Abstract
Arsenic (As) is a toxic element for plants and one of the most common anthropogenic pollutants found at contaminated sites. Despite its severe effects on plant metabolism, several species can accumulate substantial amounts of arsenic and endure the associated stress. However, the genetic mechanisms involved in arsenic tolerance remains obscure in many model plant species used for land decontamination (phytoremediation), including willows. The present study assesses the potential of Salix purpurea cv. ‘Fish Creek’ for arsenic phytoextraction and reveals the genetic responses behind arsenic tolerance, phytoextraction and metabolism. Four weeks of hydroponic exposure to 0, 5, 30 and 100 mg/L revealed that plants were able to tolerate up to 5 mg/L arsenic. Concentrations of 0 and 5 mg/L of arsenic treatment were then used to compare alterations in gene expression of roots, stems and leaves using RNA sequencing. Differential gene expression revealed transcripts encoding proteins putatively involved in entry of arsenic into the roots, storage in vacuoles and potential transport through the plant as well as primary and secondary (indirect) toxicity tolerance mechanisms. A major role for tannin as a compound used to relieve cellular toxicity is implicated as well as unexpected expression of the cadmium transporter CAX2, providing a potential means for internal arsenic mobility. These insights into the underpinning genetics of a successful phytoremediating species present novel opportunities for selection of dedicated arsenic tolerant crops as well as the potential to integrate such tolerances into a wider Salix ideotype alongside traits including biomass yield, biomass quality, low agricultural inputs and phytochemical production.
Highlights
Arsenic is a trace element recognized as a worldwide contaminant and health hazard (Martinson and Reddy, 2009)
At a concentration of 5 mg/L of arsenic, treated plants accumulated up to 183 mg/Kg arsenic in their roots while the level was below detection limit (e.g.,
Plants exposed to 30 mg/L arsenic accumulated a concentration of 1,731 mg/Kg in their roots (195 mg total arsenic) and 32 mg/Kg (6 mg total arsenic) in their aboveground tissues
Summary
Arsenic is a trace element recognized as a worldwide contaminant and health hazard (Martinson and Reddy, 2009). Natural geologic activity is thought to be the main source of global arsenic pollution but highly contaminated sites are generally related to anthropogenic activities such as agriculture, mining, as well as the use of arsenic in electronics or as a wood preservative (Mandal and Suzuki, 2002). A metalloid element, is highly toxic to microorganisms, plants and animals (Kaise et al, 1985). Arsenate (AsV) appears to be the most abundant form in aerobic conditions, while arsenite (AsIII) is the major chemical state of this metalloid under a reducing environment (Mandal and Suzuki, 2002). The chemical similarity of the arsenate ion (AsO34−) and phosphate creates competition between both compounds and once inside the cell cytoplasm, arsenate can replace phosphate in respiration processes, disrupting cellular metabolism (generating ADP-As in place of ATP) (Meharg, 1994). Arsenite (AsIII) toxicity is predominantly due to its high reactivity with sulfhydryl groups present in a broad range of metabolic enzymes (Dhankher et al, 2002)
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