Interaction of As and Sb in the hyperaccumulator Pteris vittata L.: changes in As and Sb speciation by XANES

Abstract

Arsenic (As) and antimony (Sb) are chemical analogs that display similar characteristics in the environment. The As hyperaccumulator Pteris vittata L. is a potential AsSb co-accumulating species. However, when this plant is exposed to different As and Sb speciation, the associated accumulating mechanisms and subsequent assimilation processes of As and Sb remain unclear. A 2-week hydroponic experiment was conducted by exposing P. vittata to single AsIII, AsV, SbIII, and SbV or the co-existence of AsIII and SbIII and AsV and SbV. P. vittata could co-accumulate As and Sb in the pinna (>1000 mg kg −1 ) with high translocation (>1) of As and Sb from the root to the pinna. P. vittata displayed apparent preference to the trivalent speciation of As and Sb than to the pentavalent speciation. Under the single exposure of AsIII or SbIII, the pinna concentration of As and Sb was 84 and 765 % higher than that under the single exposure of AsV or SbV, respectively. Despite the provided As speciation, the main speciation of As in the root was AsV, whereas the main speciation of As in the pinna was AsIII. The Sb in the roots comprised SbV and SbIII when exposed to SbV but was exclusively SbIII when exposed to SbIII. The Sb in the pinna was a mixture of SbV and SbIII regardless of the provided Sb speciation. Compared with the single exposure of As, the coexistence of As and Sb increased the As concentration in the pinna of P. vittata by 50-66 %, accompanied by a significant increase in the AsIII percentage in the root. Compared with the single exposure of Sb, the co-existence of Sb and As also increased the Sb concentration in the pinna by 51-100 %, but no significant change in Sb speciation was found in P. vittata.

Confocal Volumetric μXRF and Fluorescence Computed μ-Tomography Reveals Arsenic Three-Dimensional Distribution within IntactPteris vittataFronds

“…Arsenic is transported in the xylem sap of P. vittata predominantly (93-98%) as As(III), regardless of whether As(V) or As(III) was supplied to the plants, implying that the roots are the main site of As(V) reduction in P. vittata 29 . Similar reduction of another metalloid, antimony (Sb), from pentavalent Sb to trivalent Sb has been reported in the roots of P. vittata 30 . However although clearly As(V) is reduced most effectively in root endodermis and then As(III) is transported most effectively in xylem, the identification of As(V) in other tissues means that not all of it is reduced in the root and the As(III) tris-glutathione [As(SR) 3 ] form found in the surroundings of the vasculature suggests that reduction can occur also outside the root 25 .…”

“…vittata is the most well-studied hyperaccumulator. As a consequence, much is now known about the uptake and metabolic regulation of As in this species. ,,,,,,, Nevertheless, many open questions remain, specifically surrounding the adaptive advantages for As hyperaccumulation in this species and about the physiological functions of As­(V) to As­(III) conversion for storage and translocation in the fronds.…”

“…A similar reduction of another metalloid, antimony (Sb), from pentavalent Sb to trivalent Sb has been reported in the roots of P. vittata . However, even if As­(V) is reduced most effectively in the root endodermis and then As­(III) is transported most effectively in the xylem, the identification of As­(V) in other tissues means that not all of it is reduced in the root and the As­(III) tris-glutathione [As­(SR) 3 ] form found in the surroundings of the vasculature suggests that reduction can occur also outside the root …”

“…29 A similar reduction of another metalloid, antimony (Sb), from pentavalent Sb to trivalent Sb has been reported in the roots of P. vittata. 30 However, even if As(V) is reduced most effectively in the root endodermis and then As(III) is transported most effectively in the xylem, the identification of As(V) in other tissues means that not all of it is reduced in the root and the As(III) tris-glutathione [As(SR) 3 ] form found in the surroundings of the vasculature suggests that reduction can occur also outside the root. 25 Despite all the previously cited publications, no study to date has revealed the As-distribution at the cellular-scale in the P. vittata fronds, and previous data has only shown planar views of As (e.g., information projected onto a 2D plane).…”

Arsenic Soil Contamination and Its Effects on 5-Methylcytosine Levels in Onions and Arsenic Distribution and Speciation

“…The most common forms of As in the terrestrial environment are arsenate (As(V)) and arsenite (As(III)), whose toxic effects are caused by different mechanisms, such as the inhibition of oxidative phosphorylation by arsenate or the binding of sulfhydryl groups on proteins by arsenite [ 11 , 12 , 13 ]. Terrestrial plants have evolved protective mechanisms to reduce oxidative stress, usually by transforming inorganic As to less toxic forms, such as reducing arsenate to arsenite by arsenate reductases and complexation with thiolic peptides [ 12 , 13 , 14 , 15 , 16 , 17 ]. Phytochelatins (PCs), which are synthetized by the transpeptidation of [γ-Glu-Cys-]n-Gly glutathion (GSH) tripeptide monomers (n: 2–11), are most commonly present in PC 2 and PC 3 .…”