Computation of Surface Electrical Potentials of Plant Cell Membranes

摘要

A Gouy-Chapman-Stern model has been developed for the computation of surface electrical potential (ψ0) of plant cell membranes in response to ionic solutes. The present model is a modification of an earlier version developed to compute the sorption of ions by wheat (Triticum aestivum L. cv Scout 66) root plasma membranes. A single set of model parameters generates values for ψ0 that correlate highly with published ζ potentials of protoplasts and plasma membrane vesicles from diverse plant sources. The model assumes ion binding to a negatively charged site (R⁻ = 0.3074 μmol m⁻²) and to a neutral site (P⁰ = 2.4 μmol m⁻²) according to the reactions R⁻ + I^Ζ ⇌ RI^{Ζ−1 and} P⁰ + I^Ζ ⇌ PI^Ζ, where I^Ζ represents an ion of charge Ζ. Binding constants for the negative site are 21,500 m⁻¹ for H⁺, 20,000 m⁻¹ for Al³⁺, 2,200 m⁻¹ for La³⁺, 30 m⁻¹ for Ca²⁺ and Mg²⁺, and 1 m⁻¹ for Na⁺ and K⁺. Binding constants for the neutral site are 1/180 the value for binding to the negative site. Ion activities at the membrane surface, computed on the basis of ψ0, appear to determine many aspects of plant-mineral interactions, including mineral nutrition and the induction and alleviation of mineral toxicities, according to previous and ongoing studies. A computer program with instructions for the computation of ψ0, ion binding, ion concentrations, and ion activities at membrane surfaces may be requested from the authors.