Specification of Cortical Parenchyma and Stele of Maize Primary Roots by Asymmetric Levels of Auxin, Cytokinin, and Cytokinin-Regulated Proteins~1 [c][OA]

摘要

In transverse orientation, maize (Zea mays) roots are composed of a central stele that is embedded in multiple layers of corticalparenchyma. The stele functions in the transport of water, nutrients, and photosynthates, while the cortical parenchyma fulfillsmetabolic 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 withelectrospray ionization tandem mass spectrometry identified 59 proteins that were preferentially accumulated in the corticalparenchyma and 11 stele-specific proteins. Hormone profiling revealed preferential accumulation of indole acetic acid and itsconjugate 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 P-glucosidase thatfunctions in the hydrolysis of cis-zeatin O-glucoside was preferentially accumulated in the cortical parenchyma. Similarly, fourenzymes involved in ammonium assimilation that are regulated by cytokinin were preferentially accumulated in the corticalparenchyma. The antagonistic distribution of auxin and cytokinin in the stele and cortical parenchyma, together with thecortical parenchyma-specific accumulation of cytokinin-regulated proteins, suggest a molecular framework that specifies thefunction of these root tissues that also play a role in the formation of lateral roots from pericycle and endodermis cells.