Specification of Cortical Parenchyma and Stele of Maize Primary Roots by Asymmetric Levels of Auxin, Cytokinin, and Cytokinin-Regulated Proteins      

Abstract

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 ciszeatin riboside, and its conjugate cis-zeatin O-glucoside in the cortical parenchyma. A root-specific b-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.

Nonsyntenic genes drive tissue-specific dynamics of differential, nonadditive and allelic expression patterns in maize hybrids

“…This correlation reflects the developmental gradient of roots along the longitudinal axis with the youngest undifferentiated cells in the meristematic zone of the root tip (Ishikawa and Evans, 1995). Moreover, the low correlation of the cortex and stele can be explained by the functional differences of the disparate cell types present in these tissues (Saleem et al, 2010). As illustrated by these correlation analyses, overall gene expression is more divergent between different tissues of a genotype than between different genotypes within a tissue.…”

Anatomical adaptations of Astragalus gombiformis Pomel. under drought stress

“…These results are in agreement with many investigators [13][14] indicating that Salvia spendens and Triticum aestivum subjected to water deficit showed a reduction in the stem crosssectional, xylem tissue and phloem tissue thickness. This reduced xylem tissue area under water is due partly to a shift towards small diameter vessels [30] or sparsely distributed vessels [31]. For the reduction of the stem phloem tissue under stressful condition was probably not an adaptation to drought rather it was likely due to the fact that seedlings grown under water stress were smaller than untreated ones [13].…”

A High-Resolution Tissue-Specific Proteome and Phosphoproteome Atlas of Maize Primary Roots Reveals Functional Gradients along the Root Axes

“…This constraint can be overcome by tissue-specific analyses. Thus far, only a few surveys have analyzed distinct tissues such as the primary root tip (Chang et al, 2000), the elongation zone (Zhu et al, 2006(Zhu et al, , 2007, and cortical parenchyma and stele (Saleem et al, 2010). The mechanical separation of maize root cortical parenchyma (hereafter referred to as cortex) and stele made the most abundant soluble proteins of these tissues accessible (Saleem et al, 2010).…”