Benzyl viologen-mediated counteraction of diquat and paraquat phytotoxicities.

There was reason from bacterial and algal systems to expect that pretreatments with a paraquat analog might confer tolerance against a subsequent paraquat treatment. Thus, a series of compounds were tested for protective activity against bipyridinium herbicides. These included other bipyridinium compounds and derivatives, as well as compounds having similar or more positive redox potentials than paraquat and compounds known to increase or maintain high superoxide dismutase activity levels in plants.Only treatments with benzyl viologen, a benzyl analog of paraquat, protected Spirodela oligorrhiza (Kurz) Hegelm. colonies from otherwise damaging levels of diquat.NADP photoreduction by isolated thylakoids was inhibited by the same concentrations of paraquat, diquat, and benzyl viologen given separately. Thus, the benzyl viologen-mediated tolerance against the bipyridinium herbicides is probably not due to a direct interaction at the thylakoid level.Superoxide dismutase activity was about 50% higher in broken plastids of benzyl viologen-treated plants compared to controls, which may partly explain the observed tolerance.