Lee David A, Chen Alice, Schroeder Julian I
Division of Biology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0116, USA.
Plant J. 2003 Sep;35(5):637-46. doi: 10.1046/j.1365-313x.2003.01835.x.
Arsenic is one of the most toxic pollutants at contaminated sites, yet little is known about the mechanisms by which certain plants survive exposure to high arsenic levels. To gain insight into the mechanisms of arsenic tolerance in plants, we developed a genetic screen to isolate Arabidopsis thaliana mutants with altered tolerance to arsenic. We report here on the isolation of a mutant arsenic resisant 1 (ars1) with increased tolerance to arsenate. ars1 germinates and develops under conditions that completely inhibit growth of wild-type plants and shows a semi-dominant arsenic resistance phenotype. ars1 accumulates levels of arsenic similar to that accumulated by wild-type plants, suggesting that ars1 plants have an increased ability to detoxify arsenate. However, ars1 plants produce phytochelatin levels similar to levels produced by the wild type, and the enhanced resistance of ars1 is not abolished by the gamma-glutamylcysteine synthetase inhibitor l-buthionine sulfoxime (BSO). Furthermore, ars1 plants do not show resistance to arsenite or other toxic metals such as cadmium and chromium. However, ars1 plants do show a higher rate of phosphate uptake than that shown by wild-type plants, and wild-type plants grown with an excess of phosphate show increased tolerance to arsenate. Traditional models of arsenate tolerance in plants are based on the suppression of phosphate uptake pathways and consequently on the reduced uptake of arsenate. Our data suggest that arsenate tolerance in ars1 could be due to a new mechanism mediated by increased phosphate uptake in ars1. Models discussing how increased phosphate uptake could contribute to arsenate tolerance are discussed.
砷是污染场地中毒性最强的污染物之一，但对于某些植物在高砷环境下存活的机制却知之甚少。为深入了解植物对砷的耐受机制，我们开发了一种遗传筛选方法，以分离出对砷耐受性发生改变的拟南芥突变体。我们在此报告分离出了一个对砷酸盐耐受性增强的突变体——抗砷1（ars1）。ars1在完全抑制野生型植物生长的条件下仍能发芽并生长，且表现出半显性的抗砷表型。ars1积累的砷水平与野生型植物积累的水平相似，这表明ars1植物具有更强的砷酸盐解毒能力。然而，ars1植物产生的植物螯合肽水平与野生型植物产生的水平相似，并且ars1增强的抗性不会被γ-谷氨酰半胱氨酸合成酶抑制剂L-丁硫氨酸亚砜胺（BSO）消除。此外，ars1植物对亚砷酸盐或其他有毒金属如镉和铬没有抗性。但是，ars1植物的磷酸盐吸收速率确实高于野生型植物，并且在过量磷酸盐条件下生长的野生型植物对砷酸盐的耐受性也有所提高。植物对砷酸盐耐受性的传统模型基于对磷酸盐吸收途径的抑制，进而基于砷酸盐吸收的减少。我们的数据表明，ars1对砷酸盐的耐受性可能归因于ars1中磷酸盐吸收增加所介导的一种新机制。文中讨论了关于增加磷酸盐吸收如何有助于砷酸盐耐受性的模型。
