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'Resistance' in keywords Facet   Publication Year 1979  [X]
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1979[X]
1Author    Klaus Pfister, CharlesJ. ArntzenRequires cookie*
 Title    The Mode of Action of Photosystem II-Specific Inhibitors in Herbicide-Resistant Weed Biotypes  
 Abstract    This report reviews studies which provide evidence defining the mode of action and site of action of photosystem II (PS II) herbicides; the involvement of the secondary electron carrier on the reducing side of PS II (called B) is indicated as the target site for these compounds. These studies of the action of PS II-inhibitors were perform ed in chloroplasts of various weed species in order to define the mechanism which is responsible for herbicide tolerance at the level of chloroplast mem branes in newly discovered triazine-resistant weed biotypes. M any species of triazine-resistant weed biotypes have been collected in N orth America and Europe. W here data is available, these plants have been found to share the following common fe atu res: a) they were discovered in areas where triazine herbicides had been used repeatedly, b) resistance to the triazines is extrem e; it is not due to a m inor shift in herbicidal response, c) no changes in herbicide uptake, translocation or metabolism — as compared to susceptible bio­ types — can be detected, d) resistance is selective for only certain classes of photosynthetic herbicides, and, e) chloroplasts isolated from triazine-resistant weeds display high preferential resistance to the triazines in assays of photosystem II partial reactions. To focus on the mechanism which regulates preferential herbicide activity, we have characterized susceptible and resistant chloroplasts in the presence and absence of herbicides. Properties of the PS II complex of chloroplasts from several different triazine-resistant weed biotypes share the fol­ lowing tr a its : a) the herbicide binding site (as measured by direct binding of radiolabeled herbicides or by in­ hibition experiments) is modified such that the affinity for triazines is dram atically reduced. b) alterations in response to many PS II-herbicides occur such th at the triazine-resistant chloro­ plasts are very strongly resistant to all sym m etrical triazines, strongly resistant to assymmetrical triazinones, partially resistant to pyridazones and uracils, only slightly resistant to ureas or amides, and increasingly susceptible to nitrophenols, phenols and the herbicide bentazon (all as compared to susceptible chloroplasts), c) there is a change in the reaction kinetics of the electron transport step between the prim ary and secondary electron acceptors (referred to as Q and B), and d) in two examples, specific small changes in a m em brane polypeptide can be detected in the resistant thylakoids. We suggest that certain amino acids or segments of the apoprotein of B (the bound quinone which acts as the secondary electron carrier) are modified or deleted in these chloroplasts. Such a polypeptide change could affect both the redox poising of the Q~/B reaction pair, and the specific binding of herbicides. 
  Reference    Z. Naturforsch. 34c, 996—1009 (1979); received June 29 1979 
  Published    1979 
  Keywords    Herbicide, Resistance, Photosynthesis, Electron Transport, Inhibitors 
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 TEI-XML for    default:Reihe_C/34/ZNC-1979-34c-0996.pdf 
 Identifier    ZNC-1979-34c-0996 
 Volume    34