The Binding of Host-Selective Toxin Analogs to Mitochondria from Normal and 'Texas' Male Sterile Cytoplasm Maize

Authors

Kurt A. Frantzen, University of Nebraska - Lincoln
J. M. Daly, University of Nebraska - Lincoln
Herman W. Knoche, University of Nebraska-Lincoln

Document Type

Article

Date of this Version

1987

Citation

Plant Physiol. (1987) 83, 863-868

Abstract

Tritium-labeled toxin analogs were prepared by reduction with NaB³H₄ of either the toxin from Helminthosporium maydis race T or a toxin component from Phyllosticta maydis. These reduced analogs had high radiochemical specific activities, high biological activities, and plant specificities identical to the native toxins. A filtration assay was developed to test the binding of these labeled analogs to isolated- mitochondria. Binding was not energy dependent nor was there measurable matrical uptake. The analogs were shown to be lipophilic, a characteristic which gave rise to considerable nondisplaceable binding. Under conditions limiting nondisplaceable binding, -the displaceable binding was shown to be linear with respect to toxin concentration and unsaturable. No significant differences were observed in the binding characteristics between the mitochondria from normal and male-sterile (Texas) cytoplasm maize. The findings suggest that, at physiologically relevant concentrations, these toxin analogs permeate the membranes of susceptible and resistant mitochondria alike. The lack of demonstrable specific binding does not rule out the involvement of a classical receptor site but does indicate that other kinds of molecular interactions may be involved in the mechanisms for toxicity and specificity.