干旱胁迫下氮素营养与根信号在气孔运动调控中的协同作用

干旱胁迫下根系与地上部分之间的信息传递可使植物叶片及时感知土壤水势变化，从而使植物在没有真正受到干旱伤害时即可做出主动、快速的抗旱应答反应，而在这一过程中，脱落酸（abscisic acid，ABA）和pH起着关键的作用。本研究表明。干旱胁迫下鸭趾草（Commelina communis L．）、番茄（Lycopersicon esculentum Mill．）和向日葵（Helianthus annuus L．）木质部汁液中pH的变化很不相同，且该pH变化和木质部汁液中硝态氮离子浓度的变化没有直接的关系；然而，饲喂实验表明，无论对于何种植物，蒸腾流中硝态氮离子浓度的增加都可有效地增加气孔对ABA的敏感度；分根实验进一步表明，土壤中硝态氮营养的增加可明显提高气孔对根信号的敏感度。以上结果说明，氮素营养可以和根信号相互作用共同操纵气孔运动。

Nitrate as an Enhancer of Root Signal in the Regulation of Stomatal Movement in Plants under Drought Stress

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.