title: Arsenite efflux is not enhanced in the arsenate-tolerant phenotype of Holcus lanatus.
abstract: Arsenate tolerance in Holcus lanatus is achieved mainly through suppressed arsenate uptake. We recently showed that plant roots can rapidly efflux arsenite to the external medium. Here, we tested whether arsenite efflux is a component of the adaptive arsenate tolerance in H. lanatus. Tolerant and nontolerant phenotypes were exposed to different arsenate concentrations with or without phosphate for 24 h, and arsenic (As) speciation was determined in nutrient solutions, roots and xylem sap. At the same arsenate exposure concentration, the nontolerant phenotype took up more arsenate and effluxed more arsenite than the tolerant phenotype. However, arsenite efflux was proportional to arsenate uptake and was not enhanced in the tolerant phenotype. Within 2-24 h, most (80-100%) of the arsenate taken up was effluxed to the medium as arsenite. About 86-95% of the As in the roots and majority of the As in xylem sap (c. 66%) was present as arsenite, and there were no significant differences between phenotypes. Arsenite efflux is not adaptively enhanced in the tolerant phenotype H. lanatus, but it could be a basal tolerance mechanism to greatly decrease cellular As burden in both phenotypes. Tolerant and nontolerant phenotypes had a similar capacity to reduce arsenate in roots.
authors.affiliation: Rothamsted Research, Harpenden, Herts AL5 2JQ, UK.|Dipartimento di Biotecnologie per il Monitoraggio Agro-alimentare ed Ambientale (BIOMAA), Universita' Mediterranea di Reggio Calabria, Facolta' di Agraria - Loc. Feo di Vito, I-89060 Reggio Calabria, Italia.
authors.forename: B
authors.initials: B
authors.lastname: Logoteta
authors.affiliation: Rothamsted Research, Harpenden, Herts AL5 2JQ, UK.|Tianjin Agriculture University, Tianjin 300384, China; and.
authors.forename: X Y
authors.initials: XY
authors.lastname: Xu
authors.affiliation: School of Biosciences, University of Exeter, Exeter EX4 4PS, UK.
authors.forename: M R
authors.initials: MR
authors.lastname: Macnair
authors.affiliation: Rothamsted Research, Harpenden, Herts AL5 2JQ, UK.
authors.forename: S P
authors.initials: SP
authors.lastname: McGrath
authors.affiliation: Rothamsted Research, Harpenden, Herts AL5 2JQ, UK.
authors.forename: F J
authors.initials: FJ
authors.lastname: Zhao
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D001149:Arsenates / Q000378:metabolism / Q000494:pharmacology*; D018053:Arsenites / Q000378:metabolism*; D031752:Holcus / Q000187:drug effects* / Q000378:metabolism*; D010641:Phenotype; D010710:Phosphates / Q000494:pharmacology; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D012996:Solutions; D052584:Xylem / Q000187:drug effects / Q000378:metabolism
chemical_list: D001149:Arsenates; D018053:Arsenites; D010710:Phosphates; D012996:Solutions; C015001:arsenite