Journal Article

The remarkable stomata of horsetails (Equisetum): patterning, ultrastructure and development

Erin Cullen and Paula J. Rudall

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 118, issue 2, pages 207-218
Published in print August 2016 | ISSN: 0305-7364
Published online June 2016 | e-ISSN: 1095-8290 | DOI: https://dx.doi.org/10.1093/aob/mcw094
The remarkable stomata of horsetails (Equisetum): patterning, ultrastructure and development

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

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Background and Aims The stomata of Equisetum – the sole extant representative of an ancient group of land plants – are unique with respect to both structure and development, yet little is known about details of ultrastructure and patterning, and existing accounts of key developmental stages are conflicting.

Methods We used light and electron microscopy to examine mature stomata and stomatal development in Equisetum myriochaetum, and compared them with other land plants, including another putative fern relative, Psilotum. We reviewed published reports of stomatal development to provide a comprehensive discussion of stomata in more distantly related taxa.

Key Results Stomatal development in Equisetum is basipetal and sequential in strict linear cell files, in contrast with Psilotum, in which stomatal development occurs acropetally. In Equisetum, cell asymmetry occurs in the axial stomatal cell file, resulting in a meristemoidal mother cell that subsequently undergoes two successive asymmetric mitoses. Each stomatal cell complex is formed from a single precursor meristemoid, and consists of four cells: two guard cells and two mesogene subsidiary cells. Late periclinal divisions occur in the developing intervening cells.

Conclusions In addition to the unique mature structure, several highly unusual developmental features include a well-defined series of asymmetric and symmetric mitoses in Equisetum, which differs markedly from Psilotum and other land plants. The results contribute to our understanding of the diverse patterns of stomatal development in land plants, including contrasting pathways to paracytic stomata. They add to a considerable catalogue of highly unusual traits of horsetails – one of the most evolutionarily isolated land-plant taxa.

Keywords: Equisetum; meristemoids; Psilotum; sphenophytes; stomatal development

Journal Article.  5624 words.  Illustrated.

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

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