A Split-root Dynamic Mechanism Of Alternating Stress Xylem Ph Changes

We now know that roots will produce a signal and send it to shoots via xylem to control stoma behavior so to use water efficiently, when it sense the soil water condition. Recently, more scientists think ABA is a kind of signal, but there are different opinions on whether ABA is the only signal. Some people think there are some other materials which also act as a signal, such as pH, amino acid, protein. In this study , we want to use the alternative stress method to know whether pH is also a kind of signal and why pH change in xylem sap under stress.We have carried out the Hogland solution pot experiment for the maize (ShanDan 9 .cv), we have a research of influence of exogenous pH on growth, root-shoot ratio, RWC, photosynthesis, transpiration efficiency, root hair and stoma; the change of WUE, water efficiency (WUE) and the pH in xylem sap were researched. Furthermore, we try to anaylize the change of amino acid, anion, cation in xylem sap to explain the change of pH.The results show as follows:l.The pH treatment has a different influence on the growth, root-shoot ratio, WUE, stomatal aperture, relative water content (RWC), and root hair formation of different Maize (whole, de-rooted and detached leaves). More acidic treatment has an advantage on the Maize seedling growth. Under all pH treatment, the RWC of detached leaves are different, the RWC under pH7.0 and pH7.5 are lower, while under pHS.O it is higher. Root-shoot ratio are all lower under pH treatment, but, when add the PEG, the result are opposite, under pHS.O treatment it increase greatly. pH treatment has major influence on the root hair. The amount of root hair are more than other treatments under pH4.5-pH6.5, under more acidic conditions the root hair is more silmer.2.The stomal behavior changed greatly under stress, some opened, others closed. After add PEG, the aperture under -O.SMpa are lower than under -0.2Mpa, especially under pHS.O, pH6.5 and pHS.O. The WUE of detached leaves changed greatly, but no obviously. The WUE of whole maize decreased under pH treatment. The reason maybe is that the photosynthesis decreased. Stomatal conductance are also influenced by the pH treatment.3.Under stress, the growth of maize decrease. Alternative stress has a compensate effect on growth. The maize WUE decreased greatly under stress, but the alternative stress can improve the maize WUE. The pH in xylem sap increase than contrast under stress andalternative stress, but no obvious difference between them.4.The amount of acidic and base amino acid changed greatly under stress and alternative stress, the acidic amino acid decreased than contrast, under -0.2Mpa and -0.5Mpa alternative stress decrease 80.68% and 71.02% than the begining; but the base amino acid increased, under-0.2Mpa and-0.5Mpa alternative stress increase 271.42% and 197.62%. The concentration of K+ in xylem sap increased greatly, under -0.2Mpa and -O.SMpa alternative stress, it is higher 90.68% and 74.92% than contrast; but the concentration NOs" decreased obviously. The components in xylem sap change greatly especially under alternative stress.