Biochemical mechanisms of mimosine toxicity to sclerotium rolfsii sacco

Abstract

Mimosine when added at a final concentration of 2·5 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, Fe3+ at 10 mM most effectively decreased mimosine's inhibitory effect by 93 %, AI3+ at 5 mM decreased it by 80 % while Fe2+ and Cu2 + 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 (X-amylase by only 25 %. Mimosine inhibited aspartate aminotransferase non-competitively (K1 = O· 056 mM) and polyphenol oxidase competitively (K1 = o· 089 mM). ATP production in cells grown in the presence of 2·5 mM mimosine was reduced by 70 %. Decreased synthesis of DNA was shown by lower incorporation of ['Hlthymidine. Mimosine had little or no effect on RNA synthesis. Cell-free extracts of S. rolfsii degraded mimosine slightly into 3-hydroxyl-4(IH)-pyridone (DHP), mimosinic acid and an unidentified compound. A large amount of un degraded mimosine remained. No further metabolism of DHP was observed. © 1983 ASEG.

Source or Periodical Title

Australian Journal of Biological Sciences

ISSN

49417

Page

445-454

Document Type

Article

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