title: Selenium addition alters mercury uptake, bioavailability in the rhizosphere and root anatomy of rice (Oryza sativa).
abstract: OBJECTIVE
  Mercury (Hg) is an extremely toxic pollutant, especially in the form of methylmercury (MeHg), whereas selenium (Se) is an essential trace element in the human diet. This study aimed to ascertain whether addition of Se can produce rice with enriched Se and lowered Hg content when growing in Hg-contaminated paddy fields and, if so, to determine the possible mechanisms behind these effects.
  
  
  METHODS
  Two cultivars of rice (Oryza sativa, japonica and indica) were grown in either hydroponic solutions or soil rhizobags with different Se and Hg treatments. Concentrations of total Hg, MeHg and Se were determined in the roots, shoots and brown rice, together with Hg uptake kinetics and Hg bioavailability in the soil. Root anatonmy was also studied.
  
  
  RESULTS
  The high Se treatment (5 μg g(-1)) significantly increased brown rice yield by 48 % and total Se content by 2·8-fold, and decreased total Hg and MeHg by 47 and 55 %, respectively, compared with the control treatments. The high Se treatment also markedly reduced 'water-soluble' Hg and MeHg concentrations in the rhizosphere soil, decreased the uptake capacity of Hg by roots and enhanced the development of apoplastic barriers in the root endodermis.
  
  
  CONCLUSIONS
  Addition of Se to Hg-contaminated soil can help produce brown rice that is simultaneously enriched in Se and contains less total Hg and MeHg. The lowered accumulation of total Hg and MeHg appears to be the result of reduced bioavailability of Hg and production of MeHg in the rhizosphere, suppression of uptake of Hg into the root cells and an enhancement of the development of apoplastic barriers in the endodermis of the roots.
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, PR China.
authors.forename: Xun
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Biology and Chemistry, City University of Hong Kong, Hong Kong SAR, PR China State Key Laboratory in Marine Pollution, City University of Hong Kong, Hong Kong SAR, PR China.
authors.forename: Nora Fung-Yee
authors.initials: NF
authors.lastname: Tam
authors.affiliation: Fine Arts College, Sichuan Normal University, Chengdu 610110, PR China.
authors.forename: Shi
authors.initials: S
authors.lastname: Fu
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, PR China.
authors.forename: Aray
authors.initials: A
authors.lastname: Ametkhan
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, PR China.
authors.forename: Yun
authors.initials: Y
authors.lastname: Ouyang
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, PR China lssyzhh@mail.sysu.edu.cn.
authors.forename: Zhihong
authors.initials: Z
authors.lastname: Ye
mesh_terms: D001682:Biological Availability; D007700:Kinetics; D008628:Mercury / Q000378:metabolism*; D008767:Methylmercury Compounds; D012275:Oryza / Q000033:anatomy & histology* / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D018517:Plant Roots / Q000033:anatomy & histology* / Q000187:drug effects; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D058441:Rhizosphere; D012643:Selenium / Q000494:pharmacology*; D012987:Soil / Q000737:chemistry; D012995:Solubility; D014867:Water / Q000737:chemistry
chemical_list: D008767:Methylmercury Compounds; D012987:Soil; D014867:Water; D008628:Mercury; D012643:Selenium
keywords: Apoplastic barriers; Hg bioavailability; Oryza sativa; Se addition; mercury pollution; methylmercury; rice; root endodermis; selenium; uptake process