Modélisation MHD tridimensionnelle de tubes de flux coronaux utilisant l'assimilation des donnés 4D-VAR

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Cell wall composition regulates cell shape and growth behaviour in pollen tubes

L’une des particularités fondamentales caractérisant les cellules végétales des cellules animales est la présence de la paroi cellulaire entourant le protoplaste. La paroi cellulaire joue un rôle primordial dans (1) la protection du protoplaste, (2) est impliquée dans les mécanismes de filtration et (3) est le lieu de maintes réactions biochimiques nécessaires à la régulation du métabolisme et des propriétés mécaniques de la cellule. Les propriétés locales d’élasticité, d’extensibilité, de plasticité et de dureté des composants pariétaux déterminent la géométrie et la forme des cellules lors des processus de différentiation et de morphogenèse. Le but de ma thèse est de comprendre les rôles que jouent les différents composants pariétaux dans le modelage de la géométrie et le contrôle de la croissance des cellules végétales. Pour atteindre cet objectif, le modèle cellulaire sur lequel je me suis basé est le tube pollinique ou gamétophyte mâle. Le tube pollinique est une protubérance cellulaire qui se forme à partir du grain de pollen à la suite de son contact avec le stigmate. Sa fonction est la livraison des cellules spermatiques à l’ovaire pour effectuer la double fécondation. Le tube pollinique est une cellule à croissance apicale, caractérisée par la simple composition de sa paroi et par sa vitesse de croissance qui est la plus rapide du règne végétal. Ces propriétés uniques font du tube pollinique le modèle idéal pour l’étude des effets à courts termes du stress sur la croissance et le métabolisme cellulaire ainsi que sur les propriétés mécaniques de la paroi. La paroi du tube pollinique est composée de trois composantes polysaccharidiques : pectines, cellulose et callose et d’une multitude de protéines. Pour comprendre les effets que jouent ces différents composants dans la régulation de la croissance du tube pollinique, j’ai étudié les effets de mutations, de traitements enzymatiques, de l’hyper-gravité et de la gravité omni-directionnelle sur la paroi du tube pollinique. En utilisant des méthodes de modélisation mathématiques combinées à de la biologie moléculaire et de la microscopie à fluorescence et électronique à haute résolution, j’ai montré que (1) la régulation de la chimie des pectines est primordiale pour le contrôle du taux de croissance et de la forme du tube et que (2) la cellulose détermine le diamètre du tube pollinique en partie sub-apicale. De plus, j’ai examiné le rôle d’un groupe d’enzymes digestives de pectines exprimées durant le développement du tube pollinique : les pectate lyases. J’ai montré que ces enzymes sont requises lors de l’initiation de la germination du pollen. J’ai notamment directement prouvé que les pectate lyases sont sécrétées par le tube pollinique dans le but de faciliter sa pénétration au travers du style.

Destinée des S-RNases dans les tubes polliniques lors des croisements compatibles et incompatibles

L’auto-incompatibilité (AI) est la capacité génétiquement déterminée d’une plante fertile de rejeter son propre pollen. Chez les Solanacées l’AI dépend des éléments d’un locus fort complexe (locus S) multigénique. L’élément du locus-S exprimé dans le pistil est une ribonucléase (S-RNase) dont le rôle est de dégrader l’ARN chez le pollen self, tandis que l’élément du locus S exprimé dans le pollen est un ensemble de protéines du type F-box, qui sont normalement impliquées dans la dégradation des protéines. Cependant, comment les S-RNases self restent actives lors des croisements incompatibles et comment les S-RNases non-self sont inactivées lors des croisements compatibles ce n’est encore pas clair. Un modèle propose que les S-RNases non-self soient dégradées lors des croisements compatibles. Un autre modèle propose que toutes les S-RNases, self et non-self, soient d'abord séquestrées à l’intérieur d’une vacuole, et elles y resteraient lors des croisements compatibles. Lors de croisements incompatibles, par contre, elles seraient relâchées dans le cytoplasme, où elles pourront exercer leur action cytotoxique. Notre étude tente de répondre à ces questions. Notamment, nous cherchons à mettre en évidence la localisation vacuolaire et/ou cytoplasmique des S-RNases et leur concentration par immunolocalisation, en utilisant un anticorps ciblant la S11-RNase de Solanum chacoense et la microcopie électronique à transmission. Nos résultats montrent que la densité de marquage observée pour les S-RNases cytoplasmiques est significativement plus haute dans les tubes incompatibles que dans ceux compatibles ce qui nous indique que pour qu’un tube pollinique soit compatible il doit contenir une faible densité de S-RNase cytoplasmique.

The impact of a permanent Income shock on the situation of women in the household: the case of a pension reform in Argentina

Transfers to women may affect their bargaining power within the household and consequently their well-being. We analyze the effects of the 2004/2005 pension reform in Argentina, that resulted in an unexpected and substantial increase in permanent income for around 1.8 million women, on outcomes arguably related to women’s bargaining power within the household. We estimate the effects of the reform in the probability of divorce/separation, the distribution of household chores, and the probability of women being the head of the household, using a Difference-in-Differences approach. Our results show that despite the low divorce probability among seniors, transfers to senior women have substantial effects on their situation in the household. More specifically, we find that the reform had statistically significant effects on the probability of divorce/separation increasing it by 1.8 − 2.7 percentage points implying an increase of around 18 − 19% on the divorce/separation rate of 60 − 65 year old women. Moreover, the probability of being the head of the household also increased by 2.8−3.3 percentage points representing an increase of 7−19% in the probability amongst women of 60 − 65 years of age. In the case of married women, the probability of being the head of the household increased by 1.3 − 1.5 percentage points, which represents an increase of 20 − 22%. Results show that the distribution of household chores within the couples was also affected by the reform. More precisely, the probability that the wife is the only person in charge of the housework decreased by 5 percentage points, an 11% decrease. The participation of husbands in housework, however, did not change significantly.

The slow cortical evoked potential: cross modality interaction of auditory, vibro-tactile and shock stimuli

This paper discusses a study that collected cortical evoked responses when stimuli of different modalities were presented.

Forward modelling to determine the observational signatures of white-light imaging and interplanetary scintillation for the propagation of an interplanetary shock in the ecliptic plane

Recent coordinated observations of interplanetary scintillation (IPS) from the EISCAT, MERLIN, and STELab, and stereoscopic white-light imaging from the two heliospheric imagers (HIs) onboard the twin STEREO spacecraft are significant to continuously track the propagation and evolution of solar eruptions throughout interplanetary space. In order to obtain a better understanding of the observational signatures in these two remote-sensing techniques, the magnetohydrodynamics of the macro-scale interplanetary disturbance and the radio-wave scattering of the micro-scale electron-density fluctuation are coupled and investigated using a newly constructed multi-scale numerical model. This model is then applied to a case of an interplanetary shock propagation within the ecliptic plane. The shock could be nearly invisible to an HI, once entering the Thomson-scattering sphere of the HI. The asymmetry in the optical images between the western and eastern HIs suggests the shock propagation off the Sun–Earth line. Meanwhile, an IPS signal, strongly dependent on the local electron density, is insensitive to the density cavity far downstream of the shock front. When this cavity (or the shock nose) is cut through by an IPS ray-path, a single speed component at the flank (or the nose) of the shock can be recorded; when an IPS ray-path penetrates the sheath between the shock nose and this cavity, two speed components at the sheath and flank can be detected. Moreover, once a shock front touches an IPS ray-path, the derived position and speed at the irregularity source of this IPS signal, together with an assumption of a radial and constant propagation of the shock, can be used to estimate the later appearance of the shock front in the elongation of the HI field of view. The results of synthetic measurements from forward modelling are helpful in inferring the in-situ properties of coronal mass ejection from real observational data via an inverse approach.

Shock persistence in a dual economy model of India

This article examines shock persistence in agricultural and industrial output in India. Drawing on the dual economy literature, the linkages between the sectors through the terms of trade are emphasised. However different dual economy models make differing assumptions regarding the categorisation of variables as being either endogenous or exogenous and this distinction is crucial in explaining the pattern of shock persistence. Using annual data for 1955-95, our results show that shocks to both output series are permanent while those to the terms of trade are transient.

Heat-shock response in Arabidopsis thaliana explored by multiplexed quantitative proteomics using differential metabolic labeling

We have developed a general method for multiplexed quantitative proteomics using differential metabolic stable isotope labeling and mass spectrometry. The method was successfully used to study the dynamics of heat-shock response in Arabidopsis thaliana. A number of known heat-shock proteins were confirmed, and some proteins not previously associated with heat shock were discovered. The method is applicable in stable isotope labeling and allows for high degrees of multiplexing.

Heat shock protein 27 is the major differentially phosphorylated protein involved in renal epithelial cellular stress response and controls focal adhesion organization and apoptosis

We used two-dimensional difference gel electrophoresis to determine early changes in the stress-response pathways that precede focal adhesion disorganization linked to the onset of apoptosis of renal epithelial cells. Treatment of LLC-PK1 cells with the model nephrotoxicant 1,2-(dichlorovinyl)-L-cysteine (DCVC) resulted in a >1.5-fold up- and down-regulation of 14 and 9 proteins, respectively, preceding the onset of apoptosis. Proteins included those involved in metabolism, i.e. aconitase and pyruvate dehydrogenase, and those related to stress responses and cytoskeletal reorganization, i.e. cofilin, Hsp27, and alpha-b-crystallin. The most prominent changes were found for Hsp27, which was related to a pI shift in association with an altered phosphorylation status of serine residue 82. Although both p38 and JNK were activated by DCVC, only inhibition of p38 with SB203580 reduced Hsp27 phosphorylation, which was associated with accelerated reorganization of focal adhesions, cell detachment, and apoptosis. In contrast, inhibition of JNK with SP600125 maintained cell adhesion as well as protection against apoptosis. Active JNK co-localized at focal adhesions after DCVC treatment in a FAK-dependent manner. Inhibition of active JNK localization at focal adhesions did not prevent DCVC-induced phosphorylation of Hsp27. Overexpression of a phosphorylation-defective mutant Hsp27 acted as a dominant negative and accelerated the DCVC-induced changes in the focal adhesions as well as the onset of apoptosis. Our data fit a model whereby early p38 activation results in a rapid phosphorylation of Hsp27, a requirement for proper maintenance of cell adhesion, thus suppressing renal epithelial cell apoptosis.

Heat shock protein 27 is the major differentially phosphorylated protein involved in renal epithelial cellular stress response and controls focal adhesion organization and apoptosis

We used two-dimensional difference gel electrophoresis to determine early changes in the stress-response pathways that precede focal adhesion disorganization linked to the onset of apoptosis of renal epithelial cells. Treatment of LLC-PK1 cells with the model nephrotoxicant 1,2-(dichlorovinyl)-L-cysteine ( DCVC) resulted in a > 1.5-fold up- and down-regulation of 14 and 9 proteins, respectively, preceding the onset of apoptosis. Proteins included those involved in metabolism, i.e. aconitase and pyruvate dehydrogenase, and those related to stress responses and cytoskeletal reorganization, i.e. cofilin, Hsp27, and alpha-b-crystallin. The most prominent changes were found for Hsp27, which was related to a pI shift in association with an altered phosphorylation status of serine residue 82. Although both p38 and JNK were activated by DCVC, only inhibition of p38 with SB203580 reduced Hsp27 phosphorylation, which was associated with accelerated reorganization of focal adhesions, cell detachment, and apoptosis. In contrast, inhibition of JNK with SP600125 maintained cell adhesion as well as protection against apoptosis. Active JNK co-localized at focal adhesions after DCVC treatment in a FAK-dependent manner. Inhibition of active JNK localization at focal adhesions did not prevent DCVC-induced phosphorylation of Hsp27. Overexpression of a phosphorylation-defective mutant Hsp27 acted as a dominant negative and accelerated the DCVC-induced changes in the focal adhesions as well as the onset of apoptosis. Our data fit a model whereby early p38 activation results in a rapid phosphorylation of Hsp27, a requirement for proper maintenance of cell adhesion, thus suppressing renal epithelial cell apoptosis.

Halo-derivatised calix[4]tubes

Halo functionalisation of calix[4] tubes has been investigated through both derivatisation of individual calix[4]arenes and calix[4] tubes, using classical synthetic methods, to allow preparation of a series of novel derivatives. The solution and solid state properties are in accordance with the constituent calix[4] arenes adopting flattened cone arrangements which on complexation with potassium simplify to a regular cone. Electrospray and H-1 NMR studies, combined with molecular modelling have been used to ascertain the metal binding of this new series of cryptand like ionophores, demonstrating their retained selectivity for binding potassium over other Group 1 metals and the dependence on counter anion in the weak binding of silver.

Thallium pi-cation complexation by calix[4]tubes: Tl-205 NMR and X-ray evidence

Thallium cation complexation by calix[4]tubes has been investigated by a combination of (TI)-T-205, H-1 NMR and ES MS demonstrating the solution formation of a dithallium complex in which the cations are held in the calix[4]arene cavities. In addition, the structure of the complex has been determined in the solid state revealing the cations to be held exclusively by pi-cation interactions. Furthermore, this crystal structure has been used as the basis for molecular dynamics simulations to confirm that binding of the smaller K+ cation in the calix[4]tube cryptand like array occurs via the axial route featuring a g-cation intermediate.