Article révisé par les pairs
Résumé : Transfer across membranes is treated for simultaneous active pumping and passive flow of the main ionic constituents of plant cells. The chemical equilibrium conditions for H2CO3 and H2O dissociation prevailing in the external and internal solutions are taken into account. Our model assumes steady-state conditions, zero electrical current, electroneutrality inside the membrane and, in both solutions, finite space charge densities in two diffuse regions in contact with both sides of the membrane. A computer program has been developed for the integration of a set of flux equations. The results are displayed in terms of ionic flux parameters, each proportional to the ionic pump flow and to the reciprocal of the passive ionic mobility. The discussion emphasizes the role of anion inward pumping and of non-diffusible anions. The cationic pumps serve to establish different ionic balances in the cell. Transmembrane (bulk to bulk) proton pumping affects essentially the pH regulation in the cell.