The role of phytochelatins in arsenic tolerance in the hyperaccumulator Pteris vittata

Abstract

Summary Pteris vittata was the first identified arsenic (As) hyperaccumulator. Here we investigated whether phytochelatins (PCs) are involved in the hypertolerance of arsenic by P. vittata. P. vittata was exposed to 0–500 µm arsenate for 5 d, or to 50 µm arsenate for 0–7 d. In addition, l‐buthionine‐sulphoximine (BSO), an inhibitor of γ‐glutamylcysteine synthetase, was used in combination with different arsenate exposures. The relationships between As accumulation and the concentrations of PCs and glutathione (GSH) were examined. PC synthesis was induced upon exposure to arsenate in P. vittata, with only PC2 detected in the plant. The As concentration correlated significantly with PC2 concentration in both roots and shoots, but not with GSH. The molar ratio of PC‐SH to As was c. 0.09 and 0.03 for shoots and roots, respectively, suggesting that only a small proportion (1–3%) of the As in P. vittata can be complexed with PCs. In the presence of arsenate, addition of BSO decreased PC2 concentrations in roots and shoots by 89–96% and 30–33%, respectively. BSO alone was found to inhibit root growth of P. vittata markedly. The results suggest that PCs play a limited role in the hypertolerance of As in P. vittata.

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

“…Enzymatic reduction does not take place in measurable amounts in the fronds. Based on these and reported results (Wang et al, 2002;Zhao et al, 2003;Raab et al, 2004), we believe that arsenate reduction in roots is an important step in arsenic hyperaccumulation by Chinese brake fern.…”

“…With the information reported so far (Wang et al, 2002;Zhao et al, 2003;Raab et al, 2004) and obtained from this study, it is expected that arsenate is taken up by roots via phosphate transporters and is then reduced to arsenite. 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.…”

“…Many plants use enhanced synthesis of phytochelatins to detoxify toxic metals (Grill et al, 1985;Kneer et al, 1992;Schmoger et al, 2000). 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).…”

Screening Indian Mustard Genotypes for Phytoremediating Arsenic‐Contaminated Soils

“…As has been shown to inhibit the lengths of root and shoot in plants [2,28]. The reduction in growth may be due to negative effects of As on cell metabolism, such as energy being channeled into the production of stress-related substances like antioxidases [2,35] and phytochelatins [36,37].Growth inhibition at higher concentrations may be linked with lower mitotic activity in the root meristematic zone or the inhibition of cell enlargement in the elongation zone as a consequence of decreased cellular turgor [30,38]. Root lengthening is controlled by the cell division rate in the apical meristems and by expansion and elongation of the newly formed cells and is considered to be one of the most sensitive endpoints of plant toxicity, where a dose-dependent inhibition of root growth (and of the whole plant), following the administration of relatively high doses of As, has been reported for wheat [26], mung bean [39], Arabidopsis thaliana [40], broad bean [41], and rice [29,42].…”

The contents of free amino acids and elements in As-hyperaccumulator Pteris cretica and non-hyperaccumulator Pteris straminea during reversible senescence

“…The phytochelatins play a key role in As (arsenic) detoxification in non-hyperaccumulators (Raab et al 2004). In contrast to non-hyperaccumulators, hyperaccumulators complex only 1-3% As with phytochelatins (Zhao et al 2003, Vetterlein et al 2009), because As detoxification is associated with the conversion of As V to As III and As methylation (Gonzaga et al 2006). The low As content in Pteris hyperaccumulators promotes plant growth; a high content inhibits growth (Cao et al 2004).…”