Drought-Induced Changes in Xylem Sap pH, ABA and Stomatal Conductance

摘要

Upstream signals potentially regulating evaporation and stomatal conductance were investigated using 6-8-leaf-old maize (Zea may L.) seedlings which were grown in a greenhouse. Pressure chamber was used to measure leaf water potential and to collect xylem sap. The pH of xylem sap in stems was higher than that in root, and the abscisic acid (ABA) concentration in stems was the highest in well-watered seedlings. The ABA concentration and pH of xylem sap in roots, stems and leaves increased, and the ABA concentration in leaves reached the maximum during drought stress. The treatment of roots with exogenous ABA solution (100 μmol L~(-1)) increased xylem sap ABA concentration in all organs measured, and induced stomatal closure, but did not change ABA distribution among organs of maize seedlings. The combined effects of external pH buffer on pH, ABA of xylem sap and stomatal behavior indicated that pH, as a root-source signal to leaves under drought stress, regulated stomatal closure through accumulating ABA in leaves or guard cells.