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Keywords:

  • aquaporin;
  • arsenic accumulation;
  • arsenite (As(III)) efflux;
  • rice;
  • silicon transporter

Summary

  • When supplied with arsenate (As(V)), plant roots extrude a substantial amount of arsenite (As(III)) to the external medium through as yet unidentified pathways. The rice (Oryza sativa) silicon transporter Lsi1 (OsNIP2;1, an aquaporin channel) is the major entry route of arsenite into rice roots. Whether Lsi1 also mediates arsenite efflux was investigated.
  • Expression of Lsi1 in Xenopus laevis oocytes enhanced arsenite efflux, indicating that Lsi1 facilitates arsenite transport bidirectionally.
  • Arsenite was the predominant arsenic species in arsenate-exposed rice plants. During 24-h exposure to 5 μm arsenate, rice roots extruded arsenite to the external medium rapidly, accounting for 60–90% of the arsenate uptake. A rice mutant defective in Lsi1 (lsi1) extruded significantly less arsenite than the wild-type rice and, as a result, accumulated more arsenite in the roots. By contrast, Lsi2 mutation had little effect on arsenite efflux to the external medium.
  • We conclude that Lsi1 plays a role in arsenite efflux in rice roots exposed to arsenate. However, this pathway accounts for only 15–20% of the total efflux, suggesting the existence of other efflux transporters.