Molecular Plant Nutrition, Department of Physiology and Cell Biology, Leibniz Institute of Plant Genetics and Crop Plant Research, Corrensstrasse 3, 06466 Gatersleben, Germany.
Proteomics Core Facility, SYBIOMA, KU Leuven, O&N II Herestraat 49, Bus 901, 3000 Leuven, Belgium.
Plant Cell Physiol. 2020 Jul 1;61(7):1297-1308. doi: 10.1093/pcp/pcaa059.
The root system of barley plants is composed of embryogenic, seminal roots as well as lateral and nodal roots that are formed postembryonically from seminal roots and from the basal part of shoots, respectively. Due to their distinct developmental origin, seminal and nodal roots may differ in function during plant development; however, a clear comparison between these two root types has not yet been undertaken. In this study, anatomical, proteomic and physiological traits were compared between seminal and nodal roots of similar developmental stages. Nodal roots have larger diameter, larger metaxylem area and a larger number of metaxylem vessels than seminal roots. Proteome profiling uncovered a set of root-type-specific proteins, including proteins related to the cell wall and cytoskeleton organization, which could potentially be implicated with differential metaxylem development. We also found that nodal roots have higher levels of auxin, which is known to trigger metaxylem development. At millimolar nitrate supply, nodal roots had approximately 2-fold higher nitrate uptake and root-to-shoot translocation capacities than seminal roots, whereas no differences were found at micromolar nitrate supply. Since these marked differences were not reflected by the transcript levels of low-affinity nitrate transporter genes, we hypothesize that the larger metaxylem volume of nodal roots enhances predominantly the low-affinity uptake and translocation capacities of nutrients that are transported with the bulk flow of water, like nitrate.
大麦植株的根系由胚性的初生根以及侧根和节根组成，这些根在后生胚中由初生根以及由茎的基部分别形成。由于它们具有不同的发育起源，因此在植物发育过程中，初生根和节根的功能可能不同；然而，这两种根类型之间尚未进行明确的比较。在这项研究中，对相似发育阶段的初生根和节根进行了解剖学、蛋白质组学和生理学特性的比较。节根的直径较大，木质部面积较大，木质部导管数量也较多。蛋白质组分析揭示了一组根型特异性蛋白，包括与细胞壁和细胞骨架组织相关的蛋白，这些蛋白可能与木质部的不同发育有关。我们还发现，节根中的生长素水平较高，生长素已知会引发木质部发育。在毫摩尔硝态氮供应下，节根的硝态氮吸收和根到梢的转运能力比初生根高约 2 倍，而在微摩尔硝态氮供应下则没有差异。由于这些明显的差异没有反映在低亲和力硝酸盐转运体基因的转录水平上，我们假设节根较大的木质部体积主要增强了以水流为载体的养分的低亲和力吸收和转运能力，如硝酸盐。
