The Rice Aquaporin Lsi1 Mediates Uptake of Methylated Arsenic Species
The Rice Aquaporin Lsi1 Mediates Uptake of Methylated Arsenic Species
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DOI：
10.1104/pp.109.140350
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发表时间：
2009-08-01
期刊：
影响因子：
7.4
通讯作者：
Zhao, Fang-Jie
中科院分区：
文献类型：
--
作者：
Li, Ren-Ying;Ago, Yukiko;Zhao, Fang-Jie
五价甲基化砷（As）物种如单甲基胂酸[MMA（V）]和二甲基胂酸[DMA（V）]用作除草剂或杀虫剂，也可以由土壤微生物或藻类通过As甲基化合成。MMA（V）和DMA（V）摄取的机制仍然未知。最近的研究表明，水稻（Oryza sativa）根通过两个硅转运蛋白Lsi 1（水通道蛋白NIP 2;1）和Lsi 2（外排载体）吸收砷。在这里，我们研究了这两种转运蛋白是否也介导MMA（V）和DMA（V）的摄取。MMA（V）在水稻根中部分还原为三价MMA（III），但只有MMA（V）转移到地上部。DMA（V）在植物体内稳定。与野生型水稻相比，Lsi 1突变体对MMA（V）和DMA（V）的吸收能力分别损失了约80%和50%，而Lsi 2突变体的影响不大。MMA（V）的短期摄取动力学可通过Michaelis-Menten plus线性模型描述，野生型的V-max是lsi 1突变体的3.5倍。DMA（V）的摄取动力学呈线性，野生型的斜率是lsi 1突变体的2.8倍。Lsi 1在非洲爪蟾卵母细胞中的异源表达显著增加了MMA（V）的摄取，但没有DMA（V），可能是因为后者的摄取非常有限。MMA（V）和DMA（V）的野生型水稻的吸收增加的介质的pH值降低，与未解离的物种的比例增加一致。结果表明，Lsi 1介导了水稻根系对未解离甲基化砷的吸收。
Pentavalent methylated arsenic (As) species such as monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)] are used as herbicides or pesticides, and can also be synthesized by soil microorganisms or algae through As methylation. The mechanism of MMA(V) and DMA(V) uptake remains unknown. Recent studies have shown that arsenite is taken up by rice (Oryza sativa) roots through two silicon transporters, Lsi1 (the aquaporin NIP2;1) and Lsi2 (an efflux carrier). Here we investigated whether these two transporters also mediate the uptake of MMA(V) and DMA(V). MMA(V) was partly reduced to trivalent MMA(III) in rice roots, but only MMA(V) was translocated to shoots. DMA(V) was stable in plants. The rice lsi1 mutant lost about 80% and 50% of the uptake capacity for MMA(V) and DMA(V), respectively, compared with the wild-type rice, whereas Lsi2 mutation had little effect. The short-term uptake kinetics of MMA(V) can be described by a Michaelis-Menten plus linear model, with the wild type having 3.5-fold higher V-max than the lsi1 mutant. The uptake kinetics of DMA(V) were linear with the slope being 2.8-fold higher in the wild type than the lsi1 mutant. Heterologous expression of Lsi1 in Xenopus laevis oocytes significantly increased the uptake of MMA(V) but not DMA(V), possibly because of a very limited uptake of the latter. Uptake of MMA(V) and DMA(V) by wild-type rice was increased as the pH of the medium decreased, consistent with an increasing proportion of the undissociated species. The results demonstrate that Lsi1 mediates the uptake of undissociated methylated As in rice roots.