Effects of pisatin on Dictyostelium discoideum: its relationship to inducible resistance to nystatin and extension to other isoflavonoid phytoalexins

Abstract

Dictyostelium discoideum amoebae can acquire resistance to otherwise inhibitory concentrations of pisatin, an isoflavonoid phytoalexin of pea, and nystatin, a polyene antibiotic, following pretreatment with sublethal concentrations of these compounds. Additionally, growth on medium containing pisatin can induce nystatin resistance. We show here that distinct mechanisms mediate the inducible resistance to these two compounds because it is possible to isolate mutations that specifically block the induction of nystatin resistance but do not affect the induction of pisatin resistance. Pisatin did not affect wild-type sterol biosynthesis; therefore, the induction of nystatin resistance by pisatin is probably not via an alteration of membrane sterols. The inducible pisatin resistance phenotype was shown to extend to the isoflavonoid phytoalexins maackiain and biochanin A, and all three compounds inhibited the aggregation of amoebae that is normally triggered by starvation.