Journal Article

Development and persistence of sandsheaths of <i>Lyginia barbata</i> (Restionaceae): relation to root structural development and longevity

Michael W. Shane, Margaret E. McCully, Martin J. Canny, John S. Pate and Hans Lambers

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 108, issue 7, pages 1307-1322
Published in print November 2011 | ISSN: 0305-7364
Published online October 2011 | e-ISSN: 1095-8290 | DOI: https://dx.doi.org/10.1093/aob/mcr244
Development and persistence of sandsheaths of Lyginia barbata (Restionaceae): relation to root structural development and longevity

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

Strongly coherent sandsheaths that envelop perennial roots of many monocotyledonous species of arid environments have been described for over a century. This study, for the first time, details the roles played by the structural development of the subtending roots in the formation and persistence of the sheaths.

Methods

The structural development of root tissues associated with persistent sandsheaths was studied in Lyginia barbata, native to the Western Australian sand plains. Cryo-scanning electron microscopy CSEM, optical microscopy and specific staining methods were applied to fresh, field material. The role of root hairs was clarified by monitoring sheath development in roots separated from the sand profile by fine mesh.

Key Results and Conclusions

The formation of the sheaths depends entirely on the numerous living root hairs which extend into the sand and track closely around individual grains enmeshing, by approx. 12 cm from the root tip, a volume of sand more than 14 times that of the subtending root. The longevity of the perennial sheaths depends on the subsequent development of the root hairs and of the epidermis and cortex. Before dying, the root hairs develop cellulosic walls approx. 3 µm thick, incrusted with ferulic acid and lignin, which persist for the life of the sheath. The dead hairs remain in place fused to a persistent platform of sclerified epidermis and outer cortex. The mature cortex comprises this platform, a wide, sclerified inner rim and a lysigenous central region – all dead tissue. We propose that the sandsheath/root hair/epidermis/cortex complex is a structural unit facilitating water and nutrient uptake while the tissues are alive, recycling scarce phosphorus during senescence, and forming, when dead, a persistent essential structure for maintenance of a functional stele in the perennial Lyginia roots.

Keywords: CSEM; lignified and suberized root hairs; Lyginia barbata; perennial drought-tolerant roots; persistent root hairs; phosphorus recycling; Restionaceae; rhizosheaths; root hair histochemistry; sandbinding roots

Journal Article.  9535 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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