近日,，在中國科學院創(chuàng)新團隊國際合作伙伴計劃和國家自然科學基金項目的聯(lián)合資助下,，中國科學院南京土壤研究所“土壤與農(nóng)業(yè)可持續(xù)發(fā)展”國家重點實驗室周東美課題組在有關重金屬離子植物毒性評價與預測研究方面取得重要進展。
基于重金屬形態(tài)和離子競爭效應發(fā)展起來的生物配體模型(Biotic Ligand Model, BLM) 是當前環(huán)境學家研究重金屬生物毒性和環(huán)境基準及標準的重要方法之一,。該模型認為細胞質膜是主要的生物配體,，并對生物配體做化學均一化(homogeneous) 處理，認為其性質是確定的,；共存陽離子通過與重金屬離子競爭生物配體上毒性作用位點來緩解金屬毒性,，毒性效應與本體溶液中離子活度之間存在相關性。然而,，在環(huán)境體系中,，生物細胞膜表面絕大數(shù)帶負電荷，因而在細胞膜與溶液界面會形成一個雙電層結構,，這種負電荷在細胞膜表面形成電勢稱之為細胞膜膜表面電勢,。細胞膜表面電勢控制離子在細胞膜和環(huán)境本體介質(bulk-phase medium) 之間的分布，將增加陽離子在膜表面的濃度,，降低陰離子在膜表面的濃度,。課題組在研究Ca2+、Mg2+和H+等陽離子影響銅離子和砷酸根植物毒性的過程中,，發(fā)現(xiàn)當考慮細胞膜表面電勢的影響后,，可以很好地解釋金屬陽離子對有毒金屬元素毒性的界面影響機制。這種影響主要是通過細胞膜表面電勢的作用,，而不是離子之間的競爭,。該項研究為我們研究毒性離子的生物有效性/毒性提供了一個全新的視角。這項研究成果已經(jīng)發(fā)表在國際著名生物學刊物《植物生理學》（Plant Physiology）上,。（生物谷Bioon.com）
生物谷推薦原始出處：
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.
