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21Author    S. C. Sabat, V. Vijayavergiya, B. C. Tripathy, PrasannaM. OhantyRequires cookie*
 Title    Inhibitory Effect of Crown Compound on Photoelectron Transport Activity of Beet Spinach Thylakoid Membranes  
 Abstract    The effect o f K-picrate-18-crown-6 (crown) on the photoelectron transport activity o f beet spinach thylakoid membranes was investigated. A ddition o f micromolar concentration o f crown to thylakoid preparation inhibited p-benzoquinone, chloride-indophenol, methyl violo-gen supported Hill activities maximally by 75 per cent in a concentration dependent manner. However, the photosystem I catalyzed reaction remained insensitive to crown suggesting that crown specifically inhibits photosystem II electron transport. Addition o f exogenous electron donors like hydroxylamine or diphenylcarbazide failed to restore the crown induced inhibition o f photosystem II electron transport and lowering o f steady state chlorophyll a fluorescence yield. These observations suggest that crown also inhibits photosystem II catalyzed electron transport after the donation sites o f these exogenous donors. Washing o f the crown pre-treat-ed thylakoids with isolation buffer, relieved the crown inhibited electron transport activity, indicating that this inhibition is reversible. Furthermore, in hydroxylamine washed thylakoids which are devoid o f 0 2 evolution capacity, the hydroxylamine induced increase in chlorophyll a fluorescence o f variable yield was quenched by the addition o f crown. These observations suggest that crown affects the oxygen evolution and inhibits at a site close to photosystem II reaction centres. 
  Reference    Z. Naturforsch. 46c, 87 (1991); received August 14 1990 
  Published    1991 
  Keywords    Crown-Ether, Electron Transport, Photosystem II, Thylakoids, Beet Spinach ( Beta vulgaris) 
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 TEI-XML for    default:Reihe_C/46/ZNC-1991-46c-0087.pdf 
 Identifier    ZNC-1991-46c-0087 
 Volume    46 
22Author    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 
23Author    Illora Gupta, BaishnabCharan TripathyRequires cookie*
 Title    Oxidative Stress in Cucumber (Cucumis sativus L.) Seedlings Treated with Acifluorfen  
 Abstract    Illumination of acifluorfen-sprayed and 14 h-dark-incubated cucum ber seedlings with cool-white fluorescent light caused overaccumulation of protoporphyrin IX and severe oxidative stress which resulted in seedling death within 72 h. The ratio of variable fluorescence (F v)/ maximum fluorescence (F m), a measure of the functional status of PSII, declined by 30% , 58% and 85% after 24 h, 48 h and 72 h respectively. When 24 h-light-treated plants were transferred to dark for 24 h the F v/F m ratio was restored to near control levels suggesting a dark recovery from photodynamic damage. The intracellular distribution of protoporphyrin IX that accumulated in the cotyledons of acifluorfen-treated and 1 h-light-exposed plants was 22% within and 78% outside chloroplasts suggesting migration of protoporphyrin IX within one hour of exposure of plants to light. When thylakoid membranes, treated with exogenous protoporphyrin IX , were illuminated there was a reduction in photosystem II activity. Addition of L-histidine, scavenger of singlet oxygen, to illuminated thylakoid+ proto­ porphyrin IX mixture resulted in substantial protection of photosystem II activity suggesting the involvement of singlet oxygen in protoporphyrin IX-m ediated photodynamic damage. In illuminated thylakoid+protoporphyrin IX mixture no indication was found for production of superoxide radicals via type I reaction. In cucumber seedlings acifluorfen-induced synthesis of protoporphyrin IX caused severe photodynamic damage mediated by singlet oxygen gen­ erated due to type II photosensitization reaction. 
  Reference    Z. Naturforsch. 54c, 771—7 (1999); received November 2 1998/April 5 1999 
  Published    1999 
  Keywords    Chlorophyll a Fluorescence, Diphenyl ether Herbicide, Electron Transport, Photodynamic Reaction, Photosynthesis 
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 TEI-XML for    default:Reihe_C/54/ZNC-1999-54c-0771.pdf 
 Identifier    ZNC-1999-54c-0771 
 Volume    54 
24Author    Peter BögerRequires cookie*
 Title    Multiple Modes of Action of Diphenyl Ethers  
  Reference    Z. Naturforsch. 39c, 468 (1984); received N ovem ber 15 1983 
  Published    1984 
  Keywords    Herbicides, Electron Transport, Peroxidation, N itro/N on-nitro-d iphenyl Ethers, Carotenogenesis, m-Phenoxybenzamides, ATP-Synthase, Stress Response 
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 TEI-XML for    default:Reihe_C/39/ZNC-1984-39c-0468.pdf 
 Identifier    ZNC-1984-39c-0468 
 Volume    39