High As exposure induced substantial arsenite efflux in As-hyperaccumulator Pteris vittata.

Arsenite (AsIII) efflux is an important mechanism for arsenic (As) detoxification in plants. Low AsIII efflux has been observed in As-hyperaccumulator Pteris vittata, which may contribute to its highly efficient As translocation and accumulation; however, the results may be compromised by microbial AsIII oxidation, relatively low As concentration in the medium and short-term As exposure. Here, sterile P. vittata sporophytes were cultivated in sterile medium containing 10, 200 and 500 µM arsenate (AsV) for 28 d. Arsenite efflux to the growth medium and As speciation in P. vittata was investigated. Low AsIII efflux at 12% of AsV uptake was observed at 10 µM AsV, but high AsIII efflux (36-76%) was observed at 200 and 500 µM AsV, with 1987-2397 mg kg(-1) As being accumulated in the fronds. This is the first report to show efficient AsIII efflux in P. vittata. This study showed that P. vittata may use high AsIII efflux to cope with As toxicity under high As exposure, which may be necessary to sustain growth while accumulating As.