School of Agriculture and Food Sciences, The University of Queensland, St. Lucia, Queensland 4072, Australia.
Environ Sci Technol. 2011 Jun 1;45(11):4966-73. doi: 10.1021/es1041404. Epub 2011 May 12.
Cations, such as Ca and Mg, are generally thought to alleviate toxicities of trace metals through site-specific competition (as incorporated in the biotic ligand model, BLM). Short-term experiments were conducted with cowpea (Vigna unguiculata L. Walp.) seedlings in simple nutrient solutions to examine the alleviation of Cu and Pb toxicities by Al, Ca, H, Mg, and Na. For Cu, the cations depolarized the plasma membrane (PM) and reduced the negativity of ψ(0)(o) (electrical potential at the outer surface of the PM) and thereby decreased {Cu(2+)}(0)(o) (activity of Cu(2+) at the outer surface of the PM). For Pb, root elongation was generally better correlated to the activity of Pb(2+) in the bulk solution than to {Pb(2+)}(0)(o). However, we propose that the addition of cations resulted in a decrease in {Pb(2+)}(0)(o) but a simultaneous increase in the rate of Pb uptake (due to an increase in the negativity of E(m,surf), the difference in potential between the inner and outer surfaces of the PM) thus offsetting the decrease in {Pb(2+)}(0)(o). In addition, Ca was found to alleviate Pb toxicity through a specific effect. Although our data do not preclude site-specific competition (as incorporated in the BLM), we suggest that electrostatic effects have an important role.
阳离子，如 Ca 和 Mg，通常被认为通过位点特异性竞争（如生物配体模型 BLM 中所包含的）来减轻痕量金属的毒性。在简单的营养液中，用豇豆（Vigna unguiculata L. Walp.）幼苗进行短期实验，以研究 Al、Ca、H、Mg 和 Na 对 Cu 和 Pb 毒性的缓解作用。对于 Cu，阳离子使质膜去极化，并降低 ψ(0)(o)（质膜外表面的电势能）的负电性，从而降低 {Cu(2+)}(0)(o)（质膜外表面的 Cu(2+)活性）。对于 Pb，根伸长通常与 bulk 溶液中 Pb(2+)的活性更好相关，而不是与 {Pb(2+)}(0)(o) 相关。然而，我们提出，添加阳离子会导致 {Pb(2+)}(0)(o) 的降低，但同时会增加 Pb 摄取的速率（由于 E(m,surf)的负值增加，即质膜内外表面之间的电位差），从而抵消 {Pb(2+)}(0)(o) 的降低。此外，还发现 Ca 通过特定作用缓解 Pb 毒性。尽管我们的数据不排除位点特异性竞争（如 BLM 中所包含的），但我们认为静电效应具有重要作用。
