Beschreibung:
<p>Water relations parameters of Chara corallina internodes were measured using the single cell pressure probe. The effect of mercurials, which are recognized as non-specific water channel inhibitors, was examined. HgCl2 concentrations greater than 5 mmol m-3 were found to inhibit hydraulic conductivity (Lp) close to 90%, whereas pCMPS was found to have no effect on Lp. The activation energy of water flow was increased significantly from 21.0 kJ mol-1 to 45.6 kJ mol-1, following the application of HgCl2. These results are in accordance with evidence for Hg2+-sensitive water channels in the plasma membrane of charophytes (Henzler and Steudle, 1995; Tazawa et al., 1996). The metabolic effects must, however, be considered in view of the rapid inhibition of respiration and the depolarization of the membrane potential with HgCl2 concentrations lower than those found to affect Lp. It was possible to measure simultaneously water relations and membrane PD, in order to examine the contribution of potassium channels to Lp. Cells were induced into a K+ permeable state. The K+ channels, assumed to be open, were subsequently blocked by various blockers. No significant difference in Lp was found for any of these treatments. Finally, the permeability of C. corallina membranes to ethanol was examined. HgCl2 was found to cause a decrease in reflection coefficient, coinciding with a decrease in Lp, but there was no change in the ethanol permeability coefficient. This has been interpreted in terms of both the frictional model and composite model of non-electrolyte membrane transport.</p>