共存阳离子影响下小麦动态吸收转运Cd2+的非损伤微测研究

As important constituents of soil solution, co-existing cations can substantially affect the transport of heavy metals on root surface. Traditional destructive technologies have limited capabilities in analyzing root samples and sometimes may result in false conclusion. The Non-invasive Micro-test Technology (NMT) enable us to study the impact of co-existing cations on heavy metals under the real physiological condition.This project is designed to investigate the kinetic transport of cadmium ion (Cd2+) at root surface of wheat as affected by co-existing cations (Ca2+, Mg2+, Na+, K+ and H+). Laboratory experiments using non-invasive microtest technology will be carried to characterize Cd2+ uptake kinetics with the existence of individual cations at different concentrations. The Biotic Ligand Model (BLM) will be employed to quantify the conditional binding constants (Log KMBL) between different cations and biotic uptake sites (Biotic Ligand) on root surface of wheat. Furthermore, the physiological mechanism of Cd2+ transport will be examined using metabolic inhibitors and ion channel blockers. The objectives of this study are: 1) to determine the effect of co-existing cations on Cd2+ uptake kinetics at the root surface of wheat; 2) to evaluate the applicability of the BLM model for quantification of co-ion effect on kinetic transport of Cd2+; and 3) to elucidate the physiological mechanism of Cd uptake and transport by wheat. The results from this project will improve our understanding of the mechanism and kinetics of Cd uptake processes and develop new tools for the environmental risk assessment of cropland soil cadmium contamination.

共存阳离子作为土壤溶液的重要组成部分，显著影响重金属离子的根系界面迁移过程。传统方法由于对样品的破坏性常造成测试结果无法合理解释甚至导致研究假象，而非损伤微测则能真实客观反映实际生理状态下共存阳离子对重金属离子的影响规律。本项目针对农田土壤Cd污染现状，以主要粮食作物小麦为研究对象，运用非损伤微测技术，探讨共存阳离子（Ca2+、Mg2+、Na+、K+、H+）影响活体小麦动态吸收转运Cd2+的过程及机制。通过单因子控制的方法，考察活体条件下不同阳离子对小麦根表动态吸收Cd2+的影响；基于生物配体模型的理论框架，定量评估共存阳离子的影响程度；监测代谢抑制剂和离子通道抑制剂作用下小麦根表Cd2+离子流变化，着重从离子传输的动态变化角度揭示共存阳离子影响小麦吸收转运Cd2+的主要途径和机制。通过本研究将有助于认识小麦吸收Cd2+的动力学过程机制，为农田土壤Cd污染风险评估提供科学理论依据。

小麦作为我国乃至世界最重要的粮食作物之一，深入了解小麦吸收Cd2+ 的微观过程机制对控制重金属经土壤-小麦系统向食物链传递延伸以及农产品的品质安全保障具有重要现实意义。本研究通过生物累积试验和非损伤微测技术探讨了小麦幼苗对Cd的吸收机制。解偶联剂2,4-dinitrophenol (DNP) (50 μM)和P-型ATP酶抑制剂Na3VO4 (500 μM)对小麦的Cd积累量以及动态吸收速率产生显著影响（P<0.05），这表明小麦对Cd的吸收不直接依赖于代谢能量或者不需要靠H+浓度梯度来驱动。Ca2+离子通道抑制剂 La3+，Gd3+ 和 Verapamil预暴露后，小麦体内的Cd含量显著降低（P<0.05），但K+离子通道抑制剂tetraethylammonium (TEA)预暴露对Cd的吸收没有影响。Ca2+离子通道抑制剂和高浓度Ca2+存在情况下均显著降低小麦幼苗根表的Cd2+流速，这表明小麦对Cd2+的吸收可通过根表的Ca2+离子通道完成。另外，小麦对Cd的积累和动态吸速率受蛋白合成抑制剂 cycloheximide (CHX)的影响显著降低，而PC合成抑制剂 L-Buthionine-sulfoximine (BSO)处理未产生显著影响，这表明小麦对Cd的吸收受蛋白合成的影响。