Nucleolus as a Hot Spot for Iron

Many central metabolic processes require iron (Fe) as a cofactor and take place in specific subcellular compartments such as the mitochondrion or the chloroplast. Proper Fe allocation in the different organelles is thus critical to maintain cell function and integrity. To study the dynamics of Fe distribution in plant cells, we have sought to identify the different intracellular iron pools by combining three complementary imaging approaches, histochemistry, micro Particle Induced X-ray Emission (μPIXE) and synchrotron radiation micro X-Ray Fluorescence (μXRF). Pea (Pisum sativum) embryo was used as a model in this study because of its large cells size and high iron content. Histochemical staining with Ferro cyanide and diaminobenzidine (Perls/DAB) strongly labeled a unique structure in each cell, which co-labeled with the DNA fluorescent stain DAPI, thus corresponding to the nucleus. The unexpected presence of Fe in the nucleus was confirmed by elemental imaging using μPIXE. X-Ray Fluorescence on cryo-sectioned embryos further established that, quantitatively, the Fe concentration found in the nucleus was higher than in the expected Fe-rich organelles such as plastids or vacuoles. Moreover, within the nucleus, iron was particularly accumulated in a subcompartment that was identified as the nucleolus as it was shown to transiently disassemble during cell division. Taken together, our data uncover an as yet http://www.jbc.org/cgi/doi/10.1074/jbc.C111.269720 The latest version is at JBC Papers in Press. Published on June 30, 2011 as Manuscript C111.269720