Reducing water loss from vegetables is important to maintain freshness. The hydraulic conductivity coefficient
(Lp) of cell membranes is indispensable to analyze the movement of water from cells, which leads to wilting and low metabolic
activity. To measure Lp, extracellular solution must be replaced quickly to apply osmotic stress to the cells; however,
conventional methods take a relatively long time, which leads to noticeable errors. We therefore developed a new method to
measure Lp based on the principle that two liquids exhibit laminar flow through a relatively narrow space, for example, a tube
having a small inner diameter. A microchannel having a diameter of 1.4 mm was designed. The microchannel has two inlets,
and the flow rate of solution at each inlet can be used to determine the volume of each solution occupying the microchannel.
Hence, an extracellular solution of protoplast fixed in a microchannel can be changed instantaneously by changing the flow
rate of the solution. The Lp values of barley cotyledon and spinach leaf protoplasts were measured by both the developed
method and a conventional method. Lp values measured by the conventional method were lower than those measured by the
newly developed method. The developed method also showed less scattering in the measured Lp values because the errors
caused by the experimental operation were reduced. In addition, the difference in values measured by both methods was
examined by error estimation, and the values obtained by the new method were determined to be valid. With this method, the
time delay to replace the extracellular solution was negligible and Lp was obtained without any error being caused by the
time required for replacement.