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1999[X]
1Author    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