Abstract

Understanding the mechanisms through which plants generate secondary cell walls is of more than academic interest: the physical properties of plant-derived materials, including timber and textiles, all depend upon secondary wall cellulose organization. Processes controlling cellulose in the secondary cell wall and their reliance on microtubules have been documented in recent decades, but this understanding is complicated, as secondary walls normally form in the plant’s interior where live cell imaging is more difficult. We investigated secondary wall formation in the orchid velamen, a multicellular epidermal layer found around orchid roots that consists of dead cells with lignified secondary cell walls. The patterns of cell wall ridges that form within the velamen vary between different orchid species, but immunolabelling demonstrated that wall deposition is controlled by microtubules. As these patterning events occur at the outer surface of the root, and as orchids are adaptable for tissue culture and genetic manipulation, we conclude that the orchid root velamen may indeed be a suitable model system for studying the organization of the plant cell wall. Notably, roots of the commonly grown orchid Laelia anceps appear ideally suited for developing this research.

Highlights

  • We demonstrate that in Laelia anceps, the outer face of the velamen has strongly patterned cell wall ridges and that strongly bundled bands of microtubules initially run parallel to these ridges before flanking the ridges on either side

  • Cross sections through the Miltoniopsis root stained for lignin with basic fuchsin showed multiple, lignin-reinforced secondary cell walls (Figure 2)

  • We have shown that the velamina of four different orchid species that are readily available show different patterns of secondary cell wall development and that in the case of Laelia and Dendrobium, these secondary cell walls are highly structured in the cell layer immediately at the surface of the root

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Summary

Introduction

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