Water-relation Parameters of Individual Mesophyll Cells of the Crassulacean Acid Metabolism Plant Kalanchoë daigremontiana

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Abstract
Water-relation parameters of leaf mesophyll cells of the CAM plant Kalanchoë daigremontiana have been determined directly in cells of tissue slices using the pressure-probe technique. Turgor pressures measured in cells of the second to fourth layer from the cut surface showed an average of 1.82 ± 0.62 bar (mean ± sd; n = 157 cells). This was lower than expected from measurements of the osmotic pressure of the cell sap. The half-time (T1/2) for water-flux equilibration of individual cells was 2.5 to 8.8 seconds. This is the fastest T1/2 found so far for higher-plant cells. The calculated values of the hydraulic conductivity were in the range of 0.20 to 1.6 × 10−5 centimeters second−1 bar−1, with an average of (0.69 ± 0.46) × 10−5 centimeters second−1 bar−1 (mean ± sd; n = 8 cells). The T1/2 values of water exchange of individual cells are consistent with the overall rates of water-flux equilibration measured for tissue slices.