Paraquat resistance

In every case of resistance, paraquat had been applied 2 or 3 times annually during the preceding 5-11 years in some cases, a cross-resistance to atrazine was also reported. Paraquat resistance mechanisms in plants include increased epicuticular wax (preventing penetration), binding of paraquat to cell walls, restricted movement into chloroplasts, and altered redox potential. For example. 

Sensitivity of mammals to paraquat was variable, owing to inherent differences in interspecies resistance. Representative mammals were measurably affected at aerosol concentrations of 0.4 to... 

In terrestrial plants, paraquat s action is at the point of local absorption (Anonymous 1963). Characteristic damage signs to susceptible species include wilting and general collapse in herbaceous plants. Regrowth may occur in some perennial plants, but in resistant species temporary scorch may be the most marked effect (Anonymous 1963). In sugarcane (Saccharum officinarum), paraquat... 

Resistance to paraquat among mammals varied substantially owing to inherent differences in sensitivity between species, to route of administration, and to reproductive state (Table 22.5). The lowest recorded doses of paraquat causing measurable adverse effects on growth, survival, or reproduction were (Table 22.5) ... 

Eggs of migratory waterfowl seem to be especially sensitive to paraquat at recommended application rates in an oil vehicle, but were significantly more resistant to the same dose applied in water (Table 22.6). Application of paraquat in oil solution appears contraindicated in areas containing nesting waterfowl. 

Paraquat (l,r-dimethyl-4,4 -bipyridinium) and its dichloride salt (1,1 -dimethyl-4,4 -bipy-ridinium dichloride) are broad-spectrum contact plant killers and herbage desiccants that were introduced commercially during the past 35 years. Today, they rank among the most widely used herbicides globally and are frequently used in combination with other herbicides. The recommended field application rates for terrestrial weed control usually range between 0.28 and 1.12 kg paraquat/ha (0.25 and 1.0 pounds/acre) for aquatic weed control, it is 0.1 to 2.0 mg/L. Target plant species are unable to metabolize paraquat and tend to contain elevated residues paraquat-resistant... 

Islam, A.K.M.R. and S.B. Powles. 1988. Inheritance of resistance to paraquat in barley grass Hordeum glaucum Steud. Weed Res. 28 393-397. 

Polos, E., J. Mikulas, Z. Szigeti, B. Matkovics, D.Q. Hai, A. Parducz, and E. Lehoczki. 1988. Paraquat and atrazine co-resistance in Conyza canadensis (L.) Cronq. Pestic. Biochem. Physiol. 30 142-154. 

Until the mid-1990s, multiple-resistance (i.e., resistance to more than one herbicide mode of action within the same biotype) had not been reported within North America. However, Foes et al. (1996) found a kochia biotype from western Illinois resistant to atrazine and several ALS-inhibiting herbicides. Lopez-Martinez et al. (1996) reported that a triazine-resistant Echinochloa species found in atrazine-treated com also showed cross-resistance to quinclorac. Clay and Underwood (1989) and Clay (1989) reported that one triazine-resistant biotype of American willowherb was also resistant to paraquat from a hop garden in the United Kingdom treated annually for 25 years with simazine and paraquat. 

Clay, D.V. (1989). New developments in triazine and paraquat resistance and co-resistance in weed species in England. Proc. Brighton CropProt. Conf., Weeds, 1 317-324. 

Clay, D.V. and C. Underwood (1989). The identification of triazine- and paraquat-resistant weed biotypes and their response to other herbicides. In Cavalloro, R., and Noye, G., eds, Proc. E. C. Experts, Grays, Tollose, Denmark, November 15-17, 1988. Luxembourg Office for Official Publications of the European Communities, pp. 47-55. 

Cairns, A.L.P. and F.H. Eksteen (2004). Glyphosate and paraquat resistance in weeds of the Western Cape. 4th International Weed Science Congress, p. 20, S17MT08P03. 

Yu, Q., A. Caims, and S.B. Powles (2007). Glyphosate, paraquat, and ACCase multiple resistance in a Lolium rigidum biotype. Plants, 225 499-513. 

Understandably, there are examples of oxygen-tolerant cell lines which have much higher levels of constitutive antioxidant enzymes than normal [249]. The ability of other cells to protect themselves by means of antioxidant enzymes is limited by their biosynthetic response to oxidative stress. In vitro exposure to paraquat induces an increase in SOD and catalase activities in human and hamster fibroblasts [250,251]. In cultured HeLa cells, a chronic exposure to paraquat induces a simultaneous increase in Mn- and Cu/Zn-SOD activities in surviving cells [252], Interestingly, such cells have apparently acquired resistance to paraquat, and their higher level of SOD activities persists for many months following the exposure to paraquat. In Chinese hamster fibroblasts, a chronic exposure to H2O2 results in a 5-40-fold increase in catalase activity [253], which... 

Surprises or unpredicted events can happen. The early dogma, also based largely on our experience of triazine resistance, suggested that soil residual activity of herbicides was an important, if not essential, contributor to the selection of resistant biotypes. The subsequent development of multiple instances of paraquat resistance, followed by resistance to acetyl CoA carboxylase (ACCase) inhibitors, demonstrated that soil activity was not necessary for resistance to evolve. 

Paraquat is relatively immobile in soil. Paraquat resists hydrolysis, photodegradation in water, and microbial degradation under both aerobic and anaerobic conditions. Dissipation is primarily by adsorption to organic material and clay particles. As paraquat persists in clay soils, it may be found in surface water from erosion. Since it binds so strongly to clay particles, paraquat is not generally a ground-water concern. 

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