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Evidence of a low stromal magnesium concentration in intact chloroplasts in the dark studies with the ionophore a 23187


Plant Physiology (Rockville) 67(5): 985-989
Evidence of a low stromal magnesium concentration in intact chloroplasts in the dark studies with the ionophore a 23187
The loss of Mg2+ upon the addition of the ionophore A23187 in the dark was prevented by less than 0.1 mM MgCl2 with intact chloroplasts [from spinach, Spinacia oleracea] suspended in a sorbitol medium but required 1-3 mM MgCl2 if the chloroplasts were in a K+-gluconate medium. Measurements of stromal pH in the dark indicated that, in the K+-gluconate medium, the stromal pH is nearly the same as that of the medium; in the sorbitol medium it is much more acidic as reported previously. The free Mg2+ concentration in the stroma in the dark is between 1 and 3 mM. Other experiments on the inhibition by A23187 of CO2 fixation in the light and in a system capable of catalyzing CO2 fixation in the dark and on the Mg2+ binding properties of thylakoid membranes, are consistent with this conclusion. Light-induced Mg2+ concentration changes may occur in the stroma that are important in the light-dark regulation of CO2 fixation.


Accession: 005411111



Related references

Evidence of a Low Stromal Mg Concentration in Intact Chloroplasts in the Dark: I. STUDIES WITH THE IONOPHORE A23187. Plant Physiology 67(5): 985-989, 1981

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