Abstract: Plants can sense changes in soil water status before obvious water deficit occurs in shoots. Abscisic acid(ABA) and pH are key signals mediating root-to-shoot signaling. Here we report that drought leads to changes in xylem pH differently in Commelina communis L., tomato(Lycopersicon esculentum Mill.) and sunflower(Helianthus annuus L.). The drought-induced changes in pH were not related to changes in xylem nitrate content. However, for the plant species tested, nitrate was able to increase the stomatal sensitivity to ABA in detached leaves. Moreover, root-splitting experiments demonstrated that supplying extra nitrate in soil increased the stomatal sensitivity to root-sourced soil-drying signals when the nitrate concentration in the xylem was lifted. Our results suggest that nitrate can enhance the root signal and thereby jointly regulate stomatal movement under drought stress.