Abstract
SummaryIt has long been accepted that differential radial thickening of guard cells plays an important role in the turgor-driven shape changes required for stomatal pore opening to occur [1, 2, 3, 4]. This textbook description derives from an original interpretation of structure rather than measurement of mechanical properties. Here we show, using atomic force microscopy, that although mature guard cells display a radial gradient of stiffness, this is not present in immature guard cells, yet young stomata show a normal opening response. Finite element modeling supports the experimental observation that radial stiffening plays a very limited role in stomatal opening. In addition, our analysis reveals an unexpected stiffening of the polar regions of the stomata complexes, both in Arabidopsis and other plants, suggesting a widespread occurrence. Combined experimental data (analysis of guard cell wall epitopes and treatment of tissue with cell wall digesting enzymes, coupled with bioassay of guard cell function) plus modeling lead us to propose that polar stiffening reflects a mechanical, pectin-based pinning down of the guard cell ends, which restricts increase of stomatal complex length during opening. This is predicted to lead to an improved response sensitivity of stomatal aperture movement with respect to change of turgor pressure. Our results provide new insight into the mechanics of stomatal function, both negating an established view of the importance of radial thickening and providing evidence for a significant role for polar stiffening. Improved stomatal performance via altered cell-wall-mediated mechanics is likely to be of evolutionary and agronomic significance.
Highlights
(legend on page) Current Biology 27, 2974–2983, October 9, 2017 2975 using depleted CO2 to trigger stomatal opening and elevated CO2 to close stomata [6]. These results indicated that both young and mature stomata are able to open and close in response to an external trigger (Figure 1B)
We suggest that the differential thickening of the inner radial wall in mature stomata generated as a consequence of guard cell geometry acts primarily to alleviate the potential for mechanical failure, helping to maintain cell wall integrity as it undergoes repeated stress/strain cycles
Considering the pore aperture response to altered turgor pressure depicted for the baseline and fixed pole models (Figure 2D), it is clear that, above 1 MPa, a loss of polar stiffening leads to a large decrease in aperture for any given pressure as the stomatal dynamics shift from the ‘‘fixed poles’’ to the ‘‘baseline’’ curve
Summary
Textbooks state that radial stiffening of guard cells is required for stomatal opening. Carter et al show that this is not the case. They demonstrate that stomatal poles are stiffer than surrounding cells. A new ‘‘fix and flex’’ model is proposed in which polar stiffening leads to more efficient stomata, potentially allowing better water use by plants. Highlights d Stomatal poles are stiff and have a distinct cell wall composition d Loss of polar stiffening is associated with decreased degree of stomatal opening d Lack of radial guard cell stiffening does not preclude stomatal opening d A ‘‘fix and flex’’ model predicts more efficient opening of stomata via polar stiffening. 2017, Current Biology 27, 2974–2983 October 9, 2017 a 2017 The Authors.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
