title: Asymmetric growth of root epidermal cells is related to the differentiation of root hair cells in Hordeum vulgare (L.).
abstract: The root epidermis of most vascular plants harbours two cell types, namely trichoblasts (capable of producing a root hair) and atrichoblasts. Here, in vivo analysis, confocal laser-scanning microscopy, transmission electron microscopy, histological analysis, and three-dimensional reconstruction were used to characterize the cell types present in the barley root epidermis and their distribution in the tissue. Both trichoblasts and atrichoblasts were present in the wild-type cultivars and could be distinguished from one another at an early stage. Trichoblast/atrichoblast differentiation depended on asymmetric cell expansion after a period of symmetrical cell division. After asymmetric growth, only the shorter epidermal cells could produce root hairs, whereas the longer cells became atrichoblasts. Moreover, the root epidermis did not develop root hairs at all if the epidermal cells did not differentiate into two asymmetric cell types. The root hairless phenotype of bald root barley (brb) and root hairless 1.b (rhl1.b) mutants was caused by a mutation in a gene related to the asymmetric expansion of the root epidermal cells. Additionally, the results showed that the mechanism of trichoblast/atrichoblast differentiation is not evolutionally conserved across the subfamilies of the Poaceae; in the Pooideae subfamily, both asymmetric division and asymmetric cell expansion have been observed.
authors.affiliation: Department of Genetics, Faculty of Biology and Environmental Protection, University of Silesia, Katowice 40-032, Poland.
authors.forename: Marek
authors.initials: M
authors.lastname: Marzec
authors.forename: Michael
authors.initials: M
authors.lastname: Melzer
authors.forename: Iwona
authors.initials: I
authors.lastname: Szarejko
mesh_terms: D002454:Cell Differentiation; D049109:Cell Proliferation; D018506:Gene Expression Regulation, Plant; D001467:Hordeum / Q000166:cytology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D009154:Mutation; D019441:Plant Epidermis / Q000166:cytology* / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000166:cytology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D010940:Plant Proteins
keywords: Atrichoblast; Hordeum vulgare (barley); cell pattern; differentiation; epidermis; root hair; trichoblast.
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