Abstract
The effect of the organophosphorus fungicide, edifenphos (O-ethyl S, S-diphenyl phosphoro-dithiolate, EDDP, Hinosan®), on DNA, RNA, protein, chitin and lipid biosynthesis was investigated in Pyrieularia oryzae. The incorporation of [2-14C]thymidine, [2-14C]uridine and L-[U-14C]amino acid mixture into DNA, RNA and protein, respectively, was not significantly affected in mycelial cells of P. oryzae treated with 10ppm edifenphos. The fungicide scarcely inhibited chitin synthetase of the microsomal fraction at the ED50 concentration value for mycelial growth. On the other hand, addition of edifenphos to the mycelial cell suspension caused a striking decrease in the incorporation of L-[methyl-14C]methionine and S-adenosyl-L-[methyl-14C]methionine into phospha-tidylcholine, which is the most abundant phospholipid in P. oryzae, but scarcely inhibited the incorporation of [methyl-14C]choline into phosphatidylcholine and that of L-[methyl-14C]methionine into simple lipids. Of enzymes responsible for biosynthesis from glycerol to phosphatidylcholine by way of Greenberg's pathway, phospholipid Nmethyltransferase was specifically inhibited and the ED50 value was 13 ppm. These data suggest that the primary antifungal action of edifenphos is due to interference of phosphatidylcholine biosynthesis by the transmethylation reaction of Sadenosyl-L-methionine. Therefore, the mode of action of edifenphos has a strong resemblance to that of IBP (Kitazin P®).
