Background/Question/Methods Plant growth is dependent on the supply of water to the leaves. The ability to supply water and to withstand tension (drought stress) is a function of xylem cell structure, which affects both water flow rates (larger vessels) and drought tolerance (greater cavitation resistance).  Long-term structural acclimation is an important mechanism that enables plants to modify the water supply to the canopy.  Plants of two common bean cultivars (Othello and G4523) were exposed to flexing vs. non-flexing treatments under greenhouse conditions for at least four weeks.  Plants exposed to the stem flexing treatments experienced physical manipulation of the stems, (bending to a 45 º angle at least 50 times per day.   Plant growth, water-use, hydraulic conductance, and drought tolerance (measured as the tension required for a 50 % loss in stem hydraulic conductance or P₅₀) were monitored to determine if long-term exposure to flexing resulted in changes in xylem structure (hydraulic acclimation). 
Results/Conclusions Although the two cultivars did not differ significantly in biomass production, stem flexing did result in significantly less biomass compared with the non-flexing controls (9.2 vs. 11.3 g dry weight).  Root area and leaf area were also higher for non-flexed plants compared with flexing treatment plants.  Total plant water use was higher for non-flexed plants (0.14 vs 0.11 kg/day).  Stem hydraulic conductance was significantly higher in non-flex treatment plants and stomatal density was also higher.  While most measures of plant growth and hydraulic support were higher for non-flex treatment plants, the flexing treatment plants exhibited a significantly higher P₅₀ compared with non-flexed plants (1.2 vs. 0.85 MPa) indicating a shift toward higher cavitation resistance.  The increase in cavitation resistance was not a function of increasing stem density.  The two cultivars did exhibit different water use strategies, with G4523 having higher leaf area and Othello having higher stem/stomatal flow rates.  This study confirmed that physical manipulation of stems can impact xylem structural properties and result in altered plant water flow characteristics and cavitation resistance.