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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 Pectins are abundant in the cell walls of eudicot plants and have been implicated in determining the development and biomechanics of stomatal guard cells, which expand and contract dynamically to open and close stomatal pores on the plant surface, modulating photosynthesis and water transport. Pectic homogalacturonan is delivered to the cell wall in a methylesterified form but can be demethylesterified in the wall by pectin methylesterases, increasing both its ability to form crosslinks via calcium and its susceptibility to degradation by endogenous pectinases. Although a few pectin methylesterases have been implicated in stomatal development and function, this large family of proteins has not been fully characterized with respect to how they modulate stomatal guard cells. Here, we characterized the function of PECTIN METHYLESTERASE51 (PME51), a pectin methylesterase–encoding gene that is expressed in developing guard cells, in stomatal morphogenesis in seedlings and adult plants ofArabidopsis thaliana. OverexpressingPME51led to smaller adult plants with smaller stomatal complexes and subtle changes in initial responses to opening and closure stimuli, whereas knocking outPME51resulted in smaller stomatal complexes and longer roots in seedlings. We observed changes in pectin labeling in knockout and overexpression plants that imply a specific function for PME51 in modulating the degree of methylesterification for homogalacturonan. Together, these findings expand our understanding of how pectin modification by pectin methylesterases affects the development and function of stomatal guard cells, which must maintain a balance of strength and flexibility to optimize plant growth. 

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. 

Abstract Stomata are dynamic pores on plant surfaces that regulate photosynthesis and are thus of critical importance for understanding and leveraging the carbon-capturing and food-producing capabilities of plants. However, our understanding of the molecular underpinnings of stomatal kinetics and the biomechanical properties of the cell walls of stomatal guard cells that enable their dynamic responses to environmental and intrinsic stimuli is limited. Here, we built multiscale models that simulate regions of the guard cell wall, representing cellulose fibrils and matrix polysaccharides as discrete, interacting units, and used these models to help explain how molecular changes in wall composition and underlying architecture alter guard wall biomechanics that gives rise to stomatal responses in mutants with altered wall synthesis and modification. These results point to strategies for engineering guard cell walls to enhance stomatal response times and efficiency. 

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. 

Data science, an emerging multidisciplinary field, resides at the intersec- tion of computational sciences, statistical modeling, and domain-specific sciences. The current norm for data science education predominantly focuses on graduate programs, which presume a pre-existing knowledge base in one or more relevant sciences. However, this framework often overlooks those who don’t plan to pursue graduate studies, thereby limiting their exposure to this rapidly expanding field. Penn State addressed this gap by establishing one of the first undergraduate degree programs in Data Sciences, a collaboration between the College of Information Sci- ences and Technology, the Department of Computer Science and Engineering, and the Department of Statistics. One key component of this program is a project-focused, writing-intensive course designed for upper-class undergraduates. This course guides students through the entire data science project pipeline, from problem identifica- tion to solution presentation. It allows students to apply foundational data science principles to real-world problems, advancing their understanding through practi- cal application. This chapter details the objectives, rationale, and course design, alongside reflections from our teaching experience. The insights provided could be helpful to instructors developing similar data science programs or courses at an undergraduate level, broadening the influence of this important field 

Abstract The ability of plants to absorb CO 2 for photosynthesis and transport water from root to shoot depends on the reversible swelling of guard cells that open stomatal pores in the epidermis. Despite decades of experimental and theoretical work, the biomechanical drivers of stomatal opening and closure are still not clearly defined. We combined mechanical principles with a growing body of knowledge concerning water flux across the plant cell membrane and the biomechanical properties of plant cell walls to quantitatively test the long-standing hypothesis that increasing turgor pressure resulting from water uptake drives guard cell expansion during stomatal opening. To test the alternative hypothesis that water influx is the main motive force underlying guard cell expansion, we developed a system dynamics model accounting for water influx. This approach connects stomatal kinetics to whole plant physiology by including values for water flux arising from water status in the plant .