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The evolution of root hairs and rhizoids - PubMed

Review

. 2012 Jul;110(2):205-12.

doi: 10.1093/aob/mcs136. Epub 2012 Jun 23.

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Review

The evolution of root hairs and rhizoids

Victor A S Jones et al. Ann Bot. 2012 Jul.

Abstract

Background: Almost all land plants develop tip-growing filamentous cells at the interface between the plant and substrate (the soil). Root hairs form on the surface of roots of sporophytes (the multicellular diploid phase of the life cycle) in vascular plants. Rhizoids develop on the free-living gametophytes of vascular and non-vascular plants and on both gametophytes and sporophytes of the extinct rhyniophytes. Extant lycophytes (clubmosses and quillworts) and monilophytes (ferns and horsetails) develop both free-living gametophytes and free-living sporophytes. These gametophytes and sporophytes grow in close contact with the soil and develop rhizoids and root hairs, respectively.

Scope: Here we review the development and function of rhizoids and root hairs in extant groups of land plants. Root hairs are important for the uptake of nutrients with limited mobility in the soil such as phosphate. Rhizoids have a variety of functions including water transport and adhesion to surfaces in some mosses and liverworts.

Conclusions: A similar gene regulatory network controls the development of rhizoids in moss gametophytes and root hairs on the roots of vascular plant sporophytes. It is likely that this gene regulatory network first operated in the gametophyte of the earliest land plants. We propose that later it functioned in sporophytes as the diploid phase evolved a free-living habit and developed an interface with the soil. This transference of gene function from gametophyte to sporophyte could provide a mechanism that, at least in part, explains the increase in morphological diversity of sporophytes that occurred during the radiation of land plants in the Devonian Period.

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Figures

Fig. 1.
Fig. 1.

The occurrence of rhizoids and root hairs in extant land plant lineages. Streptophyte algae are the closest relatives of land plants, and some members possess rhizoids. Rhizoids develop on the gametophytes of some land plants (liverworts, mosses, hornworts, lycophytes and monilophytes). Root hairs are found only on the roots of the sporophytes of vascular plants. The lycophytes and monilophytes develop both rhizoids on their gametophytes and root hairs on their sporophytes. Rhizoids are multicellular in the mosses. All other land plants develop unicellular rhizoids and root hairs. Tree after Qiu et al. (2006).

Fig. 2.
Fig. 2.

Rhizoid and root hair morphology in Chara braunii and land plants: (A–E) rhizoids and (F–H) root hairs. (A) Rhizoids of Chara braunii; (B) rhizoids of the liverwort Marchantia polymorpha gametophyte; (C) multicellular rhizoids on the moss Physcomitrella patens gametophyte; (D) rhizoids of the hornwort Anthoceros punctatus gametophyte; (E) rhizoids on the gametophyte prothallus of the fern Ceratopteris richardii; (F) root hairs on the root of the Selaginella kraussiana sporophyte; (G) root hairs on the root of the fern Ceratopteris richardii sporophyte; (H) root hairs of the angiosperm Arabidopsis thaliana sporophyte. Arrowheads indicate rhizoids or root hairs. Scale bars = 1 mm.

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