ABSTRACT
The interaction of V. dahliae with C. arboreum induces the formation of the cotton phytoalexins gossypol, hemigossypol and their derivatives. This induction process can be assayed in cotton cell suspension cultures by monitoring the fluorescence change of membrane associated molecular probes. Within minutes after addition of an elicitor preparation from V. dahliae to G. arboreum cells a change in fluorescence of the molecular probe can be observed, which is correlated with phytoalexin formation, and starts six hours after elicitor addition. Citrate can inhibit the fluorescence change as well as the formation of phytoalexins. Citrate inhibition was concentration dependent and a 2 mM concentration of citrate was required to obtain 50% inhibition of the fluorescence change of the pH sensitive, membrane associated dye pyranine as well as 50% inhibition of pbytoalexin formation in cotton cell cultures and in cold-shocked or V. dahliae induced cotton seedlings. The inhibition by citrate was specific since other di- or tri-carboxylic hydroxy acids were not active as inhibitors, with the exception of malate which was weakly inhibitory. Specificity of citrate inhibition is further documented by the observation that other pathogenhost interactions, as for example -(1-3,1-6) glucan elicitation of soybean cells, are similarly affected by citrate.
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