Influence of membrane surface charge on nutrient uptake by plants

The original publication can be found at www.springerlink.comBiological membranes are charged due to the presence of ionisable groups on phospholipid molecules that make up the lipid bilayer and on membrane proteins extending into the external medium. In dilute media, substantial surface potentials can be generated and these potentials have the capacity to concentrate ions at the membrane surface in the vicinity of membrane transporters. We have made measurements with isolated protoplasts to assess the importance of the electrostatic nature of plant cell membranes on the characteristics of uptake of divalent trace metals. Uptake of ⁶³Ni by protoplasts was strongly inhibited by treatments that suppressed the surface potential. These treatments included increasing concentrations of a range of monovalent and divalent cations, as well as changing the pH of the external medium. We conclude that uptake of cations is more closely related to their concentrations at the membrane surface than to their concentrations in the external medium, and that the apparent kinetics of the transporters are strongly dependent on the composition of the medium in which they are being studied