K +-stimulated adenosine triphosphatase of maize roots: partial purification and inhibition by Helminthosporium maydis race T toxin

Abstract

Maize plants bearing the cytoplasmic gene cmsT for male sterility are highly susceptible to infection by the fungus Helminthosporium maydis race T while normal plants are relatively resistant. The K +-stimulated ATPase found in the microsomal fraction from susceptible plants following tissue disruption and differential centrifugation is inhibited by a toxin produced by H. maydis race T. The same enzyme activity in microsomes from normal plants is not affected by the toxin. The ATPase can be solubilized by extraction of the microsomes with 0·5 m-NaClO 4, and further purified by chromatography on a Sephade G-100 column. After the chromatographic purification the ATPases from both normal and susceptible plants are inhibited by the toxin. ATPase from either source is stimulated and partially protected from toxin inhibition by another fraction from the Sephadex column fractionation. ADP hydrolysis by the microsomes is also stimulated by K + and inhibited by toxin while 5′-nucleotidase activity is unaffected by K + or toxin.