近日，在中国科学院创新团队国际合作伙伴计划和国家自然科学基金项目的联合资助下，中国科学院南京土壤研究所“土壤与农业可持续发展”国家重点实验室周东美课题组在有关重金属离子植物毒性评价与预测研究方面取得重要进展。
基于重金属形态和离子竞争效应发展起来的生物配体模型(Biotic Ligand Model, BLM) 是当前环境学家研究重金属生物毒性和环境基准及标准的重要方法之一。该模型认为细胞质膜是主要的生物配体，并对生物配体做化学均一化(homogeneous) 处理，认为其性质是确定的；共存阳离子通过与重金属离子竞争生物配体上毒性作用位点来缓解金属毒性，毒性效应与本体溶液中离子活度之间存在相关性。然而，在环境体系中，生物细胞膜表面绝大数带负电荷，因而在细胞膜与溶液界面会形成一个双电层结构，这种负电荷在细胞膜表面形成电势称之为细胞膜膜表面电势。细胞膜表面电势控制离子在细胞膜和环境本体介质(bulk-phase medium) 之间的分布，将增加阳离子在膜表面的浓度，降低阴离子在膜表面的浓度。课题组在研究Ca2+、Mg2+和H+等阳离子影响铜离子和砷酸根植物毒性的过程中，发现当考虑细胞膜表面电势的影响后，可以很好地解释金属阳离子对有毒金属元素毒性的界面影响机制。这种影响主要是通过细胞膜表面电势的作用，而不是离子之间的竞争。该项研究为我们研究毒性离子的生物有效性/毒性提供了一个全新的视角。这项研究成果已经发表在国际著名生物学刊物《植物生理学》（Plant Physiology）上。（生物谷Bioon.com）
生物谷推荐原始出处：
Plant Physiology， 2008, 148: 2134-2143，Peng Wang，Dongmei Zhou
Cell Membrane Surface Potential (ψ0) Plays a Dominant Role in the Phytotoxicity of Copper and Arsenate1,[W]
Peng Wang, Dongmei Zhou*, Thomas B. Kinraide, Xiaosan Luo, Lianzhen Li, Dandan Li and Hailin Zhang
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China (P.W., D.Z., X.L., L.L., D.L.); Graduate School of Chinese Academy of Sciences, Beijing 100049, China (P.W., X.L., L.L., D.L.); Agricultural Research Service, United States Department of Agriculture, Beaver, West Virginia 25813–9423 (T.B.K.); and Department of Plant and Soil Sciences, Oklahoma State University, Stillwater, Oklahoma 74078 (H.Z.)
Negative charges at cell membrane surfaces (CMS) create a surface electrical potential (ψ0) that affects ion concentrations at the CMS and consequently affects the phytotoxicity of metallic cations and metalloid anions in different ways. The ι potentials of root protoplasts of wheat (Triticum aestivum), as affected by the ionic environment of the solution, were measured and compared with the values of ψ0 calculated with a Gouy-Chapman-Stern model. The mechanisms for the effects of cations (H+, Ca2+, Mg2+, Na+, and K+) on the acute toxicity of Cu2+ and As(V) to wheat were studied in terms of ψ0. The order of effectiveness of the ions in reducing the negativity of ψ0 was H+ > Ca2+ ≈ Mg2+ > Na+ ≈ K+. The calculated values of ψ0 were proportional to the measured potentials (r2 = 0.93). Increasing Ca2+ or Mg2+activities in bulk-phase media resulted in decreased CMS activities of Cu2+ ({Cu2+}0) and increased CMS activities ofAs(V) ({As(V)}0). The 48-h EA50{Cu2+}b ({Cu2+} in bulk-phase media accounting for 50% inhibition of root elongation over48 h) increased initially and then declined, whereas the 48-h EA50{As(V)}b decreased linearly. However, the intrinsic toxicity of Cu2+ (toxicity expressed in terms of {Cu2+}0) appeared to be enhanced as ψ0 became less negative and the intrinsic toxicity of As(V) appeared to be reduced. The ψ0 effects, rather than site-specific competitions among ions at the CMS (invoked by the biotic ligand model), may play the dominant role in the phytotoxicities of Cu2+ and As(V) to wheat.
