Biochemical mechanisms of mimosine toxicity of Sclerotium rolfsii Sacc

Mimosine when added at a final concentration of 2 multiplied by 5 mM to potato dextrose broth reduced the mycelial growth of S. rolfsii by 40-60% and prevented the formation of sclerotia. This inhibitory action of mimosine was alleviated by 80% by 5 mM pyridoxal-5-phosphate and by 50% by tryptophan and 5 mM tyrosine. Phenylalanine had little effect. Among the metal ions, Fe super(3+) at 10 mM most effectively decreased mimosine's inhibitory effect by 93%, Al super(3+) at 5 mM decreased it by 80% while Fe super(2+) and Cu super(2+) at 5 mM exhibited the least effect (about 25 and 9%, respectively). Mimosine decreased the specific activities of aspartate aminotransferase and polyphenol oxidase by 37 and 87% respectively, and that of alpha -amylase by only 25%. Mimosine inhibited aspartate aminotransferase non-competitively (K sub(I) = 0 multiplied by 056 mM) and polyphenol oxidase competitively (K sub(I) = 0 multiplied by 089 mM). ATP production in cells grown in the presence of 2 multiplied by 5 mM mimosine was reduced by 70%. Decreased synthesis of DNA was shown by lower incorporation of ( super(3)H)thymidine. Mimosine had little or no effect on RNA synthesis. Cell-free extracts of S. rolfsii) degraded mimosine slightly into 3-hydroxyl-4(1H)-pyridone (DHP), mimosinic acid and in unidentified compound. A large amount of undegraded mimosine remained. No further metabolism of DHP was observed.