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Published on November 17, 2006; 10.1104/pp.106.089367

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Received September 1, 2006
Accepted November 14, 2006

The Mechanical Diversity of Stomata and its Significance in Gas Exchange Control

Peter J. Franks and Graham D. Farquhar *

School of Tropical Biology, James Cook University, PO Box 6811, Cairns, Queensland 4870, Australia
Environmental Biology Group, Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra ACT 2601, Australia

* Corresponding author; email: peter.franks{at}jcu.edu.au.

Given that stomatal movement is ultimately a mechanical process, and that stomata are morphologically and mechanically diverse, we explored the influence of stomatal mechanical diversity on leaf gas exchange, and considered some of the constraints. Mechanical measurements were conducted on the guard cells of four different species exhibiting different stomatal morphologies, including three variants on the classical "kidney" form, and one "dumb-bell" type, and this information, together with gas exchange measurements, was used to model and compare their respective operational characteristics. Based on evidence from SEM images of cryo-sectioned leaves that were sampled under full sun and high humidity, and from pressure probe measurements of the stomatal aperture versus guard cell turgor relationship at maximum and zero epidermal turgor, it was concluded that maximum stomatal apertures (and maximum leaf diffusive conductance) could not be obtained in at least one of the species (the grass Triticum aestivum) without a substantial reduction in subsidiary cell osmotic (and hence turgor) pressure during stomatal opening to overcome the large mechanical advantage of subsidiary cells. A mechanism for this is proposed, with a corollary being greatly accelerated stomatal opening and closure. Gas exchange measurements on T. aestivum revealed the capability of very rapid stomatal movements, which may be explained by the unique morphology and mechanics of its dumb-bell shaped stomata coupled with "sea-sawing" of osmotic and turgor pressure between guard and subsidiary cells during stomatal opening or closure. Such properties might underlie the success of grasses.




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[Abstract] [Full Text] [PDF]


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