1. Institute of Nuclear Techniques, Budapest University of Technology and Economics, Budapest H-1111, Hungary
2. Department of Plant Physiology and Molecular Plant Biology, Eötvös Loránd University, Budapest H-1117, Hungary
3. X-ray Microspectroscopy and Imaging Group (XMI), Department of Chemistry, Ghent University, Krijgslaan 281 S12, Ghent B-9000, Belgium