How do roots control xylem sap ABA concentration in response to soil drying?
How do roots control xylem sap ABA concentration in response to soil drying?
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DOI：
10.1093/oxfordjournals.pcp.a029078
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发表时间：
1997-01-01
影响因子：
4.9
通讯作者：
Wong, MH
中科院分区：
文献类型：
--
作者：
Liang, JS;Zhang, JH;Wong, MH
玉米(Zea Mays L.)和热带树种银合欢进行不同程度的土壤干旱处理，同时测定其根系和木质部ABA含量的变化。此外，还进行了去叶、遮光和环剥等处理，以控制韧皮部向根的运输。土壤干燥后，两种植物木质部汁液中的ABA浓度与根中的ABA浓度几乎呈线性增加。这种增加在根ABA浓度较高时相对平稳，表明严重的土壤干旱可能阻碍了根的某些部分将ABA输送到木质部。当H-3-ABA被负载到根中并监测其消失时，发现根分解ABA的能力远低于报道的叶片，半衰期为1.15h，在培养21h期间，相当数量(46%)的H-3-ABA保持不变。土壤干旱显著降低了H-3-ABA的分解能力，使其半衰期延长至2.27h，原始量增加到50.7%。去叶和遮光处理显著降低了水分胁迫下植物的木质部ABA含量。用茎环剥的方法估计，在土壤干燥条件下，木质部汁液中约有25%~30%的ABA来自韧皮部。结果表明，土壤干燥过程中，除了促进根系ABA的生物合成外，根系ABA分解代谢的减慢和地上部输入的增加也是引起木质部ABA浓度敏感变化的重要原因。
Maize (Zea mays L.) and Leucaena leucocephala (a tropical tree) were subjected to different degrees of soil drying and changes in their root and xylem ABA concentrations were measured simultaneously. Additional treatments such as defoliation, light sheltering and stem girdling were applied so that phloem transport into roots was manipulated. When soil was dried, ABA concentration in xylem sap increased almost linearly with that of roots in both species. Such an increase was relatively plateaued at high root ABA concentrations, suggesting that severe soil drying might have hindered some parts of roots from delivering ABA into xylem flow. When H-3-ABA was loaded into roots and monitored for its disappearance, it was found that the capability of roots to catabolize ABA was much lower than that reported for leaves, with a half-life of 1.15 h and a considerable amount (46%) of fed H-3-ABA was remained unmodified during 21 h of incubation. Previous soil drying significantly reduced such a capability of catabolism and extended the half-life of fed H-3-ABA to 2.27 h, and the amount remaining unmodified was elevated to 50.7%. Defoliation and light-sheltering treatments significantly reduced xylem ABA concentration of water-stressed plants. Using stem girdling approach, it was estimated that about 25 to 30% of ABA in the xylem sap might come from shoot through phloem under soil drying condition. It was concluded that in addition to an enhanced ABA biosynthesis in roots during soil drying, a slowed ABA catabolism in roots and an increased import from shoots were also important contributions to the sensitive changes of xylem ABA concentration in response to such a stress.