Selenium Increased Arsenic Accumulation by Upregulating the Expression of Genes Responsible for Arsenic Reduction, Translocation, and Sequestration in Arsenic Hyperaccumulator Pteris vittata.

Selenate enhances arsenic (As) accumulation in As-hyperaccumulator Pteris vittata, but the associated molecular mechanisms are unclear. Here, we investigated the mechanisms of selenate-induced arsenic accumulation by exposing P. vittata to 50 µM arsenate (AsV50) and 1.25 (Se1.25) or 5 µM (Se5) selenate in hydroponics. After 2 weeks, plant biomass, plant As and Se contents, As speciation in plant and growth media, and important genes related to As detoxification in P. vittata were determined. These genes included P transporters PvPht1;3 and PvPht1;4 (AsV uptake), arsenate reductases PvHAC1 and PvHAC2 (AsV reduction), and arsenite (AsIII) antiporters PvACR3 and PvACR3;2 (AsIII translocation) in the roots, and AsIII antiporters PvACR3;1 and PvACR3;3 (AsIII sequestration) in the fronds. The results show that Se1.25 was more effective than Se5 in increasing As accumulation in both P. vittata roots and fronds, which increased by 27 and 153% to 353 and 506 mg kg-1. The As speciation analyses show that selenate increased the AsIII levels in P. vittata, with 124-282% more AsIII being translocated into the fronds. The qPCR analyses indicate that Se1.25 upregulated the gene expression of PvHAC1 by 1.2-fold, and PvACR3 and PvACR3;2 by 1.0- to 2.5-fold in the roots, and PvACR3;1 and PvACR3;3 by 0.6- to 1.1-fold in the fronds under AsV50 treatment. Though arsenate enhanced gene expression of P transporters PvPht1;3 and PvPht1;4, selenate had little effect. Our results indicate that selenate effectively increased As accumulation in P. vittata, mostly by increasing reduction of AsV to AsIII in the roots, AsIII translocation from the roots to fronds, and AsIII sequestration into the vacuoles in the fronds. The results suggest that selenate may be used to enhance phytoremediation of As-contaminated soils using P. vittata.

Arsenic induced plant growth by increasing its nutrient uptake in As-hyperaccumulator Pteris vittata: Comparison of arsenate and arsenite.

Arsenic-hyperaccumulator Pteris vittata is efficient in taking up arsenate (AsV) and arsenite (AsIII), however, their impacts on P. vittata growth and nutrient uptake remain unclear. The uptake of AsV and AsIII, their influences on nutrient uptake and plant biomass, and As speciation were investigated in P. vittata after exposing to 5 or 50 µM AsV or AsIII for 12 d under hydroponics. The results show that AsV uptake in P. vittata was 1.2 times more efficient than AsIII, corresponding to 1.7-2.1 fold greater biomass than the control at 50 µM As. While AsV was dominant in the roots at ∼60%, AsIII was more dominant in the fronds at ∼70% in all treatments. Macronutrients P, K, Ca, and S were increased by 118-185% at 50 µM As, with greater uptake of micronutrients Fe, Mn, Cu, and Zn at 5 µM As. Further, positive correlations between P. vittata biomass and its As contents (r = 0.97), and P. vittata biomass and its S, Mg, P, or Ca contents (r = 0.70-0.98) were observed. Our results suggest that its increased nutrient uptake probably enhanced P. vittata growth under As exposure.

Antimony uptake and speciation, and associated mechanisms in two As-hyperaccumulators Pteris vittata and Pteris cretica.

The behaviors of antimony (Sb) and arsenic (As) in plants are different, though they are chemical analogs. Here, we examined the Sb uptake and speciation in two As-hyperaccumulators P. vittata and P. cretica, which were exposed to 0.5 or 5 mg L-1 antimonate (SbV) or antimonite (SbIII) under hydroponics for 7 d. Both plants grew better under Sb exposure, especially for P. cretica. The biomass of P. cretica roots increased by 29-46% after exposing to SbV, possibly due to increased S. Further, the Sb content in P. vittata was 17-93% greater than P. cretica, with 2-3 times more SbIII than SbV in both plants and > 92% Sb being concentrated in the roots, showing limited translocation. Under SbV exposure, SbV was dominant in P. vittata roots at 86-94%, while SbIII was predominant in P. cretica roots at 36-95%. P. cretica's stronger reducing ability than P. vittata may be due to arsenate reductases HAC1 and ACR2, which were upregulated in both plants. In short, while effective in Sb accumulation, it is mostly concentrated in the roots for both plants. The differences in their accumulation and speciation may help to better understand Sb behaviors in other plants.

Copper enhanced arsenic-accumulation in As-hyperaccumulator Pteris vittata by upregulating its gene expression for As uptake, translocation, and sequestration.

In contaminated soils, arsenic (As) often co-exists with copper (Cu). However, its effects on As accumulation and the related mechanisms in As-hyperaccumulator Pteris vittata remain unclear. In this study, P. vittata plants were exposed to 50 µM As and/or 50 µM Cu under hydroponics to investigate the effects of Cu on plant growth and As accumulation, as well as gene expression related to arsenic uptake (P transporters), reduction (arsenate reductases), and translocation and sequestration (arsenite antiporters). After 14 d of growth and compared to the As treatment, the As concentration in P. vittata fronds increased by 1.4-times from 793 to 1131 mg·kg-1 and its biomass increased by 1.2-fold from 18.0 to 21.1 g·plant-1 in the As+Cu treatment. Copper-enhanced As accumulation was probably due to upregulated gene expressions related to As-metabolisms including As uptake (1.9-fold in P transporter PvPht1;3), translocation (2.1-2.4 fold in arsenite antiporters PvACR3/3;2) and sequestration (1.5-2.0 fold in arsenite antiporters PvACR3;1/3;3). Our results suggest that moderate amount of Cu can help to increase the As accumulation efficiency in P. vittata, which has implication in its application in phytoremedation in As and Cu co-contaminated soils.