A new method for the determination of hydraulic conductivity and cell volume of plant cells by pressure clamp.

Internodes of Chara corallina were used for experiments in which cell turgor pressure was clamped by means of the pressure probe technique. Essentially, the procedure consisted of a combination of volume and turgor pressure relaxations. This technique permits the determination of the cell volume by nonoptical means. The values obtained are in agreement with the ones determined by optical means. Furthermore, the hydraulic conductivity (L(p)) was determined from the initial slope of the volume relaxation; the values thus obtained are in agreement with those calculated from the half-times of pressure relaxations. The determination of L(p) from volume relaxation measurements has the advantage that the cell volume, the volumetric elastic modulus of the cell wall, and the internal osmotic pressure do not have to be known. Furthermore, the half-time of volume relaxation is longer than that of pressure relaxation, as shown by theory and experiment. This may be used to enhance the resolution of the relaxation measurement and, thus, to improve the accuracy of L(p) determinations for higher plant cells which exhibit a very fast pressure relaxation.