The biochemical mode of action of the novel selective fungicide cyazofamid: Specific inhibition of mitochondrial complex III in Phythium spinosum

Citation
S. Mitani et al., The biochemical mode of action of the novel selective fungicide cyazofamid: Specific inhibition of mitochondrial complex III in Phythium spinosum, PEST BIOCH, 71(2), 2001, pp. 107-115
Citations number
37
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Entomology/Pest Control","Biochemistry & Biophysics
Journal title
PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY
ISSN journal
0048-3575 → ACNP
Volume
71
Issue
2
Year of publication
2001
Pages
107 - 115
Database
ISI
SICI code
0048-3575(200110)71:2<107:TBMOAO>2.0.ZU;2-H
Abstract
To elucidate the background of the highly selective fungicidal activity of cyazofamid (ISO proposed common name), 4-chloro-2-eyano-N,N-dimethyl-5-p-to lylimidazole-1-sulfonamide, the biochemical mode of action of this fungicid e in Pythium spinosum was investigated. Cyazofamid inhibited mycelial growt h of P. spinosum on the order of 1 muM on agar medium containing gelatin, o n water agar, and on potato dextrose agar. The mycelial growth inhibition w as markedly potentiated in the presence of salicylhydroxamic acid (SHAM), a n inhibitor of mitochondrial alternative oxidase. Oxygen consumption of P. spinosum mycelia treated with 4 muM cyazofamid was reduced by about 60%. At 60 min after the treatment, the oxygen consumption was recovered, but the respiration was resistant to potassium cyanide and sensitive to SHAM. From the effect of cyazofamid on electron transport activity of R spinosum mitoc hondria, it was revealed that this fungicide specifically interferes with c ytochrome bc(I) complex (complex III) activity (I-50: 0.04 muM). Cyazofamid , however, exhibited no inhibition of complex III activities in mitochondri a isolated from other biological sources such as Botrytis cinerea, Saccharo myces cerevisiae, rat liver, and potato tuber. Thus, the highly selective a ctivity of cyazofamid appeared to be due to a difference in the inhibitor s usceptibility at the target enzyme. To identify the binding site ofcyazofam id in complex III, reduction kinetics of cytochrome b hemes was investigate d with P. spinosum mitochondria. The addition of cyazofamid immediately red uced cytochrome b hemes and the extent of reduction was higher than that wi thout cyazofamid. Reduction of b hemes was markedly inhibited by the combin ed use of cyazofamid and azoxystrobin (Q(o) center inhibitor). These result s suggest that cyazofamid binds to the Q(i) center of complex III. (C) 2001 Academic Press.