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'Electron Transport' in keywords Facet   Publication Year 1996  [X]
Facet   section ZfN Section C  [X]
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1996[X]
1Author    KlausP B Ad Er, Judith SchülerRequires cookie*
 Title    Inhibition of the Photosynthetic Electron Transport by Pyrethroid Insecticides in Cell Cultures and Thylakoid Suspensions from Higher Plants  
 Abstract    Synthetic pyrethroid insecticides with different molecular structures have been investigated with respect to their effect on photosynthetic electron transport reactions in chloroplast sus­ pensions and cell cultures from higher plants. The fluorescence induction curves of tobacco (Nicotiana tabacum) leaves and tomato cells were substantially affected by permethrin and cypermethrin resulting in a strong increase of the maximum fluorescence. Application of different concentrations (0.3-1.2 m M) of the respective chemical abolishes virtually any ki­ netics of the normal Kautsky effect. Oxygen evolution from cell cultures from tomato (Ly-copersicon peruvianum) was completely inhibited by cypermethrin. Analysis of partial reac­ tions of the photosynthetic electron transport showed that both a methylviologen-mediated Mehler reaction and a ferricyanide-driven Hill reaction were quantitatively inhibited by e.g. fenvalerate. On the other hand, neither a silicomolybdate-driven Hill reaction nor a methylvi-ologen-driven Mehler reaction using dichlorophenol indophenol/ascorbate as electron donors could be inhibited by the pyrethroid. The analyses suggest that pyrethroid insecticides in­ terfere with the photosynthetic electron transport at the same site as urea-type herbicides do. Depending on the molecular structure and on the halogen compound in the molecule, however, different pyrethroids are more or less phytotoxic to the investigated photosynthetic membranes -cypermethrin with two Cl-substituents requires much higher concentrations to be applied for significant inhibition of the electron transport reactions than the Br-derivative deltamethrin does. Moreover, qualitative differences have to be taken into account. In the case of fenvalerate the effect seems to exist in a type of all-or-nothing reaction when the reaction centres are inhibited by the pyrethroid. None of the S-states nor the transition probabilities are specifically influenced by increasing concentrations of fenvalerate. In the case of deltamethrin, however, it was found that the overreduced state S_i is significantly increased at the expense of both Si and S(). Moreover, the miss parameter a is increased in the case of deltamethrin addition. The results and the significance of different substituents for the investigated pyrethroids are discussed. 
  Reference    Z. Naturforsch. 51c, 721—728 (1996); received April 25/June 20 1996 
  Published    1996 
  Keywords    Photosynthesis, Electron Transport, Oxygen Evolution, Pyrethroid Insecticide, Cell Culture 
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 TEI-XML for    default:Reihe_C/51/ZNC-1996-51c-0721.pdf 
 Identifier    ZNC-1996-51c-0721 
 Volume    51 
2Author    SurendraC. Handra SabatRequires cookie*
 Title    Copper Ion Inhibition of Electron Transport Activity in Sodium Chloride Washed Photosystem II Particle Is Partially Prevented by Calcium Ion  
 Abstract    The inhibitory effects of copper ion (Cu2+) on the photosynthetic electron transport func­ tion was investigated both in NaCl washed (depleted in 17 and 23 kDa polypeptides) and native (unwashed) photosystem II membrane preparations from spinach (Beta vulgaris) chlo-roplasts. Copper in the range of 2.0 to 15 j im strongly inhibited the electron flow from water to 2,6-dichlorobenzoquinone in NaCl washed particles in a concentration dependent manner. Com plete inhibition was noticed at 15 [.im Cu2+. Oppositely in native membranes, 15 (.im C u2+ inhibited only 10-12% o f control activity. It was found that calcium ion (Ca2+) significantly reduced the Cu2+ inhibition o f electron transport activity. The Ca2+ supported prevention of Cu2+ toxicity was specific to Ca2+. Further analysis indicated that both Cu2+ and Ca2+ act competitively. Since Ca2+ is known to have stimulating/stabilizing effect at the donor side of photosystem II, it is therefore suggested that Cu2+ in NaCl washed particles exerts its inhibi­ tory effect(s) at the oxidizing side of photosystem stim ulates/stabilizes the oxygen evolution. 
  Reference    Z. Naturforsch. 51c, 179—1 (1996); received September 26 1995 
  Published    1996 
  Keywords    Calcium Ion Copper Inhibition, Electron Transport, Photosystem II Particles, Spinach (Beta vulgaris) 
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 TEI-XML for    default:Reihe_C/51/ZNC-1996-51c-0179.pdf 
 Identifier    ZNC-1996-51c-0179 
 Volume    51