Abstract
Many central metabolic processes require iron as a cofactor and take place in specific subcellular compartments such as the mitochondrion or the chloroplast. Proper iron allocation in the different organelles is thus critical to maintain cell function and integrity. To study the dynamics of iron 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, and synchrotron radiation micro X-ray fluorescence. Pea (Pisum sativum) embryo was used as a model in this study because of its large cell size and high iron content. Histochemical staining with ferrocyanide and diaminobenzidine (Perls/diaminobenzidine) 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 iron in the nucleus was confirmed by elemental imaging using micro particle-induced x-ray emission. X-ray fluorescence on cryo-sectioned embryos further established that, quantitatively, the iron concentration found in the nucleus was higher than in the expected iron-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 unidentified although abundant iron pool in the cell, which is located in the nuclei of healthy, actively dividing plant tissues. This result paves the way for the discovery of a novel cellular function for iron related to nucleus/nucleolus-associated processes.
Highlights
Metal ions play multiple structural and catalytic functions in living cells
Iron loading into these vacuoles is mediated by VIT1, an iron/manganese tonoplastic transporter [8], whereas the remobilization of this vacuolar iron pool during early germination requires the efflux activity of the two cation metal transporters NRAMP3 and NRAMP4 [7, 9]
Abolition of vacuolar influx in a vit1 mutant or efflux in an nramp3 nramp4 double mutant impairs post-germinative growth under iron-limited conditions [8, 9]. Crucial in both studies was having recourse to elemental imaging techniques to reveal the subtle changes in iron distribution occurring in seeds of the mutants, not detectable otherwise
Summary
Our data uncover an as yet unidentified abundant iron pool in the cell, which is located in the nuclei of healthy, actively dividing plant tissues This result paves the way for the discovery of a novel cellular function for iron related to nucleus/nucleolus-associated processes. Abolition of vacuolar influx in a vit mutant or efflux in an nramp nramp double mutant impairs post-germinative growth under iron-limited conditions [8, 9] Crucial in both studies was having recourse to elemental imaging techniques (synchrotron radiation x-ray fluorescence for the study of VIT1 and energydispersive x-ray microscopy for NRAMP3 and NRAMP4) to reveal the subtle changes in iron distribution occurring in seeds of the mutants, not detectable otherwise. It is likely that this compartment has been ignored, or at least overlooked, in the past because high spatial resolution iron distribution has so far been addressed in very few reported studies
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
