Bacon MA, Wilkinson S, Davies WJ
Biological Sciences Department, Institute of Environmental and Natural Sciences, Lancaster University, Bailrigg, Lancaster LA1 4YQ, United Kingdom.
Plant Physiol. 1998 Dec;118(4):1507-15. doi: 10.1104/pp.118.4.1507.
Elongation rates of barley (Hordeum vulgare L. cv Hanna) leaves decreased with decreasing soil water content, whereas the pH of xylem sap increased from 5.9 to 6.9 over 6 d as the soil dried. The reduction in leaf-elongation rate (LER) was correlated with the increase in sap pH. Artificial sap buffered to different pH values was fed via the subcrown internode to derooted seedlings. Although leaves elongated at in planta rates when fed artificial sap at a well-watered pH of 6.0, LER declined with increasing sap pH. This effect persisted in the light and in the dark. pH had no effect on the relative water content or the bulk abscisic acid (ABA) concentration of the growing zone of these leaves. LERs of the ABA-deficient mutant Az34 were uniformly high over the pH range tested, whereas those of its isogenic wild-type cultivar Steptoe were reduced as the artificial sap pH was increased from 6.0 to 7.0. However, supplying a well-watered concentration of ABA (3 x 10(-8) M) in the artificial xylem sap restored the pH response of the Az34 mutant. The results suggest that increased xylem sap pH acts as a drought signal to reduce LER via an ABA-dependent mechanism.
大麦（Hordeum vulgare L. cv Hanna）叶片的伸长速率随着土壤含水量的降低而下降，而随着土壤变干，木质部汁液的pH值在6天内从5.9升高到6.9。叶片伸长速率（LER）的降低与汁液pH值的升高相关。将缓冲至不同pH值的人工汁液通过 crown 下节间输送给去根的幼苗。尽管在pH值为6.0的水分充足的人工汁液喂养下，叶片以在植株内的速率伸长，但LER随着汁液pH值的升高而下降。这种效应在光照和黑暗条件下都持续存在。pH值对这些叶片生长区的相对含水量或脱落酸（ABA）的总浓度没有影响。在测试的pH范围内，ABA缺陷型突变体Az34的LER始终很高，而其同基因野生型品种Steptoe的LER随着人工汁液pH值从6.0增加到7.0而降低。然而，在人工木质部汁液中供应水分充足浓度的ABA（3×10^(-8) M）恢复了Az34突变体的pH响应。结果表明，木质部汁液pH值的升高通过依赖ABA的机制作为干旱信号来降低LER。
