungal toxicity by causing cell membrane damage. Here we observed that activation of a cellular response to this damage requires cell wall integrity (CWI) and the high osmolarity glycerol (HOG) pathways. Camalexin was found to activate both AbHog1 and AbSlt2 MAP kinases, and activation of the latter was abrogated in a AbHog1 deficient strain. Mutant strains lacking functional MAP kinases showed hypersensitivity to camalexin and brassinin, a structurally related phytoalexin produced by several cultivated Brassica species. Enhanced susceptibility to the membrane permeabilization activity of camalexin was observed for MAP kinase deficient mutants. These results suggest that the two signalling pathways have a pivotal role in regulating a cellular compensatory response to preserve cell integrity during exposure to camalexin. AbHog1 and AbSlt2 deficient mutants had reduced virulence on host plants that may, at least for the latter mutants, partially result from their inability to cope with defence metabolites such as indolic phytoalexins. This constitutes the first evidence that a phytoalexin activates fungal MAP kinases and that outputs of activated cascades contribute to protecting the fungus against antimicrobial plant metabolites.

Improved Resistance Against Botrytis cinerea by Grapevine-Associated Bacteria that Induce a Prime Oxidative Burst and Phytoalexin Production

Abstract: Verhagen, B., Trotel-Aziz, P., Jeandet, P., Baillieul, F., and Aziz, A. 2011. Improved resistance against Botrytis cinerea by grapevine-associated bacteria that induce a prime oxidative burst and phytoalexin production. Phytopathology 101:768-777. Bacteria such as Pantoea agglomerans (Pa-AF2), Bacillus subtilis (Bs271), Acinetobacter lwoffii (Al-113), and Pseudomonas fluorescens (PfCT2), originating from the vineyard, can induce defense responses and enhance resistance of grapevine against the fungal pathogen Botrytis cinerea. The perception of these bacteria by plant cells or tissues in relation to their activities remains unknown. In this study, we examined the relationships between the activity of each bacterium to induce or prime some defense responses, and its effectiveness to induce resistance in grapevine against B. cinerea. We showed that all selected bacteria are capable of inducing early oxidative burst and phytoalexin (transresveratrol and trans-e-viniferin) production in grapevine cells and leaves. Pf-CT2 and Al-113 induced higher H2O2 and trans-resveratrol accumulations, and were able to further prime plants for accelerated phytoalexin production after B. cinerea challenge. These two bacteria were also the most effective in inducing local and systemic resistance. A similar level of induced resistance was observed with live Pa-AF2 which also induced but not primed a greater accumulation of trans-resveratrol. However, Bs-271, which was less effective in inducing resistance, induced a lower trans-resveratrol synthesis, without priming activity. Treatment of grapevine cells with growing medium or crude extract of the bacteria quickly and strongly enhanced oxidative burst compared with the live bacteria. However, both treatments resulted in comparable amounts of phytoalexins and induced local and systemic resistance to B. cinerea as compared with those induced by living bacteria, with extracts from PfCT2 and Al-113 being the most effective. Together, these results indicate that induced resistance can be improved by treatment with bacteria or derived compounds which induced or primed plants for enhanced phytoalexin accumulation.

GmPep914, an Eight-Amino Acid Peptide Isolated from Soybean Leaves, Activates Defense-Related Genes

Abstract: Only a handful of endogenous peptide defense signals have been isolated from plants. Herein, we report a novel peptide from soybean (Glycine max) leaves that is capable of alkalinizing the media of soybean suspension cells, a response that is generally associated with defense peptides. The peptide, DHPRGGNY, was synthesized and found to be active at 0.25 nM and requiring only 5 to 10 min to obtain a maximal pH change. The peptide is located on the carboxy-terminal end of a 52-amino acid precursor protein (Glyma12g00990) deduced from the soybean genome project. A search of the soybean databank revealed a homolog (Glyma09g36370) that contained a similar peptide, DLPRGGNY, which was synthesized and shown to have identical activity. The peptides, designated GmPep914 (DHPRGGNY) and GmPep890 (DLPRGGNY), were capable of inducing the expression of both Glyma12g00990 (GmPROPEP914) and Glyma09g36370 (GmPROPEP890) in cultured soybean suspension cells within 1 h. Both peptides induced the expression of defense genes, including CYP93A1, a cytochrome P450 gene involved in phytoalexin synthesis, chitinaseb1-1, a chitinase involved in pathogen defense, and Glycine max chalcone synthase1 (Gmachs1), chalcone synthase, involved in phytoalexin production. Both GmPROPEP914 and GmPROPEP890 were highly expressed in the roots, relative to the aerial portions of the plant. However, treatment of the aerial portion of soybean plants with hormones involved in elicitation of defense responses revealed a significant increase in expression levels of GmPROPEP914 and GmPROPEP890. A search of gene databases revealed homologous sequences in other members of the Fabales and also in the closely related Cucurbitales but not in any other order of plants.

Food grade fungal stress on germinating peanut seeds induced phytoalexins and enhanced polyphenolic antioxidants.

Abstract: The effects of food grade fungus Rhizopus oligosporus stress on phytochemicals and phytoalexins of germinating peanut seeds were investigated by comparing the metabolic profiles of ungerminated (UG), germinated (G), and germinated seeds under fungal stress (GS). Three types of peanut seeds with different skin color (red, reddish brown, and black) were compared in the process. The polyphenolic contents were analyzed and correlated with antioxidant capacity for specific free radicals including peroxyl radical ROO• (ORAC), hydroxyl radical HO• (HORAC), superoxide radical O2•– (SORAC), and DPPH radical. The polyphenolic fingerprints analyzed by HPLC and LC-MSn showed that phenolic acids (coumaric, sinapinic, and ferulic acids derivatives) were the major group of phenolic compounds in ungerminated seeds. G or GS increased the level of phenolic acids, phytoalexins, and antioxidant capacity values in reddish and red peanuts but not in black peanuts. From the LC-MSn spectral data, 45 compounds were identified ten...

Resveratrol Inhibits Periodontal Pathogens In Vitro

Abstract: The gram-negative anaerobic bacteria A. actinomycetemcomitans (Aa) and P. gingivalis (Pg) are key components in the aetiology of periodontal disease, and associated hard-tissue destruction. Resveratrol is a phytoalexin, produced naturally by several plants when under attack by bacterial or fungal pathogens. It is found in many foods including mulberries, peanuts and the skin of labrusca and muscadine grapes. The objective of this study was to evaluate the effect of resveratrol on the in vitro growth of periodontal pathogens Aa and Pg. For comparison, resveratrol's effect on a variety of other oral microorganisms was also evaluated. Resveratrol demonstrates a poor solubility in water, thus different concentrations of resveratrol in the solvent dimethyl sulphoxide (DMSO) were added to calibrated suspensions of Aa and Pg. As a control, a parallel series of dilutions containing the vehicle DMSO alone was made to measure the effect of the solvent. Minimum inhibitory concentrations of the periodontal pathogens were calculated. All suspensions were incubated for 1, 3, 6 and 24 h in an anaerobic chamber at 37 °C. At each time interval, selected dilutions from each culture broth were plated on blood agar plates. Colonies appearing on blood agar plates were visually counted at 3 days for Aa, and at 5 days for Pg. The periodontal bacteria showed a significant decrease (p < 0.05) in viable counts after 1 h, whilst no colony forming units could be observed after 24 h. The results suggest that resveratrol possesses significant antimicrobial properties on periodontal pathogens in vitro. Copyright © 2011 John Wiley & Sons, Ltd.

Polyketide derivatives active against Botrytis cinerea in Gerbera hybrida

Abstract: A previously isolated cDNA molecule from Gerbera hybrida (Asteraceae) codes for a new chalcone synthase-like polyketide synthase, 2-pyrone synthase (2PS). 2PS is able to synthesise 4-hydroxy-6-methyl-2-pyrone (triacetolactone), a putative precursor for gerberin and parasorboside, two abundant glucosides in gerbera. In this study, we show that gerbera plants transformed with the gene for 2PS in an antisense orientation and unable to synthesise gerberin and parasorboside are susceptible to Botrytis cinerea infection. In addition to the preformed glucosides, the transgenic plants also lack several compounds that are induced in control plants when infected with the mould. Some of these induced substances are effective in inhibiting fungal growth both in vitro and in vivo. Two of the phytoalexins were identified as the aglycones of gerberin and trans-parasorboside. The third phytoalexin is a rare coumarin, 4-hydroxy-5-methylcoumarin; however, it is typical of many plants of the sunflower family Asteraceae. The coumarin cannot be structurally derived from either gerberin or parasorboside, but may be derived from a related polyketide intermediate.

Polyketide derivatives active against Botrytis cinerea in Gerbera hybrida Satu KoskelaPaivi P. SoderholmMiia AinasojaTero Wennberg • Karel D. KlikaVladimir V. OvcharenkoIrene KylanlahtiTiina Auerma • Jari Yli-KauhaluomaKalevi PihlajaPia M. VuorelaTeemu H. Teeri

Abstract: A previously isolated cDNA molecule from Gerbera hybrida (Asteraceae) codes for a new chalcone synthase-like polyketide synthase, 2-pyrone synthase (2PS). 2PS is able to synthesise 4-hydroxy-6-methyl-2- pyrone (triacetolactone), a putative precursor for gerberin and parasorboside, two abundant glucosides in gerbera. In this study, we show that gerbera plants transformed with the gene for 2PS in an antisense orientation and unable to synthesise gerberin and parasorboside are susceptible to Botrytis cinerea infection. In addition to the preformed glucosides, the transgenic plants also lack several com- pounds that are induced in control plants when infected with the mould. Some of these induced substances are effective in inhibiting fungal growth both in vitro and in vivo. Two of the phytoalexins were identified as the aglycones of gerberin and trans-parasorboside. The third phytoalexin is a rare coumarin, 4-hydroxy-5-methylcou- marin; however, it is typical of many plants of the sun- flower family Asteraceae. The coumarin cannot be structurally derived from either gerberin or parasorboside, but may be derived from a related polyketide intermediate.

In vitro effect of resveratrol against oxidative injury of human coronary artery endothelial cells

Abstract: Reactive oxygen species induce oxidative stress that may contribute to endothelial dysfunction. In addition to endogen antioxidants, adding antioxidants to diet has been used to reduce oxidative-stress-induced endothelial dysfunction. Resveratrol is a natural phytoalexin which has many effects including antioxidant activity. The aim of this study was to investigate whether resveratrol could protect human coronary artery endothelial cells against in vitro oxidative-stress-mediated injury. Materials and methods: Human coronary artery endothelial cells were treated with varying concentrations of hydrogen peroxide for different durations and hydrogen peroxide plus varying concentrations of resveratrol. Then cell death was measured using lactate dehydrogenase release. Human coronary artery endothelial cells were exposed to hydrogen peroxide and resveratrol plus hydrogen peroxide for 15 min, 60 min, and 6 h. Reactive oxygen species was measured using a fluorometric assay. Results: Preincubation of cells with 10 and 50 mM resveratrol for different periods caused a significantly decreased hydrogen-peroxide-induced cell death. Preincubation with resveratrol caused a significant decrease in reactive oxygen species production. Conclusion: Our results demonstrate that resveratrol protects human coronary artery endothelial cells, in vitro, against oxidative-stress-induced injury by decreasing cell death and reactive oxygen species production.

Effect of UV Light on Secondary Metabolite Biosynthesis in Plant Cell Cultures Elicited with Cyclodextrins and Methyl Jasmonate

Abstract: All the chemical reactions that occur in the cells of a living organism are called metabolism. By these reactions, a large number of organic compounds, including sugars, amino acids, fatty acids, nucleotides and their polymers derived, that is, polysaccharides, proteins, lipids, RNA, DNA, etc ... are produced. These processes are essential and common to all organisms and are known as primary metabolism and related compounds are known as primary metabolites. In the case of plants, in addition to the primary metabolic pathways, other metabolic pathways are activated under certain situations and the compounds produced are called secondary metabolites. The role of secondary metabolites may seem irrelevant, but the truth is that the plant spends a great deal of energy in their synthesis and they have remained in the plant kingdom up to date. This is because that wide variety and high diversity of secondary metabolites have apparently evolved as a means for plants to interact with the environment and for the development of resistance against both abiotic and biotic stress. In fact, secondary metabolites are useful to protect plants against herbivores (insects and vertebrates), mammals, bacteria, fungi, viruses and even other competing plants. In addition, some plants use secondary metabolites to attract pollinators and seed dispersers, as signals for communication between plants and symbiotic microorganisms or for protection against UV light and other physical stress (Wink 2003, 2008). Daucus carota L. (Umbelliferae) is a biennial herb, whose fruits (common name: wild carrot fruits) have been used in traditional Chinese medicine for the treatment of ancylostomiasis, dropsy, chronic kidney disease and bladder afflictions (Pant & Manandhar, 2007) due to a wide range of reported pharmacological effects, including antibacterial (Rossi et al., 2007), antifungal (Tavares et al., 2008), antihelminthic, hepatoprotective (Bishayee et al., 1995) and cytotoxic activities (Yang et al., 2008; Fu et al., 2009). Carrot roots contain a variety of carotenoids and anthocyanins that are responsible for the typical colour of the root. In addition, this vegetable also produces phenolic compounds such as scopoletin, p-hydroxy benzoic acid and the isocoumarin, 6-methoxymellein, all major components of the phytoalexin complex (Mercier et al., 2000). These compounds are induced in carrot by fungal infection, heavy metals or UV light (Marinelli et al., 1994), and therefore they are involved in plant defence responses. Recently, Sabater-Jara et al., (2008) have described the production of sterols in different cell cultures including D. carota.

Resveratrol induces apoptosis of KB human oral cancer cells

Abstract: Resveratrol (trans-3,4′s,5,-trihydroxystilbene), a phytoalexin present in grape skin and red wine, suppresses many types of cancers by regulating cell proliferation and apoptosis through a variety of mechanisms. However, the effects of resveratrol on oral cancer are not completely understood. Thus, effects of resveratrol on cell growth and apoptosis induction were examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, DNA fragmentation, immunoblotting, and determination of caspase activation in KB human oral cancer cells. Treatment with resveratrol induced inhibition of cell growth depending on the resveratrol treatment time and concentration in KB cells. Treatment with resveratrol induced DNA ladder formation in KB cells and promoted proteolytic cleavage of procaspase-3 and procaspase-7 with increases in the amount of cleaved caspases-3 and -7. Proteolytic processing of caspase-9 in KB cells was increased by resveratrol treatment. Activation of caspase-3/-7 was detected in living KB cells by fluorescence microscopy. These results suggest that the resveratrol can suppress cell growth and induce cell apoptosis in KB human oral cancer cells, and may have potential as an anti-cancer drug.

Biosynthesis of the 3‐ethylchromone phytoalexin lathodoratin in lathyrus odoratus

Abstract: Feeding experiments with 14C- and 13C-labelled precursors have demonstrated that the phloroglucinol ring of the 3-ethylchromone phytoalexin lathodoratin from cupric sulphate-induced pods of sweet pea (Lathyrus odoratus) has a polyketide origin. The remaining five carbon ‘isoprene unit’ is derived from the amino acid isoleucine which provides the starter unit, probably 2-methylbutanoate, for acetate-malonate chain extension. The pterocarpan phytoalexin pisatin is produced along with lathodoratin, and precursors were incorporated in agreement with earlier studies. Two minor 3-ethylchromones were also synthesized on cupric sulphate treatment of the pods. These were the previously reported 7-O-methyl ether of lathodoratin (methyl-lathodoratin) and a new compound, the 5,7-di-O-methyl ether (dimethyl-lathodoratin). Dimethyl-lathodoratin is the most fungitoxic of the 3-ethylchromone phytoalexins.

Antiproliferative effect of resveratrol in pancreatic cancer cells

Abstract: Resveratrol, a naturally occurring phytoalexin found in the skin of red grapes, was investigated for its effect on pancreatic cancer cells. It was found to inhibit the proliferation of pancreatic cancer cells by inducing apoptotic cell death.

Ingredient Spotlight: Resveratrol

Abstract: Resveratrol (3,5,4’-trihydroxystilbene) is a polyphenol synthesized by several plants in response to adverse conditions (e.g., environmental stress or pathogenic attacks). It is classified as a phytoalexin, a class of plant-derived antibiotics that serves as part of a plant’s defensive arsenal.(1) Resveratrol is found in numerous plant species such as mulberries, peanuts, and grape skin, and in less commonly known plants such as Japanese knotweed (Polygonum cuspidatum).(2)