Measurement of the respiration-dependent component of intracellular pressure with an improved pressure probe

We have improved a previously described pressure probe in the following respect to make it suitable for continous mesurements of intracelluar presure (p)ⁱ in higher plant cells. (1)The oil/cell-sap boundary (meniscus) at the tip of the microcapillary was moniterd photo-electrically with a high-resolution image sensor. (2) Adjustment of the plunger and the insertion of the probe into the target cell were performed with specilly desinged, hydraulic manipulator system. These improvements allowed us to monitor the meniscus precisely and to maintain the meniscus at a certain position without mechanical perturbation. This system has been successfully used to measure Pⁱ continuously for more than 3 h.With this pressure probe, the dependence on respiration of Pⁱ in the elongation zone of Vigna hypocotyls, which was predicted by Katou and Furumoto (1986a, b), was demonstrated directly. Changes in Pi induced by osmotic stress were also measured quite successfully. The respiration-dependent component of Pi was 30-40 kPa. While this component appears to be very small, the change in Pi under anoxia caused shrinkage of the segment of hypocotyl being examined. Regulation of P^u over a range of several tens of kPa or so should, therefore, make a significant contribution to the control of elongation growth.