Light-induced increase in free Mg²⁺ concentration in spinach chloroplasts: Measurement of free Mg²⁺ by using a fluorescent probe and necessity of stromal alkaliniza

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• 作者：Ishijima ; Sumio ; Uchibori ; Atsuhito ; Takagi ; Hiroki ; Maki ; Ryoji ; Ohnishi ; Masatake
• 关键词：Free Mg²⁺ ; mag-fura-2 ; Ca²⁺ ; Fluorescent probes ; Ionophore ; Stromal alkalinization ; Chloroplast ; Spinach
• 刊名：Archives of Biochemistry and Biophysics
• 出版年：2003
• 出版时间：April 1, 2003
• 年：2003
• 卷：412
• 期：1
• 页码：126-132
• 全文大小：127 K

文摘

Free Mg²⁺ in chloroplasts may contribute to the regulation of photosynthetic enzymes, but adequate methodology for the determination of free Mg²⁺ concentration ([Mg²⁺]) in chloroplasts has been lacking. We measured internal chloroplast [Mg²⁺] by using a Mg-sensitive fluorescent indicator, mag-fura-2. In intact, dark-kept spinach chloroplasts, internal [Mg²⁺] was estimated to be 0.50 mM, and illumination caused an increase in [Mg²⁺] to 2.0mM in the stroma. The light-induced increase in [Mg²⁺] was inhibited by a blocker of driven electron transport and uncouplers. The K⁺-specific ionophore valinomycin inhibited the [Mg²⁺] increase in the absence of external K⁺, and addition of KCl restored the [Mg²⁺] increase. NH₄Cl, which induces stromal alkalinization, enhanced the [Mg²⁺] increase. A Ca²⁺-channel blocker, ruthenium red, inhibited the [Mg²⁺] increase, but LaCl₃ had no effect. These results indicate that stromal alkalinization is essential for light-induced increase in [Mg²⁺]. This system for measuring internal chloroplast [Mg²⁺] might provide a suitable system for assay of Mg²⁺ transport activity of chloroplast membranes.