Permeability changes and production of antifungal compounds in Phaseolus vulgaris infected with Uromyces phaseoli. I. Role of the spore germination self-inhibitor

Abstract

Infection by the bean rust fungus Uromyces phaseoli induced increases in efflux of electrolytes, sugars and amino acids in both a hypersensitive resistant and in a susceptible bean variety ( Phaseolus vulgaris L.). These permeability alterations were detected earlier in the incompatible than in the compatible combination. In both combinations, increased permeability of host cell membranes by rust infection was associated with increased inhibitory activity of the efflux solution against the germination of bean rust uredospores. Further studies indicated that permeability alterations and inhibitory activity of the efflux solutions against uredospore germination in compatible and incompatible combinations respectively are caused by different factors. In the case of the compatible combination the inhibitory factor in the efflux and in leaf extracts was identified as the bean rust uredospore germination self-inhibitor (methyl-3,4-dimethoxycinnamate). This inhibitor was also detected in the efflux solution and leaf extracts of the incompatible combination but at a very low concentration. Infiltration of the cis-trans mixture of the self-inhibitor into healthy bean leaf discs of the susceptible variety caused an increase in permeability. The possible participation of the self-inhibitor in permeability alteration in the compatible combination of bean and the rust fungus is discussed.