Arsenic contamination is a major environmental issue, as it may lead to serious health hazard. The reduced trivalent form of inorganic arsenic, arsenite, is in general more toxic to plants compared with the fully oxidized pentavalent arsenate. The uptake of arsenite in plants has been shown to be mediated through a large subfamily of plant aquaglyceroporins, nodulin 26-like intrinsic proteins (NIPs). However, the efflux mechanisms, as well as the mechanism of arsenite-induced root growth inhibition, remain poorly understood. Using molecular physiology, synchrotron imaging, and root transport assay approaches, we show that the cellular transport of trivalent arsenicals in Arabidopsis thaliana is strongly modulated by PIN FORMED 2 (PIN2) auxin efflux transporter. Root transport assay using radioactive arsenite, X-ray fluorescence imaging (XFI) coupled with X-ray absorption spectroscopy (XAS), and inductively coupled plasma mass spectrometry analysis revealed that pin2 plants accumulate higher concentrations of arsenite in roots compared with the wild-type. At the cellular level, arsenite specifically targets intracellular sorting of PIN2 and thereby alters the cellular auxin homeostasis. Consistently, loss of PIN2 function results in arsenite hypersensitivity in roots. XFI coupled with XAS further revealed that loss of PIN2 function results in specific accumulation of arsenical species, but not the other metals such as iron, zinc, or calcium in the root tip. Collectively, these results suggest that PIN2 likely functions as an arsenite efflux transporter for the distribution of arsenical species in planta.

砷污染是一个主要的环境问题，因为它可能导致严重的健康危害。与完全氧化的五价砷酸盐相比，无机砷的还原三价形式亚砷酸盐通常对植物毒性更大。植物中亚砷酸盐的摄取已被证明是通过植物水甘油通道蛋白的一个大亚家族，即类结蛋白 26 的内在蛋白 (NIP) 介导的。然而，外排机制以及亚砷酸盐诱导的根系生长抑制机制仍然知之甚少。使用分子生理学、同步加速器成像和根转运测定方法，我们表明三价砷在拟南芥中的细胞转运受到 PIN FORMED 2 (PIN2) 生长素流出转运蛋白的强烈调节。使用放射性亚砷酸盐、X 射线荧光成像 (XFI) 结合 X 射线吸收光谱 (XAS) 和电感耦合等离子体质谱分析的根转运测定表明pin2与野生型相比，植物在根部积累了更高浓度的亚砷酸盐。在细胞水平上，亚砷酸盐专门针对 PIN2 的细胞内分选，从而改变细胞生长素稳态。始终如一地，PIN2 功能的丧失导致根中的亚砷酸盐超敏反应。XFI 与 XAS 结合进一步揭示了 PIN2 功能的丧失导致砷种类的特定积累，而不是根尖中的铁、锌或钙等其他金属的积累。总的来说，这些结果表明 PIN2 可能作为亚砷酸盐外排转运蛋白在植物中的砷物种分布中发挥作用。