Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
THE BINDING OF THE HOST-SPECIFIC TOXINS FROM HELMINTHOSPORIUM MAYDIS RACE T AND PHYLLOSTICTA MAYDIS TO MITOCHONDRIA ISOLATED FROM ZEA MAYS
Abstract
Helminthosporium maydis race T and Phyllosticta maydis, the causal agents of southern and yellow corn leaf blights, respectively, produce host-specific toxins. These toxins are similar in chemical structure, and each consist of a family of related compounds. The toxic specificity of these natural products is identical to the host-specificity of the pathogens for certain varieties of corn. Susceptible genotypes carry the 'Texas' type of cytoplasmic male sterility. Isolated mitochondria from susceptible plant species are highly sensitive to these toxins, whereas other plant species, including resistant corn varieties, and their mitochondria are not. The mitochondrion may be the primary cellular site of action for these toxins. The toxins from H. maydis and P. maydis were tritiated by reduction with borotritide salts. The labeled products had a high specific activity (3.8 to 8 Ci/mmole), high biological activity, and specificity identical to that of the native toxins. A filtration binding assay was developed to investigate the binding characteristics of these labeled toxins to isolated mitochondria. Mitochondria isolated from both cytoplasmic male sterile ('Texas') and normal corn demonstrated similar binding characteristics including ligand displaceable binding with both labeled toxins. Ligand displaceable binding was also detectable in mitochondria from soybeans, a nonhost plant for these fungi. The ability to displace the bound labeled toxins was generally correlated with the biological activity of the competing toxin. At least 50% of the toxin bound to the mitochondria was nondisplaceable. This was probably due to the lipophilic character of the toxins, which had octanol:water partition coefficients (log P) of 1.25 and 0.66 for tritium labeled toxins from P. maydis and H. maydis, respectively. The high nondisplaceable binding limited the ability of the study to clearly define a toxin receptor site(s). The results of this study suggest that a receptor site hypothesis for the mode of action of these toxins may not be valid.
Subject Area
Biochemistry|Molecular biology
Recommended Citation
FRANTZEN, KURT ANTHONY, "THE BINDING OF THE HOST-SPECIFIC TOXINS FROM HELMINTHOSPORIUM MAYDIS RACE T AND PHYLLOSTICTA MAYDIS TO MITOCHONDRIA ISOLATED FROM ZEA MAYS" (1985). ETD collection for University of Nebraska-Lincoln. AAI8609801.
https://digitalcommons.unl.edu/dissertations/AAI8609801