Models for oscillations in plants

Abstract

Ionic relations of plant cells comprise enzymes such as channels, pumps and co-transporters that catalyse the transition of ions through lipid membranes and, therefore, affect the membrane voltage. Since the activity of most of these enzymes is voltage dependent, these enzymes interact with each other via voltage changes. The temporal patterns of these interactions include oscillations. Models are presented here that simulate such oscillations based on physical properties of the ion transporters. Three oscillating scenarios are focussed on. Model A is adequate for short-term episodes. In model B, the external concentration of the ions is constant. This model, which applies e.g. to algae and single cells under experimental conditions, displays electric oscillations, just as model A, but also osmotic oscillations in which the internal ion concentrations play an essential role. Finally, model C applies to parenchyma cells in planta, where ion fluxes across the plasmalemma cause major concentration changes in the small apoplastic volume. In this model, internal and external buffering of ions is accounted for. For model C, it is assumed that the total quantities of substrates are constant, and portions of them are redistributed between different compartments. Oscillations of the model C are relatively rare. In most cases, model C approaches a steady state where K⁺ is in thermodynamic equilibrium.