title: Different kinetics of photoinactivation of photosystem I-mediated electron transport and P700 in isolated thylakoid membranes.
abstract: Photoinactivation kinetics of photosystem I (PSI)-mediated electron transport rate was compared to that of P700 content at room (22 degrees C) and low (4 degrees C) temperatures in isolated spinach thylakoid membranes. The high light treatment was carried out under aerobic and anaerobic conditions. At 22 degrees C the decrease of electron transport rate showed first order exponential kinetics. The amount of P700 decreased linearly, being less affected in the first hours of illumination. During photoinhibition at 4 degrees C in the presence of oxygen, the kinetics of inactivation of PSI photochemical activity and the content of P700 were different. It was found that 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) had different protective effect on the electron transport rate and on P700 content at both temperatures. Treatment with high light intensity under N(2) atmosphere had no effect on the electron transport rate or P700 content. The possible degradation of PSI reaction centre proteins was determined using immunoblot methods. In the presence of linear electron transport at 22 degrees C correlation between formation of toxic hydroxyl radicals and inhibition of oxygen uptake was observed.
authors.affiliation: Estación Experimental de Aula Dei, CSIC, Apdo. 202, 50080 Zaragoza, Spain. mayav@obzor.bio21.bas.bg
authors.forename: Maya
authors.initials: M
authors.lastname: Velitchkova
authors.forename: Inmaculada
authors.initials: I
authors.lastname: Yruela
authors.forename: Miguel
authors.initials: M
authors.lastname: Alfonso
authors.forename: Pablo J
authors.initials: PJ
authors.lastname: Alonso
authors.forename: Rafael
authors.initials: R
authors.lastname: Picorel
mesh_terms: D000693:Anaerobiosis; D002734:Chlorophyll / Q000378:metabolism / Q000528:radiation effects; D004237:Diuron / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport / Q000528:radiation effects; D006540:Herbicides / Q000494:pharmacology; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D018462:Photobiology; D045322:Photosynthetic Reaction Center Complex Proteins / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects*; D045331:Photosystem I Protein Complex; D017382:Reactive Oxygen Species / Q000378:metabolism; D018724:Spinacia oleracea / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D013696:Temperature; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects
chemical_list: D006540:Herbicides; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D017382:Reactive Oxygen Species; D002734:Chlorophyll; C001785:chlorophyll P 700; D004237:Diuron