ABSTRACT
Photosystem I (PS I) is a membrane-bound protein complex which catalyzes the light-driven oxidation of plastocyanin and reduction of ferredoxin. Paraquat disruption of PS I also results in a quenching of variable fluorescence, due to the efficient accepting of electrons by the herbicide which maintains the plastoquinone pool in an oxidized state. Paraquat and diquat have found numerous agricultural and industrial uses as nonselective, rapid-action herbicides. The most relevant method to measure resistance in agricultural weeds is to spray plants grown in soil under agriculturally relevant conditions and to examine growth or survival. Sequestration of paraquat as a mechanism for resistance has been proposed for both C. bonariensis and H. glaucum with increased binding of herbicide to cell walls suggested as the mechanism for sequestration. In addition, from the resistance point of view, paraquat has the advantages of not having the two most common pathways to resistance, metabolism of the herbicide and target site changes, available.
