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1991 (1)
1Author    U. Lrich Schreiber, H. Einz, Reising, C. Hristian, N. EubauerRequires cookie*
 Title    Contrasting pH-Optima of Light-Driven 0 2-and H 20 2-Reduction in Spinach Chloroplasts as Measured via Chlorophyll Fluorescence Quenching  
 Abstract    Quenching analysis o f chlorophyll fluorescence by the saturation pulse method is used to investigate the pH-dependency o f 0 2-dependent electron flow in intact spinach chloroplasts with high ascorbate peroxidase activity. When carboxylase/oxygenase activity is blocked, p h o­ tochem ical and non-photochemical quenching are initially low and increase with illumination time. Quenching shows a pH-optimum around pH 6.5, but only when ApH-formation is al­ lowed. It is suggested that overall 0 2-dependent electron flow involves two major com ponents, namely 0 2-reduction (M ehler reaction) and reduction o f the H 20 2 formed in the Mehler reac­ tion, involving enzymic activity o f ascorbate peroxidase and m onodehydroascorbate reduc­ tase. The separated pH-dependencies o f light driven 0 2-reduction (presence o f K C N) and o f H 20 2-reduction (anaerobic conditions) reveal contrasting pH-optim a around pH 5 and 8.5, re­ spectively. Energy-dependent, dark relaxable non-photochem ical quenching is not observed with 0 2-reduction but with H20 2-reduction, and only at pH-values above 6.5. The relevance o f these findings with respect to regulation o f photosynthetic electron flow is discussed. It is sug­ gested that upon limitation o f assimilatory electron flow 0 2-dependent non-assim ilatory flow is responsible for ApH-formation, by which it is autocatalytically stimulated. It is proposed that this autocatalytical reaction sequence is the basis o f the so-called "Kautsky effect" o f chlorophyll fluorescence induction. 
  Reference    Z. Naturforsch. 46c, 635 (1991); received March 6 1991 
  Published    1991 
  Keywords    Chlorophyll Fluorescence, Mehler Reaction, Ascorbate Peroxidase, Energy Dependent Quenching, Photosynthesis Regulation 
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 TEI-XML for    default:Reihe_C/46/ZNC-1991-46c-0635.pdf 
 Identifier    ZNC-1991-46c-0635 
 Volume    46