What role does cell membrane surface potential play in ion-plant interactions.

Almost all cell membrane surfaces (CMS) are intrinsically negatively charged. These negative charges create a surface electrical potential (Psi(0)) which affects ion concentrations at the CMS and consequently affects the phytotoxicity of metallic cations and metalloid anions in different ways. The Psi(0) is also controlled by the ionic composition of the bulk-phase medium (BM). Common cations, especially H(+), Ca(2+) and Mg(2+), can reduce the negativity of Psi(0) by ionic screening and binding. Treatments that reduce the negativity of Psi(0) would reduce the surface activity of Cu(2+) ({Cu(2+)}(0)) and increase the surface activity of arsenate ({As(V)}(0)) at the CMS, and consequently alleviation of Cu(2+) toxicity but aggravation As toxicity would be expected. It is the Psi(0), rather than site-specific competition, that plays the principal role in ionic interactions and biotic effects.