Electrophysiology of turgor regulation in charophyte cells

Abstract

The resting PD of a cell results from interaction of many transporters. Their contributions can be resolved by perturbing the membrane PD away from equilibrium. The application of the I/V technique to charophytes and higher plant cells under many conditions reveals considerable differences in PD dependencies of the major membrane conductances (transporters). The speed with which the membrane PD can be altered over hundreds of mV allows the experimenter to follow changes in transporter I/V profiles, while the cell is facing challenges such as metabolic inhibition or salinity stress. The availability of the raw data, both the clamp PD and the clamp current bipolar staircases, are vital for estimation of time dependencies of the response to PD change and artifact recognition. The analytic power of I/V technique increases as more data are acquired and modeled. The conductance-voltage (G/V) profiles, obtained as the derivatives of the I/V curves, provide an easily comprehensible record of parallel transporter combinations, as parallel conductances are directly additive. Similarly, the resistance-voltage (R/V, where R=1/G) profiles for transporters in series (on different membranes) are directly additive and more easily analyzed. With all these analytical techniques, much information can be gained on major transport systems, simultaneously responding to physical or chemical stresses.