Showing papers on "Phytoalexin published in 1979"

Differential accumulation of phytoalexins in tomato leaves but not in fruits after inoculation with virulent and avirulent races of Cladosporium fulvum

Abstract: Leaves of near-isogenic lines of tomato, carrying resistance gene Cf4 or Cf5 to Cladosporium fulvum , were both inoculated with race 4 and 5 of this fungus. Accumulation of two phytoalexins occurred more rapidly in the two incompatible combinations (Cf4 + race 5; Cf5 race 4) than in the two compatible ones (Cf4 + race 4; Cf5 + race 5) in the whole leaf as well as in the lower epidermis. Hyphal growth in incompatible combinations was inhibited 3 to 5 days after inoculation, shortly after stomatal penetration. At this time, accumulation of phytoalexins was observed only in incompatible interactions. Following prolonged incubation phytoalexins also accumulated in compatible interactions, when there was already abundant fungal growth. The identity of the phytoalexins is not yet known. Inoculation of pericarp tissue of tomato fruits of both near-isogenic lines with Cladosporium fulvum resulted in a very rapid accumulation of rishitin and four unidentified phytoalexins, two of which were identical to those occurring in tomato leaves with respect to their relative retention and R F value. The concentration of rishitin, the main phytoalexin in tomato fruit, reached its maximum 1 to 2 days after inoculation and decreased later. In contrast to tomato leaves, in fruits no differential accumulation of phytoalexins in incompatible and compatible interactions was observed at an early stage of infection. The phytoalexins in tomato leaves and fruits accumulated only after interaction with fungal material; they did not accumulate in wounded controls or after treatment with HgCl 2 and terramycin. For this reason, they cannot be regarded as general stress metabolites.

Investigations into the mechanism of mercuric chloride stimulated phytoalexin accumulation in Phaseolus vulgaris and Pisum sativum

Abstract: Phaseollin and pisatin accumulated in bean and pea cotyledons respectively, after incubation at 25 °C following treatment with mercuric chloride. Both the duration of treatment and concentration of mercuric chloride determined maximal phytoalexin concentrations. Highest levels of both phytoalexins occurred when cell damage caused by mercuric chloride was microscopically visible. With increasing amounts of dead cells the concentrations of phytoalexins decreased, and in some treatments no phytoalexins were formed even when some tissue was still alive. The accumulation of phaseollin appeared to be more closely associated with cell death than the accumulation of pisatin. Treatment of cotyledons with mercuric chloride under optimal conditions for phytoalexin formation (10 −3 m for 30 min) led to a loss of electrolytes during the initial 12 h, and to the continuous accumulation of phytoalexins over 5 days. Exudates from mercuric chloride treated cotyledons of both species stimulated phytoalexin accumulation in cut cotyledon bioassays. These results are discussed in relation to current views on the mechanism of phytoalexin accumulation.

Phytoalexin production and degradation in relation to resistance of clover leaves to Sclerotinia and Botrytis spp

Abstract: The pathogenicity to red clover of three Sclerotinia spp. and three Botrytis spp. was compared with their sensitivity to, and ability to degrade, the clover phytoalexins maackiain and medicarpin. Sclerotinia fruticola formed no lesions at all, whereas S. fructigena and Botrytis allii formed flecks under the inoculation drop. B. cinerea and B. fabae formed limited lesions slightly larger than the inoculation drop, and S. trifoliorum formed spreading lesions. In 24 h, S. trifoliorum and B. cinerea degraded both phytoalexins in vitro to less inhibitory hydroxylated derivatives. B. fabae also degraded the phytoalexins but to different products. The other Sclerotinia and Botrytis spp. did so little or not at all. In lesions caused by S. trifoliorum and B. cinerea in clover leaves, the same phytoalexin degradation products were detected as in vitro . S. trifoliorum degraded at a faster rate than B. cinerea in vitro , and in vivo S. trifoliorum was apparently able to metabolize medicarpin and maackiain at a sufficient rate to reduce their concentrations to sub-inhibitory levels. B. cinerea was less able to do so, so that high phytoalexin concentrations were reached in spite of some degradation by the fungus. Following inoculation with S. fructigena, S. fructicola and B. allii , high phytoalexin concentrations were reached in tissue and in diffusates and no degradation products were detected. These three fungi were more sensitive to the phytoalexins with respect to mycelial growth. The oxygen uptake of S. fructicola was also more strongly inhibited by maackiain than that of S. trifoliorum or B. cinerea .

ELICITOR-INDUCED PHYTOALEXIN SYNTHESIS IN SOYBEAN (Glycine max)

Abstract: Publisher Summary This chapter focuses on the elicitor-induced phytoalexin synthesis in soybean. The production of phytoalexins in response to microbes requires a mechanism that enables the plant to recognize the invading organism and, subsequently, leads to the stimulation of phytoalexin synthesis at the site of microbial penetration. Substances of microbial origin that mediate phytoalexin accumulation in plants have been called elicitors, and it has been shown in several cases that the culture medium of pathogens contained components that elicited phytoalexin accumulation in the pathogens host. Studies on the nature of elicitors have resulted in the partial purification and characterization of a number of molecules from different microbial sources. Elicitors have been reported to have dependence for activity on a polypeptide or protein, a glycoprotein, or polysaccharide component.

Additional phytoalexin‐like compounds in Ht‐gene resistance of corn to Helminthosporium turcicum

Abstract: SUMMARY Four additional compounds inhibitory to germination of Helminthosporium turcicum spores were isolated from lesion-extracts of field-grown Ht-gene corn (Zea mays) lines which were inoculated with H. turcicum. The compounds were named phytoalexins A3, A4-I, A4-II and A5. A3, A4-1 and A4-1 showed over 99% inhibition of H. turcicum spores at 1 mg/ml of 10% ethanol and LD50 of about 600 μg/ml. A5 showed an LD50 of about 800 μg/ml of 10% ethanol. The ultraviolet, infrared, nuclear magnetic resonance, electron impact mass spectra and field desorption mass spectra showed that these compounds might be related to the previously described phytoalexins A1 and A2. They seem to have the following functional groups: aromatic ring, hydroxyl and/or phenolic groups, carbonyl groups, probably a carboxylic acid or ester type and a long aliphatic side chain.