Abstract:

We investigated the osmotic stress and ion-specific effects on xylem abscisic acid (ABA), ion uptake and transport and gas exchange in one-year-old seedlings of Populus euphratica Oliv. Net photosynthetic rates (Pn) and unit transpiration rates (TRN) were both significantly decreased upon an osmotic shock caused by PEG 6000 solution (osmotic potential=-0.24 MPa) or a saline, which was applied by 50 mmol/L Na+-salts (NaNO3∶NaHCO3∶NaH2PO4=5∶4∶1, pH 6.8, osmotic potential=-0.24 MPa) or by 50 mmol/L Cl－-salts (KCl∶NH4Cl=1∶1, osmotic potential=-0.24 MPa). However, salt-treated P. euphratica plants maintained typically higher TRN than those exposed to PEG. Xylem ABA concentrations increased rapidly following the PEG treatment, exhibiting peaking values at 1 h, then returning to pre-stress levels, followed by a gradual increase. Similarly, both Na+-treated and Cl－-treated trees exhibited a rapid rise of ABA after salt stress was initiated. Notably, salt-treated plants maintained a relatively higher ABA than PEG-treated plants in a longer term. Collectively, results suggest that osmotic stress and ion-specific effects were both responsible for salt-induced ABA in P. euphratica: the initial rapid increase of xylem ABA appears to be a consequence of an osmotic shock, whereas specific salt effects seem to be responsible for ABA accumulation later on. Compared with Cl－-treated trees, a higher inhibitory effect on gas exchange (Pn and TRN) was observed in Na+-salt plants, resulting from its long-sustained ABA and higher salt concentrations in the xylem. Displacement of membrane-associated Ca2+ by Na+ and the lesser capacity in Na+ compartmentation in root vacuoles likely contribute to the high influx of Na+ and Cl－ in Na+-treated plants. Xylem K+, Ca2+ and Mg2+ concentrations were elevated by external Na+-salts and Cl－-salts, suggesting that P. euphratica maintained a higher capacity in nutrient uptake under saline conditions, which makes a contribution to its salinity tolerance.

钠盐和氯盐胁迫下胡杨木质部汁液ABA、离子浓度和叶片气体交换的变化
陈少良  李金克  王天华  王沙生 Andrea POLLE  Aloys HUTTERMANN

（1. 北京林业大学生物科学与技术学院，北京100083；2. 哥廷根大学森林植物研究所，哥廷根37077，德国）

摘要：研究了渗透胁迫和盐胁迫下一年生胡杨(Populus euphratica Oliv.)幼苗的木质部汁液脱落酸(ABA)、离子浓度及叶片气体交换的变化。PEG 6000(溶液渗透势—0．24MPa)、50mmol／L含钠离子的盐溶液(NaNO3：NaHCO3：NaH₂PO₄=5：4：1，pH6．8，渗透势-0．24MPa)和50mmol／L含氯离子的盐溶液(KCl：NH₄Cl=1：1，渗透势-0．24MPa)3种处理都显著降低了苗木的净光合速率(P_n)和蒸腾速率(TRN)，但盐处理植株的TRN高于PEG处理的苗木。木质部汁液ABA的浓度在PEG处理后1h达到峰值，之后开始下降，降到对照水平后又逐渐回升。盐处理苗木的ABA也是在处理开始后就迅速升高，但之后ABA水平明显高于PEG处理的植株。结果显示，渗透胁迫和离子胁迫都能提高胡杨木质部汁液ABA的浓度：盐处理开始后ABA的迅速升高主要是渗透胁迫的作用，而此后离子胁迫(Na⁺和Cl^-)对ABA水平的提高具有重要作用。钠盐处理对胡杨净光合速率和蒸腾速率的抑制作用高于氯盐处理，其木质部汁液中较高水平的ABA和盐离子(Na⁺和Cl^-)是可能的原因。钠盐处理苗木的盐离子(Na⁺和Cl^-)水平高于氯盐处理，主要是由以下两方面的原因所致：(1)细胞膜上的Ca2⁺被Na⁺所取代，增加了膜的透性；(2)胡杨根细胞液泡对Na⁺的区隔化能力较弱(与区隔Cl-相比)。另外，盐胁迫下胡杨能保持对营养元素K+、Ca2+和Mg2+的吸收，这也是其抗盐性强的重要原因。

通讯作者。E-mail: lschen @ bjfu. edu.cn。