Showing papers on "Phytoalexin published in 1986"
TL;DR: The present review considers the process of phytoalexin induction, at the molecular level, from the fungal elicitor to the early changes in host gene expression associated with its action.
Abstract: Summary
1. Induced resistance of plants to incompatible races of their microbial pathogens is often characterized by rapid cell death (the hypersensitive response) and the accumulation of low-Mr antimicrobial compounds termed phytoalexins. There is much indirect evidence to support a major role for phytoalexin induction as an event determining host resistance, and genetical analysis of race-specific pathogen-host interactions predicts that induced resistance occurs via interaction between a pathogen avirulence gene product and a host resistance gene product. Elicitors (inducing agents) of phytoalexin accumulation are possible candidates for the active products directly or indirectly resulting from the expression of microbial avirulence genes. The present review considers the process of phytoalexin induction, at the molecular level, from the fungal elicitor to the early changes in host gene expression associated with its action.
2. A number of microbial polysaccharides, glycoproteins, pectic enzymes, peptides and fatty acids have potent elicitor activity.
3. The results of studies on the purification and characterization of microbial elicitors depend on the nature of the bioassay used. Methods for elicitor extraction may lead to artifacts or loss of race specificity.
4. Elicitors isolated from plant pathogens may be race-specific or race-non-specific. In cases where only race-non-specific elicitors can be shown, race-specific induction of phytoalexins may result from the action of enhancer or suppressor molecules. Fungal glucans have been proposed as candidates to act in both these roles.
5. Molecular genetic approaches to the identification of phytopathogenic bacterial avirulence genes may help to prove or disprove the role of elicitors of the phytoalexin response as agents responsible for the induction of host resistance. Similar analyses, involving genetic transformation, should soon be possible for phytopathogenic fungi.
6. Studies on the nature of host receptors for microbial elicitors are still in their infancy. Such receptors are probably localized in the plant plasma membrane, and elicitation results in often striking changes in host membrane properties.
7. Cyclic 3′,5′-adenosine monophosphate and polyamines do not appear to act in plants as intracellular transducers of the phytoalexin response. Interest is now being shown in a possible role for calcium in intracellular signalling.
8. Plant cells contain endogenous elicitor molecules whose synthesis or release may play a role in the intercellular transmission of the phytoalexin response. The main candidates for endogenous elicitors are pectic fragments of the host cell wall, although no direct evidence for their involvement in plant-pathogen interactions is available. Pectic fragments may act as synergists in parallel with, rather than as couplers in series with, microbial elicitors. The role of ethylene as a response coupler for induced resistance phenomena is difficult to assess.
9. Some elicitors may themselves move to the host cell nucleus, although whether this is their effective site of action remains unclear.
10. Induction of the phytoalexin response is associated with specific changes in host gene expression related to the selective induction of new mRNA species and enzyme activities.
11. Progress is now being made in the characterization of enzymes specific for phytoalexin biosynthesis. Enzyme induction and/or infection appears to involve rapid modulation of gene transcription, although some post-translational events may also be involved in determining induction patterns.
12. Work is now commencing on the sequencing of the genes encoding elicitor-inducible enzymes. Multigene families have been identified for phenylalanine ammonia-lyase and chalcone synthase.
13. Phytoalexin accumulation may be accompanied by the rapid induction of ethylene biosynthesis and the expression of genes encoding activities involved in the synthesis of hydroxyproline-rich glycoproteins.
14. Pectic endogenous elicitors of phytoalexin accumulation are also active as inducers of systemic proteinase inhibitor synthesis in some solanaceous species.
15. Results of studies on the mechanisms of signal transmission and differential gene expression in relation to active defence reactions should be of relevance to many other aspects of the plant's response to environmental stimuli at the physiological, biochemical and molecular genetical levels.
378 citations
TL;DR: There is considerable evidence that supports the view that phytoalexin synthesis is strongly enhanced not only upon challenge of plant tissues by parasites but also following treatment with substances called elicitors, and the nature and activity of several elicitors are described.
Abstract: The biochemical basis of defense mechanisms conferring disease resistance on plants is now under active investigation. Plant resistance mechanisms are effective at different levels in host-parasite interactions and include preformed physical and chemical defense barriers as well as defenses triggered by the invader (69). One inducible defense response is the synthesis of phytoalexins at the site of attempted infection. Phytoalexins have been defined as anti microbial compounds of low-molecular weight that both are synthesized by and accumulate in plants after the exposure of the plant to microorganisms (113). They show the range and structural complexity typical of higher-plant natural products and are predominantly phenylpropanoids, isoprenoids, and acetylenes (5). The discovery of phytoalexins in interactions between parasites and host plants has encouraged many investigators to believe that these compounds are critical factors in regulating the interactions. Although this chapter presents considerable evidence that supports this view, it also discusses other results that may indicate a more limited role for phytoalexins. One particularly interesting aspect of these compounds originates from the fact that, in many systems, phytoalexin synthesis is strongly enhanced not only upon challenge of plant tissues by parasites but also following treatment with substances called elicitors. Because of their suspected role in disease processes, the nature and activity of several elicitors are described. Suitable experimental systems of reduced complexity, e.g. plant-cell cultures and elicitors, as well
374 citations
TL;DR: The results confirm and extend previous observations that oligogalacturonides derived from the pectic polysaccharides of plant cell walls can serve as regulatory molecules that induce phytoalexin accumulation in soybean.
Abstract: Recent studies have demonstrated that an apparently homogeneous preparation of an α-1,4-d-endopolygalacturonic acid lyase (EC 4.2.2.2) isolated from the phytopathogenic bacterium Erwinia carotovora induced phytoalexin accumulation in cotyledons of soybean (Glycine max [L.] Merr. cv Wayne) and that this pectin-degrading enzyme released heat-stable elicitors of phytoalexins from soybean cell walls, citrus pectin, and sodium polypectate (KR Davis et al. 1984 Plant Physiol 74: 52-60). The present paper reports the purification, by anion-exchange chromatography on QAE-Sephadex columns followed by gel-permeation chromatography on a Bio-Gel P-6 column, of the two fractions with highest specific elicitor activity present in a crude elicitor-preparation obtained by lyase treatment of sodium polypectate. Structural analysis of the fraction with highest specific elicitor activity indicated that the major, if not only, component was a decasaccharide of α-1,4-d-galactosyluronic acid that contained the expected product of lyase cleavage, 4-deoxy-β-l-5-threohexopyranos-4-enyluronic acid (4,5-unsaturated galactosyluronic acid), at the nonreducing terminus. This modified decagalacturonide fraction exhibited half-maximum and maximum elicitor activity at 1 microgram/cotyledon (6 micromolar) and 5 micrograms/cotyledon (32 micromolar) galactosyluronic acid equivalents, respectively. Reducing 90 to 95% of the carboxyl groups of the galactosyluronic acid residues abolished the elicitor activity of the decagalacturonide fraction. The second most elicitor-active fraction contained mostly undeca-α-1,4-d-galactosyluronic acid that contained 4,5-unsaturated galactosyluronic acid at the nonreducing termini. This fraction exhibited half-maximum and maximum elicitor activity at approximately 3 micrograms/cotyledon (17 micromolar) and 6 micrograms/cotyledon (34 micromolar) galactosyluronic acid equivalents, respectively. These results confirm and extend previous observations that oligogalacturonides derived from the pectic polysaccharides of plant cell walls can serve as regulatory molecules that induce phytoalexin accumulation in soybean. These results are consistent with the hypothesis that oligogalacturonides play a role in disease resistance in plants.
157 citations
TL;DR: Isoflavonoid phytoalexins are a major class of low molecular weight, inhibitory compounds synthesized by certain plants, notably members of the Leguminosae, and their biosynthesis, elicitation and biological properties are summarized.
146 citations
TL;DR: In this paper, RNA blot hybridization with 32P-labeled cDNA sequences was used to demonstrate marked accumulation of phenylalanine ammonia-lyase and chalcone synthase mRNAs in excision-wounded hypocotyls of Phaseolus vulgaris L. (dwarf French bean) and during race-cultivar-specific interactions between hypocoils of P. vulgaris and the partially biotrophic fungus Colletotrichum lindemuthianum, the causal agent of anthracnose.
Abstract: Phenylalanine ammonia-lyase and chalcone synthase catalyze the first reaction of phenylpropanoid biosynthesis and the first reaction of a branch pathway specific for flavonoid-isoflavonoid biosynthesis, respectively. These enzymes are key control elements in the synthesis of kievitone, phaseollin, and related isoflavonoid-derived phytoalexins. RNA blot hybridization with 32P-labeled cDNA sequences was used to demonstrate marked accumulation of phenylalanine ammonia-lyase and chalcone synthase mRNAs in excision-wounded hypocotyls of Phaseolus vulgaris L. (dwarf French bean) and during race-cultivar-specific interactions between hypocotyls of P. vulgaris and the partially biotrophic fungus Colletotrichum lindemuthianum, the causal agent of anthracnose. In an incompatible interaction (host resistant), early concomitant accumulation of phenylalanine ammonia-lyase and chalcone synthase mRNAs, localized mainly but not entirely in tissue adjacent to the site of infection, was observed prior to the onset of phytoalexin accumulation and expression of localized, hypersensitive resistance. In contrast, in a compatible interaction (host susceptible) there was no early accumulation of these transcripts; instead, there was a delayed widespread response associated with phytoalexin accumulation during attempted lesion limitation. Two-dimensional gel electrophoresis of [35S]methionine-labeled polypeptides synthesized in vitro by translation of isolated polysomal RNA demonstrated stimulation of the synthesis of characteristic sets of phenylalanine ammonia-lyase and chalcone synthase isopolypeptides in directly infected tissue and distant, hitherto uninfected tissue in both compatible and incompatible interactions. Our data show that specific accumulation of plant defense gene transcripts is a key early component in the sequence of events leading to expression of defense responses in wounded tissue and in infected tissue during race-cultivar-specific interactions and that an elicitation signal is transmitted intercellularly in response to infection.
140 citations
TL;DR: The results suggest that oligogalacturonides act as signals of tissue damage and, as such, can enhance the response of plant tissues to other elicitor-active molecules during the initiation of phytoalexin accumulation.
Abstract: Plants often respond to microbial infection by producing antimicrobial compounds called phytoalexins. Plants also produce phytoalexins in response to in vitro treatment with molecules called elicitors. Specific elicitors, including a hexa-β-glucosyl glucitol derived from fungal cell walls, the pectin-degrading enzyme endopolygalacturonic acid lyase, and oligogalacturonides obtained by either partial acid hydrolysis or enzymatic degradation of plant cell walls or citrus polygalacturonic acid, induce soybean (Glycine max. L.) cytoledons to accumulate phytoalexins. The experiments reported here demonstrate that the elicitor-active hexa-β-glucosyl glucitol acts synergistically with several biotic and abiotic elicitors in the induction of phytoalexins in soybean cotyledons. At concentrations below 50 ng/ml, the hexa-β-glucosyl glucitol does not induce significant phytoalexin accumulation. When assayed in combination with either endopolygalacturonic acid lyase or with a decagalacturonide released from citrus polygalacturonic acid by this lyase, however, the observed elicitor activity of the hexa-β-glucosyl glucitol is as much as 35-fold higher than the sum of the responses of these elicitors assayed separately. A similar synergism was also demonstrated for the combination of the hexa-β-glucosyl glucitol with dilute solutions of sodium acetate, sodium formate, or sodium propionate buffers. These buffers are thought to damage or kill plant cells, which may cause the release of oligogalacturonides from the plant cell wall. The results suggest that oligogalacturonides act as signals of tissue damage and, as such, can enhance the response of plant tissues to other elicitor-active molecules during the initiation of phytoalexin accumulation.
83 citations
TL;DR: Victorin was an efficient elicitor of avenalu-min production only in the Pc-2 line, giving maximum phytoalexin production, and vietorin did not elicit detectable avenalumin production in the pc-2 oat line at 10 ng ml −1, Vietorin treatment resulted in loss of chlorophyll in the C2 line at concentrations that elicited avenalumn production, but relatively little cellular necrosis occurred.
78 citations
TL;DR: The results show that infection of soybean roots with zoospores of Pmg race 1 causes a race:cultivar-specific early induction of enzymes involved in glyceollin synthesis, whereas such an induction does not occur with zoepores of race 3.
59 citations
TL;DR: Benzoate, dimethylsulphoxide, mannitol and methionine, which are scavengers of the hydroxyl radical (OH·), inhibited the accumulation of the glyceollin phytoalexins in soybean cotyledons elicited by silver nitrate.
53 citations
ARCO1
TL;DR: In vitro studies demonstrated that A. helianthi possessed the ability to rapidly degrade both scopoletin and ayapin, whereas H. carbonum was much less efficient in these traits.
Abstract: The coumarin phytoalexins ayapin and scopoletin accumulate in longitudinal stem sections of sunflower (Helianthus annuus L., Compositae) following inoculation with fungi both pathogenic (Alternaria helianthi) and nonpathogenic (Helminthosporium carbonum) to this plant. Both compounds were induced more rapidly, and they attained higher levels in tissue inoculated with the heterologous pathogen H. carbonum as compared with the sunflower pathogen A. helianthi. Similarly, scopoletin and ayapin accumulated to comparatively low concentrations following inoculation with a second sunflower pathogen, Phoma macdonaldii. Scopoletin was biosynthesized de novo following inoculation, although levels of its glucoside scopolin exceeded those of the aglucone in both infected and control tissues. Both scopoletin and scopolin were routinely detected in trace amounts in uninoculated tissue. In contrast, ayapin was not detected as a component of uninfected plants. When [14C]scopoletin was supplied to induced sunflower stem sections about 36% of the recovered radioactivity was in the form of ayapin. In vitro studies demonstrated that A. helianthi possessed the ability to rapidly degrade both scopoletin and ayapin, whereas H. carbonum was much less efficient in these traits. The differential degradation of these compounds by phytopathogenic fungi which do not attack sunflower is also discussed.
50 citations
TL;DR: The results suggest that the effect of AA on terpenoid metabolism, peroxidase activity and its protection of potato tissue from colonization by a compatible race as well as the stimulation of AA activity by glucans are highly specific.
TL;DR: Radioactivity in individual phosphoinositides from these cells was determined and no significant influence of elicitor-challenge of either soybean or parsley cells on incorporation of 3H or 32P into polyphosphoinositide was found between 0.5 and 20 min after elicitor addition.
Abstract: Abstract The phospholipids of cultured parsley and soybean cells were labelled with myo-[2-3H]inositol, [2-3H]glycerol or [32P]orthophosphate. By one-and two-dimensional chromatographic comparison of the labelled phospholipids with reference substances, the presence of 1-(3-sn-phosphatidyl)-ᴅ-myo-inositol 4-phosphate and 1-(3-sn-phosphatidyl)-ᴅ-myo-inositol 4,5-bisphosphate was demonstrated in these cultures. These results were corroborated by analysis of the deacylation products. Cells were labelled with either myo-[2-3H]inositol, [2-3H]glycerol or [32P]orthophosphate and subsequently challenged with elicitor for various lengths of time. Radioactivity in individual phosphoinositides from these cells was determined. No significant influence of elicitor-challenge of either soybean or parsley cells on incorporation of 3H or 32P into polyphosphoinositides was found between 0.5 and 20 min after elicitor addition.
TL;DR: The most elicitor-active molecules obtained by treating soybean cell walls with endopolygalacturonic acid lyase have been purified and characterized and the molecules with the highest specific elicitor activity were identified as α-1,4 -linked deca- and undecagalacturonides that contained 4,5-unsaturated galactosyluronic Acid at the nonreducing termini.
Abstract: Endopolygalacturonic acid lyase, purified from the phytopathogenic bacterium, Erwinia carotovora, induces phytoalexin accumulation in soybean (Glycine max L.) cotyledons. This pectin-degrading enzyme releases heat-stable elicitors of phytoalexin accumulation from soybean cell walls, citrus pectin, and citrus sodium polypectate. The most elicitor-active molecules obtained by treating soybean cell walls with endopolygalacturonic acid lyase have been purified and characterized. The cell-wall-derived elicitors are α-1,4-linked oligogalacturonides with degrees of polymerization of eight to twelve residues. The molecules with the highest specific elicitor activity were identified as α-1,4 -linked deca- and undecagalacturonides that contained 4,5-unsaturated galactosyluronic acid at the nonreducing termini.
TL;DR: After infection with spores of a virulent strain of Ascochyta rabiei the chickpea cultivars ILC 1929 (susceptible) and ILC 3279 (resistant) were compared with regard to pterocarpan phytoalexin and isoflavone accumulation.
Abstract: After infection with spores of a virulent strain of Ascochyta rabiei the chickpea (Cicer arietinum) cultivars ILC 1929 (susceptible) and ILC 3279 (resistant) were compared with regard to pterocarpan phytoalexin and isoflavone accumulation. Quantitative HPLC analyses of total extracts of aerial parts were used to measure the induced formation of the phytoalexins medicarpin and maackiain and the accumulation of the constitutive isoflavones biochanin A and formononetin together with their, 7-0-glucosides and their 7-0-glucoside-6″-0-malonates. The two cultivars showed no significant difference in the level of isoflavones and isoflavone conjugates. On the other hand, the resistant cultivar ILC 3279 rapidly accumulated large amounts of both, phytoalexins (20–26 nmole g−1 fr.w.) whereas cultivar ILC 1929 only produced very small amounts (5 nmole g−1 fr.w.) of medicarpin. The data are discussed with regard to isoflavonoid metabolism and the significance of induced and constitutive levels of phytoalexins and isoflavones in resistance of chickpea towards A. rabiei.
01 Jan 1986
TL;DR: The molecular mechanisms of recognition and induction processes are difficult to study in intact plant/pathogen systems, because only a limited number of plant cells are challenged by and respond to the pathogen, and because multiple infection events usually do not occur synchronously.
Abstract: Resistance of plants to pathogens usually involves a great variety of mechanisms preventing penetration, growth, and multiplication of the invading organism. Pathogen-induced reactions are an important part of the plant’s defense mechanisms. A prerequisite for induction of these responses is the perception of appropriate signals by the plant cell. The molecular mechanisms of recognition and induction processes are difficult to study in intact plant/pathogen systems, because only a limited number of plant cells are challenged by and respond to the pathogen, and because multiple infection events usually do not occur synchronously.
TL;DR: It is suggested that chitinase is induced in carrot cells in response to contact with mycelial walls and enzyme released fragments of mycelIAL walls elicit the accumulation of phenolic compounds in carrots cells.
TL;DR: The results indicate that under the methods employed isolated soybean protoplasts display a stress response which other types of soybean cells show following microbial attack or treatment with elicitor.
Abstract: Abstract Protoplasts isolated enzymatically from suspension-cultured cells of soybean (Glycine max L. Merr., cv. Harosoy 63) were used to study the production of the isoflavonoid-derived phytoalexin, glyceollin. A large enhancement in the in vivo rates of synthesis and catalytic activities of two of the enzymes associated with glyceollin biosynthesis, phenylalanine ammonia-lyase and chalcone synthase, preceded phytoalexin accumulation during early stages of culture of isolated protoplasts while cell wall regeneration occurred. A glucan elicitor from cell walls of the fungus Phytophthora megasperm a f. sp. glycinea, an effective inducer of the phytoalexin response in cultured cells, was not capable of enhancing phytoalexin formation in protoplasts. Lack of responsiveness of the protoplasts to the glucan elicitor could either be associated with their stressed metabolic state in which the response system is already saturated or with the removal from cultured cells of an essential factor of the glucan elicitor-mediated phytoalexin induction during protoplast isolation. At least two components of the protoplast isolation medium, the osmoticum and the fungal endopolygalacturonase, have the potential to initiate the observed phytoalexin synthesis during protoplast isolation. Our results indicate that under the methods employed isolated soybean protoplasts display a stress response which other types of soybean cells show following microbial attack or treatment with elicitor.
TL;DR: In this paper, the self defensive substances in rice plant against rice blast disease are described and a convenient synthesis of 16-hydroxy-9Z,12Z,14E-octadecatrienoic acid (1) and 9- hydroxy-1OE, 12Z,15Z-Octadec-catrienic acid is described.
TL;DR: It is concluded that infection of the soybean roots with an incompatible race of the fungus leads to selective induction of the phytoalexin pathway and presumably to induction of other as yet unknown defense mechanisms.
Abstract: The activities of the following enzymes in soybean roots were determined at early times after infection of the roots with zoospores of an incompatible or a compatible race of Phytophthora megasperma f.sp. glycinea: dimethylallyl-diphosphate : 3,6a,9-trihydroxypterocarpan dimethylallyltransferase (prenyltransferase), an enzyme specific for glyceollin biosynthesis; NADPH-cytochrome reductase and hydroxymethylglutaryl-CoA reductase, enzymes related to the glyceollin pathway; and isocitrate dehydrogenase. Already at 4 h after infection there was a higher activity of the prenyltransferase in the incompatible interaction than in the compatible interaction, and enzyme activity in the incompatible interaction increased considerably between 4 and 8 h after infection. In the compatible interaction prenyltransferase activity was only slightly higher than in uninfected roots. The activity of the other enzymes in infected roots was not significantly different from that in the uninfected roots. No qualitative differences could be detected between the two-dimensional patterns of unlabelled proteins or proteins labelled with L-[35S]methionine of infected and uninfected roots at early times after infection. We conclude from these and earlier results (A. Bonhoff et al. (1986) Arch. Biochem. Biophys. 246, 149-154) that infection of the soybean roots with an incompatible race of the fungus leads to selective induction of the phytoalexin pathway and presumably to induction of other as yet unknown defense mechanisms.
TL;DR: The phytoalexins lubimin, (−)-maackiain, pinosylvin and dehydroloroglossol showed significant growth inhibitory action on the cells and suppression of [3H] thymidine and leucine uptake was tested.
Abstract: We have tested the effect of the phytoalexins lubimin, (−)-maackiain and pinosylvin and the related compounds dehydroloroglossol and hordatine M on the growth of the human lymphoblastoid cell lines Molt and Raji. (−)-maackiain, pinosylvin and dehydroloroglossol showed significant growth inhibitory action on the cells. Suppression of [3H] thymidine and [3H] leucine uptake was tested and noted in pinosylvin and dehydroloroglossol. The phytoalexins and related compounds are widespread in plants and provide a potential source of antineoplastic substances.
TL;DR: In this paper, two lucerne (Medicago sativa L.) callus lines gave contrasting reaction types to Verlicillium albo-atrum when incubated at 20 °C and 28 °C.
TL;DR: It was found that arachidonic acid could elicit a response in protoplasts that was visually identical to the response caused by hyphal wall components, but other unsaturated fatty acids not able to elicit phytoalexins in tubers were also effective on protoplast.
TL;DR: In this paper, the effects of phytoalexins, rishitin, pisatin, wyerone acid and phaseollin (all at 0.1 mol m−3) on stomatal responses in epidermal strips of Commelina communis L. and Vicia faba L. were examined and compared with those of several water-stress compounds namely abscisic acid (ABA), farnesol, nonanoic and undecanoic acids, and α-linolenic acid.
Abstract: Summary
The effects of the phytoalexins, rishitin, pisatin, wyerone acid and phaseollin, (all at 0.1 mol m−3) were tested on stomatal responses in epidermal strips of Commelina communis L. and Vicia faba L. Additionally, the effects of the phytoalexins on guard cell protoplasts of C. communis were examined and compared with those of several‘water-stress' compounds namely abscisic acid (ABA), farnesol, nonanoic and undecanoic acids, and α-linolenic acid. Phytoalexins may be loosely defined as‘microbial stress' compounds while‘water-stress' compounds are denned as those which accumulate in leaf tissue under water-stress and close stomata or act as osmotic adjusters.
Wyerone acid and phaseollin inhibited stomatal opening in C. communis to the same extent as ABA, while rishitin had no significant effect and pisatin had an intermediate effect. When stomata were open, treatments with phaseollin and ABA brought about a marked closing response, while those with pisatin and rishitin were not statistically significant from the controls; wyerone acid initially opened stomata further but after 5 h exposure stomatal apertures were similar to those of the controls.
Stomatal opening in epidermis of V. faba was greatly inhibited by ABA, while all phytoalexin treatments resulted in intermediate inhibitory effects between those obtained with the control and ABA treatments, wyerone acid being the most inhibitory.
Pisatin and rishitin (at 0.1 mol m−3) had no discernible effects on guard cell protoplasts, while phaseollin and wyerone acid (at 0.1 mol m−3) caused loss of protoplast viability. The‘water-stress' compounds, nonanoic, undecanoic and α-linolenic acids, also caused gradual loss of protoplast viability and farnesol caused lysis of protoplasts. Only ABA caused protoplasts to contract without loss of vitality. Thus phaseollin and, to a lesser extent, wyerone acid have similar properties to ABA in that they inhibit stomatal opening and promote closure. However, unlike ABA but like farnesol, nonanoic, undecanoic and α-linolenic acids, their effects are likely to be associated with phytotoxicity, their phytotoxicity depending on duration of exposure and on concentration.
TL;DR: Culture filtrates and cell wall extracts of the tomato vascular pathogen Verticillium albo-atrum elicited the accumulation of the sesquiterpenoid phytoalexin rishitin in whole plants and excised stem segments of susceptible and resistant (Ve/Ve) Craigella tomato plants.
TL;DR: The pterocarpinoid phytoalexins, glyceollin, pisatin, and phaseollin stimulated adventitious root formation in a mung bean rooting bioassay only in the presence of indoleacetic acid (rooting cofactor activity).
Abstract: The pterocarpinoid phytoalexins, glyceollin, pisatin, and phaseollin, stimulated adventitious root formation in a mung bean rooting bioassay only in the presence of indoleacetic acid (rooting cofactor activity). Relatively low (5 to 50 micrograms per milliliter) concentrations of the phytoalexins were effective. The phytoalexins also increased the numbers of root primordia formed, therefore suggesting that they interacted with an early process in root formation.
01 Jan 1986
TL;DR: The data suggest that specific activation of plant defense genes is a key early component in the sequence of events leading to expression of defense reponses during race:cultivar specific interactions and that an elicitation signal is transmitted intercellularly to pre-activate defense genes in hitherto uninfected tissue.
Abstract: Plants exhibit resistance to disease involving inducible defenses including phytoalexin and hydroxyproline-rich glycoprotein (HRGP) accumulation, lignin deposition and increased activity of certain hydrolytic enzymes. Treatment of suspension-cultured cells of Phaseolus vulgaris L. with fungal elicitors redirects RNA synthesis leading to induction of mRNAs encoding phytoalexin biosynthetic enzymes such as phenylalanine ammonia-lyase and chalcone synthase; the lignin precursor biosynthetic enzyme cinnamyl alcohol dehydrogenase and HRGP. Accumulation of defense mRNAs is also observed during race:cultivar specific interactions between the fungus Colletotrichum lindemuthianum and P. vulgaris hypocotyls. There are clear temporal and spatial differences in the pattern of mRNA accumulation between incompatible (host resistant) and compatible (host susceptible) interactions. The data suggest that specific activation of plant defense genes is a key early component in the sequence of events leading to expression of defense reponses during race:cultivar specific interactions and that an elicitation signal is transmitted intercellularly to pre-activate defense genes in hitherto uninfected tissue. These observations indicate a number of potential sites for biotechnological manipulation and enhancement of disease resistance.
01 Jan 1986
TL;DR: Findings have indicated that unsaturated fatty acids and lipoconjugates are the active elicitors of phytoalexin accumulation in potato tubers, but arachidonic and eicosapentaenoic acids are not universal elicitors either.
Abstract: Early observations suggested that neutral polysaccharides from parasitic fungi could be universal elicitors of plant defence reactions [1]. However, more recent findings have indicated that unsaturated fatty acids and lipoconjugates are the active elicitors of phytoalexin accumulation in potato tubers [2]. But arachidonic and eicosapentaenoic acids are not universal elicitors either: they induce phytoalexin accumulation in potato and pepper, but not in twelve other plant species surveyed, including other Solanaceae, tobacco and tomato [3].
TL;DR: The carrot phytoalexin, 6-methoxymellein, was isolated and purified from carrot root slices infected by the fungus Chaetomium globosum and inhibited the basal and calmodulin-promoted activity of cyclic nucleotide phosphodiesterase.
01 Jan 1986
TL;DR: Elicitor treatment of soybean cell suspension cultures causes major changes in the population of total translatable mRNA, which indicates large metabolic changes associated with phytoalexin synthesis and possibly other defense responses of the challenged cells.
Abstract: Phytoalexin production is one of a number of inducible plant defense reactions which is thought to confer disease resistance against microbial infections in plants. Soybean (Glycine max) tissues produce and accumulate isof lavonoid phytoalexins (glyceollins) following either inoculation with a soybean pathogen, the fungus Phytophthora megasperma f.sp. glycinea, or treatment with a β-glucan elicitor isolated from the fungal cell walls. Studies on the regulation of phytoalexin biosynthetic enzymes suggested that the phytoalexin defense response in soybean is controlled by temporary gene activation. The activities of several of the glyceollin biosynthetic enzymes have been studied during race-cultivar specific interactions between P. megasperma zoospores and intact soybean primary roots, a natural site of attack by the fungus. Only in the incompatible (host-resistant) interaction, is there an early enhancement of the enzyme activities starting at 2–4 h after inoculation, which correlates with the onset of glyceollin accumulation and expression of the hypersensitive response. Elicitor treatment of soybean cell suspension cultures causes major changes in the population of total translatable mRNA, which indicates large metabolic changes associated with phytoalexin synthesis and possibly other defense responses of the challenged cells.