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Author Maury, W. J.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT. ♦ CHLOROPLASTS ♦ MEMBRANE TRANSPORT ♦ MAGNESIUM ♦ BIOLOGICAL EFFECTS ♦ ACIDIFICATION ♦ ANTIBIOTICS ♦ ATP-ASE ♦ CATIONS ♦ ENZYME ACTIVITY ♦ INHIBITION ♦ ION EXCHANGE ♦ PHOTOSYNTHESIS ♦ POTASSIUM ♦ SPINACH ♦ ACID ANHYDRASES ♦ ALKALI METALS ♦ ALKALINE EARTH METALS ♦ ANTI-INFECTIVE AGENTS ♦ CELL CONSTITUENTS ♦ CHARGED PARTICLES ♦ CHEMICAL REACTIONS ♦ DRUGS ♦ ELEMENTS ♦ ENZYMES ♦ FOOD ♦ HYDROLASES ♦ IONS ♦ METALS ♦ PHOSPHOHYDROLASES ♦ PHOTOCHEMICAL REACTIONS ♦ SYNTHESIS ♦ VEGETABLES ♦ Chemicals Metabolism & Toxicology- Plants- (-1987)
Abstract Addition of exogenous Mg/sup 2 +/ (millimolar) to illuminated intact spinach (Spinacia oleracea L.) chloroplasts caused acidification of the stroma and a 20% decrease in stromal K/sup +/. Addition of K/sup +/ (10-50 millimolar) reversed both stromal acidification and K/sup +/ efflux from the chloroplast caused by Mg/sup 2 +/. These data suggested that Mg/sup 2 +/ induced reversible H/sup +//K/sup +/ fluxes across the chloroplast envelope. Ca/sup 2 +/ and Mn/sup 2 +/ (2 millimolar) were as effective as 4 millimolar Mg/sup 2 +/ in causing K/sup +/ efflux from chloroplasts and inhibition of O/sub 2/ evolution. In contrast, 10 millimolar Ba/sup 2 +/ indicated that the effects of divalent cations such as Mg/sup 2 +/ 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 Mg/sup 2 +/ was small (0.07 to 0.15 pH units), but sufficient to account for the inhibition of O/sub 2/ evolution (43%) induced by Mg/sup 2 +/. Oligomycin was the only ATPase inhibitor which specifically inhibited photosynthesis in the presence of Mg/sup 2 +/ + K/sup +/, 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/sup +/ were required to reverse Mg/sup 2 +/-induced acidification and inhibition of O/sub 2/ evolution than in its absence. Oligomycin (in the absence of divalent cations) increased the inhibition of photosynthesis caused by sodium acetate. In addition, the chloroplast envelope ATPase was inhibited 45% by oligomycin. These results suggested that H/sup +/ fluxes across the chloroplast envelope are regulated by two mechanisms: an active, oligomycin-sensitive H/sup +/ efflux and a reversible, Mg/sup 2 +/-dependent, oligomycin-insensitive H/sup +//K/sup +/ exchange.
Educational Use Research
Learning Resource Type Article
Publisher Date 1981-12-01
Publisher Place United States
Journal Plant Physiol.
Volume Number 68
Issue Number 6


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