殺菌剤プロベナゾールの作用機構に関する研究

抄録

The mode of action of probenazole, a nonfungicidal systemic controlling agent against rice blast and bacterial leaf blight, has been studied phytopathologically and biochemically. Neither probenazole nor degraded or metabolic products exhibited any in vitro anti-microbial activities, in irrigation water or rice plants. The in vitro sensitive sites at each stage of the life cycle of blast fungus were found at conidial germination (+), appressorial formation (++), penetration (+++), mycelial growth (+) and reproduction of conidia (++). The in vivo sensitive sites at each stage of the life cycle were enhanced at conidial germination, penetration and mycelial growth. Probenazole was changed to allyl o-sulfamoylbenzoate, 1, 2-benzisothiazole-3-one-1, 1-dioxide and its N-glucoside within several days of its application, which have not direct anti-microbial activities in the rice plant; therefore long lasting activity of the compound against rice blast fungus was attributed to this host mediated defense action. It was observed that indoleacetic acid (IAA) or tryptophan and ethylene or methionine mimmicked the resistant reactions in the rice plant, which include the production of antimicrobial agents, the formation of a chemical barrier and augmentation of enzymic activities related to lignoid formation, the formation of a physical barrier at the invaded cell. These maximum activities of the enzymes were always found in the treated and inoculated experimental run as in the use of probenazole with the inoculation. The augmentation of peroxidase by inoculation, application of IAA or tryptophan and application of ethylene or methionine were all counteracted by the presence of abscisic acid. The de novo synthesis of peroxidase by the inoculation with or without probenazole in rice leaf slices was inhibited in the presence of cycloheximide, blasticidin S and formycin A. In the asceptic cell free extracts of conidia or mycelia of blast fungus, factors responsible for the induction of peroxidase were found. The controlling activity of probenazole against rice blast disease was counteracted in the presence of abscisic acid. Neither probenazole nor its degraded and metabolic products exhibited any plant hormonal activity. From the preceding evidence, the action area of probenazole along the resistance reaction chain (ref. scheme 1, working hypothesis “Signal transmission hypotheses”) was tentatively determined to be around the recognition system, including its related initial biochemical reactions.