Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK.
College of Resources and Environmental Science, Hebei Agricultural University, Baoding, Hebei Province 071001, China.
New Phytol. 2012 Feb;193(3):665-672. doi: 10.1111/j.1469-8137.2011.03956.x. Epub 2011 Nov 18.
• 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.
• 无机砷（iAs）是一种普遍存在的人类致癌物，而大米（Oryza sativa）是饮食中 iAs 的主要来源。五价甲基砷化物的毒性较低，在植物中通常存在；然而，目前尚不清楚植物是否能够甲基化砷。 • 在无菌条件下，将大米、番茄（Solanum lycopersicum）和红三叶草（Trifolium pratense）暴露于 iAs、一甲基砷酸（MMA(V)) 或二甲基砷酸（DMA(V)) 中。在非无菌淹水条件下，还在两种土壤中种植了水稻幼苗，并用亚砷酸盐或 DMA(V) 暴露的水稻植株在非无菌水培条件下生长成熟。通过 HPLC-ICP-MS 确定样品中的砷形态。 • 在无菌条件下暴露于 iAs 的三种植物中未发现甲基砷化物。在无菌条件下生长的水稻能够吸收 MMA(V) 或 DMA(V)，并将 MMA(V)还原为 MMA(III)，但不能将其转化为 DMA(V)。在土壤中生长的水稻的茎叶中以及非无菌水培培养的水稻籽粒中均检测到了甲基砷。对孟加拉国稻田土壤中微生物基因的 GeoChip 分析显示存在微生物砷甲基转移酶基因 arsM。 • 我们的结果表明，植物不能甲基化 iAs，而是吸收由微生物产生的甲基化 As。
