title: Light-induced increase in free Mg2+ concentration in spinach chloroplasts: measurement of free Mg2+ by using a fluorescent probe and necessity of stromal alkalinization.
abstract: Free Mg(2+) in chloroplasts may contribute to the regulation of photosynthetic enzymes, but adequate methodology for the determination of free Mg(2+) concentration ([Mg(2+)]) in chloroplasts has been lacking. We measured internal chloroplast [Mg(2+)] by using a Mg-sensitive fluorescent indicator, mag-fura-2. In intact, dark-kept spinach chloroplasts, internal [Mg(2+)] was estimated to be 0.50 mM, and illumination caused an increase in [Mg(2+)] to 2.0mM in the stroma. The light-induced increase in [Mg(2+)] was inhibited by a blocker of driven electron transport and uncouplers. The K(+)-specific ionophore valinomycin inhibited the [Mg(2+)] increase in the absence of external K(+), and addition of KCl restored the [Mg(2+)] increase. NH(4)Cl, which induces stromal alkalinization, enhanced the [Mg(2+)] increase. A Ca(2+)-channel blocker, ruthenium red, inhibited the [Mg(2+)] increase, but LaCl(3) had no effect. These results indicate that stromal alkalinization is essential for light-induced increase in [Mg(2+)]. This system for measuring internal chloroplast [Mg(2+)] might provide a suitable system for assay of Mg(2+) transport activity of chloroplast membranes.
authors.affiliation: Graduate School of Agriculture, The Prefecture University of Kyoto, Kyoto 606-8522, Japan. ishijima@kpu.ac.jp
authors.forename: Sumio
authors.initials: S
authors.lastname: Ishijima
authors.forename: Atsuhito
authors.initials: A
authors.lastname: Uchibori
authors.forename: Hiroki
authors.initials: H
authors.lastname: Takagi
authors.forename: Ryoji
authors.initials: R
authors.lastname: Maki
authors.forename: Masatake
authors.initials: M
authors.lastname: Ohnishi
mesh_terms: D002118:Calcium / Q000378:metabolism; D002138:Calibration; D002736:Chloroplasts / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes / Q000494:pharmacology; D016257:Fura-2 / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D008027:Light; D008274:Magnesium / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D012430:Ruthenium Red / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D018724:Spinacia oleracea / Q000378:metabolism*; D013997:Time Factors; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D005456:Fluorescent Dyes; D007476:Ionophores; C028521:lanthanum chloride; D012430:Ruthenium Red; D014634:Valinomycin; D011189:Potassium Chloride; D007811:Lanthanum; D008274:Magnesium; D002118:Calcium; D016257:Fura-2