Measurement of the Respiration-Dependent Component of Intracellular Pressure with an Improved Pressure Probe

We have improved a previously described pressure probe in thefollowing respect to make it suitable for continous mesurementsof intracelluar presure (p)ⁱ in higher plant cells. (1)The oil/cell-sapboundary (meniscus) at the tip of the microcapillary was moniterdphoto-electrically with a high-resolution image sensor.(2) Adjustmentof the plunger and the insertion of the probe into the targetcell were performed with specilly desinged, hydraulic manipulatorsystem. These improvements allowed us to monitor the meniscusprecisely and to maintain the meniscus at a certain positionwithout mechanical perturbation. This system has been successfullyused to measure Pⁱ continuously for more than 3 h. With this pressure probe, the dependence on respiration of Pⁱin the elongation zone of Vigna hypocotyls, which was predictedby Katou and Furumoto (1986a, b), was demonstrated directly.Changes in Pi induced by osmotic stress were also measured quitesuccessfully. The respiration-dependent component of Pi was30–40 kPa. While this component appears to be very small,the change in Pi under anoxia caused shrinkage of the segmentof hypocotyl being examined. Regulation of P^u over a range ofseveral tens of kPa or so should, therefore, make a significantcontribution to the control of elongation growth. (Received April 9, 1990; Accepted June 25, 1990)