Finnegan Patrick M, Chen Weihua
Faculty of Natural and Agricultural Sciences, School of Plant Biology and Institute of Agriculture, The University of Western Australia Crawley, WA, Australia.
Front Physiol. 2012 Jun 6;3:182. doi: 10.3389/fphys.2012.00182. eCollection 2012.
The two forms of inorganic arsenic, arsenate (AsV) and arsenite (AsIII), are easily taken up by the cells of the plant root. Once in the cell, AsV can be readily converted to AsIII, the more toxic of the two forms. AsV and AsIII both disrupt plant metabolism, but through distinct mechanisms. AsV is a chemical analog of phosphate that can disrupt at least some phosphate-dependent aspects of metabolism. AsV can be translocated across cellular membranes by phosphate transport proteins, leading to imbalances in phosphate supply. It can compete with phosphate during phosphorylation reactions, leading to the formation of AsV adducts that are often unstable and short-lived. As an example, the formation and rapid autohydrolysis of AsV-ADP sets in place a futile cycle that uncouples photophosphorylation and oxidative phosphorylation, decreasing the ability of cells to produce ATP and carry out normal metabolism. AsIII is a dithiol reactive compound that binds to and potentially inactivates enzymes containing closely spaced cysteine residues or dithiol co-factors. Arsenic exposure generally induces the production of reactive oxygen species that can lead to the production of antioxidant metabolites and numerous enzymes involved in antioxidant defense. Oxidative carbon metabolism, amino acid and protein relationships, and nitrogen and sulfur assimilation pathways are also impacted by As exposure. Readjustment of several metabolic pathways, such as glutathione production, has been shown to lead to increased arsenic tolerance in plants. Species- and cultivar-dependent variation in arsenic sensitivity and the remodeling of metabolite pools that occurs in response to As exposure gives hope that additional metabolic pathways associated with As tolerance will be identified.
无机砷的两种形式，砷酸盐（AsV）和亚砷酸盐（AsIII），很容易被植物根系细胞吸收。一旦进入细胞，AsV可以很容易地转化为AsIII，这是两种形式中毒性更强的一种。AsV和AsIII都会破坏植物的新陈代谢，但通过不同的机制。AsV是磷酸盐的化学类似物，可以破坏至少一些依赖磷酸盐的新陈代谢方面。AsV可以通过磷酸盐转运蛋白穿过细胞膜，导致磷酸盐供应失衡。它可以在磷酸化反应中与磷酸盐竞争，导致形成通常不稳定且寿命短暂的AsV加合物。例如，AsV-ADP的形成和快速自水解会引发一个无效循环，使光合磷酸化和氧化磷酸化解偶联，降低细胞产生ATP和进行正常新陈代谢的能力。AsIII是一种二硫醇反应性化合物，它会与含有紧密间隔的半胱氨酸残基或二硫醇辅因子的酶结合并可能使其失活。砷暴露通常会诱导活性氧的产生，这可能导致抗氧化代谢物和许多参与抗氧化防御的酶的产生。氧化碳代谢、氨基酸和蛋白质关系以及氮和硫同化途径也会受到砷暴露的影响。已表明几种代谢途径的重新调整，如谷胱甘肽的产生，会导致植物对砷的耐受性增加。砷敏感性的物种和品种依赖性差异以及因砷暴露而发生的代谢物库重塑，让人希望能识别出与砷耐受性相关的其他代谢途径。
