The Mode of Action of Alternaric Acid onMyrothecium verrucaria

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Abstract
Alternaric acid [produced by Alternaria solani] inhibited the endogenous respiration of M. 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 1st 2 min. Thus, the mode of action of alternaric acid apparently is the interference of uptake of metabolites by the mycelium.

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