A Pressure-Jump Method as a New Tool in Growth Physiology for Monitoring Physiological Wall Extensibility and Effective Turgor

A new method has been devised in order to allow the rapid determinationof the physiological extensibility () of the cell wall togetherwith the apparent effective turgor (P — Y'). The methodconsists of determining the elongation growth rate of a segmentof pea hypocotyl with an auxanometer and applying a very smallincrease (around 10 kPa) in xylem pressure (jumps) by the xylemperfusion method. The cell turgor pressure is increased by thewater surge from the xylem that is due to the pressure jumpand reaches a new level within a short time. The elongationrate is also increased asymptotically to a new steady-statelevel within a short time. is estimated by simply dividingthe increase in the steady-state growth rate by the increasein perfusion pressure, which is monitored by a pressure transduceror by the increase in turgor pressure measured by a pressureprobe. Minimal length of the time period required to get a newsteady elongation rate is 1.5 min. Therefore, it is possibleto scan continuously the change in by the intermittent applicationof the brief, small pulses of xylem pressure during any experimentaltreatment. The apparent effective turgor P — Y' can becalculated by dividing the initial elongation growth rate by Using this method, we have demonstrated experimentally thenon-linearity of the relationship between elongation rate andturgor (Lockhart mechanical equation). (Received April 26, 1989; Accepted July 17, 1989)