title: Ultrastructure of stomatal development in early-divergent angiosperms reveals contrasting patterning and pre-patterning.
abstract: OBJECTIVE
  Angiosperm stomata consistently possess a pair of guard cells, but differ between taxa in the patterning and developmental origin of neighbour cells. Developmental studies of phylogenetically pivotal taxa are essential as comparative yardsticks for understanding the evolution of stomatal development.
  
  
  METHODS
  We present a novel ultrastructural study of developing stomata in leaves of Amborella (Amborellales), Nymphaea and Cabomba (Nymphaeales), and Austrobaileya and Schisandra (Austrobaileyales), representing the three earliest-divergent lineages of extant angiosperms (the ANITA-grade).
  
  
  RESULTS
  Alternative developmental pathways occur in early-divergent angiosperms, resulting partly from differences in pre-patterning and partly from the presence or absence of highly polarized (asymmetric) mitoses in the stomatal cell lineage. Amplifying divisions are absent from ANITA-grade taxa, indicating that ostensible similarities with the stomatal patterning of Arabidopsis are superficial. In Amborella, 'squared' pre-patterning occurs in intercostal regions, with groups of four protodermal cells typically arranged in a rectangle; most guard-mother cells are formed by asymmetric division of a precursor cell (the mesoperigenous condition) and are typically triangular or trapezoidal. In contrast, water-lily stomata are always perigenous (lacking asymmetric divisions). Austrobaileya has occasional 'giant' stomata.
  
  
  CONCLUSIONS
  Similar mature stomatal phenotypes can result from contrasting morphogenetic factors, although the results suggest that paracytic stomata are invariably the product of at least one asymmetric division. Loss of asymmetric divisions in stomatal development could be a significant factor in land plant evolution, with implications for the diversity of key structural and physiological pathways.
authors: Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, UK.
authors: Paula J
authors: PJ
authors: Rudall
authors: Emma V W
authors: EV
authors: Knowles
mesh_terms: D005075:Biological Evolution; D002455:Cell Division; D019684:Magnoliopsida / Q000145:classification / Q000166:cytology* / Q000235:genetics / Q000254:growth & development; D008855:Microscopy, Electron, Scanning; D010802:Phylogeny; D019441:Plant Epidermis / Q000145:classification / Q000166:cytology / Q000235:genetics / Q000254:growth & development; D018515:Plant Leaves / Q000145:classification / Q000166:cytology / Q000235:genetics / Q000254:growth & development; D054046:Plant Stomata / Q000145:classification / Q000166:cytology* / Q000235:genetics / Q000254:growth & development
keywords: ANITA; Epidermal pre-patterning; early-divergent angiosperms; meristemoids; mesogenous stomata; perigenous stomata; stomatal development
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