Guard cells elongate: relationship of volume and surface area during stomatal movement
Tobias Meckel 1*, Lars Gall 2, Stefan Semrau 1, Ulrike Homann 2 and Gerhard Thiel 2
1 University of Leiden
2 Darmstadt University of Technology
* To whom correspondence should be addressed. E-mail: tobias.meckel{at}web.de.
Submitted on July 4, 2006
Revised on August 6, 2006
Accepted on 23 October 2006
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Abstract |
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Stomata in the epidermis of photosynthetically active plant organs are formed by pairs of guard cells, which create a pore, to facilitate CO2 and water exchange with the environment. In order to control this gas exchange, guard cells actively change their volume and, consequently, surface area to alter the aperture of the stomatal pore. Due to the limited elasticity of the plasma membrane, such changes in surface area require an exocytic addition or endocytic retrieval of membrane during stomatal movement. Using confocal microscopic data, we have reconstructed detailed 3D-models of open and closed stomata in order to precisely quantify the necessary area to be exo- and endocytosed by the guard cells. Images were obtained under a strong emphasis on a precise calibration of the method and by avoiding unphysiological osmotical imbalance, and hence osmocytosis. The data reveal that guard cells of Vicia faba L., whose aperture increases by 111.89 ± 22.39 %, increase in volume and surface area by 24.82 ± 6.26 % and 14.99 ± 2.62 %, respectively. In addition, the precise volume to surface area relationship allows quantitative modelling of the 3D changes. While the major volume change is caused by a slight increase in the cross-section of the cells, an elongation of the guard cells achieves the main aperture change.
Key Words:
3D reconstruction, confocal microscopy, guard cells, surface area, vesicles, volume
