Combined NanoSIMS and synchrotron X‐ray fluorescence reveal distinct cellular and subcellular distribution patterns of trace elements in rice tissues

Abstract

SummaryThe cellular and subcellular distributions of trace elements can provide important clues to understanding how the elements are transported and stored in plant cells, but mapping their distributions is a challenging task.The distributions of arsenic, iron, zinc, manganese and copper, as well as physiologically related macro-elements, were mapped in the node, internode and leaf sheath of rice (Oryza sativa) using synchrotron X-ray fluorescence (S-XRF) and high-resolution secondary ion mass spectrometry (NanoSIMS).Although copper and silicon generally showed cell wall localization, arsenic, iron and zinc were strongly localized in the vacuoles of specific cell types. Arsenic was highly localized in the companion cell vacuoles of the phloem in all vascular bundles, showing a strong co-localization with sulfur, consistent with As(III)-thiol complexation. Within the node, zinc was localized in the vacuoles of the parenchyma cell bridge bordering the enlarged and diffuse vascular bundles, whereas iron and manganese were localized in the fundamental parenchyma cells, with iron being strongly co-localized with phosphorus in the vacuoles.The highly heterogeneous and contrasting distribution patterns of these elements imply different transport activities and/or storage capacities among different cell types. Sequestration of arsenic in companion cell vacuoles may explain the limited phloem mobility of arsenite.

Evidence for the Root-Uptake of Arsenite at Lateral Root Junctions and Root Apices in Rice (Oryza sativa L.)

“…Kopittke et al [20] demonstrated that As(III) i is quickly complexed with glutathione (GSH) in rice roots exposed to As(III) i in hydroponic media. Using NanoSIMS, Moore and colleagues provided evidence for As co-localization with S in vacuoles within the pericycle for rice exposed to As(III) i [36,37]. Although µXRF does not provide as fine a resolution as NanoSIMS, our data partially corroborate this past work as we also observed co-localization of As(III) with S in the more mature root portion 500 µm from the apex within or near the vascular bundle ( Figure 4).…”

Can silicon partially alleviate micronutrient deficiency in plants? a review

“…The formation of insoluble Fe-P complexes in the vacuoles explains the relatively low mobility of Fe in plants (Marschner 2012). Copper shows a very different distribution pattern from that of the other transition metals with a strong localization to various types of vascular bundles mainly in the cell walls (Moore et al 2014). A similar study about roots will contribute to explain the Si role on metal accumulation at non-toxic concentrations and the possibilities of the accumulated metal to be transported to the shoot or not.…”

“…Silicon generally showed cell wall localization and no Si is detected in the vacuoles, probably because of the lack of Si transporters located in the tonoplast (Moore et al 2014). Moreover, Si was found to accumulate in oval granules, likely to be the starch grains, in the cytoplasm of the fundamental parenchyma of the internode (Moore et al 2014). Within the node, Zn was localized in the vacuoles of the parenchyma cell bridge bordering the enlarged and diffused vascular bundles, whereas Fe and Mn were localized in the fundamental parenchyma cells, with Fe being strongly co-localized with phosphorus in the vacuoles.…”

“…In respect to the rest of micronutrients, metal root deposits similar to those of Fe are reported in the literature under toxicity, but it is necessary to test their presence under normal growth conditions. Recently, the distributions of Si, Fe, Zn, Mn and Cu were mapped in the node, internode and leaf sheath of rice (Oryza sativa) cultured with Si in hydroponics, using synchrotron X-ray fluorescence (S-XRF) and high-resolution secondary ion mass spectrometry (NanoSIMS) (Moore et al 2014). Silicon generally showed cell wall localization and no Si is detected in the vacuoles, probably because of the lack of Si transporters located in the tonoplast (Moore et al 2014).…”

“…Recently, the distributions of Si, Fe, Zn, Mn and Cu were mapped in the node, internode and leaf sheath of rice (Oryza sativa) cultured with Si in hydroponics, using synchrotron X-ray fluorescence (S-XRF) and high-resolution secondary ion mass spectrometry (NanoSIMS) (Moore et al 2014). Silicon generally showed cell wall localization and no Si is detected in the vacuoles, probably because of the lack of Si transporters located in the tonoplast (Moore et al 2014). Moreover, Si was found to accumulate in oval granules, likely to be the starch grains, in the cytoplasm of the fundamental parenchyma of the internode (Moore et al 2014).…”