Search

Your search keyword '"Couturier, Etienne"' showing total 185 results
Start Over Author "Couturier, Etienne"
185 results on '"Couturier, Etienne"'

1. Force generation by a cylindrical cell under stationary osmolytes synthesis

Author

Kong, Wei-Yuan, Jofré, Antonio Mosciatti, Quiros, Manon, Bogeat-Triboulot, Marie-Béatrice, Kolb, Evelyne, and Couturier, Etienne

Subjects
Quantitative Biology - Subcellular Processes
Abstract

Turgor is the driving force of plant growth, making possible for roots to overcome soil resistance or for stems to counteract gravity. Maintaining a constant growth rate while avoiding the cell content dilution, which would progressively stop the inward water flux, imposes the production or import of osmolytes in proportion to the increase of volume. We coin this phenomenon stationary osmoregulation. The article explores the quantitative consequences of this hypothesis on the interaction of a cylindrical cell growing axially against an obstacle. An instantaneous axial compression of a pressurized cylindrical cell generates a force and a pressure jump which both decrease toward a lower value once water has flowed out of the cell to reach the water potential equilibrium. In a first part, the article derives analytical formula for these force and over-pressure both before and after relaxation. In a second part, we describe how the coupling of the Lockhart's growth law with the stationary osmoregulation hypothesis predicts a transient slowdown in growth due to contact before a re-acceleration in growth. We finally compare these predictions with the output of an elastic growth model which ignores the osmotic origin of growth: models only match in the early phase of contact for high stiffness obstacle.

Published
2024

2. Plant root growth against a mechanical obstacle: The early growth response of a maize root facing an axial resistance agrees with the Lockhart model

Author

Quiros, Manon, Bogeat-Triboulot, Marie-Béatrice, Couturier, Etienne, and Kolb, Evelyne

Subjects
Quantitative Biology - Tissues and Organs
Abstract

Plant root growth is dramatically reduced in compacted soils, affecting the growth of the whole plant. Through a model experiment coupling force and kinematics measurements, we probed the force-growth relationship of a primary root contacting a stiff resisting obstacle, that mimics the strongest soil impedance variation encountered by a growing root. The growth of maize roots just emerging from a corseting agarose gel and contacting a force sensor (acting as an obstacle) was monitored by time-lapse imaging simultaneously to the force. The evolution of the velocity field along the root was obtained from kinematics analysis of the root texture with a PIV derived-technique. A triangular fit was introduced to retrieve the elemental elongation rate or strain rate. A parameter-free model based on the Lockhart law quantitatively predicts how the force at the obstacle modifies several features of the growth distribution (length of the growth zone, maximal elemental elongation rate, velocity) during the first 10 minutes. These results suggest a strong similarity of the early growth responses elicited either by a directional stress (contact) or by an isotropic perturbation (hyperosmotic bath).

Published
2022

3. Compression of a pressurized spherical shell by a spherical or flat probe

Author

Couturier, Etienne, Vella, Dominic, and Boudaoud, Arezki

Subjects
Physics - Biological Physics
Abstract

Measuring the mechanical properties of cells and tissues often involves indentation with a sphere, or compression between two plates. Previously, different theoretical approaches have been developed to retrieve material parameters (e.g. elastic modulus) or state variables (e.g. pressure) from such experiments. Here, we extend previous theoretical work on indentation of a spherical pressurized shell by a point force to cover indentation by a spherical probe or a plate. We provide formulae that enable the modulus or pressure to be deduced from experimental results with realistic contact geometries, giving different results that are applicable depending on pressure level. We expect our results to be broadly useful when investigating biomechanics or mechanobiology of cells and tissues.

Published
2021

4. Self-similar shapes under Errera division rule on the cone

Author

Couturier, Etienne

Subjects
Quantitative Biology - Tissues and Organs
Abstract

This study provides a general construction method of cell shape invariant by the Errera rule of division on a cone and provides analytical bounds for the apical angle of the cone on which these cells are connected and thus biologically meaningful. This idealized model highlights how the curvature of the tissue can influence Errera rule.

Published
2019

5. Construction of a universal ordinary differential equation $C^{\infty}$ of order 3

Author

Couturier, Etienne and Jacquet, Nicolas

Subjects
Mathematics - Classical Analysis and ODEs
Abstract

A universal ordinary differential equation $C^{\infty}$ of order 3 is constructed here. The equation is universal in the sense that any continuous function on a real segment can be approximated by a solution of this equation with an arbitrary accuracy in uniform norm.

Published
2016
Full Text
View/download PDF

6. Folded Goursat surface and banana-shaped seedpod

Author

Couturier, Etienne

Subjects
Condensed Matter - Soft Condensed Matter
Abstract

Thin vegetal shells have recently been a significant source of inspiration for the de\text{sign} of smart materials and soft actuators. Herein is presented a novel analytical family of isometric deformations with folds, inspired by a banana-shaped seedpod, which converts a vertical closing into either an horizontal closing or an opening depending on the location of the fold. Similarly to the seedpod, optimum shapes for opening ease are the most elongated ones.

Published
2016
Full Text
View/download PDF

10. The filling law: a general framework for leaf shape diversity and its consequences on folded leaves

Author

Couturier, Etienne, Pont, Sylvain Courrech du, and Douady, Stéphane

Subjects
Quantitative Biology - Tissues and Organs, Nonlinear Sciences - Adaptation and Self-Organizing Systems
Abstract

Leaves are packed in a bud in different ways, being flat, enrolled, or folded, but always filling the whole bud volume. This {\guillemotleft} filling law {\guillemotright} has many consequences, in particular on the shape of growing folded leaves. This is shown here for different types of folding and packing. The folded volume is always part of an ellipsoid, with the veins on the outside rounded face, and the lamina margin on an adaxial plane or axis. The veins on the abaxial side protect the more fragile lamina. The first general consequence of the folds is the presence of symmetries on the leaf shape, but also quantitative relationships between lobes and sinus sizes. For particular geometries, the leaf lamina can be limited by lateral veins, creating spoon-like lobes, or transverse cuts, creating asymmetrical wavy perimeters. A change in the packing between cultivars induces the corresponding change in the leaf shape. Each particular case shows how pervasive are the geometrical consequences of the filling law., Comment: 27 p., 28 fig., article

Published
2010

11. Steric Constraints as a Global Regulation of Growing Leaf Shape

Author

Couturier, Etienne, Pont, Sylvain Courrech du, and Douady, Stephane

Subjects
Quantitative Biology - Tissues and Organs
Abstract

Shape is one of the important characteristics for the structures observed in living organisms. Whereas biologists have proposed models where the shape is controlled on a molecular level [1], physicists, following Turing [2] and d'Arcy Thomson [3], have developed theories where patterns arise spontaneously [4]. Here, we propose a volume constraint that restricts the possible shapes of leaves. Focusing on palmate leaves, the central observation is that developing leaves first grow folded inside a bud, limited by the previous and subsequent leaves. We show that growing folded in this small volume controls globally the leaf development. This induces a direct relationship between the way it was folded and the final unfolded shape of the leaf. These dependencies can be approximated as simple geometrical relationships that we confirm on both folded embryonic and unfolded mature leaves. We find that independently of their position in the phylogenetic tree, these relationships work for folded species, but do not work for non-folded species. This steric constraint is a simple way to impose a global regulation for the leaf growth. Such steric regulation should be more general and considered as a new simple means of global regulation., Comment: 6 pages 4 figures, Supplementary materials (8 pages, 7 figures)

Published
2009
Full Text
View/download PDF

18. Force generation by a cylindrical cell under stationary osmolyte synthesis

Author

Kong, Weiyuan, Mosciatti Jofré, Antonio, Quiros, Manon, Bogeat-Triboulot, Marie-Béatrice, Kolb, Evelyne, and Couturier, Etienne

Abstract

Turgor is the driving force of plant growth, making it possible for roots to overcome soil resistance or for stems to counteract gravity. Maintaining a constant growth rate while avoiding cell content dilution, which would progressively stop the inward water flux, imposes the production or import of osmolytes in proportion to the increase of volume. We coin this phenomenon stationary osmoregulation. The article explores the quantitative consequences of this hypothesis on the interaction of a cylindrical cell growing axially against an obstacle. An instantaneous axial compression of a pressurized cylindrical cell generates a force and a pressure jump, which both decrease towards a lower value once water has flowed out of the cell to reach the water potential equilibrium. In the first part, the article derives analytical formulae for these forces and over-pressure both before and after relaxation. In the second part, we describe how the coupling of the Lockhart growth law with the stationary osmoregulation hypothesis predicts a transient slowdown in growth due to contact before a re-acceleration in growth. We finally compare these predictions with the output of an elastic growth model which ignores the osmotic origin of growth: models only match in the early phase of contact for a high-stiffness obstacle.

Published
2024
Full Text
View/download PDF

21. Mechanical control of morphogenesis at the shoot apex

Author

Robinson, Sarah, Burian, Agata, Couturier, Etienne, Landrein, Benoit, Louveaux, Marion, Neumann, Enrique D., Peaucelle, Alexis, Weber, Alain, Nakayama, Naomi, Robinson, Sarah, Burian, Agata, Couturier, Etienne, Landrein, Benoit, Louveaux, Marion, Neumann, Enrique D., Peaucelle, Alexis, Weber, Alain, and Nakayama, Naomi

Abstract

Morphogenesis does not just require the correct expression of patterning genes; these genes must induce the precise mechanical changes necessary to produce a new form. Mechanical characterization of plant growth is not new; however, in recent years, new technologies and interdisciplinary collaborations have made it feasible in young tissues such as the shoot apex. Analysis of tissues where active growth and developmental patterning are taking place has revealed biologically significant variability in mechanical properties and has even suggested that mechanical changes in the tissue can feed back to direct morphogenesis. Here, an overview is given of the current understanding of the mechanical dynamics and its influence on cellular and developmental processes in the shoot apex. We are only starting to uncover the mechanical basis of morphogenesis, and many exciting questions remain to be answered

Published
2017

22. Folds and shapes of leaves

Author

Couturier, Etienne, Matière et Systèmes Complexes (MSC (UMR_7057)), Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Université Paris-Diderot - Paris VII, Stéphane Douady, and Couturier, Etienne

Subjects
Pli, [PHYS]Physics [physics], geometry, botanique, prefoliatiin, Feuille, botany, limitation by contact, [PHYS] Physics [physics], Leaf, préfoliaison, géométrie, [SDV.BV]Life Sciences [q-bio]/Vegetal Biology, [SDV.BV] Life Sciences [q-bio]/Vegetal Biology, Fold, development, limitation par contact, développement
Abstract

We have noticed an original analogy between the leaf configuration in the bud the paper dolls. If you fold a paper sheet and cut it with scissors, each fold will either a sinus either a lobe when you unfold it. A lot of leaves follow this geometry in the bud. The leaf margin is folded on a plane as if it had been cut with scissor For this purely geometric reason, lobes and sinuses of the unfolded leaf exactely correspond to the initial folds. We have called these leaves “kirigami”, which means cut-paper. The purely geometric first part of this thesis shows how much the leaves geometries are constrained by their folded development. We also show that these geometries are very diverse and create very different leaves shapes. The second more biologic part proposes a mecanism for the fold development and a candidate to the scissor role. We conclude by giving an original insight on leaf shape evolution., Nous sommes partis d'une analogie inédite entre la configuration de certaines feuilles dans le bourgeon et les ribambelles de papier. Quand on plie du papier et qu'on le coupe avec des ciseaux, à chaque pli va correspondre une pointe ou un creux de la ribambelle déployée. De nombreuses feuilles adoptent la même géométrie dans le bourgeon. Le bord de la feuille est replié sur un plan comme si il avait été découpé avec des ciseaux. Pour cette raison purement géométrique, les lobes et creux de la feuille déployée correspondront exactement aux plis initiaux. Nous avons nommé ces feuilles « kirigami », ce qui veut dire couper-papier en japonais. La première partie de cette thèse, purement géométrique, montre à quel point les géométries des feuilles sont contraintes par leur développement plié. Nous montrons aussi que la richesse des géométries que permet le kirigami se retrouve au sein des feuilles. La deuxième partie, plus biologique, propose à la fois un mécanisme pour le développement des plis et un candidat pour les mystérieux ciseaux. Nous concluons sur l'intérêt évolutif d'une telle organisation des feuilles dans le bourgeon.

Published
2009

28. Hypertriglyceridemie secondaire majeure

Author

Bevilacqua, Stefano, Couturier, Etienne, Vertongen, Françoise, Mols, Pierre, Bevilacqua, Stefano, Couturier, Etienne, Vertongen, Françoise, and Mols, Pierre

Abstract

A 65 year old patient presents himself to the Emergency Room with general physical alteration, diarrhea, and abdominal pain. After a thorough medical exam and workup, two hypotheses are retained; secondary dyslipidemia due to a non insulin dependent diabetes, and angiocholitis. The presentation of this case report is to stress the following two messages: 1) major hypertriglyceridemia, to the point of rendering the blood lactescent, can be secondary and transitional; 2) hypertriglyceridemia of this importance can render the evaluation of blood samples difficult., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1997

30. Ionophore-mediated Ca2+ countertransport: role of Na+, Li+ or H+ gradient

Author

Malaisse, Willy J., Anjaneyulu, Kowluru, Anjaneyulu, Renu, and Couturier, Etienne

Abstract

In an artificial system, the ionophore A23187, which transports Ca2+ but not Na+, is able to mediate the uphill translocation of Ca2+ from one aqueous medium to another across an organic immiscible phase, provided that a Na+, Li+ or H+ gradient is imposed on the system. Therefore, in the process known as Na-Ca countertransport, the downhill influx of Na+ may not be necessary for causing Ca2+ extrusion against its electrochemical gradient.

Published
1980
Full Text
View/download PDF

35. The increase in zincaemia provoked by starvation does not influence the intestinal absorption of zinc

Author

Couturier, Etienne, Prae, J.P., Vis, Henri-Louis, Devroede, Paul Ernest, Couturier, Etienne, Prae, J.P., Vis, Henri-Louis, and Devroede, Paul Ernest

Abstract

Serum zinc, measured in obese patients undergoing two weeks of therapeutic starvation (0 kcal, water ad libitum) increased significantly during the starvation period (+ 48% at day 10) and returned to prestarvation values after refeeding with a 500 kcal diet. Intestinal absorption of zinc was investigated by an oral zinc tolerance test (with 75 mg of zinc acetate) on the second and the tenth day of starvation. No significant differences were observed between the first and the second test. In our experimental conditions 10 days of starvation failed to induce a loss of zinc exceeding 0.75% of the total body stores. It is concluded that the concentration of zinc in blood per se does not regulate intestinal absorption in the absence of a significant change in zinc requirements. © 1987., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1987

37. Long term alloxan diabetes in the rat. Study of mesangial cell morphology by serial biopsies

Author

Anjo, A., Couturier, Etienne, Anjo, A., and Couturier, Etienne

Abstract

Diabetes mellitus, induced in the rat by alloxan (40 mg/kg b.w.) resulted in permanent hyperglycemia (mean glycemia: 403.0 mg/100 ml). The animals were left untreated for more than 16 mth. The mesangial cells of the renal glomeruli were studied by serial biopsies performed each mth under light anesthesia in the diabetic animals and in normal controls of the same age. Large dense bodies appeared in the cytoplasm after 3 mth in the diabetics and after 10 mth in the controls. With time, a larger number of mesangial cells contained these dense bodies. At the end stage they seem to be mainly lipidic substances. When NO3Ag is given in the drinking water the dense bodies accumulate particles of silver, suggesting that they contain fragments of the basement membrane. While the acid phosphatase reaction was negative in biopsy specimens from diabetic animals, it remains possible that the large dense bodies belong to the lysosomal system. This point, as well as the pathologic significance of the dense bodies is under investigation., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1976

39. Mesangial changes of the renal glomerulus in long term diabetic rats

Author

Anjo, A., Couturier, Etienne, Anjo, A., and Couturier, Etienne

Abstract

The primitive morphological lesions of intercapillary glomerulosclerosis is not known but could be at the level of mesangial cells. The kidneys of nine long term (12 months) diabetic rats and seven controls were studied by electron microscopy. They showed the same kind of lesions as those described by Kimmelstiel in the kidneys of human diabetics: fine fibrillar or granular deposits in the cytoplasm of mesangial cells and an enlargement of the mesangial area by accumulation of membrane like material. The cytoplasmic inclusions resemble the basement membrane of the capillaries. At this stage there is no widening of the basement membrane of the capillaries. Thus, mesangial cell inclusions seem to be a precocious stage of the diabetic nephropathy and could result from an impairment of the capacity of the mesangial cell to catabolize the basement membrane., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1975

42. Inhibition by sodium of A23187-mediated calcium translocation

Author

Couturier, Etienne, Deleers, Michel, Malaisse, Willy, Couturier, Etienne, Deleers, Michel, and Malaisse, Willy

Abstract

Sodium inhibits in a dose-related fashion the translocation of calcium from an aqueous milieu into an organic phase containing the divalent-cation ionophore A23187. This inhibitory effect is reproduced by other monovalent cations, modulated by the nature of the anion in the sodium halide, and inversely related to the absolute amount of calcium translocated. The inhibitory effect cannot be attributed to a change in osmolarity or ionic strength, to sequestration of the ionophoretic molecule at the interface between the aqueous and organic phases, or to translocation of sodium or chloride. These findings indicate that sodium may directly affect the handling of calcium by ionophoretic systems specifically mediating the transport of divalent cations. © 1980., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1980

45. Regulation of calcium fluxes in pancreatic islets: glucose-induced calcium-calcium exchange.

Author

Herchuelz, André, Couturier, Etienne, Malaisse, Willy, Herchuelz, André, Couturier, Etienne, and Malaisse, Willy

Abstract

Glucose provokes an initial fall followed by a secondary rise in 45Ca efflux from prelabeled pancreatic islets. Prior exposure of the islets to calcium-depleted media does not suppress the secondary rise, provided that the extracellular calcium concentration is normalized 2 min before addition of glucose. Such a treatment significantly reduces insulin release. The secondary rise, as distinct from the initial fall, is inhibited under conditions known to interfere with calcium entry into the beta-cell, e.g. in the presence of ruthenium red or cobalt. Calcium itself in high concentrations provokes a dramatic increase in 45Ca efflux. The magnitude of this calcium-induced efflux is enhanced by prior exposure of the islets to calcium-depleted media. Imidazole and the theophylline do not modify the effect of glucose on 45Ca efflux. It is proposed that the glucose-induced secondary rise in 45Ca efflux corresponds to a calcium-calcium exchange process in which influent 40Ca displaces 45Ca from intracellular sites., In Vitro, Journal Article, SCOPUS: NotDefined.j, SCOPUS: ar.j, info:eu-repo/semantics/published

Published
1980

46. Mode of action of clonidine upon islet function: dissociated effects upon the time course and magnitude of insulin release.

Author

Leclercq Meyer, Viviane, Herchuelz, André, Valverde, Isabel, Couturier, Etienne, Marchand, Jocelyne, Malaisse, Willy, Leclercq Meyer, Viviane, Herchuelz, André, Valverde, Isabel, Couturier, Etienne, Marchand, Jocelyne, and Malaisse, Willy

Abstract

Clonidine (0.08 to 80.0 ng/ml) caused a dose-related inhibition of glucose-stimulated insulin release, but failed to affect glucose oxidation, glucose-stimulated 45Ca net uptake, and adenylate cyclase activity in isolated rat islets. Phentolamine antagonized the effect of clonidine upon insulin release. Despite profound inhibition of insulin secretion, the drug failed to affect the time course for the changes evoked by glucose in either 45Ca fractional outflow rate from perfused islets or insulin release from the isolated perfused pancreas. The latter changes were multiphasic, revealing an initial secretory peak, a period of low secretory activity, and a second secretory elevation before establishing a period characterized by a steadily and slowly increasing insulin output. In the clonidine-treated islets, the secretory rate was not significantly different from the basal value during the period after the initial secretory response. Thus, despite continuous stimulation with glucose, insulin release appears as a discontinuous phenomenon, even when little insulin is secreted during the initial phase of stimulation., In Vitro, Journal Article, info:eu-repo/semantics/published

Published
1980

48. Cobalt-induced inhibition of ionophore-mediated calcium translocation

Author

Couturier, Etienne, Malaisse, Willy, Couturier, Etienne, and Malaisse, Willy

Abstract

The transport of calcium across the plasma membrane of living cells and the phenomenon of ionophore-mediated calcium translocation across a hydrophobic domain display several analogies. The present work extends this series of analogies to the effect of cobalt, which is currently used as a selective blocker of the late calcium channels in excitable cells. The results indicate that cobalt is a potent inhibitor of A23187-mediated calcium translocation into a hydrophobic domain. Other cations, such as magnesium and barium also inhibit calcium translocation, apparently by competing with calcium for common reactive sites in the ionophoretic molecule. Cobalt may act in a comparable manner. The affinity constant of A23187 for divalent cations is reported to be 3 orders of magnitude higher with cobalt (3.5 x 10-4) than calcium (3.7 x 10-7). The latter value is in good agreement with the data here found in the absence of cobalt (approximately 2 x 10-7). In conclusion, cobalt may affect calcium handling in living cells, in part at least, by interfering with calcium transport by native ionophoretic systems., SCOPUS: NotDefined.j, info:eu-repo/semantics/published

Published
1980

49. Effects of gliclazide and diazoxide upon ionophore-mediated calcium countertransport

Author

Couturier, Etienne, Anjaneyulu, Renu, Anjaneyulu, Kowluru, Deleers, Michel, Malaisse, Willy, Couturier, Etienne, Anjaneyulu, Renu, Anjaneyulu, Kowluru, Deleers, Michel, and Malaisse, Willy

Abstract

Comm. 16th Annual Meeting of the European Association for the Study of Diabetes - Athens, 26.9.1980, SCOPUS: NotDefined.j, info:eu-repo/semantics/published

Published
1980

Catalog

Books, media, physical & digital resources
See catalog results