The function of pseudostomata in Sphagnum.


Exploding a myth: the capsule dehiscence mechanism and the function of pseudostomata in Sphagnum.

by Duckett J. G., Pressel S., P’ng K. M., Renzaglia K. S. (2009)

School of Biological and Chemical Sciences, Queen Mary University of London, UK.

Duckett J. G., Queen Mary University of London, UK.

Pressel S.,

P’ng K. M.,

Karen Renzaglia, Research Professor, Plant Biology.Official photo is frame #12
Karen S. Renzaglia, Southern Illinois University, USA


in New Phytol 2009,183:1053-1063. – doi: 10.1111/j.1469-8137.2009.02905.x.

(PubMed Abstract | Publisher Full Text)

Living specimens of Sphagnum palustre. (a) Capitulum showing several pale-brown mature sporophytes surrounded by perichaetial leaves and a dark-brown sporophyte on a partially elongated pseudopodium. Note the calyptra beginning to peel off the capsule (arrowhead). (b) Fully elongated pseudopodium with a still intact calyptra around the sporophyte. (c) Dehisced hydrated sporophytes. (d) Pierced sporophytes (holes arrowed) that have shrunk and lost their lids after drying out for 5 h. (e) Intact sporophyte with a partially detached lid after 5 h drying out. (f) Undehisced sporophyte after 3 h drying out and squashed in immersion oil to show the formation of a large internal air space. Bars, (a–c) 2 mm, (d–f) 1 mm. –


  • • The nineteenth century air-gun explanation for explosive spore discharge in Sphagnum has never been tested experimentally. Similarly, the function of the numerous stomata ubiquitous in the capsule walls has never been investigated.
  • • Both intact and pricked Sphagnum capsules, that were allowed to dry out, all dehisced over an 8–12 h period during which time the stomatal guard cells gradually collapsed and their potassium content, measured by X-ray microanalysis in a cryoscanning electron microscope, gradually increased. By contrast, guard cell potassium fell in water-stressed Arabidopsis.
  • • The pricking experiments demonstrate that the air-gun notion for explosive spore discharge in Sphagnum is inaccurate; differential shrinkage of the capsule walls causes popping off the rigid operculum. The absence of evidence for a potassium-regulating mechanism in the stomatal guard cells and their gradual collapse before spore discharge indicates that their sole role is facilitation of sporophyte desiccation that ultimately leads to capsule dehiscence.
  • • Our novel functional data on Sphagnum, when considered in relation to bryophyte phylogeny, suggest the possibility that stomata first appeared in land plants as structures that facilitated sporophyte drying out before spore discharge and only subsequently acquired their role in the regulation of gaseous exchange.

Read the full article: Wiley Online Library


Published by

Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.

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