POLYGALACTURONASE INVOLVED IN EXPANSION3 Functions in Seedling Development, Rosette Growth, and Stomatal Dynamics in Arabidopsis thaliana.

Plant cell separation and expansion require pectin degradation by endogenous pectinases such as polygalacturonases, few of which have been functionally characterized. Stomata are a unique system to study both processes because stomatal maturation involves limited separation between sister guard cells and stomatal responses require reversible guard cell elongation and contraction. However, the molecular mechanisms for how stomatal pores form and how guard cell walls facilitate dynamic stomatal responses remain poorly understood. We characterized POLYGALACTURONASE INVOLVED IN EXPANSION3 (PGX3), which is expressed in expanding tissues and guard cells. PGX3-GFP localizes to the cell wall and is enriched at sites of stomatal pore initiation in cotyledons. In seedlings, ablating or overexpressing PGX3 affects both cotyledon shape and the spacing and pore dimensions of developing stomata. In adult plants, PGX3 affects rosette size. Although stomata in true leaves display normal density and morphology when PGX3 expression is altered, loss of PGX3 prevents smooth stomatal closure, and overexpression of PGX3 accelerates stomatal opening. These phenotypes correspond with changes in pectin molecular mass and abundance that can affect wall mechanics. Together, these results demonstrate that PGX3-mediated pectin degradation affects stomatal development in cotyledons, promotes rosette expansion, and modulates guard cell mechanics in adult plants.

Comparison of Fracture Resistance of Endodontically Treated Teeth Restored with FiberSite Postsystem and Glass Fiber, Combined with Different Root Canal Sealers.

This study is aimed at evaluating the effects of FiberSite and glass fiber postsystems on the fracture resistance of endodontically restored teeth, when combined with various root canal sealers. Forty human mandibular premolar teeth, each having a single root with anatomically comparable dimension and length, were selected. The teeth in each experimental group (n = 10) were instrumented, obturated, and restored with the following procedures: in group 1, AH Plus root canal sealer and a glass fiber post with a composite core; in group 2, AH Plus root canal sealer and a FiberSite postsystem; in group 3, Sure-Seal Root canal sealer and a glass fiber post with a composite core; and in group 4, Sure-Seal Root canal sealer and a FiberSite postsystem. The specimens were placed on a universal test machine. The fracture resistance of all specimens was tested using generic test equipment, and the value of the force in newton (N) during fracture was measured for each root. A statistical analysis was conducted through the Kruskal-Wallis test as well as the post hoc test. The tests showed a significant difference between groups 2 and 3, with group 3 producing load values that were significantly higher than group 2. In contrast, no significant differences were found to exist between the other groups. Regardless of postsystems, groups 3 and 4 showed higher mean fracture values (but no statistically significant differences) than groups 1 and 2.

Development and validation of Image Stimuli for Emotion Elicitation (ISEE): A novel affective pictorial system with test-retest repeatability.

The aim of this study was to develop a novel set of pictorial stimuli for emotion elicitation. The Image Stimuli for Emotion Elicitation (ISEE), are the first set of stimuli for which there was an unbiased initial selection method and with images specifically selected for high retest correlation coefficients and high agreement across time. In order to protect against a researcher's subjective bias in screening initial pictures, we crawled 10,696 images from the biggest image hosting website (Flickr.com) based on a computational selection method. In the initial screening study, participants rated stimuli twice for emotion elicitation across a 1-week interval and 1620 images were selected based on the number of ratings of participants and retest reliability of each picture. Using this set of stimuli, a second phase of the study was conducted, again having participants rate images twice with a 1-week interval, in which we found a total of 158 unique images that elicited various levels of emotionality with both good reliability and good agreement over time. The newly developed pictorial stimuli set is expected to facilitate cumulative science on human emotions.

Balancing Strength and Flexibility: How the Synthesis, Organization, and Modification of Guard Cell Walls Govern Stomatal Development and Dynamics.

Guard cells are pairs of epidermal cells that control gas diffusion by regulating the opening and closure of stomatal pores. Guard cells, like other types of plant cells, are surrounded by a three-dimensional, extracellular network of polysaccharide-based wall polymers. In contrast to the walls of diffusely growing cells, guard cell walls have been hypothesized to be uniquely strong and elastic to meet the functional requirements of withstanding high turgor and allowing for reversible stomatal movements. Although the walls of guard cells were long underexplored as compared to extensive studies of stomatal development and guard cell signaling, recent research has provided new genetic, cytological, and physiological data demonstrating that guard cell walls function centrally in stomatal development and dynamics. In this review, we highlight and discuss the latest evidence for how wall polysaccharides are synthesized, deposited, reorganized, modified, and degraded in guard cells, and how these processes influence stomatal form and function. We also raise open questions and provide a perspective on experimental approaches that could be used in the future to shed light on the composition and architecture of guard cell walls.

Mechanical Effects of Cellulose, Xyloglucan, and Pectins on Stomatal Guard Cells of Arabidopsis thaliana.

Stomata function as osmotically tunable pores that facilitate gas exchange at the surface of plants. Stomatal opening and closure are regulated by turgor changes in guard cells that result in mechanically regulated deformations of guard cell walls. However, how the molecular, architectural, and mechanical heterogeneities that exist in guard cell walls affect stomatal dynamics is unclear. In this work, stomata of wild type Arabidopsis thaliana plants or of mutants lacking normal cellulose, hemicellulose, or pectins were experimentally induced to close or open. Three-dimensional images of these stomatal complexes were collected using confocal microscopy, images were landmarked, and three-dimensional finite element models (FEMs) were constructed for each complex. Stomatal opening was simulated with a 5 MPa turgor increase. By comparing experimentally measured and computationally modeled changes in stomatal geometry across genotypes, anisotropic mechanical properties of guard cell walls were determined and mapped to cell wall components. Deficiencies in cellulose or hemicellulose were both predicted to stiffen guard cell walls, but differentially affected stomatal pore area and the degree of stomatal opening. Additionally, reducing pectin molecular mass altered the anisotropy of calculated shear moduli in guard cell walls and enhanced stomatal opening. Based on the unique architecture of guard cell walls and our modeled changes in their mechanical properties in cell wall mutants, we discuss how each polysaccharide class contributes to wall architecture and mechanics in guard cells. This study provides new insights into how the walls of guard cells are constructed to meet the mechanical requirements of stomatal dynamics.

Integrating cell biology, image analysis, and computational mechanical modeling to analyze the contributions of cellulose and xyloglucan to stomatal function.

Cell walls are likely to be essential determinants of the amazing strength and flexibility of the guard cells that surround each stomatal pore in plants, but surprisingly little is known about cell wall composition, organization, and dynamics in guard cells. Recent analyses of cell wall organization and stomatal function in the guard cells of Arabidopsis thaliana mutants with defects in cellulose and xyloglucan have allowed for the development of new hypotheses about the relative contributions of these components to guard cell function. Advanced image analysis methods can allow for the automated detection of key structures, such as microtubules (MTs) and Cellulose Synthesis Complexes (CSCs), in guard cells, to help determine their contributions to stomatal function. A major challenge in the mechanical modeling of dynamic biological structures, such as guard cell walls, is to connect nanoscale features (e.g., wall polymers and their molecular interactions) with cell-scale mechanics; this challenge can be addressed by applying multiscale computational modeling that spans multiple spatial scales and physical attributes for cell walls.