title: The role of the rice aquaporin Lsi1 in arsenite efflux from roots.
abstract: *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 mum 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.
authors.affiliation: Rothamsted Research, Harpenden, Herts AL5 2JQ, UK.
authors.forename: Fang-Jie
authors.initials: FJ
authors.lastname: Zhao
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Ago
authors.forename: Namiki
authors.initials: N
authors.lastname: Mitani
authors.forename: Ren-Ying
authors.initials: RY
authors.lastname: Li
authors.forename: Yu-Hong
authors.initials: YH
authors.lastname: Su
authors.forename: Naoki
authors.initials: N
authors.lastname: Yamaji
authors.forename: Steve P
authors.initials: SP
authors.lastname: McGrath
authors.forename: Jian Feng
authors.initials: JF
authors.lastname: Ma
mesh_terms: D000818:Animals; D020346:Aquaporins / Q000235:genetics / Q000378:metabolism*; D018053:Arsenites / Q000302:isolation & purification / Q000378:metabolism*; D001681:Biological Assay; D008628:Mercury / Q000633:toxicity; D009154:Mutation / Q000235:genetics; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D012275:Oryza / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism*; D014981:Xenopus
chemical_list: D020346:Aquaporins; D018053:Arsenites; D010940:Plant Proteins; D008628:Mercury; C015001:arsenite