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Studies on the Mode of Action of the Phytoalexin Phaseollin. H. D. VanEtten, Assistant Professor, Department of Plant Pathology, Cornell University, Ithaca, New York 14850; D. F. Bateman, Professor, Department of Plant Pathology, Cornell University, Ithaca, New York 14850. Phytopathology 61:1363-1372. Accepted for publication 21 June 1971. DOI: 10.1094/Phyto-61-1363.

Phaseollin at 15 µg/ml inhibited dry weight increase of Rhizoctonia solani for 12 to 18 hr; 47 µg/ml caused an initial decrease in fungal dry weight. Phaseollin decreased the ability of R. solani to take up glucose-U-¹⁴C. Mycelium which had previously incorporated ¹⁴C rapidly released materials containing ¹⁴C upon exposure to phaseollin. The respiration rate of actively growing mycelia was decreased by phaseollin, but the respiration rate of “starved” mycelia was stimulated. When R. solani was exposed to phaseollin-¹⁴C for 1 hr and then fractionated, most of the ¹⁴C was associated with the hyphal fraction removed by centrifugation at 500 g for 15 min. Exposure of R. solani hyphae to phaseollin resulted in an immediate cessation of protoplasmic streaming and in shrinkage of the protoplast from the hyphal tip. Phaseollin at 23 µg/ml and above rapidly lysed erythrocytes. There was little effect of phaseollin on endogenous or exogenous respiration rate of bean hypocotyl tissue, but phaseollin caused a rapid release of ⁸⁶Rb+ from hypocotyl tissue into which ⁸⁶Rb+ had previously been incorporated. The hypothesis is advanced that phaseollin acts on the plasma membrane or affects some process needed for membrane function.