Fig. 3.

Experimental set-up for in planta bending and pressure measurements. The poplar tree (scion in dormancy) is continuously perfused with a nutrient solution containing nitrate applied with a small pump. This treatment generates a high physiological root pressure that refills xylem at the whole-plant level and increases the sap pressure in the vascular system of the stem so the pressure becomes positive. The stem was bent quickly by dropping a mass around a circular support with a known radius of curvature. Two sensors were placed at basal and apical positions of the stem to measure the xylem pressure. (This figure is available in colour at JXB online.)