Kopittke PM Kinraide TB Wang P et al.. Pb Rhizotoxicities in Cowpea (Vigna unguiculata) as Related to Ion Activities at Root-Cell Plasma Membrane Surface. Environmental Science & Technology 2011 45(11): 4966-4973. (IF 4.827 环境科学，二区Top）
Abstract
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 ψ0o (electrical potential at the outer surface of the PM) and thereby decreased {Cu2+}0o (activity of Cu2+ at the outer surface of the PM). For Pb root elongation was generally better correlated to the activity of Pb2+ in the bulk solution than to {Pb2+}0o. However we propose that the addition of cations resulted in a decrease in {Pb2+}0o but a simultaneous increase in the rate of Pb uptake (due to an increase in the negativity of Emsurf the difference in potential between the inner and outer surfaces of the PM) thus offsetting the decrease in {Pb2+}0o. 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.
