Showing papers on "Phytoalexin published in 1991"
119 citations
TL;DR: The reductase protein contains a leucine-zipper motif and reveals a marked similarity with other oxidoreductases most of which are involved in carbohydrate metabolism.
Abstract: In soybean (Glycine max L.), pathogen attack induces the formation of glyceollin-type phytoalexins. The biosynthetic key enzyme is a reductase which synthesizes 4,2', 4'-trihydroxychalcone in co-action with chalcone synthase. Screening of a soybean cDNA library from elicitor-induced RNA in lambda gt11 yielded two classes of reductase-specific clones. The deduced proteins match to 100% and 95%, respectively, with 229 amino acids sequenced in the purified plant protein. Four clones of class A were expressed in Escherichia coli, and the proteins were tested for enzyme activity in extracts supplemented with chalcone synthase. All were active in 4,2',4'-trihydroxychalcone formation, and the quantification showed that shorter lengths of the cDNAs at the 5' end correlated with progressively decreasing enzyme activities. Genomic blots with DNA from plants capable of 4,2',4'-trihydroxychalcone synthesis revealed related sequences in bean (Phaseolus vulgaris L.) and peanut (Arachis hypogaea L.), but not in pea (Pisum sativum L.). No hybridization was observed with parsley (Petroselinum crispum) and carrot (Daucus carota) which synthesize other phytoalexins. The reductase protein contains a leucine-zipper motif and reveals a marked similarity with other oxidoreductases most of which are involved in carbohydrate metabolism.
115 citations
TL;DR: It is concluded that the changes observed in intracellular thiols following exposure of cells to fungal elicitor are a consequence rather than a cause of the initial elicitation signal(s).
Abstract: Both reduced glutathione (GSH) and oxidized glutathione elicited the phytoalexin response in cell-suspension cultures of bean (Phaseolus vulgaris L.) but had no effect in those of alfalfa (Medicago sativa L.). In bean cells, homoglutathione (HGSH) was the predominant soluble thiol and treatment of cells with fungal elicitor resulted in the accumulation of HGSH but not GSH. In contrast, GSH was more abundant than HGSH in unelicited alfalfa cells, and the intracellular levels of both thiols increased in response to fungal elicitor. Treatment of bean or alfalfa cells with l-oxothiazolidine-4-carboxylate, an artificial precursor for GSH biosynthesis, increased intracellular thiols in an analogous manner to that observed following treatment with fungal elicitor, but did not result in elicitation of the cultures. Differences were observed in the initial metabolic fates of exogenously supplied [35S]GSH in bean and alfalfa, but our data do not yet provide a basis for explaining how GSH acts as an elicitor. We conclude that the changes observed in intracellular thiols following exposure of cells to fungal elicitor are a consequence rather than a cause of the initial elicitation signal(s).
107 citations
TL;DR: The two fungi did not mutually influence the course of infection when they were inoculated together and glyceollin accumulated in mycorrhizal plants to the same extent as in control plants when they was inoculated with R. solani.
Abstract: A container system was constructed to study the response of soybean roots to infection by mycorrhizal or pathogenic fungi. The system allows a rapid and synchronous inoculation byGlomus mosseae orRhizoctonia solani. The phytoalexin glyceollin was measured in roots of inoculated and uninoculated plants for a period of 30 days. A significantly increased content of phytoalexin was found inR. solani-infected roots as compared to uninfected control roots. However, there was no difference in the glyceollin contents of the mycorrhizal and the control roots for up to 23 days after inoculation. The accumulation of glyceollin inR. solani-infected roots was not influenced by a subsequent inoculation withG. mosseae. Moreover glyceollin accumulated in mycorrhizal plants to the same extent as in control plants when they were inoculated withR. solani. The two fungi did not mutually influence the course of infection when they were inoculated together.
99 citations
TL;DR: Microspectrophotometry was performed on intact, pigmented vesicle-like inclusions within living sorghum cells that were accumulating phytoalexins as a response to attempted fungal infection and confirmed that at the infection site the deoxyanthocyanidins accumulate to levels in substantial excess of those required for inhibition of the fungus.
89 citations
TL;DR: The accumulation of large amounts of specific phytoalexins could be correlated with the presence of the different Brassica genomes and could be related to resistance to L. maculans.
Abstract: Forty three accessions of Brassica species and one each of Sinapis and Raphanus were assessed for (i) resistance to Leptosphaeria maculans according to a coty-ledon-inoculation test and (ii) indole phytoalexin accumulation following abiotic elicitation with CuCl2. Five indole phytoalexins were determined in the lines following elicitation. Brassilexin, cyclobrassinin and cyclobrassinin sulphoxide were found within at least some lines of all species, whereas brassinin was only detected in B. oleracea and B. napus and methoxybrassinin within these two species and B. rapa and B. carinata. None of the five indole phytoalexins could be found in Raphanus sativus or Sinapis alba. The accumulation of large amounts of specific phytoalexins could be correlated with the presence of the different Brassica genomes. Lines possessing the B genome (B. nigra, B. juncea and B. carinata) which accumulated high amounts of brassilexin, displayed a hypersensitive resistance to infection whereas the majority of lines of B. oleracea, B. napus and B. rapa which did not accumulate large amounts of brassilexin, were susceptible. However, a B. nigra and a B. rapa line which only accumulated low amounts of brassilexin were highly resistant to the pathogen. Neither the accumulation of the other phytoalexins nor the total accumulation of indole phytoalexins could be related to resistance to L. maculans.
60 citations
TL;DR: The data suggest that altered protein expression may be triggered by free radicals connected to activated oxygen metabolism, and that phytoalexins do not account for either free radicals detected earlier by the electron paramagnetic resonance signals or altered plant membrane function.
54 citations
TL;DR: The data indicate that the effect of allixin on AFB1-induced mutagenesis and binding of metabolites to DNA may be mediated through an inhibition of microsomal P-450 enzymes, and may thus be useful in the chemoprevention of cancer.
44 citations
TL;DR: In this paper, 13-hydroperoxides of linoleic and linolenic acids were inoculated with Pyricularia oryzae, and the highest concentrations of ROOH and ROH were reached within 24 hours after inoculating with P. oryziae.
Abstract: 13-Hydroperoxides (ROOH) and 13-hydroxides (ROH) of both linoleic and linolenic acids rapidly increased after inoculating press-injured spots of rice leaves with Pyricularia oryzae. The highest concentrations of ROOH and ROH were reached within 24 hr after inoculating with P. oryzae. On the contrary, the production of momilactone A, a terpenoid rice phytoalexin, began 24 hr after inoculating with P. oryzae, while the momilactone A level peaked at 96 hr after the inoculation. The 13-hydroperoxides and 13-hydroxides of linoleic and linolenic acids can thus induce phytoalexins production. Quinacrine, an inhibitor of phospholipase A2, and the lipoxygenase inhibitor, nor-dihydroguaiaretic acid (NDGA), inhibited not only the production of ROOH and ROH, but also any phytoalexin accumulation following invasion by P. oryzae. Chlorogenic acid, by inhibiting the peroxidase of rice plants, inhibited the production of ROH and the rice phytoalexins accompanying an accumulation of ROOH. These data suggest that the oxyge...
42 citations
TL;DR: In this paper, Agrobacterium rhizogenes transformed root cultures of Lotus corniculatus were treated with glutathione, isoflavan phytoalexins accumulated in both tissue and culture medium.
Abstract: When Agrobacterium rhizogenes transformed root cultures of Lotus corniculatus were treated with glutathione, isoflavan phytoalexins accumulated in both tissue and culture medium. This accumulation of phytoalexins was preceded by a transient increase in the activity of phenylalanine ammonia lyase (PAL). Elicitation of PAL occurred throughout the growth curve of Lotus ‘hairy roots’ and in different sectors of transformed root material.
40 citations
TL;DR: The results of these studies suggest an unconventional pathway for umbelliferone biosynthesis and demonstrate both the transcriptional and post-transcriptional control of a novel pathway to feruloyl-CoA.
Abstract: Cultured cells of the Apiaceae, e. g. PETROSELINUM CRISPUM and AMMI MAJUS, produce large quantities of coumarin phytoalexins upon treatment with fungal elicitors and concomitantly reinforce their cell walls by ferulic ester incorporation. In these reactions, the cells mimic the disease resistance response commonly expressed in plants following infection by phytopathogenic fungi. Both coumarins and ferulic esters are derived from the general phenylpropanoid pathway. The elicited Apiaceae cell cultures have therefore served as model systems for the investigation of the biosynthetic and regulatory mechanisms involved in phenylpropanoid accumulation. The results of these studies suggest an unconventional pathway for umbelliferone biosynthesis and demonstrate both the transcriptional and post-transcriptional control of a novel pathway to feruloyl-CoA. They underline the enormous contribution of such model systems to the present knowledge on regulatory patterns and DNA coding in secondary metabolism.
TL;DR: It is concluded that the massive difference in phytoalexin accumulation between cell suspension cultures from the resistant and susceptible cultivar is determined mainly by the differential induction of form ononetin 2′-hydroxylase activity.
Abstract: A yeast glucan elicitor causes the accumulation of the pterocarpan phytoalexins medicarpin and maackiain in chickpea (Cicer arietinum) cell suspension cultures established from seeds. A cell culture line from a chickpea cultivar resistant against its main fungal pathogen Ascochyta rabiei accumulates large amounts (944 nm ol/g fr. wt.) whereas a cell culture line from a susceptible cultivar accumulates only low amounts (38 nm ol/g fr. wt.) of the phytoalexins. This is consistent with differential accumulation of pterocarpan phytoalexins in intact plants [1], The first reactions in the pterocarpan-specific branch of biosynthesis are hydroxylation of the isoflavone intermediate form ononetin in position 2′ or 3′, catalyzed by microsomal cytochrome P-450 monooxygenases. Upon elicitation form ononetin 2′-hydroxylase undergoes a strong transient induction in the cell suspension culture of the resistant cultivar, whereas in the cell culture from the susceptible cultivar it is only slightly induced. In both cell suspension cultures the induction of cinnamic acid 4-hydroxylase and of form ononetin 3′-hydroxylase does not show a clear correlation with phytoalexin accumulation. Experiments with different elicitor concentrations confirm that formononetin 2′-hydroxylase is much more induced in cell cultures from the resistant cultivar than from the susceptible one. It is concluded that the massive difference in phytoalexin accumulation between cell suspension cultures from the resistant and susceptible cultivar is determined mainly by the differential induction of form ononetin 2′-hydroxylase activity.
TL;DR: Upon application of an elicitor from yeast to the cell cultures a substantial increase in the level of the phytoalexin aglycones medicarpin and maackiain was observed although a delayed but significantly higher rise of the conjugates also occurred.
Abstract: The pterocarpan phytoalexin conjugates medicarpin 3-O-glucoside-6'-O-malonate and maackiain 3-O-glucoside-6'-O-malonate were isolated from cell suspension cultures of chickpea (Cicer arietinum L.) cultivar ILC 3279 and structurally elucidated. Both pterocarpan conjugates are constitutive metabolites of the chickpea cell cultures. Upon application of an elicitor from yeast to the cell cultures a substantial increase in the level of the phytoalexin aglycones medicarpin and maackiain was observed although a delayed but significantly higher rise of the conjugates also occurred. The significance of the pterocarpan conjugates for phytoalexin production is discussed.
TL;DR: The rapid rate of phytoalexin accumulation shortly after inoculation could account for inhibition of fungal growth on the leaf surfaces and for resistance to A. brassicae.
TL;DR: Production of the carrot phytoalexin and its immediate biosynthetic precursor, 6-hydroxymellein, was induced in suspension cultures by biotic elicitors and by the abiotic elicitor HgCl2.
01 Jan 1991
TL;DR: An extracellular glycoprotein of 42 kDa is purified from the culture filtrate of the soybean pathogen Phytophthora megasperma f.
Abstract: Plants respond to pathogen attack by rapid activation of defense genes. In selected experimental systems, the transcription of these genes is also induced when cultured plant cells or protoplasts are treated with elicitors. We have purified an extracellular glycoprotein of 42 kDa from the culture filtrate of the soybean pathogen Phytophthora megasperma f. sp. glycinea (Pmg), which is a potent elicitor of phytoalexin accumulation and defense gene activation in parsley (1Petroselinum crispum) cells and protoplasts. Reversible binding of the 25I-labelled glycoprotein to microsomes and protoplasts indicates the presence of specific binding sites on the parsley plasma membrane. The transduction of the elicitor signal from the cell surface to the nucleus was found to involve a rapid and transient uptake of Ca2+, alkalization of the culture medium and effluxes of K+ and C1-. These ion fluxes probably result from opening of elicitor-responsive ion channels, as indicated by preliminary results from patch-clamp analysis of parsley protoplasts in the presence of pure glycoprotein elicitor. Omission of Ca2+ from the culture medium substantially reduced the elicitor-induced transcription rates of plant defense genes. Treatment of cultured parsley cells or protoplasts with amphotericin B resulted in ion fluxes and defense gene activation similar to those elicited by the crude Pmg elicitor. The callose elicitors chitosan and digitonin, however, induced ion fluxes of different intensities, activated only some defense genes, and did not stimulate the synthesis of phytoalexins at concentrations optimal for elicitation of callose formation.
TL;DR: Positive phytoalexin responses presented a trend similar to that previously observed for a broad sample of dicotyledonous plants and are more frequently positive for the more primitive (or slower growing) trees than for the advanced (or faster growing) herbs.
Abstract: Phytoalexin responses were measured by modified drop-diffusate and facilitated diffusion techniques after fungal inoculation of leaves of 32 Rubiaceae species from Brazilian forest and savanna. Such responses presented a trend similar to that previously observed for a broad sample of dicotyledonous plants and are more frequently positive for the more primitive (or slower growing) trees than for the advanced (or faster growing) herbs. Fifteen of these species analyzed during a one-year period showed that positive phytoalexin responses are stronger for the rainy (and hotter) than for the dry (and cooler) season. Species that contain relatively large quantities of phenolics gave invariably negative responses. Positive responses are not necessarily associated with the appearance of new substances within leaf tissue and are thus caused by inhibitins rather than by phytoalexins. These results are discussed recognizing that the tested plants are subject to the multifarious influences of their natural environment and of a possible conjugate-caused compartmentation of plant metabolites.
TL;DR: In this article, the major and minor terpenoid phytoalexins of potatoes are presented and discussed with reference to their characterization and function, including their physicochemical properties.
TL;DR: Results indicate that rapid mechanical defensive mechanisms play an important role in the resistance of potato cultivars to seed-piece infection by V. dahliae, while in the cultivars studied the production of phytoalexins is not correlated with resistance.
TL;DR: Oryzalides A and B, and oryzalic acid A, which were isolated from healthy flag leaves of a bacterial leaf blight-resistant cultivar of rice plant as a group of novel antimicrobial compounds, were confirmed by chemical and spectroscopic studies to be ent-kaurane or ent-kaurene analogues.
Abstract: Oryzalides A and B, and oryzalic acid A, which were isolated from healthy flag leaves of a bacterial leaf blight-resistant cultivar of rice plant as a group of novel antimicrobial compounds, were confirmed by chemical and spectroscopic studies to be ent-kaurane (C19 and C20) or ent-kaurene (C19) analogues, i.e., oryzalide A, ent-15α,16-epoxy-1β-hydroxy-2-oxa-kauran-3-one; B, ent-1β,15α-dihydroxy-2-oxa-16-kauren-3-one; and oryzalic acid A, ent-15α,16-epoxy-2,3-secokauran-2,3-dioic acid.
TL;DR: It is concluded that in soybean roots, an early burst of ethylene biosynthesis is a characteristic symptom of the incompatible reaction that cannot be mimicked by treatment with fungal elicitors.
01 Jan 1991
TL;DR: A novel endo-(1-4)-β-xylanase purified from fungal filtrates of Trichoderma viride was found to be a strong activator of PR proteins synthesis in tobacco leaves highlighting a novel ethylene independent pathway for PR proteins.
Abstract: Antisera to acidic isoforms of pathogenesis-related (PR) proteins were used to measure the activity of these genes in tobacco plants. A novel endo-(1-4)-β-xylanase purified from fungal filtrates of Trichoderma viride was found to be a strong activator of PR proteins synthesis in tobacco leaves. The induction was not inhibited by blockers of either ethylene biosynthesis or ethylene action highlighting a novel ethylene independent pathway for PR proteins. Concomitant with the induction of PR proteins phytoalexins are induced. The regulation of the phytoalexin capsidiol showed identical ethylene dependent and independent pathways described for PR proteins.
TL;DR: An initial small increase in accumulation of the phytoalexin 4 hr after inoculation was detected using this spectrofluorimetric method, but not by measurement of ultraviolet absorbance, which is far less specific and less sensitive.
TL;DR: In in vitro experiments, C. fulvum appeared to readily metabolize falcarindiol, as did a Lycopersicon cell suspension culture, suggesting that adaptation or recovery was possible at the concentrations tested.
Abstract: The production and distribution of the phytoalexin falcarindiol in tomato foliage infected with leaf mold was examined to determine how the fungus Cladosporium fulvum is able to colonize and sporulate in an apparently antifungal environment. In a compatible interaction (cv. Potentate – C. fulvum race 2.3), by 12 and 15 days after inoculation, solvent-extractable falcarindiol and two other phytoalexins from tomato, compound 2 (probably falcarinol) and compound 3 (unidentified), reached concentrations considerably in excess of ED50 values for inhibition of the fungus. In contrast, intercellular (apoplastic) fluids obtained from similarly infected leaflets contained only traces of falcarindiol. ED50 values for germination and germ-tube growth of C. fulvum increased as the incubation time was extended, suggesting that adaptation or recovery was possible at the concentrations tested. In in vitro experiments, C. fulvum appeared to readily metabolize falcarindiol, as did a Lycopersicon cell suspension culture. B...
TL;DR: The authors showed that 6-methoxymellein production took place at almost the same rate as the O-methyl group transfer reaction to a hydroxyl group of 6-hydroxymelleins.
TL;DR: The results demonstrate the requirement of two different classes of hydroxylase activities that appear to introduce the antimycotic quality to the dianthramides for phytoalexin defense.
TL;DR: The relative distribution of phytoalexins induced by Fusarium oxysporum fsp.
TL;DR: The inhibitory action of 4'-methoxyaucuparin against Pestalotiopsis sp.
Abstract: Accumulation and antifungal activity of a newly isolated phytoalexin, 4'-methoxyaucuparin, were described. The phytoalexin was accumulated in the leaves of Rhaphiolepis umbellata Makino inoculated with Pestalotiopsis sp. or Entomosporium mespili. Accumulation of 4'-methoxyaucuparin also occurred with treatment of 10-3M NaN3 or HgCl2 as abiotic elicitors. Of the elicitors tested, HgCl2 was found to be the most effective, being able to induce 4'-methoxyaucuparin at the concentration of 4, 385μg g-1 fresh weight. The inhibitory action of 4'-methoxyaucuparin against Pestalotiopsis sp., pathogenic fungus of R. umbellata, was weaker than that against non pathogenic fungi.
TL;DR: It is concluded that signals provided by WCS417r at the root induced sensitization of defense responses in the stem for Fusarium and of the synthesis and accumulation of phytoalexins.
Abstract: Peer, R.van and Schippers, B. 1990. Biological control of Fusarium wilt by Pseudomonas sp. strain WCS417r: induced resistance and phytoalexin accumulation. The involvement of other mechanisms besides competition for iron in the biological control of Fusarium oxysporum f. sp. dianthi in carnation by Pseudomonas sp. strain WCS417r was investigated. Competition between both micro-organisms was excluded by a spatial separation of the bacterization on the root and inoculation with microconidia of F. o. dianthi in the stem. Numbers of diseased carnation plants were significantly reduced when roots were bacterized one week prior to stem inoculation with F. o. dianthi. Pseudomonas sp. strain WCS417r could never be isolated from the stem tissue. Therefore, control is not due to competition between F. o. dianthi and WCS417r. Strain WCS417r was capable to induce resistance to F. o. dianthi in plants. Along with the induced resistance an accumulation of phytoalexins was found in the stem segments. No accumulation of these compounds was found when plants were bacterized only. It is concluded that signals provided by WCS417r at the root induced sensitization of defense responses in the stem for Fusarium and of the synthesis and accumulation of phytoalexins. In addition, similar results on disease suppression were obtained when purified lipopolysaccharides (LPS) of WCS417r were applied to the root instead of viable cells. Apparently the inducing factor is located on the LPS.