摘要
生物配体模型(BLM)是基于稳定态假设的一个平衡模型,能够较准确地运用于预测重金属的毒性及其生物有效性.根据BLM模型的假设条件模拟土壤溶液,研究了Ca2+、Mg2+、Cu2+和Ni2+对小麦根吸收Cd2+动力学的影响,阐述了BLM在应用中存在的局限性.结果表明:在8h内的短期动力学吸收实验中,小麦根对Cd的吸收及吸附量呈线性增加,但未达到稳定值,这说明Cd2+在根-液界面未达到稳定平衡;并且小麦根对Cd的吸收是受溶液中Cd2+扩散速率影响的.小麦根对Cd的吸收通量与Cd2+浓度[Cd2+]和Cd与小麦根表上的配体结合浓度{Cd-Rcel}l都具有较好的线性关系,但随着Cd2+浓度的增加稳定常数KM-Rcell、渗透常数p和同化速率常数kint均呈降低趋势.Ca2+、Mg2+和Cu2+降低了小麦根对Cd2+的吸收通量,而Ni2+对Cd2+的竞争作用不显著.由于Cd与Ca、Ni有共同的吸收通道,Ca通道吸收达到饱和后可降低小麦根对Cd的吸收,但是Ca2+、Mg2+和Cu2+通过降低内化速率常数也可使小麦根对Cd的内化通量减少,因此不能完全用竞争效应解释其结果.另外,阳离子的存在会改变小麦根表的性质,Ca2+、Mg2+的存在会增加亨利系数KCd,即生物配体浓度{Rcel}l和(或)离子与生物配体结合稳定常数KCd-Rcell会增加,同时这些离子的存在还会降低渗透常数p和kint;Cu2+、Ni2+的存在会降低KCd;且p和k在低浓度Cd(0.01～0.05μM)条件下增加,在高浓度Cd条件下降低.
Bioavailability of trace metals to plants is often accurately predicted by one of the steady-state models Terrestrial Biotic Ligand Model（t-BLM）. According to the conditions of BLM model, the soil solution were prepared. A series of experiments concerning short-term kinetic biouptake of Cd2＋ by wheat（Triticum aestivum）were carried out in the presence or absence of major cations（Ca2＋ or Mg2＋）or trace metals（Cu2＋ or Ni2＋）in soil solution to study the limitation of the application of BLM model. The results indicat that the biouptake of Cd in the root of wheat and the adsorbed Cd2＋ on the surface of the root of wheat increased linearly with time for at least 8h, suggesting that the biouptake and adsorption of Cd2＋ did not arrive the steady state in 8h. Moreover, the rate of diffusion of Cd2＋ influenced on the uptake of the root of wheat. A linear relationship was established between the internalization flux of root of the wheat and the concentration of Cd2＋ in solution（[Cd2＋]）and the transporter-bound metal concentration{Cd-Rcell}. However, the stability constant KM-Rcell and the internalization rate constant kint decreased with increasing concentrations of Cd2＋, indicating that the biouptake way was not single but lied at least two pathways（the high-affinity and the low-affinity way）. Ca2＋, Mg2＋and Cu2＋ in solution decreased the internalization flux of Cd2＋, but the Ni2＋ did not inhibit the uptake of Cd2＋ in the root of wheat. This may be that the Ca2＋ arriving at saturation in channels decrease the uptake of Cd2＋ due to the Cd2＋, Ca2＋ and Ni2＋ entering the cell via same channels. In addition, Ca2＋, Mg2＋ and Cu2＋ could decrease the internalization flux of Cd2＋ by the internalization rate constant kint. Therefore, the competing effect was not the only factor to explain the decreased internalization flux of Cd2＋. Additionally, cations in solution changed the quality of the surface of the wheat root. Ca2＋ and Mg2＋ increased KCd and decrea
出处
《生态毒理学报》
CAS
CSCD
2010年第4期580-586,共7页
Asian Journal of Ecotoxicology
基金
国家重点基础研究发展规划项目(No.2007CB936604)
关键词
生物配体模型BLM
重金属
生物有效性
阳离子
terrestrial biotic ligand model（BLM）
heavy metal
bioavailability
cations
