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1981 (1)
1979 (1)
1Author    H. Gimmler, B. Heilmann, B. Demmig, W. HartungRequires cookie*
 Title    The Permeability Coefficients of the Plasmalemma and the Chloroplast Envelope of Spinach Mesophyll Cells for Phytohormones  
 Abstract    The uptake of auxin (LAA), abscisic acid (ABA) the synthetic cytokinin benzylaminopurine (BA), gibberellic acid (GA3) and mevalonic acid (lactone) (MVA) into intact chloroplasts and protoplasts from spinach mesophyll cells was measured and the permeability coefficients Ps of the chloroplast envelope and the plasmalemma were calculated. With all solutes tested uptake and P s values were considerably higher in the chloroplast system than in the protoplast system. At an external pH of 7.0, rates of uptake exhibited the order BA > LAA > MVA > ABA > GA3 in both systems. However, the P s values (corrected for the undissociated species of the solutes) exhibited the order LAA > GA3 > (ABA or BA) > MVA. This corrected sequence indicates the theoretical capacity of penetration under the assumption that preferentially the protonated species of phytohormones are capable of readily penetrating membranes. P s values for phytohormones appeared largely to be determined by the distribution coefficient K d and to a lesser extent by the molecular weight (Mr). In the Collander-plot the relation between the logarithm of Ps values for phytohormones and some other solutes such as acetate, glycerol, glucose, sorbitol and sucrose and the logarithm of K J M T 1.5 approached linearity. 
  Reference    Z. Naturforsch. 36c, 672—678 (1981); received March 9 1981 
  Published    1981 
  Keywords    Chloroplast Envelope, Permeability Coefficients, Phytohormones, Plasmalemma, Spinach 
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 TEI-XML for    default:Reihe_C/36/ZNC-1981-36c-0672.pdf 
 Identifier    ZNC-1981-36c-0672 
 Volume    36 
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