砷在水稻韧皮部的运输形态对稻米中砷富集的影响研究

Arsenic(As) contamination of rice is a prominent environmental problem. It's reported that phloem transport of As is high correlated to As accumulation in the grain. The speciation and mobility of As transported in rice phloem remains unknown, and the correlation between As speciation in the rice phloem and As speciation in rice grain needs to be further investigated. To help answer these questions, we will study that As speciation transported in rice phloem and the different mobility of different species of As in it by determination of As speciation and concentration of phloem exudates.The chemical species of As and phytochelatins(PCs) in phloem exudates and leaves of rice will be quantified to evolve the possible metablism in it.In addition,we will apply a stem-girdling treatment to the rice, limiting phloem transport to the grain,to reveal the effects of As speciation of phloem transport on As accumulation in rice grain. This study will help to elucidate the mechanisms of As transport, metabolism and accumulation in rice.

近年来稻米中砷（As）污染问题引起人们广泛关注。有研究结果表明，砷在水稻韧皮部的运输对稻米中砷总量的富集至关重要。关于不同种类砷在水稻韧皮部的运输形态，及其对稻米中砷富集形态和浓度的影响尚未明确。本项目拟通过水稻韧皮部液中砷形态和浓度的测试，研究介质中的砷进入水稻体内后在韧皮部的运输形态，及不同形态砷在水稻韧皮部迁移能力的大小；通过韧皮部液和水稻叶片中砷形态及植物络合素的检测，分析砷在韧皮部运输过程中可能发生的形态转化和代谢反应；此外利用蒸汽环割的方式阻断水稻韧皮部的运输，通过对比未环割试验，探明水稻韧皮部砷的运输形态对稻米中砷富集浓度和形态的影响。该研究将为探明水稻对砷的运输、代谢和富集机理奠定理论基础。

为了了解砷是如何在水稻韧皮部的运输，我们进行了此项目的研究。首先我们对水稻暴露于不同形态砷（砷酸盐，亚砷酸盐，单甲基砷和双甲基砷）时其韧皮部砷的运输形态进行研究。研究发现当水稻暴露于砷酸盐时，韧皮部砷的主要形态是As(V)（占58%），而当水稻暴露于亚砷酸盐时，韧皮部砷的主要形态是As(III)（69%）。当对水稻处理甲基化砷时，在其韧皮部发现大量的As(V)（41%-45%）。当营养液中As(V)处理浓度升高时水稻韧皮部中发现高浓度的植物络合物。韧皮部运输对稻米中砷富集的影响主要是通过环割和未环割试验的对比来做的相关研究。通过向水稻处理以相同浓度的亚砷酸盐，砷酸盐，单甲基砷和双甲基砷时，研究结果显示有机砷在韧皮部的运输能力远高于无机砷且在稻米中的富集量高出无机砷数倍。同时研究结果还表明，在亚砷酸盐，砷酸盐，单甲基砷和双甲基砷处理时，环割作用分别降低了稻米中54%、56%、100%和89%的砷含量。营养液中磷酸盐含量的增加显著影响了韧皮部和稻米中砷的总量和As(III)百分比。该研究为探明水稻对砷的运输、代谢和富集机理奠定理论基础。