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1984 (1)
1979 (1)
1Author    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 
2Author    ElenaA. Kotova, MarinaD. Il 'inaRequires cookie*
 Title    Effect of Electron Transfer Inhibitors and Uncoupling Agents on the Chlorophyll Fluorescence Lifetime during Slow Fluorescence D ecline in Bean Leaves and Intact Chloroplasts  
 Abstract    Fluorescence m easurem ents were performed with bean leaves and intact chloroplasts, which are characterized by a slow fluorescence decline. The fluorescence lifetime (r) ana the fluores­ cence relative quantum yield (q>) o f intact chloroplasts, measured with the phase fluorometer, showed nearly proportional light-induced decrease with a halftime o f ~ 3 0 s, which was removed by 3-(3.4-dichlorophe n y l)-1.1 -dimethylurea (DC M U), by 4.5,6,7-tetrachloro-2'-trifluoromethyl-benzimidazole (TTFB). by carbonyl cyanide /?-trifluoromethoxyphenylhydrazone (FCCP) at a low concentration and by gramicidin D. Simultaneously the slow light-induced increase in absorbance at 518 nm (A A 518), reflecting thylakoid membrane energization, was elim inated. The data on r o f intact chloroplasts are original, the other results agree with literature data. In leaves, the slow light-induced fluorescence decline, with r dropping from ~ 2 to ~ 0.6 ns, was abolished by FCCP at a concentration o f 5 ^m. However, while r was stabilized at a level close to the initial (maximum) one or som ewhat higher, q> became close to the minimum value. Besides, the amplitude o f A A 518 was lowered about three times. These effects seemed to be due to multiple action o f FCCP as a protonophoric uncoupler and an electron transfer inhibitor. In the presence o f another uncoupling agent, TTFB, which, besides, is a diuron-like inhibitor o f the electron transfer in chloroplasts, we observed the light-dependent, but hardly linked to changes in membrane potential, great increase in r o f a leaf from ~ 1.9 to ~ 4 .3 ns, with cp decreasing slightly. Addition o f DC M U together with FCCP to the incubation medium or infiltration o f a leaf with DCM U alone stimulated the rise in r only to ~ 3 ns. The increase in r o f a leaf observed in the presence o f FCCP and DCM U, and especially with TTFB, may be associated with protein conformation changes which (i) alter the lifetime o f nanosecond recombination lum inescence o f the photosystem II a n d /o r (ii) disturb excitation energy transfer from the light-harvesting chlorophyll a /b com plex to other pigment-protein complexes. 
  Reference    Z. Naturforsch. 39c, 93—101 (1984); received October 5 1983 
  Published    1984 
  Keywords    Photosynthesis, C hlorophyll Fluorescence Lifetime, Electron Transfer Inhibitors, Uncouplers, Bean Leaves, Intact Chloroplast 
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 TEI-XML for    default:Reihe_C/39/ZNC-1984-39c-0093.pdf 
 Identifier    ZNC-1984-39c-0093 
 Volume    39