MAIN CONCLUSION: Fe uptake machinery of chloroplasts prefers to utilise Fe(III)-citrate over Fe-nicotianamine complexes. Iron uptake in chloroplasts is a process of prime importance. Although a few members of their iron transport machinery were identified, the substrate preference of the system is still unknown. Intact chloroplasts of oilseed rape (Brassica napus) were purified and subjected to iron uptake studies using natural and artificial iron complexes. Fe-nicotianamine (NA) complexes were characterised by 5 K, 5 T Mössbauer spectrometry. Expression of components of the chloroplast Fe uptake machinery was also studied. Fe(III)-NA contained a minor paramagnetic Fe(II) component (ca. 9%), a paramagnetic Fe(III) component exhibiting dimeric or oligomeric structure (ca. 20%), and a Fe(III) complex, likely being a monomeric structure, which undergoes slow electronic relaxation at 5 K (ca. 61%). Fe(II)-NA contained more than one similar chemical Fe(II) environment with no sign of Fe(III) components. Chloroplasts preferred Fe(III)-citrate compared to Fe(III)-NA and Fe(II)-NA, but also to Fe(III)-EDTA and Fe(III)-o,o'EDDHA, and the Km value was lower for Fe(III)-citrate than for the Fe-NA complexes. Only the uptake of Fe(III)-citrate was light-dependent. Regarding the components of the chloroplast Fe uptake system, only genes of the reduction-based Fe uptake system showed high expression. Chloroplasts more effectively utilize Fe(III)-citrate, but hardly Fe-NA complexes in Fe uptake.

Centre for Energy Research Hungarian Academy of Sciences Konkoly Thege Miklós út 29 33 Budapest 1121 Hungary

Department of Plant Nutrition Aula Dei Experimental Station Spanish Council for Scientific Research P O Box 13034 50080 Saragossa Spain

Department of Plant Physiology and Molecular Plant Biology Institute of Biology ELTE Eötvös Loránd University Pázmány Péter sétány 1 C 1117 Budapest Hungary

Departments of Experimental Physics and Physical Chemistry Faculty of Science Regional Centre of Advanced Technologies and Materials Palacký University Šlechtitelů 27 783 71 Olomouc Czech Republic

Laboratory of Nuclear Chemistry Institute of Chemistry ELTE Eötvös Loránd University Pázmány Péter sétány 1 A 1117 Budapest Hungary

RT Europe Nonprofit Research Ltd Vár tér 2 E Building Mosonmagyaróvár 9200 Hungary

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