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Biochemistry and Cell Biology

A Possible Mechanism of Control of Rice Blast Disease by a Novel Alkoxyiminoacetamide Fungicide, SSF126. Akira Mizutani, Aburahi Laboratories, Shionogi & Co., Ltd., 1405 Gotanda, Koka-cho, Koka-gun, Shiga 520-34, Japan; Nobuo Miki(2), Hideo Yukioka(3), Hiroto Tamura(4), and Michio Masuko(5). (2)(3)(4)(5)Aburahi Laboratories, Shionogi & Co., Ltd., 1405 Gotanda, Koka-cho, Koka-gun, Shiga 520-34, Japan; (4)Current address: Department of Agricultural Chemistry, Meijo University, Shiogamaguchi, Tempaku-ku, Nagoya 468, Japan. Phytopathology 86:295-300. Accepted for publication 16 November 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-295.

When the mycelial cells of Pyricularia grisea were pulse-labeled with [35S]-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 poly-peptide is processed into the 40-kDa mature protein responsible for the cyanide-resistant respiration in P. grisea. Furthermore, superoxide anion (O2-) 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 O2- generated by blockage of electron flux through the cytochrome bc1 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.

Additional keywords: bc1 complex, chemiluminescence, mitochondrial protein import, respiratory inhibitor, superoxide dismutase.