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研究报告

A comparative study of inorganic and methylated arsenic on absorption and transportation in rice plants

摘要：由于含甲基砷的农药残留或土壤中微生物的砷甲基化作用,除了无机砷,水稻籽粒中也可以检测到相当含量的不同形态的甲基砷.通过水培试验研究了不同形态砷在水稻幼苗中的吸收、转运、转化和外排.结果表明,水稻中各形态砷的含量排序为:亚砷酸盐(As(Ⅲ))>单甲基砷盐(MMA(Ⅴ))>砷酸盐(As(Ⅴ))>二甲基砷盐(DMA(Ⅴ)),但从地下部向地上部的转运系数排序为:DMA(Ⅴ)>As(Ⅲ)>As(Ⅴ)>MMA(Ⅴ).实验中未发现水稻体内无机砷向甲基砷的转化,甲基砷向无机砷的转化比例也较低,但观察到MMA(Ⅴ)部分被还原为MMA(Ⅲ).相比其地上部和地下部的吸收量,DMA(Ⅴ)在水稻中通过木质部(向上)和韧皮部(向下)的转运比例在4种形态砷中最高.甲基砷(MMA(Ⅴ)和DMA(Ⅴ))通过根系外排的速率和比例明显的高于无机砷(As(Ⅲ)和As(Ⅴ)).实验结果表明,不同形态砷的累积与其在水稻体内的吸收、运移及砷的根系外排密切相关.

Abstract：Due to the use of herbicides or pesticides and the As methylation in soil by microbes,methylated As were also detected in rice grains,on top of the inorganic As.Rice culture in solution was conducted to investigate the uptake,transportation,transformation and efflux of the inorganic As (As(Ⅲ) and As(Ⅴ)) and methylated As (MMA(Ⅴ) and DMA(Ⅴ)) species.The results showed that uptake efficiency of As into rice roots was in the order of As(Ⅲ) > MMA(Ⅴ) > As(Ⅴ) > DMA(Ⅴ),but the transportation index (T_i) from root to shoot followed the order of DMA(Ⅴ) > As(Ⅲ) > As(Ⅴ) > MMA(Ⅴ).No methylated As was observed in rice plants by the inorganic As treatments,and the demethylation of organic As in rice plants by the methylated As treatments was also in small proportion.However,a small portion of MMA(Ⅴ) in rice plants was reduced to MMA(Ⅲ) in the MMA(Ⅴ) treatment.The DMA(Ⅴ) transported much faster upwards and downwards in rice plants than the other As species in xylem sap and phloem sap,compared to its concentrations in shoots and roots.The efflux of methylated As species in roots were also much faster than the inorganic As species.The results showed that the accumulation of different As species was dependent on the absorption and transportation of As in rice plants,and also the efflux of As out of the roots.