Root Hydraulic Conductance of Tomato Is Reduced When Exposed to Abscisic Acid

Plants in retail settings routinely get inadequate water.  As a result, their aesthetic value drops, which in turn reduces their salability.  The phytohormone abscisic acid (ABA) is known to be naturally produced in response to drought stress, resulting in stomatal closure and reduced transpiration.  Recent breakthroughs have made it more cost-effective to produce ABA, enabling researchers to examine its potential to function as a plant growth regulator.  Previous work has shown that exogenous ABA applications can greatly reduce transpiration, and extend shelf life of unwatered plants.  Paradoxically, we have seen that high rates of ABA may actually induce wilting.  These wilting symptoms occur despite the presence of ample water in the substrate.  This suggests that high ABA levels may interfere with the ability of plants to take up water from the substrate.  Our objective was to quantify the effect of ABA on the hydraulic conductance of the root system of tomatoes.  Tomatoes were grown in a glass greenhouse prior to the study for 8 weeks.  The plants were cut off at the first node and connected to a vacuum pump, applying negative pressure to the xylem to simulate the effect of transpirational pull.  Each pot received 50 mL of ABA solution with concentrations ranging from 0 to 1000 ppm.  The amount of water pulled through the root system was recorded after four days, at which time the study was ended and the roots were examined.  Results indicate that as ABA concentration increased, root system conductance decreased.  The volume of water conducted by the root systems during the four-day period ranged from 14.34 mL in the control treatments to 3.98 mL in the 1000 ppm ABA treatment, a reduction of 72%.  The roots were examined at the end of the experiment, and ABA did not impart any negative visual symptoms on the roots.  We hypothesize that ABA affects aquaporins in the roots, limiting water uptake.  Further work will need to be done to fully understand the way ABA affects the roots.