Takei Kentaro, Takahashi Toru, Sugiyama Tatsuo, Yamaya Tomoyuki, Sakakibara Hitoshi
Laboratory for Communication Mechanism, Plant Science Center, RIKEN (The Institute of Physical and Chemical Research) Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
J Exp Bot. 2002 Apr;53(370):971-7. doi: 10.1093/jexbot/53.370.971.
In higher plants, inorganic nitrogen has crucial effects on growth and development, providing cellular components and modulating gene expression. To date, not only nitrogen assimilatory genes but also a substantial number of genes with other functions have been shown to be selectively regulated by the availability of nitrogen. In terms of the communicating substance(s) between root and shoot, accumulating evidence suggests that nitrate itself is the primary signal molecule triggering the activation of transcription of nitrate assimilation and related genes. On the other hand, some of the genes involved in photosynthesis, cell cycling and translation machinery are also regulated, at least in part, by nitrate and other nitrogen sources and, in some cases, the effect can be mimicked by cytokinin treatment. Spatial and temporal studies on the accumulation levels and the translocation of cytokinin in response to nitrate replenishment in maize showed subsequent accumulation of various cytokinin species in the roots, xylem sap and leaves. In Arabidopsis thaliana, trans-zeatin riboside-5'-monophosphate and/or trans-zeatin riboside also accumulated in the roots in response to nitrate resupply. These studies suggest that cytokinin metabolism and translocation could be commonly modulated by nitrogen availability in higher plants. Thus, in addition to nitrate, cytokinin could be another root-to-shoot signal communicating nitrogen availability.
在高等植物中，无机氮对生长发育具有关键作用，它为细胞组分的合成提供原料并调控基因表达。迄今为止，不仅氮同化基因，还有大量具有其他功能的基因已被证明会受到氮供应情况的选择性调控。就根和地上部分之间的信号传递物质而言，越来越多的证据表明，硝酸盐本身就是触发硝酸盐同化及相关基因转录激活的主要信号分子。另一方面，一些参与光合作用、细胞周期和翻译机制的基因也至少部分地受到硝酸盐和其他氮源的调控，在某些情况下，细胞分裂素处理可模拟这种效应。对玉米中细胞分裂素响应硝酸盐补充的积累水平和转运情况进行的时空研究表明，随后各种细胞分裂素在根、木质部汁液和叶片中积累。在拟南芥中，反式玉米素核糖苷 -5'- 单磷酸和 / 或反式玉米素核糖苷也会响应硝酸盐再供应而在根中积累。这些研究表明，高等植物中细胞分裂素的代谢和转运可能普遍受到氮供应情况的调节。因此，除了硝酸盐外，细胞分裂素可能是另一种从根向地上部分传递氮供应情况的信号。
