Center for Plant Molecular Biology, Department of General Genetics, University of Tuebingen, 72076 Tuebingen, Germany.
Plant Physiol. 2010 Jan;152(1):4-18. doi: 10.1104/pp.109.150425. Epub 2009 Nov 20.
In transverse orientation, maize (Zea mays) roots are composed of a central stele that is embedded in multiple layers of cortical parenchyma. The stele functions in the transport of water, nutrients, and photosynthates, while the cortical parenchyma fulfills metabolic functions that are not very well characterized. To better understand the molecular functions of these root tissues, protein- and phytohormone-profiling experiments were conducted. Two-dimensional gel electrophoresis combined with electrospray ionization tandem mass spectrometry identified 59 proteins that were preferentially accumulated in the cortical parenchyma and 11 stele-specific proteins. Hormone profiling revealed preferential accumulation of indole acetic acid and its conjugate indole acetic acid-aspartate in the stele and predominant localization of the cytokinin cis-zeatin, its precursor cis-zeatin riboside, and its conjugate cis-zeatin O-glucoside in the cortical parenchyma. A root-specific beta-glucosidase that functions in the hydrolysis of cis-zeatin O-glucoside was preferentially accumulated in the cortical parenchyma. Similarly, four enzymes involved in ammonium assimilation that are regulated by cytokinin were preferentially accumulated in the cortical parenchyma. The antagonistic distribution of auxin and cytokinin in the stele and cortical parenchyma, together with the cortical parenchyma-specific accumulation of cytokinin-regulated proteins, suggest a molecular framework that specifies the function of these root tissues that also play a role in the formation of lateral roots from pericycle and endodermis cells.
在横切面上，玉米（Zea mays）根由嵌入多层皮层细胞的中央中柱组成。中柱的功能是运输水、养分和光合产物，而皮层细胞则履行代谢功能，但这些功能尚未得到很好的描述。为了更好地了解这些根组织的分子功能，进行了蛋白质和植物激素分析实验。二维凝胶电泳结合电喷雾串联质谱鉴定了 59 种在皮层细胞中优先积累的蛋白质和 11 种中柱特异性蛋白质。激素分析显示，吲哚乙酸及其缀合物吲哚乙酸-天冬氨酸优先积累在中柱中，细胞分裂素顺式玉米素、其前体顺式玉米素核苷和其缀合物顺式玉米素 O-葡萄糖苷主要定位于皮层细胞中。一种在顺式玉米素 O-葡萄糖苷水解中起作用的根特异性β-葡萄糖苷酶优先积累在皮层细胞中。同样，四种受细胞分裂素调节的参与铵同化的酶也优先积累在皮层细胞中。生长素和细胞分裂素在中柱和皮层细胞中的拮抗分布，加上细胞分裂素调节蛋白在皮层细胞中的特异性积累，表明了一个分子框架，指定了这些根组织的功能，这些组织也在从周鞘和内皮层细胞形成侧根中发挥作用。
