10P-E-4 A Dynamic Measurement Technique Characterizes the Turgor Pressure Change in Characean Internodal Cells: the hydraulic conductivity of the plasma membrane is isotropic and independent of the external hydrostatic pressure(Room E International sessio

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Assuming that the magnitude of the peak-to-peak difference in strain (ΔSn) caused by an external constant sinusoidal stress is proportionate to the turgidity of the viscoelastic material, I applied this dynamic measuring technique to characterize the turgor pressure change (ΔP) in a giant cylindrical Characean intermodal cell in response to the step-change of extracellular hydrostatic pressure (π_e). This technique, the "vibro method", is not only simpler than those reported by other authors, but is also non-invasive to the living cell. Furthermore, this enables the measurement of P as a function of time, with a temporal resolution as high as 100 msec. Tn the apparatus used in my experiments, the cell length (1) or diameter (d) and ΔSn can be measured simultaneously, with a distance resolution better than 1μm. Results suggest that there is no evidence to prove that the plasma membrane itself is a rectifier for water volume flow, but that the apparent rectification is due to the mechanical properties of the cell wall and/or to the change in water motive force across the membrane. Furthermore, there is no evidence to prove a change in hydraulic conductivity L_p in response to π_e up to 1.5MPa within at least 5 sec immediately after the onset. On the other hand, however, in long-term studies longer than lOsec the correlation gets worse and shows a rectification.
2010-10-09