The relation of turgor pressure to cell volume inNitella with special reference to mechanical properties of the cell wall

Summary

• 1. A method was developed, by which it was possible to measure the volume of an internodal cell ofNitella flexilis as a function of interior pressure. For this to be done, the cell wall tube, closed at one end with the natural septum, was filled with mercury and pressure was applied to the mercury. The accompanying change in volume of the cell wall tube was measured simultaneously with the applied pressure.

• 2. The time course of volume change of the cell in response to change in interior pressure indicates that cell wall elasticity is composed of at least two components, an instantaneous elastic component, and a retarded elastic component with a retardation time of about 1–5 minutes.

• 3. Both instantaneous and slow processes in volume change vary according to the level of the pressure applied and to the direction of the pressure change.

• 4. The volume of the cell can be kept at different values, under the same interior pressure, according to the direction of the pressure change; in other words, the interior pressure-volume relation shows a hysteresis.

• 5. Taking into consideration the hysteresis character in mechanical properties of the cell wall, the osmotic pressure, turgor pressure and suction force (diffusion pressure deficit) of an internodal cell ofNitella flexilis was illustrated in relation to the cell volume in an osmotic diagram after Höfler. A characteristic of the diagram is that the cell can have different turgor pressures and suction forces within certain limits even though the volume of the cell is the same.

• 6. The length of the living cell was measured under different turgor pressures. The facts that the pressure-cell length relation showed also a distinct hysteresis character and that the wall elasticity of the living cells was in the same order as that of the cells filled with mercury, indicate that the results obtained with cell wall tubes were also true of the living cells.

• 7. The cell wall of the internodal cell ofNitella flexilis extends more in the direction of transverse axis of the cell than in the direction of longitudinal axis under the influence of turgor pressure. When equal tensions in the respective direction are considered, however, the cell wall extends to the same extent in each direction.

• 8. The uniaxial longitudinal tension, caused by loading, elongates the cell about 3–4 times more than does the longitudinal component of the equivalent tension caused by turgor pressure.