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Peng Wang, Dongmei Zhou, Thomas B. Kinraide, Xiaosan Luo, Lianzhen Li, Dandan Li, Hailin Zhang, Cell Membrane Surface Potential (ψ 0) Plays a Dominant Role in the Phytotoxicity of Copper and Arsenate, Plant Physiology, Volume 148, Issue 4, December 2008, Pages 2134–2143, https://doi.org/10.1104/pp.108.127464
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Abstract
Negative charges at cell membrane surfaces (CMS) create a surface electrical potential (ψ 0) that affects ion concentrations at the CMS and consequently affects the phytotoxicity of metallic cations and metalloid anions in different ways. The ζ 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 ψ 0 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 ψ 0. The order of effectiveness of the ions in reducing the negativity of ψ 0 was H+ > Ca2+ ≈ Mg2+ > Na+ ≈ K+. The calculated values of ψ 0 were proportional to the measured ζ potentials (r 2 = 0.93). Increasing Ca2+ or Mg2+ activities in bulk-phase media resulted in decreased CMS activities of Cu2+ ({Cu2+}0) and increased CMS activities of As(V) ({As(V)}0). The 48-h EA50{Cu2+}b ({Cu2+} in bulk-phase media accounting for 50% inhibition of root elongation over 48 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 ψ 0 became less negative and the intrinsic toxicity of As(V) appeared to be reduced. The ψ 0 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.
