Yoshimoto Kaori, Takamura Hiroyoshi, Kadota Isao, Motose Hiroyasu, Takahashi Taku
Department of Biological Science, Graduate School of Natural Science and Technology, Okayama University, Tsushimanaka 3-1-1, Okayama 700-8530, Japan.
Department of Chemistry, Graduate School of Natural Science and Technology, Okayama University, Tsushimanaka 3-1-1, Okayama 700-8530, Japan.
Sci Rep. 2016 Feb 16;6:21487. doi: 10.1038/srep21487.
The xylem conducts water and minerals from the root to the shoot and provides mechanical strength to the plant body. The vascular precursor cells of the procambium differentiate to form continuous vascular strands, from which xylem and phloem cells are generated in the proper spatiotemporal pattern. Procambium formation and xylem differentiation are directed by auxin. In angiosperms, thermospermine, a structural isomer of spermine, suppresses xylem differentiation by limiting auxin signalling. However, the process of auxin-inducible xylem differentiation has not been fully elucidated and remains difficult to manipulate. Here, we found that an antagonist of spermidine can act as an inhibitor of thermospermine biosynthesis and results in excessive xylem differentiation, which is a phenocopy of a thermospermine-deficient mutant acaulis5 in Arabidopsis thaliana. We named this compound xylemin owing to its xylem-inducing effect. Application of a combination of xylemin and thermospermine to wild-type seedlings negates the effect of xylemin, whereas co-treatment with xylemin and a synthetic proauxin, which undergoes hydrolysis to release active auxin, has a synergistic inductive effect on xylem differentiation. Thus, xylemin may serve as a useful transformative chemical tool not only for the study of thermospermine function in various plant species but also for the control of xylem induction and woody biomass production.
木质部将水分和矿物质从根部输送到地上部分，并为植物体提供机械强度。原形成层的维管前体细胞分化形成连续的维管束，木质部和韧皮部细胞按照适当的时空模式从中产生。原形成层的形成和木质部的分化受生长素调控。在被子植物中，热精胺是精胺的结构异构体，它通过限制生长素信号传导来抑制木质部的分化。然而，生长素诱导的木质部分化过程尚未完全阐明，且仍然难以操控。在这里，我们发现亚精胺的一种拮抗剂可以作为热精胺生物合成的抑制剂，并导致过度的木质部分化，这是拟南芥中热精胺缺陷型突变体acaulis5的表型模拟。由于其诱导木质部的作用，我们将这种化合物命名为木质素。将木质素和热精胺组合应用于野生型幼苗可消除木质素的作用，而将木质素与一种合成的生长素原共同处理，该生长素原经过水解释放出活性生长素，则对木质部分化具有协同诱导作用。因此，木质素不仅可以作为一种有用的转化化学工具，用于研究各种植物物种中热精胺的功能，还可用于控制木质部诱导和木质生物量的生产。
