Root hair cell walls: filling in the frameworkThis review is one of a selection of papers published in the Special Issue on Plant Cell Biology.

Abstract

Rapid progress is being made in determining the composition, synthesis, and mechanical properties of plant cell walls. Although tip-growing root hairs provide an excellent example of high-speed cell wall assembly, they have been relatively neglected by researchers interested in cell walls and those interested in tip growth. This review aims to present the root hair as an experimental system for future cell wall studies by assembling recent discoveries about the walls onto the existing framework based on older information. Most recent data come from arabidopsis ( Arabidopsis thaliana (L.) Heynh) and model legumes. Evidence supporting the turgor-mediated expansion of hair cell walls is considered, along with a survey of three components needed for cell wall expansion without rupture: cellulose (the role of CesA cellulose synthases is also addressed), Csld3, a cellulose synthase-like protein, and Lrx1, a cell wall protein. Further clues about hair cell wall composition have been obtained from gene expression studies and the use of monoclonal antibodies. Finally, there is a review of the experimental evidence that (i) hairs near the hypocotyl differ developmentally and structurally from other hairs and (ii) biosynthesis of wall components in hairs may differ significantly from the epidermal cells that they grew from. All of these recent advances suggest that root hairs could provide valuable data to augment models of plant cell walls based on more conventional cell types.