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Properties of the Isolated Intact Chloroplast at Cytoplasmic K Concentrations : I. Light-Induced Cation Uptake into Intact Chloroplasts is Driven by an Electrical Potential Difference.
MedLine Citation:
PMID:  16663169     Owner:  NLM     Status:  PubMed-not-MEDLINE    
Abstract/OtherAbstract:
Photosynthesis, stroma-pH, and internal K(+) and Cl(-) concentrations of isolated intact chloroplasts from Spinacia oleracea, as well as ion (K(+), H(+), Cl(-)) movements across the envelope, were measured over a wide range of external KCl concentrations (1-100 millimolar).Isolated intact chloroplasts are a Donnan system which accumulates cations (K(+) or added Tetraphenylphosphonium(+)) and excludes anions (Cl(-)) at low ionic strength of the medium. The internally negative dark potential becomes still more negative in the light as estimated by Tetraphenylphosphonium(+) distribution. At 100 millimolar external KCl, potentials both in the light and in the dark and also the light-induced uptake of K(+) or Na(+) and the release of protons all become very small. Light-induced K(+) uptake is not abolished by valinomycin suggesting that the K(+) uptake is not primarily active. Intact chloroplasts contain higher K(+) concentrations (112-157 millimolar) than chloroplasts isolated in standard media. Photosynthetic activity of intact chloroplasts is higher at 100 millimolar external KCl than at 5 to 25 millimolar. The pH optimum of CO(2) fixation at high K(+) concentrations is broadened towards low pH values. This can be correlated with the observation that high external KCl concentrations at a constant pH of the suspending medium produce an increase of stroma-pH both in the light and in the dark. These results demonstrate a requirement of high external concentrations of monovalent cations for CO(2) fixation in intact chloroplasts.
Authors:
B Demmig; H Gimmler
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Plant physiology     Volume:  73     ISSN:  0032-0889     ISO Abbreviation:  Plant Physiol.     Publication Date:  1983 Sep 
Date Detail:
Created Date:  2010-06-29     Completed Date:  2010-06-29     Revised Date:  2010-09-15    
Medline Journal Info:
Nlm Unique ID:  0401224     Medline TA:  Plant Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  169-74     Citation Subset:  -    
Affiliation:
Lehrstuhl Botanik I, Universität Würzburg, 8700 Würzburg, West Germany.
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