Showing papers on "Phytoalexin published in 1978"
TL;DR: The authors are attempting to identify a bacterial elicitor, known that the soybean pathogen Phytophthora magasperma is an oligosaccharide composed only of glucose, of general biological interest since it shows that oligOSaccharides can act as regulatory molecules.
Abstract: The ability to synthesize phytoalexins is a mechanism by which plants are able to stop the growth of microorganisms which have not become pathogenic on the phytoalexin-producing plant. Although not sufficient for its complete resistence to pathogens, an ability to synthesize phytoalexins is likely to be one essential criterion for a plant to be resistant to pathogens. Plants recognize the presence of many nonpathogenic fungi by recognizing a structural component of the mycelial walls of the fungi. Other microorganisms do not have structural glucans in their walls. There is, likely, some other components of bacteria, for instance, which act as elicitors in plants since it is known that they do elicit phytoalexin production in plants. The authors are attempting to identify a bacterial elicitor. It is known that the soybean pathogen Phytophthora magasperma is an oligosaccharide composed only of glucose. This is of general biological interest since it shows that oligosaccharides can act as regulatory molecules.
269 citations
TL;DR: The results indicate that bean cells contain a constitutive component capable of eliciting phytoalexin production, which occurs in response to infection by Colletotrichum lindemuthianum and in Response to other external stimuli.
Abstract: Phaseollin and phaseollidin were the predominant phytoalexins formed when live and dead bean hypocotyl tissues were incubated in contact with each other. The phytoalexins were produced by the live cells which were in close association with the dead tissue and were then taken up and accumulated in the dead cells. Small amounts of phytoalexins were produced when live tissues were incubated together, but none were formed when dead tissue was incubated alone. Aqueous extracts of bean tissue stimulated phytoalexin formation, suggesting that when bean cells were damaged, e.g. by freezing or maceration, a water-soluble component capable of eliciting phytoalexin formation was released. The active component was insoluble in organic solvents, was heat stable and passed through a dialysis membrane. Phaseollin and phaseollidin levels decreased in solutions which contained live tissue, dead tissue or isolated hypocotyl cell walls. Both phytoalexins were easily extracted from dead tissue or cell wall material but very little could be recovered from live tissue. The results indicate that bean cells contain a constitutive component capable of eliciting phytoalexin production. This possibility, along with the accumulation of phytoalexins by dead cells and their metabolism by living cells, is discussed in relation to the accumulation of these phytoalexins which occurs in response to infection by Colletotrichum lindemuthianum and in response to other external stimuli.
143 citations
TL;DR: Levels of glyceollin, a phytoalexin produced by soybean [Glycine max (L.) Merr.] hypocotyls in response to infection with the fungal pathogen Phytophthora megasperma var.
Abstract: PHYTOALEXINS are inducibly formed higher plant metabolites that are antibiotic to certain potential plant pathogens1. At least 75 plant species representing 20 families have been shown to accumulate phytoalexins in response to infection1–3. Phytoalexins also accumulate in plants in response to various agents termed elicitors1, including substances of pathogen origin (biotic elicitors) and abiotic elicitors such as heavy metal salts and detergents1–3. Elicitors may be useful for investigation of the molecular basis of phytoalexin production or disease resistance expression1. However, the mechanisms by which such diverse elicitor molecules induce phytoalexin accumulation in plants are unknown. I have found4 that levels of glyceollin, a phytoalexin produced by soybean [Glycine max (L.) Merr.] hypocotyls in response to infection with the fungal pathogen Phytophthora megasperma var. sojae A. A. Hildb., are regulated by relative rates of induced biosynthesis and constitutive degrading activity. I report here the effects of various biotic and abiotic elicitors on biosynthesis and degradation of glyceollin in soybean tissues.
96 citations
TL;DR: The results prove that stimulation of the enzymes of flavonoid biosynthesis and probably glyceollin biosynthesis are caused by the effect of the P. megasperma elicitor and not merely by wounding the plant material.
82 citations
TL;DR: The role of phyto-alexins as defense substances is not yet fully clear as discussed by the authors, however, the basic features of the biosynthesis of the phyttoalexin are known.
Abstract: Phytoalexins are defense substances with antimicrobial properties which are produced by plants after infection. They include various groups of natural substances (e.g. isoflavonoids, terpenoids, polyacetylenes and dihydrophenanthrenes). Induction of phytoalexin formation can be caused not only by living microorganisms but also by products of microbial origin (elicitors) or by stress treatment (cold, UV light). The elicitor from the mycelial walls of the fungus Phytophthora megasperma var. sojae (Pms) is a β-1,3-glucan with branches at C-6. In some cases the basic features of the biosynthesis of the phytoalexins are known. The activity of the enzymes involved in phytoalexin biosynthesis is increased by the action of the elicitor on plant tissues. The ability of some microorganisms to chemically modify the phytoalexins may be related to their pathogenicity. The role of phytoalexins as defense substances is not yet fully clear.
78 citations
TL;DR: Suspension cultures of Phaseolus vulgaris accumulated phytoalexins after treatment with an extract of bean hypocotyls and phaseollin was converted to phaseollinosoflavan by these cultures and this conversion occurred during accumulation of the phy toalexin accumulation.
67 citations
TL;DR: A beta-glucan isolated from the mycelial walls of Phytophthora megasperma var.
Abstract: A β-glucan isolated from the mycelial walls of Phytophthora megasperma var. sojae and a glucan purified from yeast extract stimulate the accumulation of phytoalexins in red kidney bean, Phaseolus vulgaris , and stimulate the accumulation of the phytoalexin, rishitin, in potato tubers, Solanum tuberosum. These glucans have previously been shown to be potent elicitors of glyceollin accumulation in soybean, Glycine max. Treatment of kidney bean cotyledons with the glucan elicitors resulted in the accumulation of at least five fungistatic compounds. These compounds migrate during thin layer chromatography identically to the fungistatic compounds which accumulate in kidney beans which have been inoculated with Colletotrichum lindemuthianum , a fungal pathogen of kidney beans. Potatoes accumulate as much as 29 micrograms of rishitin per gram fresh weight following exposure to the glucan from Phytophthora megasperma var. sojae and as much as 19.5 micrograms of rishitin per gram fresh weight following exposure to yeast glucan. Potatoes accumulated 28 micrograms of rishitin per gram fresh weight following inoculation with live Phytophthora megasperma var. sojae.
66 citations
TL;DR: The phytoalexin response in this callus tissue culture system compares well with natural plant systems and should be an excellent system for investigating regulation of phy Toalxin synthesis.
Abstract: Jackbean, Canavalia ensiformis (L.), callus tissues synthesized the phytoalexin, medicarpin (3-hydroxy-9-methoxypterocarpan), when treated with spore suspensions of Pithomyces chartarum (Berk. and Curt.) M. B. Ellis, a nonpathogen of jackbean. Medicarpin was isolated from treated callus tissue and identified by its ultraviolet and mass spectra. The minimum spore concentration found to elicit medicarpin synthesis after 26 hours was 1 x 10(5) spores/ml; levels of medicarpin in callus tissue increased linearly up to 1 x 10(7) spores/ml, indicating that the recognition sites for presumed elicitors were not saturated. Medicarpin was first detected in callus treated with 1 x 10(7) spores/ml, 6 to 12 hours after application, and the concentration reached a maximum at 48 hours, slowly declining thereafter to 72 hours. In callus treated with 3.15 mm HgCl(2), medicarpin concentrations were also maximum by 48 hours. Phenylalanine ammonia-lyase (EC 4.3.1.5) activity increased 2-fold in spore-treated callus after 36 hours. Isoliquiritigenin, daidzein, and genistein o-methyltransferase (EC 2.1.1.6) activities were increased 3- to 4-fold in treated callus. Caffeic acid and naringenin were more efficient substrates for o-methyltransferase activity than the other flavonoids or apigenin, but there was no increase in these o-methyltransferase activities in spore-treated callus. The phytoalexin response in this callus tissue culture system compares well with natural plant systems and should be an excellent system for investigating regulation of phytoalexin synthesis.
41 citations
23 citations
19 citations
TL;DR: The results are consistent with the hypothesis that differences in susceptibility can be based on differences in the levels of accumulated phytoalexins and suggest that phaseollin and kievitone are involved in lesion limitation.
Abstract: Botrytis cinerea infection of two bean cultivars with different degrees of susceptibility to this parasite was studied. Four fungitoxic compounds, identified as phaseollin, phaseollidin, phaseollinisoflavan and kievitone, were found to accumulate after infection in both cultivars. A fifth isoflavonoid, designated D, toxic to Cladosporium cucumerinum , was present only in extracts of the more susceptible cultivar. All four phytoalexins were toxic to B. cinerea , and accumulated to higher levels in the less susceptible cultivar. Phaseollin and kievitone were found in higher amounts than phaseollidin and phaseollinisoflavan, and their concentrations in the less susceptible cultivar reached a maximum when fungal growth stopped. The results are consistent with the hypothesis that differences in susceptibility can be based on differences in the levels of accumulated phytoalexins and suggest that phaseollin and kievitone are involved in lesion limitation.
TL;DR: The production of phytoalexins in leaf diffusates, leaf tissue and stem segments of lucerne cultivars resistant and susceptible to infection by Verticillium albo-atrum has been determined.
Abstract: The production of phytoalexins (determined as sativan and medicarpin) in leaf diffusates, leaf tissue and stem segments of lucerne cultivars resistant and susceptible to infection by Verticillium albo-atrum has been determined. No relationship between resistance and the formation of the antifungal compounds by leaves was observed. With stem segments, however, both the rates and amounts of phytoalexin synthesis were directly related to host resistance.
TL;DR: Elimination of the high-coumarin character from sweet clover cultivars does not appear to affect phytoalexin production, and in consequence, low-cOUmarin varieties should not be more susceptible to fungal colonisation than their high-CoumarIn counterparts.
Abstract: The isoflavonoid phytoalexin medicarpin has been found to accumulate in leaflets of high- and low-coumarin cultivars of Melilotus alba and Melilotus officinalis following inoculation with the fungus Helminthosporium carbonum. Little or no medicarpin was isolated from leaflets treated with deionised water. Medicarpin was also produced when leaflets were irradiated with short-wavelength ultraviolet light. Elimination of the high-coumarin character from sweet clover cultivars does not appear to affect phytoalexin production, and in consequence, low-coumarin varieties should not be more susceptible to fungal colonisation than their high-coumarin counterparts.
01 Jan 1978
TL;DR: A fl-glucan isolated from the mycelial wails of Phytophthora megasperma var. sojae and a glucan purified from yeast extract was shown to stimulate the accumulation of phytoalexins in red kidney beans, Phaseolus vulgaris, and stimulate rishitin in potato tubers, Solanum tuberosum as discussed by the authors.
Abstract: A fl-glucan isolated from the mycelial wails of Phytophthora megasperma var. sojae and a glucan purified from yeast extract stimulate the accumulation of phytoalexins in red kidney bean, Phaseolus vulgaris, and stimulate the accumulation of the phytoalexin, rishitin, in potato tubers, Solanum tuberosum. These glucans have previously been shown to be potent elicitors of glyceollin accumulation in soybean, Glycine max. Treatment of kidney bean cotyledons with the glucan elicitors resulted in the accumulation of at least five fungistatic compounds. These compounds migrate during thin layer chromatography identically to the fungistatic compounds which accumulate in kidney beans which have been inoculated with Colletotrichum lindemuthianum, a fungal pathogen of kidney beans. Potatoes accumulate as much as 29 micrograms of rishitin per gram fresh weight following exposure to the glucan from Phytophthora megasperma var. sojae and as much as 19.5 micrograms of rishitin per gram fresh weight following exposure to yeast glucan. Potatoes accumulated 28 micrograms of rishitin per gram fresh weight following inoculation with live Phytophthora megasperma var. sojae.