Showing papers on "Phytoalexin published in 1992"

Concentration of the Phytoalexin Resveratrol in Wine

Abstract: Resveratrol is a phytoalexin found in grapes. Recent research had shown that orally administered resveratrol lowered lipid levels in the liver of rats. Wine had been shown to lower serum lipid levels in humans. The concentration of resveratrol was measured in selected wines using HPLC and spectrophotometry. Geographical origin, variety, growing methods, and winemaking procedures all seemed to affect resveratrol concentration. Analysis of wines indicated that resveratrol may be the active ingredient in wines causing reduction of serum lipids.

Molecular plant pathology : a practical approach

Abstract: Part 1 Defence response (gene products): callose and callose synthase, H. Kauss lignin and associated phenolic acids in cell walls, J. Friend preparation and analysis of intercellular fluid, K.E. Hammond-Kosack biochemical analysis of chitinases and beta-1,3- glucanases, T. Boller localization of proteins and carbohydrates using immunogold labelling in light and electron microscopy, K.A. Van den Bosch isoflavonoid phytoalexins and their biosynthetic enzymes, R. Edwards and H. Kessmann analysis of terpernoid phytoalexins and their biosynthetic enzymes, D.R. Threlfall and I.M. Whitehead. Part 2 Elicitors: preparation and characterization of oligosaccharide elicitors of phytoalexin accumulation, M.G. Hahn et al xyloglucan oligosaccharides, S.C. Fry. Part 3 Signal transduction pathways: analysis of calcium involvement in host-pathogen interactions, B.K. Drobak et al analysis of components of the plant phosphoinositide system, B.K. Drobak and K. Roberts metabolic changes following infection of leaves by fungi and viruses, R.C. Leegood and J.D. Scholes. Part 4 Disease resistance genes: strategies for cloning disease resistance genes, R.W. Michelmore et al.

Phytoalexin Accumulation in Arabidopsis thaliana during the Hypersensitive Reaction to Pseudomonas syringae pv syringae

Abstract: Inoculation of leaves of Arabidopsis thaliana (L.) Heynh. with the wheat pathogen, Pseudomonas syringae pv syringae, resulted in the expression of the hypersensitive reaction and in phytoalexin accumulation. No phytoalexin accumulation was detected after infiltration of leaves with a mutant of P. s. syringae deficient in the ability to elicit a hypersensitive reaction; with the crucifer pathogen, Xanthomonas campestris pv campestris; or with 10 millimolar potassium phosphate buffer (pH 6.9). Phytoalexin accumulation was correlated with the restricted in vivo growth of P. s. syringae. A phytoalexin was purified by a combination of reverse phase flash chromatography, thin layer chromatography, followed by reverse phase high performance liquid chromatography. The Arabidopsis phytoalexin was identified as 3-thiazol-2′-yl-indole on the basis of ultraviolet, infrared, mass spectral, 1H-nuclear magnetic resonance, and 13C-nuclear magnetic resonance data.

Influence of root colonizing bacteria on the defense responses of bean

Abstract: Colonization of plant roots by fluorescent pseudomonads has been correlated with disease suppression. One mechanism may involve altered defense responses in the plant upon colonization. Altered defense responses were observed in bean (Phaseolus vulgaris) inoculated with fluorescent pseudomonads. Systemic effects of root inoculation by Pseudomonas putida isolate Corvallis, P. tolaasii (P9A) and P. aureofaciens REW1-I-1 were observed in bean leaves from 14-day-old plants. SDS- polyacrylamide gel electrophoresis demonstrated that levels of certain acid-soluble proteins increased in the leaf extracts of inoculated plants. Plants inoculated with REW1-I-1 produced more of a 57 Mr protein, and plants inoculated with isolates P9A and REW1-I-1 produced more of a 38 Mr protein. Northern hybridization revealed enhanced accumulation of mRNAs, that encode the pathogenesis-related protein PR1a, in leaves of plants inoculated with P. putida and REW1-I-1. Only REW1-I-1, but not P9A or P. putida induced symptoms of an hypersensitive response on tobacco leaves, bean cotyledons, and in bean suspension cultures. Phenolics and phytoalexins accumulated in bean cotyledons exposed to REW1-I-1 for 24 h but little change in levels of these compounds occurred in cotyledons inoculated with P9A and P. putida. Both suspension culture cells and roots treated with REW1-I-1 rapidly evolved more hydrogen peroxide than those exposed to P9A and P. putida. However, roots from 14-day-old plants colonized by P9A, P. putida or REW1-I-1 did not have higher levels of phenolics, phytoalexins or mRNAs for two enzymes involved in phenolic biosynthesis, phenylalanine-ammonia lyase and chalcone synthase. A selective induction of plant defense strategies upon root colonization by certain pseudomonads is apparent.

Elicitation of Diterpene Biosynthesis in Rice (Oryza sativa L.) by Chitin

Abstract: Cell-free extracts of UV-irradiated rice (Oryza sativa L.) leaves have a much greater capacity for the synthesis from geranylgeranyl pyrophosphate of diterpene hydrocarbons, including the putative precursors of rice phytoalexins, than extracts of unstressed leaves (KA Wickham, CA West [1992] Arch Biochem Biophys 293: 320-332). An elicitor bioassay was developed on the basis of these observations in which 6-day-old rice cell suspension cultures were incubated for 40 hours with the substance to be tested, and an enzyme extract of the treated cells was assayed for its diterpene hydrocarbon synthesis activity as a measure of the response to elicitor. Four types of cell wall polysaccharides and oligosaccharide fragments that have elicitor activity for other plants were tested. Of these, polymeric chitin was the most active; a suspension concentration of approximately 7 micrograms per milliliter gave 50% of the maximum response in the bioassay. Chitosan and a branched β-1,3-glucan fraction from Phytophthora megasperma f. sp. glycinea cell walls were only weakly active, and a mixture of oligogalacturonides was only slightly active. A crude mycelial cell wall preparation from the rice pathogen, Fusarium moniliforme, gave a response comparable to that of chitin, and this activity was sensitive to predigestion of the cell wall material with chitinase before the elicitor assay. N-Acetylglucosamine, chitobiose, chitotriose, and chitotetrose were inactive as elicitors, whereas a mixture of chitin fragments solubilized from insoluble chitin by partial acid hydrolysis was highly active. Constitutive chitinase activity was detected in the culture filtrate and enzyme extract of cells from a 6-day-old rice cell culture; the amount of chitinase activity increased markedly in both the culture filtrate and cell extracts after treatment of the culture with chitin. We propose on the basis of these results that soluble chitin fragments released from fungal cell walls through the action of constitutive rice chitinases serve as biotic elicitors of defense-related responses in rice.

Involvement of the oxidative burst in phytoalexin accumulation and the hypersensitive reaction.

Abstract: The role of the oxidative burst, transient production of activated oxygen species such as H(2)O(2) and superoxide (O(2) (-)) in elicitation of phytoalexins and the hypersensitive reaction (HR) was investigated in white clover (Trifolium repens L.) and tobacco (Nicotiana tabacum L.). H(2)O(2) and O(2) (-) production was measured as chemiluminescence (CL) mediated by luminol, which was added to suspension-cultured white clover just before measurement in an out-of-coincidence mode scintillation counter. Maximum CL occurred between 10 and 20 min after addition of 0.4 x 10(8) colony-forming units/mL of incompatible Pseudomonas corrugata or 158 mum HgCl(2). Autoclaved P. corrugata produced a slightly higher response. Elicitation of cells with 25 mum HgCl(2) did not produce CL. Preincubation of plant cells in superoxide dismutase, which converts O(2) (-) to H(2)O(2), for 2 min before addition of bacteria did not significantly increase maximum CL levels (P >/= 0.05). Preincubation of plant cells with catalase for 2 min before addition of bacteria prevented the increase in CL, confirming that H(2)O(2) is the substrate for the luminol reaction. Addition of live bacteria or HgCl(2) (25 and 158 mum) to white clover increased levels of the phytoalexin medicarpin during a 24-h period, but addition of autoclaved bacteria did not elicit formation of medicarpin. Preincubation of plant cells with catalase, which quenched the bacteria-induced oxidative burst, did not decrease phytoalexin accumulation. Live bacteria infiltrated into Havana 44 tobacco leaf panels induced development of the HR, but autoclaved bacteria did not. Incubation of live bacteria with superoxide dismutase and catalase before infiltration into tobacco leaves did not interfere with development of the HR. Tobacco leaf panels infiltrated with up to 158 mum HgCl(2) did not develop an HR. These results suggest that an oxidative burst consisting of H(2)O(2) and O(2) (-) does occur during these two plant defense responses, but it may not be a necessary element of the signaling system for HR and phytoalexin formation.

Ultraviolet Illumination Induces Scoparone Production in Kumquat and Orange Fruit and Improves Decay Resistance

Abstract: Additional index words. postharvest, phytoalexin, Fortunella margarita, Citrus sinensis Abstract. Ultraviolet (UV) illumination (254 nm) induced production of the phytoalexin scoparone in flavedo of kumquat (Fortunella margarita Lour. Swingle cv. Nagami) and orange (Citrus sinensis (L.) Osbeck cvs. Shamouti and Valencia). Trace amounts of scoparone (<2.0 µg·g -1 fresh weight of flavedo) were detected in nontreated fruits. Phytoalexin accumulation in kumquat reached a peak of 530 µg·g -1 11 days after illumination, hut the amount declined rapidly, returning to a trace level 1 month after treatment.. Production of scoparone in illuminated fruits was enhanced by increasing the UV dose from 1.5 × 10 3 to 9.0 × 10 3 J·m -2 for orange and from 0.2 × 10 3 to 1.5 × 10 3 J·m -2 for kumquat and by raising the storage temperature from 2 to 17C. Phytoalexin accumulation correlated with an increase in antifungal activity of flavedo extracts. UV-illuminated kumquat fruit inoculated with Penicillium digitatum Sacc. 2 days after treatment had a lower incidence of decay than the control. Illumination of previously inoculated fruit failed to prevent decay. Kumquat fruit stored at 17C showed signs of UV-induced peel damage. Chemical name used: 6,7-dimethoxycoumarin (scoparone). Phytoalexins, the low-molecular antimicrobial substances of various chemical structures, are elicited in plant tissues by either biotic (pathogen challenge) or abiotic (wounding, chemicals, irradiation, etc.) (Bailey and Mansfield, 1982) stresses. Short- wave ultraviolet light (UV) is known as a nonspecific phyto- alexin elicitor. Since 1971, when Hadwiger and Schwochau described the induction of the isoflavonoid phytoalexin pisatin in UV-treated pea pods, many studies on diverse plants have been devoted to this subject (Beier and Oertli, 1983; Bridge and

Rapid Stimulation of 5-Lipoxygenase Activity in Potato by the Fungal Elicitor Arachidonic Acid'

Abstract: The activity of lipoxygenase (LOX) in aged potato tuber discs increased by almost 2-fold following treatment of the discs with the fungal elicitor arachidonic acid (AA). Enzyme activity increased above that in untreated discs within 30 min after AA treatment, peaked at 1 to 3 h, and returned to near control levels by 6 h. The majority of the activity was detected in a soluble fraction (105,000g supernatant), but a minor portion was also associated with a particulate fraction enriched in microsomal membranes (105,000g pellet); both activities were similarly induced. 5-Hydroperoxyeicosatetraenoic acid was the principal product following incubation of these extracts with AA. Antibodies to soybean LOX strongly reacted with a protein with a molecular mass of approximately 95-kD present in both soluble and particulate fractions whose abundance generally corresponded with LOX activity in extracts. LOX activity was not enhanced by treatment of the discs with nonelicitor fatty acids or by branched β-glucans from the mycelium of Phytophthora infestans. Prior treatment of the discs with abscisic acid, salicylhydroxamic acid, or n-propyl gallate, all of which have been shown to suppress AA induction of the hypersensitive response, inhibited the AA-induced increment in LOX activity. Cycloheximide pretreatment, which abolishes AA elicitor activity for other responses such as phytoalexin induction, did not inhibit LOX activity in water- or elicitor-treated discs but enhanced activity similar to that observed by AA treatment. The elicitor-induced increase in 5-LOX activity preceded or temporally paralleled the induction of other studied responses to AA, including the accumulation of mRNAs for 3-hydroxy-3-methylglutaryl coenzyme A reductase and phenylalanine ammonia lyase reported here. The results are discussed in relation to the proposed role of the 5-LOX in signal-response coupling of arachidonate elicitation of the hypersensitive response.

Three Genes for Metabolism of the Phytoalexin Maackiain in the Plant Pathogen Nectria haematococca: Meiotic Instability and Relationship to a New Gene for Pisatin Demethylase.

Abstract: Some isolates of the plant-pathogenic fungus Nectria haematococca mating population (MP) VI metabolize maackiain and medicarpin, two antimicrobial compounds (phytoalexins) synthesized by chickpea (Cicer arietinum L.). The enzymatic modifications by the fungus convert the phytoalexins to less toxic derivatives, and this detoxification has been proposed to be important for pathogenesis on chickpea. In the present study, loci controlling maackiain metabolism (Mak genes) were identified by crosses among isolates of N. haematococca MP VI that differed in their ability to metabolize the phytoalexin. Strains carrying Mak1 or Mak2 converted maackiain to 1a-hydroxymaackiain, while those with Mak3 converted it to 6a-hydroxymaackiain. Mak1 and Mak2 were unusual in that they often failed to be inherited by progeny. Mak1 was closely linked to Pda6, a new member in a family of genes in N. haematococca MP VI that encode enzymes for detoxification of pisatin, the phytoalexin synthesized by garden pea. Like Mak1, Pda6 was also transmitted irregularly to progeny. Although the unusual meiotic behaviors of some Mak genes complicate genetic analysis, identification of these genes should afford a more through evaluation of the role of phytoalexin detoxification in the pathogenesis of N. haematococca MP VI on chickpea.

Phytoalexins of woody plants

Abstract: Phytoalexins accumulated in selected woody plants in response to microbial attack or stress are reviewed and listed with respect to their chemical structure and probable biogenetic origin. The host-pathogen systems from which they have been isolated are described. The review also considers the antimicrobial activity of the phytoalexins to the causal pathogens and other microorganisms.

Isolation, Purification, and Identification of 2-( p -Hydroxyphenoxy)-5, 7-Dihydroxychromone: A Fungal-Induced Phytoalexin from Cassia obtusifolia

Abstract: A single phytoalexin was isolated and purified from 12- to 14-day-old leaves of Cassia obtusifolia L. inoculated with Alternaria cassiae Jurair & Khan. The structure was elucidated by 1H- and 13C-nuclear magnetic resonance and mass spectrometry as 2-(p-hydroxyphenoxy)-5,7-dihydroxychromone. The compound was shown to be derived in part from phenylalanine. Radial growth of A. cassiae was inhibited 50% by the compound at 0.3 millimolar. This moderate toxicity is compensated for by the relatively high levels (3 millimolar) accumulated. Phenoxychromones have been previously reported only as constitutive secondary metabolites in Artemisia capillaris Thunb., in which their function is unknown.

Inducible Phytoalexins in Juvenile Soybean Genotypes Predict Soybean Looper Resistance in the Fully Developed Plants

Abstract: The hypocotyl of different soybean genotypes was tested for its inducible phytoalexin (i.e. glyceollin or coumestrol) accumulation and its inducible soybean looper resistance in response to chemical elicitation. A very highly insect-resistant soybean genotype (PI 227687) produced significantly more phytoalexins than a relatively insect-susceptible one (Davis) in response to the same chemical elicitation. The resultant standardized hypocotyl assay allowed quick categorization of unknown soybean genotypes regarding the level of insect resistance in the fully developed plants. Glyceollin was a better indicator of inducible resistance than coumestrol. Elicitor concentration influenced the amount of glyceollin and coumestrol accumulated. Younger seedlings (4-5 d old) responded stronger to chemical elicitation than did older ones (7-10 d old). The elicited accumulation of glyceollin showed a temporal pattern that peaked at 72 h. Accumulation of coumestrol showed a gradual increase. Elicitation of phytoalexins in juvenile soybean plants by sulfhydryl-binding reagents was found to be useful for the prediction of genotypic differences in the level of insect resistance in the fully developed plants.

Genetic Analysis of the Role of Phytoalexin Detoxification in Virulence of the Fungus Nectria haematococca on Chickpea (Cicer arietinum).

Abstract: Chickpea (Cicer arietium L.) produces the antimicrobial compounds (phytoalexins) medicarpin and maackiain in response to infection by microorganisms. Nectria haematococca mating population (MP) VI, a fungus pathogenic on chickpea, can metabolize maackiain and medicarpin to less toxic products. These reactions are thought to be detoxification mechanisms in N. haematococca MP VI and required for pathogenesis by this fungus on chickpea. In the present study, these hypotheses were tested by examining the phenotypes of progeny from crosses of the fungus that segregated for genes (Mak genes) controlling phytoalexin metabolism. Mak1 and Mak2, two genes that individually confer the ability to convert maackiain to its 1a-hydroxydienone derivative, were linked to higher tolerance of the phytoalexins and high virulence on chickpea. These results indicate that this metabolic reaction is a mechanism for increased phytoalexin tolerance in the fungus, which thereby allows a higher virulence on chickpea. Mak3, a gene conferring the ability to convert maackiain to its 6a-hydroxypterocarpan derivative, also increased tolerance to maackiain in strains which carried it; however, the contribution of Mak3 to the overall level of pathogenesis could not be evaluated because most progeny from the cross segregating for this gene were low in virulence. Thus, metabolic detoxification of phytoalexins appeared to be necessary, as demonstrated in the Mak1 and Mak2 crosses, but not sufficient by itself, as in the Mak3 cross, for high virulence of N. haematococca MP VI on chickpea.

An extracellular enzyme from Fusarium solani f. sp. phaseoli which catalyses hydration of the isoflavonoid phytoalexin, phaseollidin.

Abstract: Among the antimicrobial phytoalexins produced by Phaseolus vulgaris (French bean) are the prenylated isoflavonoids kievitone and phaseollidin. Two enzyme activities, kievitone hydratase and phaseollidin hydratase, occur in culture filtrates of the bean pathogen, Fusarium solani f. sp. phaseoli, and catalyse similar hydration reactions on the dimethylallyl moieties of the phytoalexins. The enzymes nearly co-purified during hydroxyapatite chromatography followed by preparative native gel electrophoresis. Eluates from successive slices taken from the native gel were assayed for both activities. Although they were not completely separated in the native gel, the activity profiles indicated that the two activities were distinct. The Km of phaseollidin hydratase for phaseollidin was approximately 7 μM.

Molecular analysis of plant defense responses to plant pathogens.

Abstract: A number of inducible plant responses are believed to contribute to disease resistance. These responses include the hypersensitive reaction, phytoalexin synthesis, and the production of chitinase, glucanase, and hydroxyproline-rich glycoproteins. Because of the coordinate induction of these responses, it has been difficult to determine whether they are functional defense responses, and if they are, how they specifically contribute to disease resistance. Recent developments in molecular biology have provided experimental techniques that will reveal the specific contribution of each response to disease resistance. In this paper, we describe a strategy to determine if the hypersensitive reaction is a functional plant defense mechanism. Key words: chalcone isomerase, chalcone synthase, chitinase, hrp genes, hypersensitive reaction, nematode, phenylalanine ammonia-lyase, phytoalexin, Pseudomonas syringae, resistance.

The role of free radicals in the decomposition of the phytoalexin desoxyhemigossypol

Abstract: The cotton phytoalexin desoxyhemigossypol (dHG) decomposed rapidly in solution to give hemigossypol (HG). The rate of decomposition was retarded by the reducing agents ascorbic acid, reduced glutathione and cysteine, by the metal chelator diethylenetriaminepentaacetic acid, and by the enzyme catalase. However, the chelator, ethylenediaminetetraacetic acid did not reduce the rate of decomposition and the enzyme superoxide dismutase increased the rate of decomposition. Solutions of the phytoalexin desoxyhemigossypol-6-methyl ether were significantly more stable than were those of dHG. Oxygen-18 from water but not from oxygen gas was incorporated into HG during this decomposition. A hydroperoxynaphthalenone which loses hydrogen peroxide is proposed as an intermediate to explain this observation. The formation of hydrogen peroxide may be involved in the toxicity of this phytoalexin to plant pathogens such as Verticillium dahliae.

Novel study on the elicitation of hypersensitive response by polyunsaturated fatty acids in potato tuber

Abstract: A GC-MS procedure was carried out for the simultaneous and unequivocal quantitation of both potato phytoalexin (rishitin and lubimin) accumulation and the rate of disappearance of polyunsaturated fatty acids (PUFA) and some of their esters tested as possible elicitors. Potato 5-lipoxygenase and lipolytic acyl hydrolase play a key role in hypersensitive response (HR) induction. As expected, arachidonic acid, its hydrolysable esters, and eicosapentaenoic acid elicited much higher HR than the other PUFA tested, although the latter were equally affected by potato 5-lipoxygenase. Hydroxyl radicals appear to be actively involved in the browning process. The polyaminoacid poly-L-lysine did not show any eliciting activity. © 1992 Wiley-Liss, Inc.

Accumulation of a complex of pigments in sorghum mesocotyls in response to wounding

Abstract: Sorghum mesocotyls upon mechanical injury with an abrasive (carborundum) or inoculation with the fungi Helminthosporium carbonum (non-pathogen) or Colletotrichum graminicola (pathogen) accumulate a methanol-soluble pigment complex with an absorption maximum around 480–490 nm. Spectral and thin-layer chromatographic analyses showed that the complexes which accumulated either in response to wounding or inoculation are similar. Thus, it is suggested that the accumulation of the pigmented phytoalexins in sorghum mesocotyls is a non-specific response of the tissues towards mechanical injury or fungal infection.