Membranes and the electrophysiology of turgor regulation

In many types of plant and algal cells, the turgor is regulated, either at a constant level, or in some reproducible time-dependent way. This review considers the electrophysiology of turgor control in marine algae, guard cells, and motor cells of pulvini. There is a basic complement of electrophysiological components in the plasma membranes of these cells. These components are responsible for controlling the fluxes of potassium salts, the major inorganic component of the osmoticum responsible for changing internal osmotic pressure, and hence turgor, and consist essentially of inwardly and outwardly rectifying K channels, Cl channels, H/Cl symporters, sucrose transporters and the proton pump. There are also Ca channels in the plasma membrane, allowing influx of Ca to the cytosol, that in turn acts, with other second messengers, to co-ordinate the operation of the various ion channels, the fluxes, and the turgor regulation. The review discusses the ways in which these components work together in the various systems, and highlights various areas where more information is required for an adequate description of turgor regulation.