Arsenic distribution and speciation in the fronds of the hyperaccumulator Pteris vittata

Abstract

Summary• Pteris vittata is the first plant reported to be a hyperaccumulator of arsenic (As), and little is known about the mechanisms of As hyperaccumulation in this plant.• Arsenic distribution at the whole plant (fronds) and cellular level was investigated using chemical analyses and energy dispersive X-ray microanalyses (EDXA). Speciation of As in the fronds was determined using X-ray absorption near edge spectroscopy (XANES) analyses.• The majority of As was found in the pinnae (96% of total As). The concentration of As in pinnae decreased from the base to the apex of the fronds. Arsenic concentrations in spores and midribs were much lower than in the pinnae. EDXA analyses revealed that As was compartmentalized mainly in the upper and lower epidermal cells, probably in the vacuoles. The distribution pattern of potassium was similar to As, whereas other elements (Ca, Cl, K, Mg, P and S) were distributed differently.• XANES analyses showed that approximately 75% of the As in fronds was present in the As(III) oxidation state and the remaining as As(V).

Characterization of Arsenate Reductase in the Extract of Roots and Fronds of Chinese Brake Fern, an Arsenic Hyperaccumulator

“…2). Arsenite is then transported to shoots, where it may be stored in the vacuoles (Lombi et al, 2002). Pickering et al (2000) showed a similar behavior of As in Indian mustard, where arsenate was also reduced to arsenite in roots and transported to shoots in the reduced form.…”

“…Although arsenite is more toxic than arsenate, plants may have specific transporters to pump arsenite to the vacuole, as Lombi et al (2002) reported that As is stored primarily in the vacuole of Chinese brake fern. The reason for the reduction could then be looked at as a means of preparing for arsenite translocation (out of the cell or into the vacuole) without interfering with the phosphate status of the cells.…”

“…However, the proportion of As complexed with phytochelatins relative to the total As was small (about 1%) in As-treated Chinese brake fern (Zhao et al, 2003;Raab et al, 2004), and the actual mechanism is not yet fully known. Nevertheless, in the fronds of Chinese brake fern grown in the presence of arsenate, arsenite is the main storage form of As (.85%; Lombi et al, 2002;Wang et al, 2002;Zhang et al, 2002) and is mainly stored in the vacuoles (Lombi et al, 2002). This information suggests that the reduction of arsenate to arsenite may be a key step in the detoxification pathways.…”

Multivariate analysis of elements in chinese brake fern as determined using neutron activation analysis

“…In this study, the correlation between As and K, Na, La, and Sm revealed by multivariate analysis might suggest that the four cations act as antagonists to As during uptake and transportation. An EXAFS study found that As tends to accumulate in the cell walls and vacuoles in the Chinese brake fern with K (19,20), whereas Na is not an essential element for the plant, but it also tends to be stored in the cell walls and vacuoles (29). La and Sm belong to rare earth elements (REEs) and plants tend to uptake and accumulate them (30).…”

“…High-performance liquid chromatography-mass spectrometry (HPLC-MS) and synchrotron radiation extended X-ray absorption fine structure EXAFS studies have reveled that As exists mainly as inorganic arsenite and arsenate forms in the Chinese brake fern, with arsenite as the major form (18)(19)(20). These highlight the importance of the correlation between As and other elements, as plants usually take up elements in a synergic or antagonistic way in their transportation and, through these, to get an ion balance (21).…”