Dodd I C, Tan L P, He J
Department of Botany, The University of Queensland, Brisbane, QLD 4072, Australia.
J Exp Bot. 2003 Apr;54(385):1281-8. doi: 10.1093/jxb/erg122.
Stomatal conductance (g(s)) of pepper (Capsicum annuum L.) plants decreased during the second photoperiod (day 2) after withholding nitrate (N). Stomatal closure of N-deprived plants was not associated with a decreased shoot water potential (Psi(shoot)); conversely Psi(shoot) was lower in N-supplied plants. N deprivation transiently (days 2 and 3) alkalized (0.2-0.3 pH units) xylem sap exuded from de-topped root systems under root pressure, and xylem sap expressed from excised shoots by pressurization. The ABA concentration of expressed sap increased 3-4-fold when measured on days 2 and 4. On day 2, leaves detached from N-deprived and N-supplied plants showed decreased transpiration rates when fed an alkaline (pH 7) artificial xylem (AX) solution, independent of the ABA concentration (10-100 nM) supplied. Thus changes in xylem sap composition following N deprivation can potentially close stomata. However, the lower transpiration rate of detached N-deprived leaves relative to N-supplied leaves shows that factors residing within N-deprived leaves also mediate stomatal closure, and that these factors assume greater importance as the duration of N deprivation increases.
在停止供应硝酸盐（N）后的第二个光周期（第2天），辣椒（Capsicum annuum L.）植株的气孔导度（g(s)）下降。缺氮植株的气孔关闭与地上部水势（Ψ(shoot)）降低无关；相反，供应氮的植株中Ψ(shoot)较低。缺氮会使在根压下从去顶根系中渗出的木质部汁液以及通过加压从离体枝条中挤出的木质部汁液暂时（在第2天和第3天）碱化（0.2 - 0.3个pH单位）。在第2天和第4天测量时，挤出汁液中的脱落酸（ABA）浓度增加了3 - 4倍。在第2天，当给来自缺氮和供氮植株的离体叶片饲喂碱性（pH 7）人工木质部（AX）溶液时，其蒸腾速率降低，这与所供应的ABA浓度（10 - 100 nM）无关。因此，缺氮后木质部汁液成分的变化可能会导致气孔关闭。然而，相对于供氮叶片，缺氮离体叶片的蒸腾速率较低，这表明缺氮叶片内的因素也介导气孔关闭，并且随着缺氮持续时间的增加，这些因素的重要性更大。
