scholarly journals A mechanical cusp catastrophe imposes a universal developmental constraint on the shapes of tip-growing cells

2020 ◽  
Author(s):  
Jacques Dumais ◽  
Enrique R. Rojas
Keyword(s):  
Mechanical Model ◽  
Tip Growth ◽  
Turgor Pressure ◽  
Developmental Constraint ◽  
Growth Profiles ◽  
Mechanistic Basis ◽  
Slow Growing ◽  
Parameter Function ◽  
Two Parameter ◽  
Cell Wall Expansion

AbstractUnderstanding the mechanistic basis for cell morphology is a central problem in biology. Evolution has converged on tip growth many times, yielding filamentous cells, yet tip-growing cells display a range of apical morphologies. To understand this variability, we measured the spatial profiles of cell-wall expansion for three species that spanned the phylogeny and morphology of tip-growth. Profiles were consistent with a mechanical model whereby the wall was stratified and stretched by turgor pressure during cell growth. We calculated the spatial profiles of wall mechanical properties, which could be accurately fit with an empirical two-parameter function. Combined with the mechanical model, this function yielded a “morphospace” that accounted for the shapes of diverse tip-growing species. However, natural shapes were bounded by a cusp bifurcation in the morphospace that separated thin, fast-growing cells from (nonexistent) wide, slow-growing cells. This constraint has important implications for our understanding of the evolution of tip-growing cells.

Fountain streaming contributes to fast tip-growth through regulating the gradients of turgor pressure and concentration in pollen tubes

Soft Matter ◽  
2017 ◽  
Vol 13 (16) ◽  
pp. 2919-2927 ◽  
Author(s):  
ShaoBao Liu ◽  
Han Liu ◽  
ShangSheng Feng ◽  
Min Lin ◽  
Feng Xu ◽  
...  
Keyword(s):  
Tip Growth ◽  
Turgor Pressure ◽  
Pollen Tubes ◽  
Fountain Streaming

scholarly journals A model for core formation in dark matter haloes and ultra-diffuse galaxies by outflow episodes

2019 ◽  
Vol 491 (3) ◽  
pp. 4523-4542 ◽  
Author(s):  
Jonathan Freundlich ◽  
Avishai Dekel ◽  
Fangzhou Jiang ◽  
Guy Ishai ◽  
Nicolas Cornuault ◽  
...  
Keyword(s):  
Dark Matter ◽  
Mass Gain ◽  
Mass Range ◽  
Dark Matter Halo ◽  
Specific Mass ◽  
Spherical System ◽  
Energy Conserving ◽  
Parameter Function ◽  
Two Parameter ◽  
Analytic Potential

ABSTRACT We present a simple model for the response of a dissipationless spherical system to an instantaneous mass change at its centre, describing the formation of flat cores in dark matter haloes and ultra-diffuse galaxies (UDGs) from feedback-driven outflow episodes in a specific mass range. This model generalizes an earlier simplified analysis of an isolated shell into a system with continuous density, velocity, and potential profiles. The response is divided into an instantaneous change of potential at constant velocities due to a given mass-loss or mass-gain, followed by energy-conserving relaxation to a new Jeans equilibrium. The halo profile is modelled by a two-parameter function with a variable inner slope and an analytic potential profile, which enables determining the associated kinetic energy at equilibrium. The model is tested against NIHAO cosmological zoom-in simulations, where it successfully predicts the evolution of the inner dark matter profile between successive snapshots in about 75 per cent of the cases, failing mainly in merger situations. This model provides a simple understanding of the formation of dark matter halo cores and UDGs by supernova-driven outflows, and a useful analytic tool for studying such processes.

scholarly journals Mapping the Growth of Fungal Hyphae: Orthogonal Cell Wall Expansion during Tip Growth and the Role of Turgor

2000 ◽  
Vol 79 (5) ◽  
pp. 2382-2390 ◽  
Author(s):  
Salomon Bartnicki-Garcia ◽  
Charles E. Bracker ◽  
Gerhard Gierz ◽  
Rosamaría López-Franco ◽  
Haisheng Lu
Keyword(s):  
Cell Wall ◽  
Tip Growth ◽  
Fungal Hyphae ◽  
Cell Wall Expansion

Merostabilization in radical ions, triplets, and biradicals. 4. Substituent effects on the half-wave reduction potentials and n,π* triplet energies of aromatic ketones

1980 ◽  
Vol 58 (23) ◽  
pp. 2537-2549 ◽  
Author(s):  
William J. Leigh ◽  
Donald R. Arnold ◽  
Robert W. R. Humphreys ◽  
Po Cheong Wong
Keyword(s):  
Substituent Effects ◽  
Radical Ions ◽  
Normal Behaviour ◽  
Reduction Potentials ◽  
Half Wave ◽  
Substituent Constants ◽  
Parameter Function ◽  
Two Parameter ◽  
Wave Reduction ◽  
Abinitio Calculations

The half-wave reduction potentials, measured by cyclic voltammetry, and n,π* triplet energies, measured by phosphorescence spectroscopy, were determined for a series of eighteen symmetrically and unsymmetrically substituted benzophenones. Attempts are made to correlate the results with Hammett substituent constants. Better correlations are observed when the data are correlated with a two-parameter function consisting of Hammett substituent constants and a set of substituent parameters describing variations in free radical stability. Significant deviations from "normal" behaviour are observed for benzophenones substituted by both electron-donating and electron-withdrawing substituents. These deviations are attributed to merostabilization of the radical-like species, and an empirical approach designed to evaluate the importance of this effect is developed. Abinitio calculations of molecular orbital energies in meta- and para-substituted benzaldehydes are used to evaluate the substituent effects on E1/2red and ETn,π* in terms of the effect on the energies of the n- and π*-orbitals.

scholarly journals Validation of two parameter function height diameter models

2018 ◽  
Vol 9 (2) ◽  
pp. 331-334
Author(s):  
M. Iqbal Jeelani ◽  
Manish Kr Sharma ◽  
Anil Bhat ◽  
Mansha Gul
Keyword(s):  
Parameter Function ◽  
Two Parameter

scholarly journals The Invariant Two-Parameter Function of Algebras ψ

2019 ◽  
Vol 24 (4) ◽  
pp. 89 ◽  
Author(s):  
Escobar ◽  
Núñez-Valdés ◽  
Pérez-Fernández
Keyword(s):  
Invariant Functions ◽  
Parameter Function ◽  
Two Parameter

At present, the research on invariant functions for algebras is very extended since Hrivnákand Novotný defined in 2007 the invariant functions [...]

Gas exchange and water relations responses to drought of fast- and slow-growing black spruce families

1997 ◽  
Vol 75 (10) ◽  
pp. 1700-1706 ◽  
Author(s):  
Weixing Tan ◽  
Terence J. Blake
Keyword(s):  
Growth Rate ◽  
Stomatal Conductance ◽  
Gas Exchange ◽  
Soil Water ◽  
Water Relations ◽  
Picea Mariana ◽  
Black Spruce ◽  
Turgor Pressure ◽  
Fast Growing ◽  
Slow Growing

To determine how different mechanisms of drought tolerance contribute to growth rate under drought, this study compared four full-sib black spruce (Picea mariana (Mill.) B.S.P.) families which differed in growth rate when soil water became limiting, stomatal conductance, photosynthesis, and water relations responses to drought. Repeated drought cycles were imposed by withholding soil water in a nursery and physiological responses were measured near the end of the first and third cycle. The most vigorous family under drought had greater osmotic adjustment and maintained higher rates of net photosynthesis during the first cycle of drought and resumed higher rates of photosynthesis sooner upon stress relief, compared with two slow-growing families. Pressure–volume analysis of drought-stressed shoot tissues indicated that the fast-growing family exhibited a larger degree of elastic enhancement (i.e., decrease in bulk modulus of elasticity), which would explain its higher turgor pressure, compared with the two less vigorous families. However, family differences in gas exchange and water relations largely diminished when seedlings were exposed to repeated cycles of drought. Therefore, fast-growing black spruce families under drought may gain selective growth advantage by a better ability to tolerate, rather than postpone, momentary dehydration. Short-term screening trials could be used to detect drought tolerant genotypes in black spruce. Key words: drought, family variation, photosynthesis, Picea mariana, stomatal conductance, water relations.

Estimation of green moisture content distribution in hemfir timber by stochastic simulation

Holzforschung ◽  
2004 ◽  
Vol 58 (4) ◽  
pp. 413-417 ◽  
Author(s):  
D. Elustondo ◽  
S. Avramidis ◽  
L. Oliveira
Keyword(s):  
Moisture Content ◽  
Stochastic Model ◽  
Stochastic Simulation ◽  
Saturation Point ◽  
Moisture Concentration ◽  
Log Normal ◽  
Nondestructive Measurements ◽  
Parameter Function ◽  
Two Parameter ◽  
Good Agreement

AbstractThis paper describes an improved stochastic model designed to simulate systems, such as green timbers, that cannot be analyzed as a unit but as a collection of a large number of similar components. The stochastic model provides a piecewise green moisture content frequency distribution curve by using nondestructive measurements such as of timber weight. A new, relatively simple two-parameter function was designed to describe the log-normal moisture concentration distribution above the fiber saturation point, and the parameters of this function were determined by fitting the experimental timber weights with the results of the stochastic model. The simulated green moisture content distributions showed good agreement with the experimental data for Pacific coast hemlock (hemfir) timbers, thus providing a piece of information that is indispensable for applying stochastic simulation to industrial drying of timbers.

Integration and regulation of hyphal tip growth

1995 ◽  
Vol 73 (S1) ◽  
pp. 131-139 ◽  
Author(s):  
I. Brent Heath
Keyword(s):  
Cell Wall ◽  
Tip Growth ◽  
Apical Cell ◽  
Turgor Pressure ◽  
Feedback Regulation ◽  
Regulation Mechanism ◽  
Hyphal Tip Growth ◽  
Species Specific ◽  
Stretch Activated Channels ◽  
Hyphal Tip

Hyphal tip growth is an exquisitely controlled process that forms developmentally regulated, species-specific, even-diameter tubes at rates of up to about 50 μm/min. The traditional view is that this process results from the balance between the expansive force of turgor pressure and the controlled extensibility of the apical cell wall. While these elements are involved, the model places regulation into either the global domain (turgor pressure) or the extracellular environment (the cell wall), neither of which seem well suited to the level of control evinced. Recent evidence suggests that F-actin-rich elements of the cytoskeleton are important in tip morphogenesis. Our current models propose that tip expansion is regulated (restrained under normal turgor pressure and protruded under low turgor) by a peripheral network of F-actin that is attached to the plasmalemma and the cell wall by integrin-containing linkages, thus placing control in the cytoplasm where it is accessible to normal intracellular regulatory systems. The F-actin system also functions in cytoplasmic and organelle motility; control of plasmalemma-located, stretch-activated, Ca2+-transporting, ion channel distribution; vectoral vesicle transport; and exocytosis. Regulation of the system may involve Ca2+, the concentration of which is influenced by the tip-high gradient of the stretch-activated channels, thus suggesting a possible feedback regulation mechanism. Key words: tip growth, fungi, stretch-activated channels, F-actin, Ca2+, hyphae.

Photocontrol of extension growth: a biophysical approach

1983 ◽  
Vol 303 (1116) ◽  
pp. 453-465 ◽  
Keyword(s):  
Cell Wall ◽  
Hydraulic Conductivity ◽  
Blue Light ◽  
Stem Elongation ◽  
Turgor Pressure ◽  
Water Source ◽  
Cell Enlargement ◽  
Wall Properties ◽  
Cell Wall Properties ◽  
Cell Wall Expansion

The analysis of plant growth as a physical process is briefly reviewed. Growth requires the coordinated uptake of water and the irreversible expansion of the cell wall. Any agent that affects the growth rate must act on one or more of the parameters governing water absorption (e.g. the hydraulic conductivity or the difference in osmotic pressure of the cell contents and the water source) or cell wall expansion (e.g. wall extensibility or the yield threshold). When the hydraulic conductivity of the pathway for water transport is small enough to impede the rate of cell enlargement, a substantial gradient in water potential within the growing tissue will develop to sustain the absorption of water. In such a case, the analysis shows that turgor pressure is a key indicator for determining whether an agent acts predominantly on the osmotic properties of the tissue or on the cell wall properties. Furthermore, the dynamic response to a slight perturbation from steady-state conditions is shown to be a function of parameters for both the water relations and cell wall expansion of the tissue. Blue irradiation of etiolated seedlings causes a large inhibition of stem elongation with lag times as short as 30 s and half-times as short as 20 to 25 s. The biophysical mechanism of blue-light suppression of growth was studied in cucumber and sunflower seedlings by means of direct and indirect measurements of turgor pressure. The results indicate that ( a ) blue light suppresses growth by influencing the cell wall properties of the growing tissue, and ( b ) the hydraulic conductivity of the growing tissue is large enough for it not to limit the rate of cell enlargement.

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