Ion fluxes and cytosolic pool sizes: examining fundamental relationships in transmembrane flux regulation.

The relationships among cellular ion fluxes, ion compartmentation, and the turnover kinetics of cytosolic ion pools are crucial to the understanding of the regulatory mechanisms and thermodynamic gradients that determine plasma membrane ion fluxes. We here provide an analysis of published data to quantify these relationships for the two major nutrient elements in plants, nitrogen and potassium. We discuss the implications of these relationships for plant ion fluxes in general, and focus more specifically on problems associated with the accurate measurement of fluxes to and from rapidly exchanging pools, particularly the cytosolic calcium pool.