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. 1980 Feb;65(2):350–354. doi: 10.1104/pp.65.2.350

Effects of Magnesium on Intact Chloroplasts

I. EVIDENCE FOR ACTIVATION OF (SODIUM) POTASSIUM/PROTON EXCHANGE ACROSS THE CHLOROPLAST ENVELOPE 1

Steven C Huber 2, Wendy Maury 3
PMCID: PMC440325  PMID: 16661188

Abstract

Exogenous Mg2+ (2 millimolar) altered the stromal pH of intact spinach chloroplasts. Without added KCl in the medium, Mg2+ decreased the stromal pH in the light by approximately 0.3 pH unit. External KCl (25 millimolar) largely prevented the acidification caused by Mg2+. Effects on the stromal pH were not caused by changes in H+ pumping across the thylakoid membrane because Mg2+ had no effect on the light-induced quenching of atebrin fluorescence by intact chloroplasts. However, Mg2+ affected H+ fluxes across the envelope. Addition of Mg2+ to intact chloroplasts in the dark caused a significant acidification of the medium that was dependent on the presence of K+.

External K+ or Na+ also prevented the inhibition of CO2-dependent O2 evolution by Mg2+, whereas choline chloride was less effective. The combination of Mg2+ and K+ stimulated O2 evolution at suboptimal pH, inhibited O2 evolution at optimal and superoptimal pH, and prevented the inhibition of photosynthesis caused by acetate. In the absence of added K+, Mg2+ was most inhibitory to O2 evolution at suboptimal pH.

The results suggested that Mg2+ activated a reversible (Na+)K+/H+ exchange across the chloroplast envelope. It is postulated that changes in the stromal pH may explain the inhibition of photosynthesis caused by the presence of exogenous Mg2+.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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