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 c onsiders the electrophysiology of turgor control in marine algae, guard cel ls, and motor cells of pulvini. There is a basic complement of electrophysi ological components in the plasma membranes of these cells. These component s are responsible for controlling the fluxes of potassium salts, the major inorganic component of the osmoticum responsible for changing internal osmo tic pressure, and hence turgor, and consist essentially of inwardly and out wardly rectifying K channels, Cl channels, H/Cl symporters, sucrose transpo rters and the proton pump. There are also Ca channels in the plasma membran e, allowing influx of Ca to the cytosol, that in turn acts, with other seco nd messengers, to co-ordinate the operation of the various ion channels, th e fluxes, and the turgor regulation. The review discusses the ways in which these components work together in the various systems, and highlights vari ous areas where more information is required for an adequate description of turgor regulation.