title: Phloem transport of arsenic species from flag leaf to grain during grain filling.
abstract: • Strategies to reduce arsenic (As) in rice grain, below concentrations that represent a serious human health concern, require that the mechanisms of As accumulation within grain be established. Therefore, retranslocation of As species from flag leaves into filling rice grain was investigated. • Arsenic species were delivered through cut flag leaves during grain fill. Spatial unloading within grains was investigated using synchrotron X-ray fluorescence (SXRF) microtomography. Additionally, the effect of germanic acid (a silicic acid analog) on grain As accumulation in arsenite-treated panicles was examined. • Dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) were extremely efficiently retranslocated from flag leaves to rice grain; arsenate was poorly retranslocated, and was rapidly reduced to arsenite within flag leaves; arsenite displayed no retranslocation. Within grains, DMA rapidly dispersed while MMA and inorganic As remained close to the entry point. Germanic acid addition did not affect grain As in arsenite-treated panicles. Three-dimensional SXRF microtomography gave further information on arsenite localization in the ovular vascular trace (OVT) of rice grains. • These results demonstrate that inorganic As is poorly remobilized, while organic species are readily remobilized, from leaves to grain. Stem translocation of inorganic As may not rely solely on silicic acid transporters.
authors.affiliation: Institute of Biological and Environmental Sciences, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Carey
authors.affiliation: Institute of Biological and Environmental Sciences, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK.
authors.forename: Gareth J
authors.initials: GJ
authors.lastname: Norton
authors.affiliation: Institute of Biological and Environmental Sciences, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK.
authors.forename: Claire
authors.initials: C
authors.lastname: Deacon
authors.affiliation: National Risk Management Research Laboratory, US Environmental Protection Agency, 5995 Centre Hill Avenue, Cincinnati, OH 45224, USA.
authors.forename: Kirk G
authors.initials: KG
authors.lastname: Scheckel
authors.affiliation: Centre for Environmental Risk Assessment and Remediation, University of South Australia, Building X, Mawson Lakes Campus Mawson Lakes, S. Australia, SA-5095 Australia.
authors.forename: Enzo
authors.initials: E
authors.lastname: Lombi
authors.affiliation: Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA.
authors.forename: Tracy
authors.initials: T
authors.lastname: Punshon
authors.affiliation: Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA.
authors.forename: Mary Lou
authors.initials: ML
authors.lastname: Guerinot
authors.affiliation: Centre for Advanced Radiation Sources, the University of Chicago, Chicago, IL 60637, USA.
authors.forename: Antonio
authors.initials: A
authors.lastname: Lanzirotti
authors.affiliation: Centre for Advanced Radiation Sources, the University of Chicago, Chicago, IL 60637, USA.
authors.forename: Matt
authors.initials: M
authors.lastname: Newville
authors.affiliation: Centre for Advanced Radiation Sources, the University of Chicago, Chicago, IL 60637, USA.
authors.forename: Yongseong
authors.initials: Y
authors.lastname: Choi
authors.affiliation: Institute of Biological and Environmental Sciences, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK.
authors.forename: Adam H
authors.initials: AH
authors.lastname: Price
authors.affiliation: Institute of Biological and Environmental Sciences, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Meharg
mesh_terms: D001151:Arsenic / Q000378:metabolism*; D001692:Biological Transport; D005453:Fluorescence; D005857:Germanium / Q000378:metabolism; D006801:Humans; D021621:Imaging, Three-Dimensional; D012275:Oryza / Q000378:metabolism*; D052585:Phloem / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism*; D012639:Seeds / Q000378:metabolism*; D056928:X-Ray Absorption Spectroscopy; D052584:Xylem / Q000378:metabolism
chemical_list: D005857:Germanium; D001151:Arsenic