VIEW ARTICLE

Physiology and Biochemistry

The Mode of Action of Alternaric Acid on Myrothecium verrucaria. Charles C. Reilly, Former graduate research assistant, Department of Plant Pathology, University of Illinois, Urbana, 61801, Present address of senior author: Metabolism and Radiation Research Laboratory, State University Station, Fargo, ND 58102; David Gottlieb, professor, Department of Plant Pathology, University of Illinois, Urbana, 61801. Phytopathology 69:550-555. Accepted for publication 7 November 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-550.

Alternaric acid inhibited the endogenous respiration of Myrothecium verrucaria but maximum effects of the toxin were reached after 5–6 min. The toxin reduced the production of ¹⁴CO₂ by 80–95% during aerobic respiration when (1-¹⁴C)-acetate, (2-¹⁴C)- acetate or (U-¹⁴C)-glucose were the substrates. Alternaric acid totally inhibited the incorporation of ¹⁴C from (U-¹⁴C)-glucose into the cell wall, protein, nucleic acid, lipid, and trichloroacetic acid-extractable cell fractions of the fungus. The toxin did not cause leakage of electrolytes from the mycelium of M. verrucaria. Oxidation of exogenous substrates by isolated mitochondria, and oxidative phosphorylation, were not affected by the antibiotic. Alternaric acid had no noticeable effect on the activity of any enzyme of the Embden-Meyerhof-Parnas pathway, the hexose monophosphate pathway, or the tricarboxylic acid cycle. Alternaric acid reduced the uptake of several common metabolites by the mycelium, although not all to the same extent. The inhibition of uptake occurred within the first 2 min. Thus, the mode of action of alternaric acid appears to be the interference of uptake of metabolites by the mycelium.