UV-B诱导的玉米幼苗系统信号网对根系生长的影响

通过对玉米幼苗根系生物量、NO释放量、NOS和β-D-内、外切葡聚糖酶活性的分析测定,发现UV-B光对玉米幼苗地上部分的辐射能够明显地抑制根系NO的释放,提高β-D-内、外切葡聚糖酶活性,增加根系生物量;NOS活性和NO释放不受NOS专一抑制剂LNNA的影响,自由基清除剂NAC反而能够刺激NO的释放,可见,NO的产生与NOS的活性没有相关性,但NO的释放与根系生物量和β-D-内、外切葡聚糖酶活性成负相关。因此,在根系NO的产生几乎完全依赖NADPH硝酸还原酶途径,该酶的活性极为敏感地被UV-B光胁迫所引起的氧化猝发而诱导的系统信号网所抑制。由此表明:ROS是UV-B光信号的下游信号分子,是抑制内源NO的产生和释放的上游信号分子,而NO则是抑制β-D-内、外切葡聚糖酶活性和根系生长的上游信号分子。

Effect of the systemic signal network induced by UV-B on the root growth of maize seedlings

The biomasses, the rate of NO release, NOS activity as well as β-D-endo and exo–glucanase activity in cell wall were analyzed and determined in the roots of maize seedlings. It was found that radiation of UV-B on aerial part of the seedling markedly inhibited the rate of NO-release in roots, and raised the activity of β-D-endo and exo–glucanase, increased the biomasses of roots. The patent inhibitor of NOS (LNNA) was not able to inhibit NOS activity and NO generation. ROS eliminator inversely stimulated the rate of apparent NO release. There was not any relationship between NOS activity and NO generation but the rate of apparent NO release showed a negative correlation with the biomasses and the activity of β-D-endo and exo–glucanase. Therefore, the absence of an effect of LNNA on the NO production, and the promotion of NAC to NO production implicated that NO in the roots was from a by-product of nitrate reductase whose activity was sensitively repressed by the network of systemic signal induced with UV-B. It indicated that the downstream signal molecule of UV-B light was probably ROS which may be a upstream signal molecule inhibiting NO generation. NO was perhaps a messenger of restraining β-D-endo and exo–glucanase activity in cell wall and the growth of roots.