Evidence for exocellular Arsenic in Fronds of Pteris vittata

Abstract

The arsenic (As) hyperaccumulating fern species Pteris vittata (PV) is capable of accumulating large quantities of As in its aboveground tissues. Transformation to AsIII and vacuolar sequestration is believed to be the As detoxification mechanism in PV. Here we present evidence for a preponderance of exocellular As in fronds of Pteris vittata despite numerous reports of a tolerance mechanism involving intracellular compartmentalization. Results of an extraction experiment show that 43–71% of the As extruded out of the fronds of PV grown in 0.67, 3.3 and 6.7 mM AsV. SEM-EDX analysis showed that As was localized largely on the lower pinna surface, with smaller amounts on the upper surface, as crystalline deposits. X-ray fluorescence imaging of pinna cross-sections revealed preferential localization of As on the pinna surface in the proximity of veins, with the majority localized near the midrib. Majority of the As in the pinnae is contained in the apoplast rather than vacuoles. Our results provide evidence that exocellular sequestration is potentially a mechanism of As detoxification in PV, particularly at higher As concentrations, raising concern about its use for phytoremediation.

Synchrotron-Based X-Ray Fluorescence Microscopy as a Technique for Imaging of Elements in Plants

“…Furthermore, XFM analysis showed that As is localized on the pinna surface in the proximity of veins (Fig. 1, C and D) and is present especially in the apoplast (Datta et al, 2017). Speciation imaging techniques have numerous potential applications in plants, but their greatest utility is in situations where different K (red), and Ca (blue).…”

The combination of phytoremediation and electrokinetics remediation technology on arsenic contaminated remediation in tailing storage facilities from gold mine

“…In general, high As accumulation is found in the cortex, epidermis, and xylem of plant roots and stems, similar to iron and phosphate accumulation via phosphate transporters (Seyfferth et al, 2017). As accumulation in leaves occurs only in hyperaccumulators and not in non-hyperaccumulators; As accumulation behavior is similar to that of sulfur, with high accumulation in the collenchyma and lower epidermis and movement through xylem (Datta et al, 2017). The mobility and distribution of aluminum (Al), calcium (Ca), chromium (Cr), potassium (K), manganese (Mn), phosphorus (P), sulfur (S), and zinc (Zn) in the roots, stems, and leaves of Mott dwarf Napier grass were determined to be different (Figure 4).…”

“…In general, high As accumulation is found in the cortex, epidermis, and xylem of plant roots and stems, similar to iron and phosphate accumulation via phosphate transporters ( Seyfferth et al., 2017 ). As accumulation in leaves occurs only in hyperaccumulators and not in non-hyperaccumulators; As accumulation behavior is similar to that of sulfur, with high accumulation in the collenchyma and lower epidermis and movement through xylem ( Datta et al., 2017 ).…”

Arsenic in Pteris vittata is localized to the cell wall in a water-soluble state

“…Furthermore, they also reported a lack of As accumulation in sporocytes, revealing that As does not accumulate evenly throughout the plant tissue. In addition, Datta et al reported that As accumulated in P. vittata may be localized to the extracellular cell wall, rather than intracellularly 13 . However, there is a concern that the condition of the sample may change during the analysis because the sample is irradiated with a powerful beam in µ-XRF.…”