Cercospora beticola Toxin Inhibits Vanadate-Sensitive H+ Transport in Corn Root Membrane Vesicles

The effect of Cercospora beticola toxin on the transport of protons by vanadate-sensitive ATPase was studied with corn (Zea mays) root microsomal vesicles prepared by differential centrifugation, sedimentation through a sucrose cushion, and washing with Triton X-100 plus KBr. In these preparations, addition of ATP induced intravesicular H(+)-accumulation as evidenced by a rapid quenching of the fluorescence of 9-amino-6-chloro-2-methoxy acridine. This quenching was relatively unaffected by inhibitors of mitochondrial and tonoplast-type ATPases, but was strongly reduced by inhibitors of plasma membrane H(+)-ATPase. C. beticola toxin markedly inhibited ATP dependent H(+)-transport, and this effect increased with the length of preincubation with the toxin. The same observations were made concerning ATPase activity. Inhibition of H(+)-transport was greater at pH 7.3 than at pH 5.7. Lineweaver-Burk plot analysis showed that inhibition kinetics were competitive with respect to ATP. These data suggest a direct effect of C. beticola toxin on vanadate-sensitive ATPase presumed to be associated with the plasma membrane.