Biological activity of purified host-specific pathotoxin produced by Bipolaris ( Helminthosporium) maydis, race T

Abstract

A purified, chemically characterized toxin from Helminthosporium maydis, race T, was examined for its host-specific effect on Texas male sterile (T) cytoplasm corn. This preparation consists of several nearly identical linear polyketols and it is shown that each component has the same specific toxicity for oxidation by mitochondria from susceptible corn. The stability of the dry preparation and knowledge of its mol. wts enabled a quantitative comparison to the dosage required to affect ion balance, dark CO 2 fixation, coleoptile elongation, and mitochondrial oxidation. Unexpectedly, the toxin was active at concentrations between 5 and 50 ng ml −1 (6·5 × 10 −9 to 6·5 × 10 −8 m on all these processes in T corn, despite potentially different barriers to toxin penetration. N cytoplasm corn was not affected at concentrations 1000 times greater. These results are discussed in relation to possible modes of action. The quantitative specific effects of this preparation are compared to data on other race T toxin preparations for which chemical structures have been postulated.