Institute of Biotechnology and Department of Biosciences, University of Helsinki, FIN-00014 Helsinki, Finland.
Curr Biol. 2011 Jun 7;21(11):927-32. doi: 10.1016/j.cub.2011.04.049. Epub 2011 May 27.
Cytokinin phytohormones regulate a variety of developmental processes in the root such as meristem size, vascular pattern, and root architecture [1-3]. Long-distance transport of cytokinin is supported by the discovery of cytokinins in xylem and phloem sap [4] and by grafting experiments between wild-type and cytokinin biosynthesis mutants [5]. Acropetal transport of cytokinin (toward the shoot apex) has also been implicated in the control of shoot branching [6]. However, neither the mode of transport nor a developmental role has been shown for basipetal transport of cytokinin (toward the root apex). In this paper, we combine the use of a new technology that blocks symplastic connections in the phloem with a novel approach to visualize radiolabeled hormones in planta to examine the basipetal transport of cytokinin. We show that this occurs through symplastic connections in the phloem. The reduction of cytokinin levels in the phloem leads to a destabilization of the root vascular pattern in a manner similar to mutants affected in auxin transport or cytokinin signaling [7]. Together, our results demonstrate a role for long-distance basipetal transport of cytokinin in controlling polar auxin transport and maintaining the vascular pattern in the root meristem.
细胞分裂素植物激素调节根的多种发育过程，如分生组织大小、脉管模式和根结构[1-3]。细胞分裂素在木质部和韧皮部汁液中的发现[4]以及野生型和细胞分裂素生物合成突变体之间的嫁接实验[5]支持细胞分裂素的长距离运输。细胞分裂素向根尖的向顶运输也与控制芽分枝有关[6]。然而，对于细胞分裂素的向基运输（向根尖），既没有显示出其运输方式，也没有显示出其发育作用。在本文中，我们将使用一种新技术（该技术阻断韧皮部中的共质体连接）与一种新方法（在体内可视化放射性标记激素）结合，研究细胞分裂素的向基运输。我们表明，这种运输是通过韧皮部中的共质体连接进行的。韧皮部中细胞分裂素水平的降低导致根脉管模式的不稳定性，类似于受生长素运输或细胞分裂素信号转导影响的突变体[7]。总之，我们的结果表明，细胞分裂素的长距离向基运输在控制极性生长素运输和维持根分生组织的脉管模式方面发挥了作用。
