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. 1991 Oct;97(2):580–587. doi: 10.1104/pp.97.2.580

Surface Charge-Mediated Effects of Mg2+ on K+ Flux across the Chloroplast Envelope Are Associated with Regulation of Stromal pH and Photosynthesis 1

Weihua Wu 1, Jeanne Peters 1, Gerald A Berkowitz 1
PMCID: PMC1081046  PMID: 16668438

Abstract

Studies of Spinacia oleracea L. were undertaken to characterize further how Mg2+ external to the isolated intact chloroplast interacts with stromal K+, pH, and photosynthetic capacity. Data presented in this report were consistent with the previously developed hypothesis that millimolar levels of external, unchelated Mg2+ result in lower stromal K+, which somehow is linked to stromal acidification. Stromal acidification directly results in photosynthetic inhibition. These effects were attributed to Mg2+ interaction (binding) to negative surface charges on the chloroplast envelope. Chloroplast envelope-bound Mg2+ was found to decrease the envelope membrane potential (inside negative) of the illuminated chloroplast by 10 millivolts. It was concluded that Mg2+ effects on photosynthesis were likely not mediated by this effect on membrane potential. Further experiments indicated that envelope-bound Mg2+ caused lower stromal K+ by restricting the rate of K+ influx; Mg2+ did not affect K+ efflux from the stroma. Mg2+ restriction of K+ influx appeared consistent with the typical effects imposed on monovalent cation channels by polyvalent cations that bind to negatively charged sites on a membrane surface near the outer pore of the channel. It was hypothesized that this interaction of Mg2+ with the chloroplast envelope likely mediated external Mg2+ effects on chloroplast metabolism.

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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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