Effect of a new fungicide (PNDP) on the minor nucleotide content of Fusarium oxysporum.

The minor nucleotide constituents of rRNA from the plant pathogenic fungus Fusarium oxysporum were investigated. When the fungus was grown for 8 days in aerated liquid culture the following minor nucleotides were identified from 18S and 25S rRNA: m6A, m2A , m2(6)A, m1G, m2G , m2(2)G, m3C , Cm, m5C, m3U , Um, cm5U , rT and psi. PNDP (+/- threo-1-phenyl-2-nitro-1,3 diacetoxy-propane), a new fungicide of unknown biochemical mode of action, caused a great decrease in the minor nucleotide content of the fungus. Only seven minor nucleotides were present in the rRNA of the fungus grown in PNDP -containing medium. A hypermodified nucleotide, mcm5S2U , was found in treated but not in untreated fusarium. On comparing the effect of PNDP with that of known protein synthesis inhibitors such as cycloheximide and chloramphenicol, it was concluded that PNDP acted similarly to cycloheximide, a cytoplasmic protein synthesis inhibitor. It is suggested that the mode of action of PNDP may be the inhibition of the synthesis of RNA modifying enzymes of F. oxysporum.