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Le développement d’un organisme multicellulaire requière la coordination de la croissance, détermination tissulaire et différenciation cellulaire. Cependant, alors que les bases de la génétique de la morphogenèse ont été rigoureusement étudiées, le processus permettant la conversion de l’activité génétique en des structures biologiques complexes est bien moins compris. Chez Arabidopsis thaliana, les feuilles et fleurs initiés à partir du Méristème Apical Primaire (MAP) ont une expression génétique casi similaire. Toutefois, leur forme est considérablement différente dès les premières étapes de leur développement. Une compréhension de ce paradoxe requière avant tout de précisément quantifier la croissance dans toutes les dimensions de ces organes. Dans cet article, je présente une méthode de quantification spatio-temporelle complète de la croissance et de la prolifération des feuilles et des fleurs chez A. thaliana. En analysant des séries d’images confocales, j’en ai conclu que la différence morphologique observée entre feuilles et fleurs émerge principalement d’une asymétrie de la distribution de la croissance entre leurs côtés abaxial et adaxial, tôt dans leur développement. Je montre que le tissue contribuant principalement au développement des primordia est la couche 2 (L2) chez les feuilles et la couche 3 (L3) chez les fleurs. Mes résultats préliminaires démontrent que les premiers signes de l’initiation d’organes est un changement de distribution de la croissance, et non de la prolifération. Dans le futur, en appliquant, par exemple, cette méthodologie à l’étude de gènes de développement, il sera possible de finalement réconcilier la morphogenèse et la génétique de l’initiation des plantes. / The development of a multicellular organism requires the proper coordination of growth, pattern determination and cell differentiation. Still, while the genetic basis of morphogenesis has been extensively studied, the process converting gene activity into intricate biological shapes is less understood. In Arabidopsis thaliana, flowers and leaves, both initiated from the shoot apical meristem (SAM), have a very similar genetic expression profile. Yet, their shape differs considerably from early developmental stages. A full comprehension of this paradox requires an accurate quantification of cellular growth in those organs. In this paper, I am presenting a methodology for the complete spatio-temporal quantitative analysis of growth and proliferation of initiating leaves and flowers in wild type Arabidopsis thaliana. By analyzing time series of leaf and flower confocal images, I conclude that the morphological differences observed between flowers and leaves mainly arises from asymmetrical distributions of growth between their adaxial and abaxial sides during their initiation. I show that the tissue that mainly contributes to the development of early primordium is the layer 2 (L2) in leaves, and the layer 3 (L3) in flowers. My preliminary results also demonstrate that the first signs of organ initiation are a change in growth distribution, not cell proliferation. In the future, by applying this methodology, for example, to study morphogen reporter lines, it could finally bridge the gap between the morphogenesis and the genetics of plant initiation.

Many cellular and molecular mechanisms are involved in the structural changes (morphogenesis) taking place during embryonic development. Indeed, the cytoskeleton is dynamically modified by intracellular signaling cascades, controlling cell morphogenesis during division or epithelial organization. Signal transduction mechanisms establishes homeostasis during morphogenetic processes. The cell cortex, composed by plasma membrane and underlying cytoskeleton meshwork, is responsible for integrating cell shape changes and organizing structural elements required for intercellular communication. The composition of the cell cortex is thus constantly changing in response to morphogenetic needs. However, the signaling network controlling this cortical plasticity is still unclear. This work has identified a new signaling pathway involved in cell cortex organization. The laboratories of Dr Carréno and Dr Hipfner use Drosophila as a model organism to study cell and tissue morphogenesis. Dr Carréno and Dr Hipfner had previously found that Ste20 Slik kinase was responsible for dMoesin activation by phosphorylation. dMoesin acts as a cross-linker between the cytoskeleton and the plasma membrane. This way, activation of dMoesin by Slik controls cortical stability during mitosis and epithelial integrity in Drosophila. This research project found that dSTRIPAK phosphatase activity promotes cortical localization of Slik in order to activate dMoesin at the plasma membrane. In addition, it showed that dSTRIPAK, as Slik and dMoesin, controls mitotic morphogenesis and epithelial tissue integrity. On top of that, Dr Hipfner has previously shown that Slik induces growth signaling at distance and independently of its catalytic activity. My research has led to the discovery that Slik is located along specialized signaling filopodia, called cytonemes. In addition, our data showed that Slik lengthens cytonemes, while dSTRIPAK is necessary for their biogenesis and signaling function. Slik and dSTRIPAK thus control tissue growth during the embryonic development of Drosophila. We have not determined the molecular mechanisms involved in the formation of cytonemes by dSTRIPAK/Slik yet. Together, our research projects led to the discovery that the dSTRIPAK complex regulates the catalytic and non-catalytic functions of Slik. We have thus identified a new signaling pathway controlling cell and tissue morphogenesis, through the cytoskeleton and intercellular communication. These processes are essential for maintaining homeostasis during embryogenesis. However, alteration of these morphogenetic processes can cause tumorigenesis. Our research might lead to the exploration of new anti-cancer therapeutic avenues. / De nombreux mécanismes moléculaires et cellulaires sont à la base des changements structurels (appelés la morphogenèse) qui ont lieu durant le développement d’un organisme. En effet, le cytosquelette est dynamiquement modifié par des cascades de signalisation intracellulaires contrôlant ainsi la morphogenèse cellulaire durant la division ou l’organisation d’un épithélium. L’homéostasie entre les différents processus morphogénétiques est établie grâce à des échanges de molécules signalisatrices. Le cortex de la cellule, composé de la membrane plasmique et du réseau de protéines du cytosquelette sous-jacent, est responsable d’intégrer les changements de forme cellulaire et d’organiser les éléments structurels requis pour la communication intercellulaire. Donc la composition du cortex cellulaire varie constamment en réponse aux besoins morphogénétiques. Toutefois, les réseaux de signalisation qui contrôlent cette plasticité corticale ne sont pas toujours connus. Ce travail a identifié une nouvelle voie de signalisation impliquée dans l’organisation du cortex cellulaire. Le laboratoire d’accueil (Dr Carréno) ainsi que celui du Dr Hipfner utilisent la drosophile comme organisme modèle pour l’étude fondamentale de la morphogenèse cellulaire et tissulaire. Le Dr Carréno et le Dr Hipfner avaient précédemment découvert que la kinase Ste20 Slik était responsable d’activer la dMoésine par phosphorylation. Celle-ci lie le cytosquelette à la membrane plasmique. L’activation de la dMoésine par Slik contrôle ainsi la stabilité corticale durant la mitose et l'intégrité épithéliale chez la drosophile. Durant mon projet de recherche, nous avons ensuite mis en évidence que le complexe phosphatase-kinase dSTRIPAK promeut la localisation corticale de Slik afin d’activer la dMoésine à la membrane plasmique. Nous avons également révélé que dSTRIPAK contrôle, tout comme Slik et dMoésine, la morphogenèse mitotique et l’intégrité du tissu épithélial. D'autre part, le Dr Hipfner avait précédemment constaté que Slik induisait une signalisation de croissance à distance, de façon indépendante de son activité catalytique. Mes recherches ont amené à découvrir que Slik est localisée le long de filopodes spécialisés dans la signalisation à distance, appelés cytonèmes. En outre, nos résultats révèlent que Slik allonge les cytonèmes, alors que dSTRIPAK est nécessaire à leur biogenèse et fonction de signalisation. Slik et dSTRIPAK contrôlent ainsi la croissance tissulaire au cours du développement embryonnaire de la mouche. Il reste à déterminer les mécanismes moléculaires impliqués dans la formation des cytonèmes par dSTRIPAK/Slik. Au final nos recherches ont mené à la découverte que le complexe dSTRIPAK régule les fonctions catalytiques et non-catalytiques de Slik. Nous avons ainsi identifié une nouvelle voie de signalisation contrôlant la morphogenèse cellulaire et tissulaire, par le biais du cytosquelette et de la communication intercellulaire. Ces processus sont essentiels au maintien de l’homéostasie durant l’embryogenèse. Toutefois, l’altération de ces processus morphogénétiques peut causer la tumorigenèse. Notre travail de recherche participe donc potentiellement à l’exploration de nouvelles stratégies thérapeutiques anti-cancéreuses.

Le développement des plantes nécessite la coordination des mécanismes de différenciation des cellules méristématiques en cellules hautement spécialisées: la division, la croissance et la formation de la géométrie cellulaire. La différenciation et la morphogenèse cellulaires sont étroitement liées et régulées par les propriétés mécaniques de la paroi cellulaire. Les mécanismes conduisant à l’émergence de diverses formes et fonctions des tissus végétaux sont complexes et encore peu compris. Ma thèse de doctorat approfondie les principes mécaniques à la base de la formation des cellules épidermiques ondulées. Je me suis également penché sur l’étude des avantages mécaniques que confèrent les motifs imbriqués. Les cellules épidermiques sont constituées de deux parois cellulaires périclines parallèles reliées par des parois anticlines. Aux jonctions, les cellules épidermiques forment des cavités et des saillies imbriquées les unes aux autres. Des images en 3D, prises en microscopie confocale, de cotylédons marqués par des fluorophores spécifiques à la cellulose montrent une déposition accrue de cellulose au niveau des cavités des parois périclines s’étendant le long des parois anticlines. Le marquage des cotylédons par COS488 démontre également une plus grande abondance de pectines dé-estérifiées aux mêmes sites. J'ai développé des modèles par éléments finis de la déformation de la paroi cellulaire et simulé les disparités biochimiques en alternant les régions plus rigides à travers et au long des parois périclines des deux côtés d'une paroi anticline. Le modèle montre que les parois rigidifiées non déformables se développent en cavités lorsque la pression interne étire la paroi cellulaire. Le modèle suggère également la présence de contraintes mécaniques plus élevées au niveau des saillies. Les résultats du modèle indiquent qu'une boucle de rétroaction positive entre la contrainte et la rigidité de la paroi cellulaire générerait les formes ondulées à partir de différences infinitésimales de rigidité ou de contrainte de la paroi cellulaire. En outre, le modèle suggère que des événements de flambage stochastiques peuvent initier la morphogenèse des cellules. On a longtemps émis l'hypothèse que le motif imbriqué de cellules épidermiques améliore l'adhérence cellule-cellule et donc la résistance de traction de l'épiderme. L'étirage des feuilles d'Arabidopsis de type sauvage ou du mutant any1 (caractérisé par une réduction de l'ondulation cellulaire) n'a montré aucun détachement cellulaire en cas de rupture du tissu. J'ai émis l'hypothèse que les jonctions des cellules ondulantes renforcent la résistance de l'épiderme contre la propagation de fissures. J'ai observé une grande anisotropie dans la réponse mécanique à la rupture de l'épiderme d'oignon selon l’orientation des cellules. Les fissures qui suivent l’alignement des cellules se propagent sans trop de résistance, entraînant une rupture fragile du tissu. Ceci découlerait de la propagation de la ligne de rupture par suite du détachement des cellules. Les fissures se propagent difficilement lorsqu’elles sont perpendiculaires à l'axe principal des cellules. En fracturant des feuilles dont les cellules épidermiques sont ondulées, j'ai remarqué que les fissures se propageaient, par intermittence, à la fois au niveau des jonctions de la cellule et de la paroi cellulaire. J'ai émis l'hypothèse que ce motif de fracture d'épiderme à cellules ondulées se caractérisait par une augmentation de la résistance à la fracture. Pour n’étudier que les effets de la géométrie des cellules sur cette résistance, j’ai éliminé le rôle que jouerait l’anisotropie des matériaux en concevant des modèles physiques macroscopiques de l'épiderme. J’ai gravé au laser des motifs cellulaires sur du poly-méthacrylate de méthyle. De cette façon, le matériau isotrope permettait d'étudier uniquement l'effet de la géométrie cellulaire. Alors que la fracturation des spécimens de contrôle sans gravure et des spécimens avec des cellules gravées longitudinalement ont démontré une rupture fragile, une fracturation transversale aux rangées cellulaires, dans les modèles mimant des cellules d’oignon ou des cellules ondulées de cotylédons d’Arabidopsis, a montré une résistance accrue à la fracture. En conclusion, je démontre que la forme ondulée des cellules épidermiques est le résultat d’une distribution alternée de la rigidité dans la paroi cellulaire, un processus qui pourrait être initié par une anisotropie de stress stochastique due au flambement. De plus, ces formes cellulaires augmentent la résistance à la rupture de l'épiderme végétal en le protégeant contre la propagation des fissures; un mécanisme de défense ingénieux pour les surfaces les plus exposées. / Plant development entails cell division, cell growth and shaping, and the differentiation of meristematic cells into highly specialized cell types. Differentiation and cell shape are closely linked and involve the regulation of the mechanical properties of the cell wall. The mechanisms leading to the generation of the diverse array of shapes and functionalities found in plant tissues are perplexing and poorly understood. In my Ph.D. research, I investigated the mechanical principles underlying the formation of wavy leaf pavement cells. Further, I studied the putative mechanical advantage that emerges from the interlocking patterns. Epidermal pavement cells consist of two parallel periclinal walls connected by vertical anticlinal walls. At the borders, wavy pavement cells make interlocking indentations and protrusions. 3D confocal micrographs of cotyledons stained with cellulose-specific fluorophores revealed a significant accumulation of cellulose at the sites of indentation on the periclinal walls extending down the anticlinal walls. Staining the cotyledon samples with COS488 also suggested a higher abundance of de-esterified pectin at these sites. I developed finite element models of the cell wall deformation and simulated the biochemical inhomogeneities by assigning alternately stiffened regions across and along the periclinal walls on two sides of an anticlinal wall. It was observed that the non-deforming stiffened regions develop into sites of indentations when the internal pressure stretches the cell wall. The model also suggested higher stresses to associate with the neck regions. The model results indicate that a positive feedback loop between stress and cell wall stiffness could generate wavy shapes starting from infinitesimally small differences in cell wall stiffness or stress. Further, the model suggests that stochastic buckling events can initiate the cell shaping process. It has been long hypothesized that the interlocking pattern of pavement cells improves cell-cell adhesion and thus the tensile strength of the epidermis. Stretching to rupture the leaf samples of wild-type Arabidopsis or any1 mutant with reduced cell waviness did not show any cell detachment upon failure. However, I hypothesized the undulating cell borders could enhance the resistance of the epidermis against the propagation of damage. I observed a considerable anisotropy in the tear behavior of onion epidermis parallel and perpendicular to the cells’ main axis. Tears along the cell lines propagated without much resistance resulting in brittle failure of the tissue. This was observed to originate from tears propagating by cell detachment. Perpendicular to the cells’ main axis, tears had considerable difficulty in propagating. Fracturing the leaf samples with wavy epidermal cells, I noticed the cracks propagated in both the cell borders and the cell wall intermittently. I hypothesized that this pattern of fracture in the epidermis with wavy cells indicates an increase in the fracture toughness. To untangle the influence of material anisotropy from the cell geometry on fracture toughness, I designed macroscopic physical models of the epidermis by laser engraving the cell patterns on polymethylmethacrylate. This way, the isotropic material would allow studying only the effect of cell geometry. While fracturing the control specimens with no engraving and the specimens with longitudinally placed cells demonstrated a brittle fracture, fractures transverse to cell lines in the onion cell patterns or across the Arabidopsis cotyledon wavy cell pattern showed an increased fracture toughness. I suggest the wavy shape of pavement cells in the epidermis results from the alternate placement of stiffer regions in the cell wall, a process that can initiate from a stochastic stress anisotropy due to buckling. Further, these shapes increase the fracture toughness of the plant epidermis protecting it against the spread of damage; an ingenious defense mechanism at the most exposed surfaces.

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Les plantes présentent une incroyable diversité de tailles, formes et couleurs, étroitement liée à certaines de leurs fonctions biologiques telles que la photosynthèse, la reproduction, etc. De ce fait, la façon dont ces organismes multicellulaires acquièrent des formes complexes est une question clé en biologie du développement. La morphologie des organes végétaux résulte en effet de la modulation, à l’échelle cellulaire, de patrons d’expression génétique, de croissance et de différenciation. Bien que la morphogénèse ait été largement étudiée d’un point de vue moléculaire, nous ne savons toujours pas comment ces réseaux génétiques sont traduits en formes biologiques. Le but de ce projet de recherche est donc d’étudier le développement des organes latéraux (feuilles juvéniles, feuilles caulinaires et organes floraux, id sépales, pétales et anthères) chez l’espèce modèle Arabidopsis thaliana. Afin d’approcher la question du rôle des interactions complexes entre cellules et organes lors du développement, nous nous intéressons à la variabilité entre les organes, mais aussi à la variabilité cellulaire intrinsèque de chaque organe. Nous avons donc testé (1) si la diversité de formes observées chez les organes latéraux résulte de modulations d’un programme développemental commun; (2) si la croissance et le développement des organes latéraux est un phénomène stochastique ou dépend de mécanismes sous-jacents spécifiques. Pour ce faire, nous utilisons une approche multidisciplinaire basée sur la génétique, la microscopie confocale et l’analyse d’images 3D pour extraire les patrons de croissance inhérents aux différents organes. Les résultats de la première étude (Chapitre 2) montrent que la forme des organes dépend de l’équilibre entre croissance et différentiation, dont la régulation précise permet l'acquisition de fonctions hautement spécialisées. La feuille caulinaire, par exemple, présente un retard de différenciation qui permet une activité morphogénétique prolongée et une redistribution de la croissance. À travers la suppression transitoire de la croissance lors des premiers stades de développement, la trajectoire développementale de la feuille caulinaire permet sa double fonction, à la fois protectrice et photosynthétique.\par La deuxième étude (Chapitre 3), quant-à-elle, s’intéresse aux comportements des cellules individuelles, dont la croissance, bien que contrôlée par des informations positionnelles, est souvent hétérogène. Cette variabilité résulte de la différenciation de cellules spécialisés, les stomates, qui suivent un programme de développement spécifique. Le comportement autonome de ces cellules, asynchrone, est la principale source de variabilité dans des tissus dont la croissance est autrement homogènes. Dans l’ensemble, cette thèse a permis de mettre en lumière l’importance de la temporalité lors du développement des organes végétaux. Que ce soit à l’échelle de l’organe, du tissu ou de la cellule, la modulation et la synchronisation de la croissance et de la différentiation sont nécessaires à l’acquisition des formes stéréotypiques des organes et à leur complexité fonctionnelle. / Plants display an incredible diversity of sizes, shapes, and colors, closely linked to some of their biological functions, such as photosynthesis, reproduction, etc. How these multicellular organisms acquire complex shapes is, therefore, a key question in developmental biology. The morphology of plant organs results from cell-level modulation of patterns of gene expression, growth, and differentiation. Although morphogenesis has been extensively studied from a molecular point of view, how genetic networks are translated into biological forms is still unclear. Thus, the aim of this research project is to study the development of lateral organs (rosette leaves, cauline leaves, and floral organs, i.e. sepals, petals, and anthers) in the model species Arabidopsis thaliana. To address the question of the role of complex cell-organ interactions during development, we are interested not only in variability between organs but also in the intrinsic cellular variability of each organ. We, therefore, tested (1) whether the diversity of shapes observed in lateral organs results from modulations of a common developmental program; (2) whether the growth and development of lateral organs is a stochastic phenomenon or depends on specific underlying mechanisms. To this end, we are using a multidisciplinary approach based on genetics, confocal microscopy, and 3D image analysis to extract the growth patterns inherent in the different organs. The results of the first study (Chapter 2) show that organ shape depends on the balance between growth and differentiation, which fine regulation enables the acquisition of highly specialized functions. The cauline leaf, for example, shows a delay in differentiation that allows for prolonged morphogenetic activity and growth redistribution. Through the transient growth suppression at early stages, the cauline leaf developmental trajectory allows for its dual function, from protection to photosynthesis. The second study (Chapter 3) focuses on the behavior of individual cells, whose growth, although controlled by positional information, is often heterogeneous. This variability results from the differentiation of specialized cells, the stomata, which follow a specific developmental program. The autonomous, asynchronous behavior of these cells is the main source of variability in tissues whose growth is otherwise homogeneous. Overall, this thesis has shed light on the importance of timing in plant organ development. Whether at the organ, tissue, or cell level, modulation and synchronization of growth and differentiation are necessary for the acquisition of stereotypic organ shapes and functional complexity.

Yes / Bone morphogenetic proteins (BMPs) play essential roles in the control of skin development, postnatal tissue remodelling and tumorigenesis. To explore whether some of the effects of BMP signalling are mediated by microRNAs, we performed genome-wide microRNA (miRNA) screening in primary mouse keratinocytes after BMP4 treatment. Microarray analysis revealed substantial BMP4-dependent changes in the expression of distinct miRNAs, including miR-21. Real-time PCR confirmed that BMP4 dramatically inhibits miR-21 expression in the keratinocytes. Consistently, significantly increased levels of miR-21 were observed in transgenic mice overexpressing the BMP antagonist noggin under control of the K14 promoter (K14-noggin). By in situ hybridization, miR-21 expression was observed in the epidermis and hair follicle epithelium in normal mouse skin. In K14-noggin skin, miR-21 was prominently expressed in the epidermis, as well as in the peripheral portion of trichofolliculoma-like hair follicle-derived tumours that contain proliferating and poorly differentiated cells. By transfecting keratinocytes with a miR-21 mimic, we identified the existence of two groups of the BMP target genes, which are differentially regulated by miR-21. These included selected BMP-dependent tumour-suppressor genes (Pten, Pdcd4, Timp3 and Tpm1) negatively regulated by miR-21, as well as miR-21-independent Id1, Id2, Id3 and Msx2 that predominantly mediate the effects of BMPs on cell differentiation. In primary keratinocytes and HaCaT cells, miR-21 prevented the inhibitory effects of BMP4 on cell proliferation and migration. Thus, our study establishes a novel mechanism for the regulation of BMP-induced effects in the skin and suggests miRNAs are important modulators of the effects of growth factor signalling pathways on skin development and tumorigenesis.

Made available in DSpace on 2016-12-08T16:24:12Z (GMT). No. of bitstreams: 1 PGCA13MA094.pdf: 3484558 bytes, checksum: 4cd098df0840598b9d19fbbc52ff65cb (MD5) Previous issue date: 2013-03-04 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In regions with subtropical climates the use of grasses intercropping, mainly oats and ryegrass is a common practice, but the advantages and disadvantages of the intercrop in relation the pure culture are little studied. The aim of this work was to evaluate the production and persistence of black oat and ryegrass swards grown pure or intercropping throughout the period of use. The three treatments were randomly distributed into a complete blocks design with four replicates. The pre-grazing sward heights were 23, 20 and 17 cm for the oat, intercrop and ryegrass treatments, respectively. The post-grazing sward heights were 40% lower than their initial heights. Morphogenesis was performed using the technique of marked tillers and dynamic and tiller population density (TPD) was determined with three 10-cmdiameter PVC rings per paddock. The treatments did not differ in the final length of intact leaf, being the October month with the lowest values (approximately 48% lower). The phyllochron was not affected by the form of cultivation, but the values were increasing with the advance of the growing season. The leaf elongation rate decreased over the months, with a mean value of 0.14 cm / perfilhos.graus-day for all treatments. The advance of the growing season resulted in increases stem elongation rates, with the species in the intercrop having smaller increments in the final months. In general, rates of senescence reduced with the advance of months, and the intercrop increased tissue death of ryegrass. The intercrop TPD remained constant until October, inverting the participation of species in August. Of the tillers existing on the last grazing cycle, approximately 0, 40 and 20% were first generation of the oats, ryegrass and intercrop, respectively. Thus, despite of ryegrass pure have the lowest rate of tillering, it have the same rate of population stability of the intercrop. The pure ryegrass had the highest average net accumulation rates by offering smaller forage losses by senescence. Tiller size/density compensation was observed in the three plant communities (treatments) according to the self-thinning rule. In addition, no relationships were found when each species was analysed individually in the intercrop treatment. For the species tested the developmental stage of sward has greater influence on the morphogenesis and structural characteristics than cultivation form. The morphological similarity of oats and ryegrass enables evaluated traits similar in both forms of cultivation. When intercropping the temperate climate grasses under rotational grazing, size/density compensation mechanisms occurred throughout the grazing cycles and in the plant communities the same form of the pure cultivation to maintain the leaf area index and production capacities of the pastures / Em regiões de clima subtropical a utilização de gramíneas em consórcio, principalmente aveia e azevém, é uma prática comum, porém as vantagens e desvantagens do consórcio em relação ao cultivo puro são pouco estudadas. Objetivou-se avaliar a produção e a longevidade de pastos de aveia-preta e azevém anual cultivados puros ou em consórcio ao longo de todo o período de utilização. Os três tratamentos foram distribuídos em blocos completos casualizados com quatro repetições, tendo cada unidade experimental 98 m2. As alturas em pré-pastejo foram 23, 20 e 17 cm para a aveia, o consórcio e o azevém, respectivamente, sendo rebaixados em 40% destas alturas. A morfogênese foi realizada por meio da técnica de perfilhos marcados e a dinâmica e densidade populacional de perfilhos (DPP) em três anéis de PVC com 10 cm de diâmetro por piquete. Os tratamentos não diferiram quanto ao comprimento final de folha intacta, ficando o mês de outubro com os menores valores (aproximadamente 48% menor). Não houve efeito da forma de cultivo para os valores de filocrono, porém os valores foram crescentes com o avanço da estação de crescimento. A taxa de alongamento foliar reduziu com o passar dos meses, com valor médio de 0,14 cm/perfilho.grau-dia para todos os tratamentos. O avanço da estação de crescimento resultou em incrementos nas taxas de alongamento de colmos, com as espécies no consórcio apresentando menores incrementos nos meses finais. De maneira geral, as taxas de senescência foliar reduziram com o avanço dos meses, sendo que o consórcio aumentou a morte de tecidos do azevém. O consórcio manteve a DPP constante até outubro, apresentando uma inversão na participação das duas espécies em agosto. Dos perfilhos existentes no último ciclo de pastejo, aproximadamente 0, 40 e 20% eram da primeira geração no azevém, na aveia e no consórcio, respectivamente. Com isso, apesar de apresentar a menor taxa de aparecimento de perfilhos o azevém cultivado puro apresentou o mesmo índice de estabilidade populacional do consórcio. O azevém cultivado puro apresentou as maiores taxas de acúmulo líquido médio por apresentar as menores perdas de forragem por senescência. A compensação tamanho/densidade de perfilhos foi observada segundo a lei do auto-desbaste (self thinning rule) nos três tratamentos quando levados em conta todos os perfilhos da área, não sendo encontrada relação quando as espécies foram analisadas individualmente no consórcio. Para as espécies testadas o estádio de desenvolvimento dos pastos apresenta maior influência sobre as características morfogênicas e estruturais do que a forma de cultivo. A semelhança morfológica da aveia e do azevém possibilita características morfogênicas e estruturais parecidas em ambas as formas de cultivo. É sugestivo que em consórcios entre gramíneas de clima temperado sob lotação intermitente os mecanismos de compensação tamanho/densidade operem na comunidade de plantas e ao longo dos ciclos de pastejo da mesma forma que nos cultivos puros, mantendo elevado índice de área foliar e capacidade produtiva

A small proportion of people claim to live and consume in ways they consider more sustainable in social and environmental terms. As yet, we do not know how many exactly, but possibly no more than 5-10% of the population. The thesis intentionally focuses on this minority finding there are at least three reasons why it is interesting to do so. First because they are all but ignored in sociologies of practice in the context of sustainable consumption which considers this minority an insignificance and focuses almost exclusively on 'mainstream' majority which more closely maps onto the stereotype of 'consumer society'. Second because we think we can learn much from juxtapositioning this group empirically against the spectrum of theories of practice to devise more robust and appropriate theoretical explanation of how these subjects, in the context of everyday practice, negotiate the many interpretations and contradictions involved in trying to put 'sustainability' into practice. Third because by understanding them better we can reflect on theoretical, empirical and policy implications for nudging this minority of the population to a higher percentage. The thesis sits at one end of a spectrum of positions in theories of practice applied to consumption, and in particular with a normative interest in sustainable consumption. It aligns with those who seek to re-insert the reflexive agent into accounts of practice, with particular reference to the conceptual construct of the 'citizen-consumer' and the context of political consumption (Spaargaren & Oosterveer 2010). Referring to theories of consumption, the thesis adds perspectives on how people negotiate multiple domains of consumption simultaneously since everyday practice involves interactions across multiple domains (such as eating, mobility, householding); and yet typically in theories of practice these are artificially separated into single domains. The study therefore considers the implications which domains have on how particular practices are carried out, first separately (per domain) and then as they come together (in a cross-cutting domain perspective). The study then takes theories of practice as a springboard to develop a theoretical position and framework which better fits the narrated accounts of the 37 subjects who participated in this study. In iteratively co-developing a theoretical framework and multiple 'stages' of empirical research (using grounded theory methodology) the study seeks to explain theoretically how subjects justify their 'doings' (drawing on 'conventions' and 'orders of worth' (Boltanski & Thévenot 2006)); how they appear to muddle through as best they can (introducing 'bricolage' (Lévi-Strauss 1972)); and how subjects appear to devise decision short-cuts when approaching decisions characterised by the multiple contradictions of sustainable consumption and incomplete or 'too much' information (introducing heuristics (Gigerenzer & Gaissmaier 2011)). In joining calls to re-insert the reflexive agent to account for how, when and why subjects enact changes towards trajectories which they consider 'more sustainable' in their own terms, the study takes inspiration from Margaret Archer's morphogenesis approach (1998) and explores her model of multiple modes of reflexivity, announcing certain modes as 'better fitting' conditions of late modernity. The study finally finds that contrary to a notion of the un-reflexive agent, the citizen-consumer is able to articulate visions of the 'good life'. In addition she is able to fold these visions back onto everyday practices performed in the past, present and future, laying out normative guidelines and positive accounts of how to achieve personal or societal well-being and happiness. The overarching positioning of the study is much inspired by Andrew Sayer's (2011; 2000) 'normative turn' calling upon social sciences to re-instate research into the things about which people care. The study is therefore guided by the overarching question of how people translate their environmental and/or social concerns into the ways in which they live and consume.