Methylated arsenic species in plants originate from soil microorganisms

Charlotte Lomax, Wen-Ju Liu, Liyou Wu, Kai Xue, Jinbo Xiong, Jizhong Zhou, Steve P. McGrath, Andrew A. Meharg, Anthony J. Miller, Fang-Jie Zhao

Research output: Contribution to journalArticlepeer-review

203 Citations (Scopus)

Abstract

Inorganic arsenic (iAs) is a ubiquitous human carcinogen, and rice (Oryza sativa) is the main contributor to iAs in the diet. Methylated pentavalent As species are less toxic and are routinely found in plants; however, it is currently unknown whether plants are able to methylate As. Rice, tomato (Solanum lycopersicum) and red clover (Trifolium pratense) were exposed to iAs, monomethylarsonic acid (MMA(V)), or dimethylarsinic acid (DMA(V)), under axenic conditions. Rice seedlings were also grown in two soils under nonsterile flooded conditions, and rice plants exposed to arsenite or DMA(V) were grown to maturity in nonsterile hydroponic culture. Arsenic speciation in samples was determined by HPLC-ICP-MS. Methylated arsenicals were not found in the three plant species exposed to iAs under axenic conditions. Axenically grown rice was able to take up MMA(V) or DMA(V), and reduce MMA(V) to MMA(III) but not convert it to DMA(V). Methylated As was detected in the shoots of soil-grown rice, and in rice grain from nonsterile hydroponic culture. GeoChip analysis of microbial genes in a Bangladeshi paddy soil showed the presence of the microbial As methyltransferase gene arsM. Our results suggest that plants are unable to methylate iAs, and instead take up methylated As produced by microorganisms.

Original languageEnglish
Pages (from-to)665-672
Number of pages8
JournalNew Phytologist
Volume193
Issue number3
Early online date18 Nov 2011
DOIs
Publication statusPublished - Feb 2012

Keywords

  • arsenic
  • arsenic methylation
  • arsenic speciation
  • food safety
  • Oryza sativa (rice)
  • dietary exposure
  • rice cultivars
  • grain
  • accumulation
  • metabolism
  • speciation
  • toxicity
  • water
  • methyltransferase
  • translocation

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