Transcriptomic Response of Purple Willow (Salix purpurea) to Arsenic Stress

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.

Assessment of Water Mimosa (Neptunia oleracea Lour.) Morphological, Physiological, and Removal Efficiency for Phytoremediation of Arsenic-Polluted Water

“…Each of the arsenic concentrations applied to the water mimosas had significant detrimental effects on the plants' growth and development. These results are in parallel with reports on other high-tolerance species such as Salix purpurea (Purple willow) [45], Pteris vittata (Chinese brake) [46], Oryza sativa (rice) [47], and Typha latifolia [48]. It has been shown that severe concentration of arsenic dosages inhibited the normal life cycle of plants and in the detrimental phase, could kill plants.…”

“…However, this plant also showed general plant dysfunction at high concentrations. The same results were achieved in a study on purple willow (Salix purpurea) under 30 and 100 ppm arsenic concentrations [45]. Interestingly, water hyacinths treated with 70 and 100 ppm arsenic showed the same absorption of foliar-applied arsenic with the arsenic hyper-accumulating fern (Pteris vittata L.) [78].…”

“…Plants exposed to 70 mg L −1 arsenic accumulated a concentration of 17 mg Kg −1 in their roots (0.97 mg total arsenic) and the highest accumulation was recorded at 30 ppm with 28.192 mg Kg −1 (0.3 mg total arsenic). Although arsenic has been recorded at the lowest arsenic treatment, small amounts of arsenic potentially have been translocated from the growth solution to the leaves [45]. A comparison of the amount of arsenic in plants and water showed that almost all arsenic accumulation was retained in the roots at 70 ppm and only a small amount was translocated to the shoots.…”

Arsenic forms in phytoextraction of this metalloid in organs of 2-year-old Acer platanoides seedlings

“…Inorganic arsenite (As(III)) and arsenate (As(V)) are the dominant forms in water and soil. As(V) is the major form in aerobic conditions, whereas As(III) is the most abundant under a reducing environment (Yanitch et al 2017 ). Inorganic As can be converted in plants to two organic forms (monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA)) present in extensive amounts (Mishra et al 2017 ; Zhu et al 2017 ).…”

“…The high survivability and easy adaptation of trees, undisturbed growth, and effective phytoextraction of toxic elements/metalloids make them highly suitable for remediation of substrates polluted by As forms. The chemical structure of As(V) is similar to phosphorus (P); therefore, it can be easily incorporated through phosphate (Pi) transporters into plants (Yanitch et al 2017 ). As(III) is similar to sulfur (S), which is uptaken from substrate by nodulin26-like intrinsic aquaporin channels (NIPs) and bounds to the sulfhydryl groups of peptides and proteins inhibiting their activity (Mishra et al 2017 ).…”