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Abstract BackgroundLike all plant cells, the guard cells of stomatal complexes are encased in cell walls that are composed of diverse, interacting networks of polysaccharide polymers. The properties of these cell walls underpin the dynamic deformations that occur in guard cells as they expand and contract to drive the opening and closing of the stomatal pore, the regulation of which is crucial for photosynthesis and water transport in plants. ScopeOur understanding of how cell wall mechanics are influenced by the nanoscale assembly of cell wall polymers in guard cell walls, how this architecture changes over stomatal development, maturation and ageing and how the cell walls of stomatal guard cells might be tuned to optimize stomatal responses to dynamic environmental stimuli is still in its infancy. ConclusionIn this review, we discuss advances in our ability to probe experimentally and to model the structure and dynamics of guard cell walls quantitatively across a range of plant species, highlighting new ideas and exciting opportunities for further research into these actively moving plant cells. 

Abstract Stomatal function in plants is regulated by the nanoscale architecture of the cell wall and turgor pressure, which together control stomatal pore size to facilitate gas exchange and photosynthesis. The mechanical properties of the cell wall and cell geometry are critical determinants of stomatal dynamics. However, the specific biomechanical functions of wall constituents, for example, cellulose and pectins, and their impact on the work required to open or close the stomatal pore are unclear. Here, we use nanoindentation in normal and lateral directions, computational modeling, and microscopic imaging of cells from the model plant Arabidopsis thaliana to investigate the precise influences of wall architecture and turgor pressure on stomatal biomechanics. This approach allows us to quantify and compare the unique anisotropic properties of guard cells with normal composition, lower cellulose content, or alterations in pectin molecular weight. Using these data to calculate the work required to open the stomata reveals that the wild type, with a circumferential-to-longitudinal modulus ratio of 3:1, is the most energy-efficient of those studied. In addition, the tested genotypes displayed similar changes in their pore size despite large differences in wall thickness and biomechanical properties. These findings imply that homeostasis in stomatal function is maintained in the face of varying wall compositions and biomechanics by tuning wall thickness. 

SUMMARY Stomata are pores at the leaf surface that enable gas exchange and transpiration. The signaling pathways that regulate the differentiation of stomatal guard cells and the mechanisms of stomatal pore formation have been characterized inArabidopsis thaliana. However, the process by which stomatal complexes develop after pore formation into fully mature complexes is poorly understood. We tracked the morphogenesis of young stomatal complexes over time to establish characteristic geometric milestones along the path of stomatal maturation. Using 3D‐nanoindentation coupled with finite element modeling of young and mature stomata, we found that despite having thicker cell walls than young guard cells, mature guard cells are more energy efficient with respect to stomatal opening, potentially attributable to the increased mechanical anisotropy of their cell walls and smaller changes in turgor pressure between the closed and open states. Comparing geometric changes in young and mature guard cells of wild‐type and cellulose‐deficient plants revealed that although cellulose is required for normal stomatal maturation, mechanical anisotropy appears to be achieved by the collective influence of cellulose and additional wall components. Together, these data elucidate the dynamic geometric and biomechanical mechanisms underlying the development process of stomatal maturation.