Uptake and translocation of arsenite and arsenate by Pteris vittata L.: Effects of silicon, boron and mercury

To better understand arsenite (AsIII) uptake via aquaporin channels by arsenic hyperaccumulator Pteris vittata, the effects of silicic and boric acid (AsIII analogues) and HgCl2 (aquaporin inhibitor) on plant arsenic uptake and translocation were investigated. P. vittata was grown in 0.2-strength Hoagland solution containing (1) 15 μM AsIII or arsenate (AsV) for 1 d with or without 0.5 mM silicic acid (Si experiment) or 0.3 mM boric acid (B experiment), or (2) 15 μM AsIII for 2 d with or without 10 μM HgCl2 (Hg experiment). Silicic acid and boric acid had no effect on AsIII and AsV uptake by P. vittata, nor did HgCl2. It is possible that AsIII was taken up by different aquaporins in P. vittata or those aquaporins in P. vittata had high capacity and they were insensitive to Hg. While AsV was stable in the growth media, substantial amount of AsIII was oxidized to AsV, i.e., 16–76%. In the presence of 210 μM P at pH 6, P. vittata was more efficient in taking up and translocating AsIII than AsV as demonstrated by greater arsenic concentrations in the fronds and roots (6.6 and 46 mg kg−1) in the AsIII treatment than those in the AsV treatment (2.3 and 8.2 mg kg−1). However, at 15 μM AsIII, its AsIII translocation rate from the roots to the fronds was slower than its AsIII uptake rate by the roots since the arsenic concentration in the fronds was only ∼14% of that in the roots. Our data also demonstrated that both AsIII oxidation and AsV reduction occurred in the roots of P. vittata. However, how and if AsIII uptake by P. vittata is via aquaporins still need further investigation.