Considerations in measuring Potassium efflux from plant cells using Rb-87 magnetic resonance

In order to stay metabolically active, plant cells must transport Potassium ions across their plasmalemma. Ion transport is subject to many complex me tabolic regulatory processes. Information on Potassium metabolism can be ob tained with Rb-87 NMR spectroscopy, using Rubidium as a congener for Potass ium. However, due to the presence of the vacuole, another non-metabolic mec hanism for ion flux regulation exists. Using simple biophysical arguments, it is shown that an increase in vacuole size, without a change in total cel l volume, could initiate a change in Potassium efflux. This change in efflu x can be significant, especially for large vacuoles.