Interactions of cations with paraquat in leaf sections of resistant and sensitive biotypes of Conyza bonariensis

• Published in: Pesticide biochemistry and physiology 1997-03, Vol.57 (3), p.181-191
• Main Authors: Norman, M.A. (Washington State University, Pullman, WA.), Fuerst, E.P
• Format: Article
• Language: English
• Subjects: ACTIVITY; Biological and medical sciences; BIOTYPES; CATIONS; Chemical control; CONYZA; Fundamental and applied biological sciences. Psychology; HERBICIDAL ACTIVITY; HERBICIDES; PARAQUAT; Parasitic plants. Weeds; Phytopathology. Animal pests. Plant and forest protection; RESISTANCE MECHANISMS; RESISTANCE TO CHEMICALS; SUSCEPTIBILITY; Weeds
• ISSN: 0048-3575; 1095-9939
• DOI: 10.1006/pest.1997.2276

The influence of cations on paraquat activity was evaluated in leaf sections of a paraquat-resistant biotype (R) and a paraquat-sensitive biotype (S) of Conyza bonariensis. The organic polyamine, putrescine, antagonized paraquat activity in S but synergized paraquat activity in R. Putrescine synergism in R may be due to competitive inhibition of paraquat sequestration. Inorganic cations antagonized paraquat-induced chlorophyll bleaching in both biotypes. These cations were, from most potent to least potent, La3+ Ca2+ greater than or equal to Mg2+ K+. This antagonism of paraquat activity by inorganic cations can primarily be attributed to the reduction of cell surface electrical potential by cations. However, the antagonism of paraquat activity was not equivalent in the two biotypes: La3+, Ca2+, and Mg2+ antagonized the activity of 250 micromolar paraquat in R more than they antagonized 1 micromolar paraquat in S; this implies a possible secondary basis for interaction of these cations in R. It is possible that such cations increase paraquat sequestration by enhancing the integrity of a membrane-bound sequestration site. Since exogenous cations antagonized paraquat activity, it was postulated that removal of endogenous cations might synergize paraquat activity. Ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) is a Ca2+ chelator which synergized paraquat activity only in R. This suggests that Ca2+ interacts with paraquat sequestration. However, the sequestration mechanism is not Ca2+-dependent, because EGTA synergism was reversed to varying degrees by addition of La3+, Ca2+, Mg2+, or K+. Since EGTA and La3+ do not readily cross the plasmalemma, their interactions imply that resistance is due, at least in part, to paraquat exclusion at the plasmalemma. Inorganic cations, polyamines, and chelators should be useful tools in future evaluations of the site(s) and mechanism(s) of paraquat sequestration.