A possible mechanism of control of rice blast disease by a novel alkoxyiminoacetamide fungicide, SSF126

When the mycelial cells of Pyricularia grisea were pulse-labeled with [S-35]-methionine in the presence of (E)-2-methoxyimino-N-methyl-2-(2-phenoxyphenyl) acetamide (SSF126), the radioactivity was time-dependently incorporated into a 40-kDa mitochondrial protein. The appearance of the pulse-labeled 40-kDa protein paralleled the SSF126-dependent induction of cyanide-resistant respiratory activity in the mycelial cells. The SSF126-dependent induction of cyanide-resistant respiration was reversibly blocked by carbonylcyanide-p-trifluoro-methoxyphenyl-hydrazone (FCCP). When the mycelial cells were pulse-labeled with radioactive methionine in the presence of SSF126 and FCCP, the radioactivity was incorporated into a 41.4-kDa mitochondrial polypeptide. Upon removal of FCCP, this polypeptide was converted into a 40-kDa protein and cyanide-resistant respiratory activity was induced in the mycelial cells. These findings suggested that the 41.4-kDa polypeptide is processed into the 40-kDa mature protein responsible for the cyanide-resistant respiration in P. grisea. Furthermore, superoxide anion (O-2(-)) was suggested to be involved in the SSF126-dependent induction mechanism of the cyanide-resistant respiration in the mycelial cells. Flavonoids found in plants had the ability to scavenge O-2(-) generated by blockage of electron flux through the cytochrome bc(1) segment in the mitochondrial respiratory chain and they inhibited SSF126-dependent induction of cyanide-resistant respiration. Consequently, it is feasible that SSF126 controls rice blast caused by P. grisea in conjunction with rice plant components.