This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Maury, W. J. Articles by Moreland, D. E. Search for Related Content PubMed PubMed Citation Articles by Maury, W. J. Articles by Moreland, D. E. Agricola Articles by Maury, W. J. Articles by Moreland, D. E.

Articles

Effects of Magnesium on Intact Chloroplasts ¹

II. CATION SPECIFICITY AND INVOLVEMENT OF THE ENVELOPE ATPase IN (SODIUM) POTASSIUM/PROTON EXCHANGE ACROSS THE ENVELOPE

United States Department of Agriculture, Science and Education Administration, Agricultural Research, North Carolina State University, Raleigh, North Carolina 27650, Department of Crop Science, North Carolina State University, Raleigh, North Carolina 27650, Department of Botany, North Carolina State University, Raleigh, North Carolina 27650

Addition of exogenous Mg²⁺ (2 millimolar) to illuminated intact spinach (Spinacia oleracea L.) chloroplasts caused acidification of the stroma and a 20% decrease in stromal K⁺. Addition of K⁺ (10-50 millimolar) reversed both stromal acidification and K⁺ efflux from the chloroplast caused by Mg²⁺. These data suggested that Mg²⁺ induced reversible H⁺/K⁺ fluxes across the chloroplast envelope. Ca²⁺ and Mn²⁺ (2 millimolar) were as effective as 4 millimolar Mg²⁺ in causing K⁺ efflux from chloroplasts and inhibition of O₂ evolution. In contrast, 10 millimolar Ba²⁺ induced only a small amount of inhibition. The lack of strong inhibition by Ba²⁺ indicated that the effects of divalent cations such as Mg²⁺ cannot be attributed to generalized electrostatic interactions of the cation with the chloroplast envelope. With the chloroplasts used in this study, stromal acidification caused by 2 millimolar Mg²⁺ was small (0.07 to 0.15 pH units), but sufficient to account for the inhibition of O₂ evolution (43%) induced by Mg²⁺.

A variety of ATPase inhibitors were tested for effects on Mg²⁺-induced H⁺/K⁺ fluxes. Oligomycin was the only ATPase inhibitor which specifically inhibited photosynthesis in the presence of Mg²⁺ + K⁺, but had little or no effect in the absence of these cations. In the presence of oligomycin, much higher concentrations (50 millimolar) of exogenous K⁺ were required to reverse Mg²⁺-induced acidification and inhibition of O₂ evolution than in its absence. Oligomycin (in the absence of divalent cations) increased the inhibition of photosynthesis caused by sodium acetate, which acts by causing stromal acidification. In addition, the chloroplast envelope ATPase was inhibited partially (45%) by oligomycin. These results suggested that H⁺ fluxes across the chloroplast envelope are regulated by two mechanisms: (a) an active, oligomycin-sensitive H⁺ efflux and (b) a reversible, Mg²⁺-dependent, oligomycin-insensitive H⁺/K⁺ exchange.

This article has been cited by other articles:

				C.-P. Song, Y. Guo, Q. Qiu, G. Lambert, D. W. Galbraith, A. Jagendorf, and J.-K. Zhu A probable Na+(K+)/H+ exchanger on the chloroplast envelope functions in pH homeostasis and chloroplast development in Arabidopsis thaliana PNAS, July 6, 2004; 101(27): 10211 - 10216. [Abstract] [Full Text] [PDF]

				S. Mackenzie and L. McIntosh Higher Plant Mitochondria PLANT CELL, April 1, 1999; 11(4): 571 - 586. [Full Text]