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Netherlands Journal of Plant Pathology

, Volume 74, Supplement 1, pp 127–136 | Cite as

The development of resistance in Cladosporium cucumerinum aganst 6-azauracil, a chemotherapeutant of cucumber scab, and its relation to biosynthesis of RNA-precursors

  • J. Dekker
Article

Abstract

Growth of the fungusCladosporium cucumerinum is inhibited by 6-azauracil (AzU), 6-azauridine (AzUR) and 6-azauridine-5′-monophosphate (AzUMP) on artificial media as well as on the cucumber plant. In cell-free extracts of this fungus the decarboxylation of orotidine-5′-monophosphate (OMP) is inhibited by AzUMP, but not by AzU or AzUR. The fungus itself is able to convert AzU and AzUR to the toxic AzUMP, an example of “lethal synthesis”.

By irradiation of conidia with UV two types of AzU-resistant strains were obtained. The first type (III) did not convert AzU to AzUR. Therefore no lethal synthesis occurred when AzU was administered to this strain. The strain was, however, sensitive to AzUR and AzUMP. The second type (R) appeared resistant not only to AzU, but also to AzUR and AzUMP, in spite of the fact that conversion of AzU to AzUR and AzUMP did occur. No indications were obtained that the resistance of the latter type might be due to insufficient permeability towards the inhibitors or to a higher OMP-decarboxylase activity. The presence of an isoenzyme, more resistant to AzUMP than the original OMP-decarboxylase, was ruled out.

The tolerance of the cucumber plant to AzU was paralleled by an extremely high activity of the enzyme OMP-decarboxylase in comparison with that found in the fungus.

Samenvatting

De groei van de schimmelCladosporium cucumerinum wordt zowel op kunstmatige voedingsbodems als in de komkommerplant geremd door 6-azauracil (AzU), 6-azauridine (AzUR) en 6-azauridine-5′-monofosfaat (AzUMP). In celvrije extracten van deze schimmel wordt de decarboxylering van orotidine-5′-monofosfaat (OMP) geremd door AzUMP, maar niet door AzU of AzUR. De schimmel zelf zet AzU en AzUR om in het toxische AzUMP, een voorbeeld van “letale synthese”.

Door bestraling van conidiën met UV werden twee typen AzU-resistente stammen verkregen. Het ene type (III) zette AzU niet om in AzUR. Er had derhalve geen letale synthese plaats, wanneer AzU aan deze stam werd toegediend. Dit type was evenwel wèl gevoelig voor AzUR en AzUMP. Het andere type (R) bleek resistent te zijn tegen AzU, hoewel omzetting van AzU in AzUR en AzUMP hierin wel plaats vond; het bleek dan bovendien resistent tegen AzUR en AzUMP. Er werden geen aanwijzingen verkregen dat de resistentie in het laatste geval zou kunnen berusten op onvoldoende permeabiliteit voor de remstoffen, of op een hogere OMP-decarboxylase activiteit. De mogelijkheid dat een isoënzym aanwezig was met een grotere resistentie voor AzUMP dan het oprspronkelijke OMP-decarboxylase kon uitgesloten worden.

De tolerantie van de komkommerplant voor AzU ging gepaard met een bijzonder hoge activiteit van het enzym OMP-decarboxylase in vergelijking tot die welke in de schimmel aangetroffen werd.

Keywords

Monophosphate Stam Cladosporium Artificial Medium Cucumber Plant 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

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Copyright information

© Koninklijke Nederlandse Planteziektenkundige Vereniging 1968

Authors and Affiliations

  • J. Dekker
    • 1
  1. 1.Laboratory of PhytopathologyAgricultural UniversityWageningenThe Netherlands

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