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1Author    MarcelA K Jansen, ChristoM. Alan, Yoseph Shaaltiel, Jonathan GresselRequires cookie*
 Title    Mode of Evolved Photooxidant Resistance to Herbicides and Xenobiotics  
 Abstract    A few species have evolved resistance to paraquat after repeated selection. As paraquat still inhibited N A D P reduction, we hypothesized that resistance might be due to (a) detoxification o f the paraquat-generated active oxygen species and (b) that resistant plants would have some cross resistance to other xenobiotic oxidants as well as to photoinhibition, which we subse­ quently demonstrated. The levels o f plastid isozymes o f the oxygen detoxification pathway: (CuZn) superoxide dismutase, ascorbate peroxidase and glutathione reductase were genetical­ ly higher in the resistant than in the sensitive biotype o f C onyza bonariensis through the F2 generation. Resistance was suppressed by chelators o f copper and/or zinc. Intact chloroplasts from resistant plants had less membrane damage with and without paraquat, than those from sensitive plants. Resistant C onyza plants recover from paraquat inhibition o f photosynthesis in 3 -4 h in high light, whereas sensitive plants died. Both resistant and sensitive plants recov­ ered from paraquat in 3 -4 h in low light intensities. Paraquat-resistant Conyza plants were cross-tolerant to S 0 2, atrazine, acifluorfen and to photoinhibition. Drought-tolerant maize inbreds were cross-tolerant to paraquat, SO, and acifluorfen (compared to sensitive lines) and they also possessed higher levels o f (Cu/Zn) superoxide dismutase and glutathione reductase. The tolerance to oxidant stresses in C onyza and maize increases with plant age, suggesting that the shift to resistance is a constitutive, earlier expression o f the genes normally expressed later in development. 
  Reference    Z. Naturforsch. 45c, 463 (1990); received November 9 1989 
  Published    1990 
  Keywords    Paraquat, Acifluorfen, Atrazine, Photoinhibition, Superoxide Dismutase 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0463.pdf 
 Identifier    ZNC-1990-45c-0463 
 Volume    45 
2Author    HartmutB. Stegmann, Paul Schuler, Stefan Westphal, Edgar WagnerRequires cookie*
 Title    Oxidative Stress of Crops Monitored by EPR  
 Abstract    Treatm ent of leaves of spinach, corn, and peas with the herbicides paraquat, am itrole or acifluorfen leads to oxidative stress resulting in a light driven drastically increased production of ascorbic acid radical (monodehydroascorbic acid, M DAA) which could be dem onstrated by in vivo EPR analysis. A discrimination of the M D A A form ation between the action of elec­ tron uncouplers and catalase inhibitors can be achieved by observation of the radical rise ki­ netics. Significant M DAA signal intensities are detected in the darkness likewise. These signals are probably due to the action of ascorbic acid oxidase activated by membrane destruction. 
  Reference    Z. Naturforsch. 48c, 766—772 (1993); received M arch 3/July 1 1993 
  Published    1993 
  Keywords    Herbicides, Paraquat, Amitrole, Ascorbic Acid Radicals 
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 TEI-XML for    default:Reihe_C/48/ZNC-1993-48c-0766.pdf 
 Identifier    ZNC-1993-48c-0766 
 Volume    48 
3Author    RichardJ. Youngman, AlanD. DodgeRequires cookie*
 Title    Mechanism of Paraquat Action: Inhibition of the Herbicidal Effect by a Copper Chelate with Superoxide Dismutating Activity  
 Abstract    The treatment of flax cotyledons (Linum usitatissimum) with paraquat was shown to decrease the levels of chlorophyll and carotenoid pigments. The fatty acid content of chloroplast fragments isolated from treated tissue was determined and shown to be greatly decreased by paraquat treat­ ment. The superoxide radical was demonstrated to play an important role in the phytotoxic action of paraquat by the use of a copper chelate of D-penicillamine, which has a high superoxide dismutat­ ing activity. The action of paraquat was inhibited by this compound. The role of superoxide is discussed with reference to the generation of more toxic species, such as singlet oxygen. 
  Reference    Z. Naturforsch. 34c, 1032—1035 (1979); received May 26 1979 
  Published    1979 
  Keywords    Paraquat, Plant Pigments, Fatty Acids, Superoxide, Copper Chelate, Flax Cotyledons 
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 TEI-XML for    default:Reihe_C/34/ZNC-1979-34c-1032.pdf 
 Identifier    ZNC-1979-34c-1032 
 Volume    34 
4Author    P. Camilleri, J. R. Bowyer, P. H. McneilRequires cookie*
 Title    The Effects of Photosystem I Electron Acceptors on Leaf Discs  
 Abstract    A leaf-disc chamber has been used to measure changes in photosynthesis by soybean leaf discs which have been supplied with photosystem I (PS I) electron acceptors via the transpiration stream. The uncharged heteropentalenes induce an inhibitory effect on C O ; fixation which is d e­ pendent on the /7-octanol-water partition coefficient o f these molecules. Paraquat, which carries a di-positive charge, was ineffective under the same conditions and at a concentration o f 10-4 m. Cationic species such as K +, Ca2+ and Mg2+ greatly enhanced the effect of paraquat on C 0 2 fixation while the presence o f these ions did not affect inhibition by the heteropentalenes. Such differences betw een uncharged and charged PS I electron acceptors have been explained in terms of electrostatic interactions encountered by paraquat on its way to the site o f action within the chloroplast, via the transpiration stream. 
  Reference    Z. Naturforsch. 42c, 829 (1987); received D ecem ber 1 1986 
  Published    1987 
  Keywords    Photosynthesis, Photosystem I Electron A cceptors, H eteropentalenes, Paraquat, Leaf Discs 
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 TEI-XML for    default:Reihe_C/42/ZNC-1987-42c-0829.pdf 
 Identifier    ZNC-1987-42c-0829 
 Volume    42