Figure 3.

PLC in the xylem of walnut petioles exposed to a water stress. The water stress was provoked by exposing excised petioles to different pneumatic pressures (▪) or different centrifugal forces (○). Samples exposed to a centrifugal force were either measured while the xylem was still under centrifugal force with negative xylem pressure (○) or shortly after the xylem pressure was returned to 0 MPa (●). The error bars represent ± 1 sd. Each closed circle represents a different sample. The different techniques yielded close results. Whatever the technique, the threshold water potential for embolism induction was always less than −1.0 MPa.