Cell Size Pattern Research Articles

Experimental study of innovative periodic cellular structures as air volumetric absorbers

This work presents an experimental thermal evaluation of new and innovative porous morphologies suitable for volumetric solar receivers. Five new morphologies, four of them based on the repetition of single unit cells: diamond, rotated cube, tetrakaidecahedron, cube shifted, and a random morphology following the Voronoi tessellation technique were tested. In addition, for emerging geometries, two different cell size configurations were evaluated: one with constant cell size dimension and one with cell's size changing with flux direction. All the lattices were analysed experimentally in a lab-scale solar simulator. The results were compared with the ones of the already established and more conventional silicon carbide honeycomb and random foams proving that a gain in performance is achievable with the Voronoi morphology, both with constant cell size and increasing cell size pattern.

Sinorhizobium meliloti, a Slow-Growing Bacterium, Exhibits Growth Rate Dependence of Cell Size under Nutrient Limitation.

Bacterial cells need to coordinate the cell cycle with biomass growth to maintain cell size homeostasis. For fast-growing bacterial species like Escherichia coli and Bacillus subtilis, it is well-known that cell size exhibits a strong dependence on the growth rate under different nutrient conditions (known as the nutrient growth law). However, cell size changes little with slow growth (doubling time of >90 min) for E. coli, posing the interesting question of whether slow-growing bacteria species also observe the nutrient growth law. Here, we quantitatively characterize the cell size and cell cycle parameter of a slow-growing bacterium, Sinorhizobium meliloti, at different nutrient conditions. We find that S. meliloti exhibits a threefold change in its cell size when its doubling time varies from 2 h to 6 h. Moreover, the progression rate of its cell cycle is much longer than that of E. coli, suggesting a delicate coordination between the cell cycle progression rate and the biomass growth rate. Our study shows that the nutrient growth law holds robustly regardless of the growth capacity of the bacterial species, generalizing its applicability among the bacterial kingdom.IMPORTANCE The dependence of cell size on growth rate is a fundamental principle in the field of bacterial cell size regulation. Previous studies of cell size regulation mainly focus on fast-growing bacterial species such as Escherichia coli and Bacillussubtilis We find here that Sinorhizobium meliloti, a slow-growing bacterium, exhibits a remarkable growth rate-dependent cell size pattern under nutrient limitation, generalizing the applicability of the empirical nutrient growth law of cell size. Moreover, S. meliloti exhibits a much slower speed of cell cycle progression than E. coli does, suggesting a delicate coordination between the cell cycle progression rate and the biomass growth rate.

Larger cell or colony size in winter, smaller in summer – a pattern shared by many species of Lake Kinneret phytoplankton

We examined an 8.5-year record (2004–2012) of cell size data for phytoplankton species from Lake Kinneret, Israel, sampled weekly or at 2-week intervals and determined microscopically by the same person. Many of the species abundant enough to be counted year-round showed a typical seasonal cell size pattern that repeated annually: cell diameter was maximal in winter and minimal in summer. This pattern was shared by species from different taxonomic groups including cyanobacteria, chlorophyta, and dinoflagellates. Similarly, in colonial species of diatoms, chlorophyta, and cyanobacteria the number of cells per colony was larger in winter and smaller in summer. We postulated that the seasonal changes in cell or colony size constituted an adaptation that enabled species to overcome temperature-dependent changes in water density and viscosity and adjust their sinking velocities in the different seasons. A series of computations based on Stokes’ law supported our hypothesis. If this phenomenon of larger cells or colonies of the same species at lower temperatures is widespread in lake phytoplankton, then (1) phytoplankton biomass estimates should be based on seasonally determined biovolume per species data rather than fixed values; and (2) we would expect to see smaller-sized organisms in the future as global warming changes ambient temperatures.

An individual-based model for the analysis of Prochlorococcus diel cycle behavior

Prochlorococcus spp. are the smallest and most numerous phytoplankton in the ocean. The tightly-phased diel dynamics of cellular growth and division can be used to estimate population growth and mortality rates of Prochlorococcus in the field. However, traditional approaches for making these estimates involve deconvolving cell cycle phases from DNA distributions, a potential source of error. In this study, we used an individual-based model (IBM) to capture the cell size patterns, DNA content, and cell cycle phase distributions of Prochlorococcus. Model parameters were estimated from cell cycle data of field populations in the North Atlantic Ocean and then optimized using the Nelder–Mead algorithm. The model reproduced observed field diel growth and cell cycle dynamics well. Model optimization can be used to estimate population growth rates and other cell cycle parameters directly from DNA distributions, independent of cell cycle phase deconvolution.

Influence of geography and climate on patterns of cell size and body size in the lizardAnolis carolinensis

Geographic patterns in body size are often associated with latitude, elevation, or environmental and climatic variables. This study investigated patterns of body size and cell size of the green anole lizard, Anolis carolinensis, and potential associations with geography or climatic variables. Lizards were sampled from 19 populations across the native range, and body size, red blood cell size and size and number of muscle cells were measured. Climatic data from local weather stations and latitude and longitude were entered into model selection with Akaike's information criterion to explain patterns in cell and body sizes. Climatic variables did not drive any major patterns in cell size or body size; rather, latitude and longitude were the best predictors of cell and body size. In general, smaller body and cell sizes in Florida anoles drove geographic patterns in A. carolinensis. Small size in Florida may be attributable to the geological history of the peninsular state or the unique ecological factors in this area, including a recently introduced congener. In contrast to previous studies, we found that A. carolinensis does not follow Bergmann's rule when the influence of Florida is excluded. Rather, the opposite pattern of larger lizards in southern populations is evident in the absence of Florida populations, and mirrors the general pattern in squamates. Muscle cell size was negatively related to latitude and red blood cell size showed no latitudinal trend outside of Florida. Different patterns in the sizes of the 2 cell types confirm the importance of examining multiple cell types when studying geographic variation in cell size.

Intra-annual patterns of tracheid size in the Mediterranean tree Juniperus thurifera as an indicator of seasonal water stress

Because climate can affect xylem cell anatomy, series of intra-annual cell anatomical features have the potential to retrospectively supply seasonal climatic information. In this study, we explored the ability to extract information about water stress conditions from tracheid features of the Mediterranean conifer Juniperus thurifera L. Tracheidograms of four climatic years from two drought-sensitive sites in Spain were compared to evaluate whether it is possible to link intra-annual cell size patterns to seasonal climatic conditions. Results indicated site-specific anatomical adjustment such as smaller and thicker tracheids at the dryer site but also showed a strong climatic imprint on the intra-annual pattern of tracheid size. Site differences in cell size reflected expected structural adjustments against cavitation failures. Differences between intra-annual patterns, however, indicated a response to seasonal changes in water availability whereby cells formed under drought conditions were smaller and thicker, and vice versa. This relationship was more manifest and stable at the dryer site.

Cell size is positively correlated between different tissues in passerine birds and amphibians, but not necessarily in mammals

We examined cell size correlations between tissues, and cell size to body mass relationships in passerine birds, amphibians and mammals. The size correlated highly between all cell types in birds and amphibians; mammalian tissues clustered by size correlation in three tissue groups. Erythrocyte size correlated well with the volume of other cell types in birds and amphibians, but poorly in mammals. In birds, body mass correlated positively with the size of all cell types including erythrocytes, and in mammals only with the sizes of some cell types. Size of mammalian erythrocytes correlated with body mass only within the most taxonomically uniform group of species (rodents and lagomorphs). Cell volume increased with body mass of birds and mammals to less than 0.3 power, indicating that body size evolved mostly by changes in cell number. Our evidence suggests that epigenetic mechanisms determining cell size relationships in tissues are conservative in birds and amphibians, but less stringent in mammals. The patterns of cell size to body mass relationships we obtained challenge some key assumptions of fractal and cellular models used by allometric theory to explain mass-scaling of metabolism. We suggest that the assumptions in both models are not universal, and that such models need reformulation.

Variability in the control of cell division underlies sepal epidermal patterning in Arabidopsis thaliana.

Author SummaryHow the regulation of cell division contributes to cell patterning in an organ is an important question in developmental biology. We chose to study cell size patterning in the Arabidopsis sepal, the green leaf-like floral organ, because it contains a wide range of cell sizes—from giant cells to small cells—and because sepals, as the outermost floral organ, are accessible for live cell imaging. In this study we image the early development of living sepals and follow each of the cell divisions to determine how cells of different sizes are created. We observe that the times when cells divide and when they stop dividing are highly variable. Using computational modeling, we then show that a model in which these decisions are made randomly with the probabilities we observed in vivo can recapitulate the production of the range of cell sizes seen in the living sepal. We also show that changing these probabilities within our model robustly predicts the novel cell patterns observed in mutant plants with altered cell division timing. We conclude that probabilistic decisions of individual cells—rather than deterministic, organ-wide mechanisms—can produce a characteristic and robust cell size pattern in development.

The time for sex: A biennial life cycle in a marine planktonic diatom

Whereas it is accepted that the population dynamics of higher organisms is strongly grounded in life history processes, such as the time taken to mature and reproduce, regulation in the abundance of aquatic protists is generally attributed to proximate properties of the environment in which they grow. We used 10 yr of data from the Gulf of Naples to determine the life history of a planktonic diatom, Pseudo‐nitzschia multistriata, through the analysis of cell abundances and cell size patterns. Asexual and sexual phases recurred with remarkable regularity. Maximum abundance occurred annually, between the end of summer and the beginning of autumn, but cohorts of large cells, derived from sexual events, were found only every second year. We developed a model of population growth, based on parameters determined from laboratory cultures, with further tuning using information from natural populations. The model simulated the birth, maturation, and disappearance of age classes like those in natural populations, but only when we imposed seasonal variation in the rate of cell division and timed sexual reproduction during the stationary phase of a bloom. The model predicts that P. multistriata will become locally extinct if sexual reproduction does not occur within 4 yr. Our data and model show that coherent life cycle properties can emerge in natural populations of unicellular organisms, analogous to those in multicellular organisms, as a result of finely tuned regulation of cell division and sexual competence.

Pattern formation in plant development: four vignettes

In their development, plants precisely control the patterns of cell size, cell shape and cell division, the position of differentiation of cell types, and the position and number of organs. In the past year, progress has been made in understanding four of these five levels of control of plant pattern formation, including specification of cell fate by cell size in the alga Volvox carteri, genetic control of cell shape in the leaf hairs of the flowering plant Arabidopsis thaliana, precise control of cell division and cellular enlargement in Arabidopsis root meristems, and control of cell number in meristems of Arabidopsis, tobacco, and maize. These examples indicate that both the fate and shape of differentiated plant cells can be determined by the size of their undifferentiated precursors, and that the primary effect of mutations that alter cell fate and cellular shape can be on cell size. Furthermore, specific genes have been found that are necessary for normal patterns and numbers of cell divisions. Molecular cloning of these genes is revealing the molecular basis of plant cell division control.

An Ontogenetic Model for the Mississippian Seed Plant Family Calamopityaceae

Constructing characters to reflect homology accurately remains a critical problem in systematic analysis of vascular plants, especially where evidence consists primarily of heterogeneous position-related subunits making up an overall complex pattern, which we term "biological fabric." Ideally, accurate assessment of homology lies at the developmental level rather than at the level of mature structure. However, elucidating developmental patterns requires appropriate analytic methods. As an example of a useful approach to analysis of plant tissue fabrics, we present a model of ontogeny in the Calamopityaceae, a family of early seed plants. Members of this group have an unusually thick cortex with complex patterns of cell size and shape. Adopting the methodological assumption that physical stress is the primary causal agent in patterning these tissues, we utilize cell size, shape, and orientation to infer a likely sequence of developmental events. We have employed Fry analysis, a technique of strain analysis derived from structural geology, in order to measure and compare cell shape and orientation in various tissue regions, and from this to infer patterns of tissue strain and cell division. Our analysis indicates that tissue patterning in the mature calamopityacean cortex is a consequence of differential cell growth and proliferation of different cell types and tissue regions, which establish regions of local and regional tissue strain. Increased diameter of the stem takes place by a combination of vascular cambial activity and diffuse secondary growth in the cortex, especially around petiole bases. Whereas most regions of the cortex accommodate expansion of secondary tissues through cell division, inner cortex and tissues immediately surrounding outer fiber bundles retain a surprising degree of primary architecture. The inner cortex displays a complex pattern of strain as a consequence of low cell division rates and complex forces exerted by expansion of secondary vascular tissues and emission of leaf traces. The hypodermis of fiber strands, limited vascular cambial development, and a cortex that remains largely intact through development indicate that at least lateral growth of calamopityacean shoots was determinate. Preliminary observations indicate that the ontogenetic model derived here from Calamopitys is applicable to other members of the Calamopityaceae, and in part to other early seed plants as well. However, the massive and complex calamopityacean cortex is unique among early seed plants and is probably a consequence of the production of large compound leaves in these plants. In assessing functional, ecological, and evolutionary significance of these features, it is necessary to consider them as manifestations of the same developmental process in the plant as a whole rather than as isolated functional units.