title: Contact activity of difenzoquat differs from that of paraquat.
abstract: Difenzoquat herbicide is used for post-emergence control of wild oat (Avena fatua L) in small grain crops. Its mechanism of action is not known, but appears to have both paraquat-like contact activity and systemic growth-inhibition activity. Experiments were conducted in vitro to compare the contact activity of difenzoquat and paraquat, to examine the contact activity of difenzoquat in difenzoquat-resistant (accession LCS) and -susceptible (accession SB 18) A fatua biotypes and -tolerant 'Ernest' and -susceptible 'Verde' hard red spring wheat (Triticum aestivum L) cultivars, and to investigate the role of differential DNA synthesis as a mechanism for difenzoquat resistance. Difenzoquat at 1 mM induced significant electrolyte leakage from resistant and susceptible A fatua leaf tissue in both light and dark, but paraquat at 1 mM induced electrolyte leakage only in light and not in dark. Difenzoquat at 1 mM under light induced more electrolyte leakage from resistant and susceptible A fatua than from tolerant 'Ernest' and susceptible 'Verde' wheat. Paraquat under light conditions induced more electrolyte leakage than difenzoquat, but no significant differences among A fatua accessions and wheat cultivars were detected. Difenzoquat under light did not decrease chlorophyll levels for either A fatua accessions or wheat cultivars, whereas paraquat decreased chlorophyll content of all four plant types. Inhibition of DNA synthesis was not significantly different between susceptible and resistant A fatua, but was significantly greater in susceptible 'Verde' than tolerant 'Ernest' wheat. These data suggest that difenzoquat and paraquat, have different modes of contact activity.
authors.affiliation: Crop Chemical Control Center, College of Crop Science, China Agricultural University, Beijing 100094, People's Republic of China.
authors.forename: Zhaohu
authors.initials: Z
authors.lastname: Li
authors.forename: Vijay K
authors.initials: VK
authors.lastname: Nandula
authors.forename: Calvin G
authors.initials: CG
authors.lastname: Messersmith
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D003624:Darkness; D004351:Drug Resistance; D004573:Electrolytes / Q000378:metabolism; D006540:Herbicides / Q000494:pharmacology*; D008027:Light; D010269:Paraquat / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D006109:Poaceae / Q000187:drug effects; D011720:Pyrazoles / Q000494:pharmacology*; D014908:Triticum / Q000187:drug effects
chemical_list: D004573:Electrolytes; D006540:Herbicides; D011720:Pyrazoles; D002734:Chlorophyll; C031394:difenzoquat; D004247:DNA; D010269:Paraquat