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Synchrotron-based X-ray absorption near-edge spectroscopy imaging for laterally resolved speciation of selenium in fresh roots and leaves of wheat and rice.

Wang P, Menzies NW, Lombi E, McKenna BA, James S, Tang C, Kopittke PM - J. Exp. Bot. (2015)

Bottom Line: Indeed, even in the rhizodermis which is exposed directly to the bulk solution, only 12-31% of the Se was present as uncomplexed selenate.In a similar manner, for plants exposed to selenite, the Se was efficiently converted to C-Se-C compounds within the roots, with only a small proportion of uncomplexed selenite observed within the outer root tissues.This resulted in a substantial decrease in translocation of Se from the roots to leaves of selenite-exposed plants.

View Article: PubMed Central - PubMed

Affiliation: The University of Queensland, School of Agriculture and Food Sciences, St. Lucia, Queensland, 4072, Australia p.wang3@uq.edu.au.

No MeSH data available.


Related in: MedlinePlus

Rice (Oryza sativa L.) roots exposed to nutrient solution containing 1 μM Se(VI) for 1 week. A full description is given in the legend of Fig. 1. (A and B) Elemental survey maps showing total Se distribution collected in the ‘pre-XANES survey scan’ followed by fluorescence-XANES imaging (‘XANES imaging scan’), with the white box (0.95 mm×0.20mm) indicating the area examined by XANES imaging. (C) The spatial distribution of three pixel populations (outer, middle, and inner) identified by comparing energy intensities. (D) Normalized Se K-edge XANES spectra corresponding to the three pixel populations ‘outer’, ‘middle’, and ‘inner’ shown in (C) plus the spectrum for MeSeCys. (E and F) Projected volumetric concentrations of C-Se-C compounds (i.e. MeSeCys or SeMet, filled circles) and uncomplexed Se(VI) (open circles) in the cross- or longitudinal transects indicated by the red or green rectangle in (B).
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Figure 4: Rice (Oryza sativa L.) roots exposed to nutrient solution containing 1 μM Se(VI) for 1 week. A full description is given in the legend of Fig. 1. (A and B) Elemental survey maps showing total Se distribution collected in the ‘pre-XANES survey scan’ followed by fluorescence-XANES imaging (‘XANES imaging scan’), with the white box (0.95 mm×0.20mm) indicating the area examined by XANES imaging. (C) The spatial distribution of three pixel populations (outer, middle, and inner) identified by comparing energy intensities. (D) Normalized Se K-edge XANES spectra corresponding to the three pixel populations ‘outer’, ‘middle’, and ‘inner’ shown in (C) plus the spectrum for MeSeCys. (E and F) Projected volumetric concentrations of C-Se-C compounds (i.e. MeSeCys or SeMet, filled circles) and uncomplexed Se(VI) (open circles) in the cross- or longitudinal transects indicated by the red or green rectangle in (B).

Mentions: In a manner similar to that observed in Se(IV)-exposed roots, when rice roots were exposed to 1 μM Se(VI), Se appeared to move more readily into the stele, with the concentration in the stele higher than in the surrounding cortex and rhizodermis in the more proximal portions of roots (Fig. 4A). Overall, 80% of the total Se in the analysed roots was present as C-Se-C compounds, with 20% present as uncomplexed Se(VI) [but none could be detected as the intermediate, uncomplexed Se(IV); data not presented]. Interestingly, the proportion of this uncomplexed Se(VI) decreased with increasing distance from the root surface, with 31% in the outer tissues and 16% in the inner tissues (Table 2), this being evident by a decrease in the magnitude of the white line at 12.667 keV with increasing distance from the root surface (Fig. 4D). Again, use of the mathematical model indicated that at 600 μm behind the root apex, the highest concentrations of C-Se-C compounds were within the stele (632 μg cm–3), but the highest concentrations of uncomplexed Se(VI) were in the cortex (157 μg cm–3), followed by the rhizodermis (116 μg cm–3), and lowest in the stele (23.7 μg cm–3) (Fig. 4E; Table 3). Similarly, for a virtual longitudinal transect along the root, whilst concentrations of C-Se-C compounds remained relatively constant, the concentration (and hence proportion) of uncomplexed Se(VI) increased with increasing distance from the root apex (Fig. 4F), presumably due to the increased loading of this species towards the fully developed vascular tissues for transport to the shoot. For example, 8% of the Se was present as uncomplexed Se(VI) at 500 μm from the apex but 34% at 700 μm from the apex (Fig. 4F). It is noteworthy that Se concentrations in the more proximal root tissues were too low to allow for analysis using fluorescence-XANES imaging.


Synchrotron-based X-ray absorption near-edge spectroscopy imaging for laterally resolved speciation of selenium in fresh roots and leaves of wheat and rice.

Wang P, Menzies NW, Lombi E, McKenna BA, James S, Tang C, Kopittke PM - J. Exp. Bot. (2015)

Rice (Oryza sativa L.) roots exposed to nutrient solution containing 1 μM Se(VI) for 1 week. A full description is given in the legend of Fig. 1. (A and B) Elemental survey maps showing total Se distribution collected in the ‘pre-XANES survey scan’ followed by fluorescence-XANES imaging (‘XANES imaging scan’), with the white box (0.95 mm×0.20mm) indicating the area examined by XANES imaging. (C) The spatial distribution of three pixel populations (outer, middle, and inner) identified by comparing energy intensities. (D) Normalized Se K-edge XANES spectra corresponding to the three pixel populations ‘outer’, ‘middle’, and ‘inner’ shown in (C) plus the spectrum for MeSeCys. (E and F) Projected volumetric concentrations of C-Se-C compounds (i.e. MeSeCys or SeMet, filled circles) and uncomplexed Se(VI) (open circles) in the cross- or longitudinal transects indicated by the red or green rectangle in (B).
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Related In: Results  -  Collection

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Figure 4: Rice (Oryza sativa L.) roots exposed to nutrient solution containing 1 μM Se(VI) for 1 week. A full description is given in the legend of Fig. 1. (A and B) Elemental survey maps showing total Se distribution collected in the ‘pre-XANES survey scan’ followed by fluorescence-XANES imaging (‘XANES imaging scan’), with the white box (0.95 mm×0.20mm) indicating the area examined by XANES imaging. (C) The spatial distribution of three pixel populations (outer, middle, and inner) identified by comparing energy intensities. (D) Normalized Se K-edge XANES spectra corresponding to the three pixel populations ‘outer’, ‘middle’, and ‘inner’ shown in (C) plus the spectrum for MeSeCys. (E and F) Projected volumetric concentrations of C-Se-C compounds (i.e. MeSeCys or SeMet, filled circles) and uncomplexed Se(VI) (open circles) in the cross- or longitudinal transects indicated by the red or green rectangle in (B).
Mentions: In a manner similar to that observed in Se(IV)-exposed roots, when rice roots were exposed to 1 μM Se(VI), Se appeared to move more readily into the stele, with the concentration in the stele higher than in the surrounding cortex and rhizodermis in the more proximal portions of roots (Fig. 4A). Overall, 80% of the total Se in the analysed roots was present as C-Se-C compounds, with 20% present as uncomplexed Se(VI) [but none could be detected as the intermediate, uncomplexed Se(IV); data not presented]. Interestingly, the proportion of this uncomplexed Se(VI) decreased with increasing distance from the root surface, with 31% in the outer tissues and 16% in the inner tissues (Table 2), this being evident by a decrease in the magnitude of the white line at 12.667 keV with increasing distance from the root surface (Fig. 4D). Again, use of the mathematical model indicated that at 600 μm behind the root apex, the highest concentrations of C-Se-C compounds were within the stele (632 μg cm–3), but the highest concentrations of uncomplexed Se(VI) were in the cortex (157 μg cm–3), followed by the rhizodermis (116 μg cm–3), and lowest in the stele (23.7 μg cm–3) (Fig. 4E; Table 3). Similarly, for a virtual longitudinal transect along the root, whilst concentrations of C-Se-C compounds remained relatively constant, the concentration (and hence proportion) of uncomplexed Se(VI) increased with increasing distance from the root apex (Fig. 4F), presumably due to the increased loading of this species towards the fully developed vascular tissues for transport to the shoot. For example, 8% of the Se was present as uncomplexed Se(VI) at 500 μm from the apex but 34% at 700 μm from the apex (Fig. 4F). It is noteworthy that Se concentrations in the more proximal root tissues were too low to allow for analysis using fluorescence-XANES imaging.

Bottom Line: Indeed, even in the rhizodermis which is exposed directly to the bulk solution, only 12-31% of the Se was present as uncomplexed selenate.In a similar manner, for plants exposed to selenite, the Se was efficiently converted to C-Se-C compounds within the roots, with only a small proportion of uncomplexed selenite observed within the outer root tissues.This resulted in a substantial decrease in translocation of Se from the roots to leaves of selenite-exposed plants.

View Article: PubMed Central - PubMed

Affiliation: The University of Queensland, School of Agriculture and Food Sciences, St. Lucia, Queensland, 4072, Australia p.wang3@uq.edu.au.

No MeSH data available.


Related in: MedlinePlus