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'Light Activation' in keywords Facet   section ZfN Section C  [X]
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1988 (1)
1979 (1)
1Author    Roland Pschorn, Wolfgang Rühle, Aloysius WildRequires cookie*
 Title    The Influence of the Proton Gradient on the Activation of Ferredoxin-NADP + -oxidoreductase by Light  
 Abstract    Ferredoxin-NADP + -oxidoreductase (FNR, EC 1.18.1.2) has been shown to be activated by light within a few seconds during dark-light transitions and inactivated in the dark. In previous papers this could be pointed out by the correlation of cytochrome /induction kinetics to the rate of NADP-photoreduction and the variable fluorescence. The present study deals with the role of the proton gradient during the activation process. The transition from an inactive to an active form is followed continuously in an in situ system. The steady-state rate of NADP-photoreduction is affected only by ionophores which inhibit a formation of the proton gradient, but not by inhibitors of the electric field. It correlates to the 9-aminoacridine fluorescence quench and the light scattering signals at 535 nm. The perception of the pH-gradient through the enzyme is still a matter of discussion. 
  Reference    Z. Naturforsch. 43c, 207—212 (1988); received December 28 1987 
  Published    1988 
  Keywords    Electron Transport, Ferredoxin-NADP + -oxidoreductase, Light Activation, Proton Gradient 
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 TEI-XML for    default:Reihe_C/43/ZNC-1988-43c-0207.pdf 
 Identifier    ZNC-1988-43c-0207 
 Volume    43 
2Author    B. Demmig, H. GimmlerRequires cookie*
 Title    Effect of Divalent Cations on Cation Fluxes Across the Chloroplast Envelope and on Photosynthesis of Intact Chloroplasts  
 Abstract    The effect of divalent cations on cation fluxes across the chloroplast envelope and on photo­ synthetic reactions of intact spinach chloroplasts was investigated. In the absence of EDTA, divalent cations inhibited photosynthetic C 0 2-fixation and PGA-reduction at low PGA concentrations, but had almost no effect on the reduction of OAA, BQ, and on PGA-reduction at high PGA concentrations. The inhibitory effect of Ca2+ was greater than that of M g2+. Inhibition of photosynthesis was greater when the divalent cations were added in the dark than when added in the light. In spite of its inhibitory effect, Mg2+ partially restored the Ca2+ inhibited photosynthesis, indicating the involvement of a Mg2+ /Ca2+ antagonism in the inhibitory effect. The inhibitory effect of divalent cations is stronger in a medium with low concentrations of K + than in the presence of 20 — 50 m M KC1. Mg2+ induced a release of plastidal K + and an in­ crease of stromal H + concentration. The results indicate that external Mg2+ in the absence of EDTA does not influence neither photosynthetic electron transport nor photophosphorylation, but inhibits the light activation of some enzymes of the carbon reduction cycle. The latter is assumed to be due to an acidification of the stroma pH and the decrease of endogenous K + level. Since the chloroplast envelope has only a very low permeability towards Mg2+, possible mechanisms are discussed by which M g2+ changes the properties of the chloroplast envelope and thus secondarily induces the observed effects. 
  Reference    Z. Naturforsch. 34c, 233—241 (1979); received December 28 1978 
  Published    1979 
  Keywords    Intact Chloroplasts, Chloroplast Envelope, Assimilation of C 0 2, Magnesium, Light Activation 
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 TEI-XML for    default:Reihe_C/34/ZNC-1979-34c-0233.pdf 
 Identifier    ZNC-1979-34c-0233 
 Volume    34