title: Does a voltage-sensitive outer envelope transport mechanism contributes to the chloroplast iron uptake?
abstract: Based on the effects of inorganic salts on chloroplast Fe uptake, the presence of a voltage-dependent step is proposed to play a role in Fe uptake through the outer envelope. Although iron (Fe) plays a crucial role in chloroplast physiology, only few pieces of information are available on the mechanisms of chloroplast Fe acquisition. Here, the effect of inorganic salts on the Fe uptake of intact chloroplasts was tested, assessing Fe and transition metal uptake using bathophenantroline-based spectrophotometric detection and plasma emission-coupled mass spectrometry, respectively. The microenvironment of Fe was studied by Mössbauer spectroscopy. Transition metal cations (Cd2+, Zn2+, and Mn2+) enhanced, whereas oxoanions (NO3-, SO42-, and BO33-) reduced the chloroplast Fe uptake. The effect was insensitive to diuron (DCMU), an inhibitor of chloroplast inner envelope-associated Fe uptake. The inorganic salts affected neither Fe forms in the uptake assay buffer nor those incorporated into the chloroplasts. The significantly lower Zn and Mn uptake compared to that of Fe indicates that different mechanisms/transporters are involved in their acquisition. The enhancing effect of transition metals on chloroplast Fe uptake is likely related to outer envelope-associated processes, since divalent metal cations are known to inhibit Fe2+transport across the inner envelope. Thus, a voltage-dependent step is proposed to play a role in Fe uptake through the chloroplast outer envelope on the basis of the contrasting effects of transition metal cations and oxoaninons.
authors.affiliation: Department of Plant Physiology and Molecular Plant Biology, Institute of Biology, Faculty of Sciences, Eötvös Loránd University, Pázmány P. Sétány 1/C, Budapest, 1117, Hungary. adam.solti@ttk.elte.hu.
authors.forename: Ádám
authors.initials: Á
authors.lastname: Solti
authors.affiliation: Laboratory of Nuclear Chemistry, Department of Analytical Chemistry, Institute of Chemistry, Faculty of Sciences, Eötvös Loránd University, Pázmány P. Sétány 1/A, Budapest, 1117, Hungary.
authors.forename: Krisztina
authors.initials: K
authors.lastname: Kovács
authors.affiliation: Department of Plant Physiology and Molecular Plant Biology, Institute of Biology, Faculty of Sciences, Eötvös Loránd University, Pázmány P. Sétány 1/C, Budapest, 1117, Hungary.
authors.forename: Brigitta
authors.initials: B
authors.lastname: Müller
authors.affiliation: Department of Plant Nutrition, Aula Dei Experimental Station, Spanish Council for Scientific Research (CSIC), P.O. Box 13034, 50080, Saragossa, Spain.|Faculty of Science, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Sutton Bonington, Leicestershire, LE12 5RD, UK.
authors.forename: Saúl
authors.initials: S
authors.lastname: Vázquez
authors.affiliation: Department of Plant Physiology and Molecular Plant Biology, Institute of Biology, Faculty of Sciences, Eötvös Loránd University, Pázmány P. Sétány 1/C, Budapest, 1117, Hungary.
authors.forename: Éva
authors.initials: É
authors.lastname: Hamar
authors.affiliation: Department of Plant Physiology and Molecular Plant Biology, Institute of Biology, Faculty of Sciences, Eötvös Loránd University, Pázmány P. Sétány 1/C, Budapest, 1117, Hungary.
authors.forename: Hong Diep
authors.initials: HD
authors.lastname: Pham
authors.affiliation: Department of Agricultural Botany, Crop Physiology and Biotechnology, Institute of Crop Sciences, Faculty of Agricultural and Food Sciences and Environmental Management, University of Debrecen, Böszörményi út 138, Debrecen, 4032, Hungary.
authors.forename: Brigitta
authors.initials: B
authors.lastname: Tóth
authors.affiliation: Department of Plant Nutrition, Aula Dei Experimental Station, Spanish Council for Scientific Research (CSIC), P.O. Box 13034, 50080, Saragossa, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Abadía
authors.affiliation: Department of Plant Physiology and Molecular Plant Biology, Institute of Biology, Faculty of Sciences, Eötvös Loránd University, Pázmány P. Sétány 1/C, Budapest, 1117, Hungary.
authors.forename: Ferenc
authors.initials: F
authors.lastname: Fodor
mesh_terms: D027461:Beta vulgaris / Q000378:metabolism / Q000502:physiology; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology*; D002104:Cadmium / Q000378:metabolism; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D004237:Diuron / Q000494:pharmacology; D006540:Herbicides / Q000494:pharmacology; D007501:Iron / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism; D015204:Spectroscopy, Mossbauer; D015032:Zinc / Q000378:metabolism
chemical_list: D006540:Herbicides; D002104:Cadmium; D008345:Manganese; D004237:Diuron; D007501:Iron; D015032:Zinc
keywords: Chloroplast; Envelope membrane; Iron metabolism; Mössbauer spectrosopy; Voltage-dependent transport