Kaufmann M R, Eckard A N
Department of Plant Sciences, University of California, Riverside, California 92502.
Plant Physiol. 1971 Apr;47(4):453-6. doi: 10.1104/pp.47.4.453.
The water relations of pepper plants (Capsicum frutescens L.) under conditions conducive to guttation were studied to evaluate the control of plant water stress with polyethylene glycols. The addition of polyethylene glycol 6000 to the nutrient solution resulted in water relations similar to those expected in soil at the same water potentials. Specifically, xylem pressure potential in the root and leaf became more negative during a 24-hour treatment period, while osmotic potential of the root xylem sap remained constant. The decrease in pressure potential was closely correlated with the decrease in osmotic potential of the nutrient solution. In contrast, the addition of polyethylene glycol 400 to the nutrient medium resulted in a reduction of osmotic potential in the root xylem sap; this osmotic adjustment in the xylem was large enough to establish an osmotic gradient for entry of water and cause guttation at a nutrient solution osmotic potential of -4.8 bars. Pressure potential in the root and leaf xylem became negative only at nutrient solution osmotic potentials lower than -4.8 bars. About half of the xylem osmotic adjustment in the presence of polyethylene glycol 400 was caused by increased accumulation of K(+), Na(+), Ca(2+), and Mg(2+) in the root xylem. These studies indicate that larger polyethylene glycol molecules such as polyethylene glycol 6000 are more useful for simulating soil water stress than smaller molecules such as polyethylene glycol 400.
研究了在有利于吐水的条件下辣椒植株（辣椒）的水分关系，以评估聚乙二醇对植物水分胁迫的控制作用。向营养液中添加聚乙二醇6000会导致水分关系与在相同水势下土壤中的预期情况相似。具体而言，在24小时的处理期间，根和叶中的木质部压力势变得更负，而根木质部汁液的渗透势保持不变。压力势的降低与营养液渗透势的降低密切相关。相比之下，向营养培养基中添加聚乙二醇400会导致根木质部汁液的渗透势降低；木质部中的这种渗透调节足够大，能够建立水进入的渗透梯度，并在营养液渗透势为-4.8巴时导致吐水。仅在营养液渗透势低于-4.8巴时，根和叶木质部中的压力势才变为负值。在聚乙二醇400存在的情况下，木质部渗透调节的大约一半是由根木质部中K(+)、Na(+)、Ca(2+)和Mg(2+)积累增加引起的。这些研究表明，较大的聚乙二醇分子（如聚乙二醇6000）比较小的分子（如聚乙二醇400）更有助于模拟土壤水分胁迫。
