Setaria viridis tem sido utilizada como organismo modelo para gramíneas com metabolismo C4, buscando elucidar processos biológicos de plantas. A importância das monocotiledôneas com o metabolismo de C4 deve-se ao melhor balanço fotossintético quando comparado às plantas com metabolismo C3 em condições climáticas com altas temperaturas, como as que prevalecem no Brasil. Setaria viridis representa um sistema modelo de grande importância para a agricultura brasileira, uma vez que tanto a produção brasileira de biocombustíveis como de alimentos está fortemente relacionada aos organismos C4. Os hormônios vegetais são cruciais no estabelecimento de órgãos complexos desde o zigoto até o desenvolvimento da planta adulta. A auxina em particular, desempenha um papel fundamental na formação de um complexo sistema radicular nas plantas. Sabe-se que o transporte polar desse hormônio concentra a auxina em determinados tecidos, desempenhando um papel essencial na expressão diferencial de genes que modulam o desenvolvimento dos vários órgãos da planta. Monocotiledôneas e em particular Poaeceaes exibem um complexo sistema radicular que parece ser chave para o seu vasto potencial adaptativo, mas pouco se sabe sobre os fatores que envolvem as respostas sensoriais e de desenvolvimento que guiam a escolha de quais tipos de raiz as plantas elegem. O objetivo deste estudo foi explorar as vias hormonais e abióticas que influenciam a arquitetura das raízes / Setaria viridis has been used as a model organism for grasses with C4 metabolism, seeking to elucidate plant biological processes. The importance of monocotyledons with C4 metabolism is due to better photosynthetic balance when compared to plants with C3 metabolism in climatic conditions with high temperatures, such as those that prevail in Brazil. Setaria viridis represents a model system of great importance for Brazilian agriculture since both the Brazilian production of biofuels and food is strongly related to C4 organisms. Plant hormones are crucial in the establishment of complex organs from zygote to the adult plant development. Auxin in particular, plays a key role in the formation of a complex radicular system in plants. The polar transport of this hormone is known to concentrate auxin in particular tissues, playing an essential roll in the differential expression of genes that will modulate the development of the various plant organs. Monocots and in particular Poaeceae display a complex radicular system that seems to be key for it vast adaptive potential, but little is known about the factors involving the sensing and developmental responses that guide the choice of which root types to elect. The aim of this study was to explore the hormonal and abiotic cues that influence the root architecture

Setaria viridis tem sido utilizada como organismo modelo para gramíneas com metabolismo C4, buscando elucidar processos biológicos de plantas. A importância das monocotiledôneas com o metabolismo de C4 deve-se ao melhor balanço fotossintético quando comparado às plantas com metabolismo C3 em condições climáticas com altas temperaturas, como as que prevalecem no Brasil. Setaria viridis representa um sistema modelo de grande importância para a agricultura brasileira, uma vez que tanto a produção brasileira de biocombustíveis como de alimentos está fortemente relacionada aos organismos C4. Os hormônios vegetais são cruciais no estabelecimento de órgãos complexos desde o zigoto até o desenvolvimento da planta adulta. A auxina em particular, desempenha um papel fundamental na formação de um complexo sistema radicular nas plantas. Sabe-se que o transporte polar desse hormônio concentra a auxina em determinados tecidos, desempenhando um papel essencial na expressão diferencial de genes que modulam o desenvolvimento dos vários órgãos da planta. Monocotiledôneas e em particular Poaeceaes exibem um complexo sistema radicular que parece ser chave para o seu vasto potencial adaptativo, mas pouco se sabe sobre os fatores que envolvem as respostas sensoriais e de desenvolvimento que guiam a escolha de quais tipos de raiz as plantas elegem. O objetivo deste estudo foi explorar as vias hormonais e abióticas que influenciam a arquitetura das raízes / Setaria viridis has been used as a model organism for grasses with C4 metabolism, seeking to elucidate plant biological processes. The importance of monocotyledons with C4 metabolism is due to better photosynthetic balance when compared to plants with C3 metabolism in climatic conditions with high temperatures, such as those that prevail in Brazil. Setaria viridis represents a model system of great importance for Brazilian agriculture since both the Brazilian production of biofuels and food is strongly related to C4 organisms. Plant hormones are crucial in the establishment of complex organs from zygote to the adult plant development. Auxin in particular, plays a key role in the formation of a complex radicular system in plants. The polar transport of this hormone is known to concentrate auxin in particular tissues, playing an essential roll in the differential expression of genes that will modulate the development of the various plant organs. Monocots and in particular Poaeceae display a complex radicular system that seems to be key for it vast adaptive potential, but little is known about the factors involving the sensing and developmental responses that guide the choice of which root types to elect. The aim of this study was to explore the hormonal and abiotic cues that influence the root architecture

Moniliophthora perniciosa é o agente causal da doença vassoura-de-bruxa em cacaueiro (Theobroma cacao). Os sintomas da doença compreendem perda de dominância apical, inchamento e excesso de brotações em ramos novos, reversão de meristemas florais em vegetativos, partenocarpia e lesões necróticas em frutos, sugerindo a ocorrência de alterações hormonais no hospedeiro. A disponibilidade de isolados do biótipo-S capazes de infectar o tomateiro, permitiu a utilização da cultivar miniatura \'Micro-Tom\' (MT) como um modelo para estudo da interação Moniliophthora perniciosa x Solanum lycopersicum. Além de provocar sintomas característicos no MT, a disponibilidade de mutantes e linhas transgênicas introgredidos em MT, com alterações que afetam o metabolismo e sensibilidade hormonal, permitem investigar o papel dos hormônios vegetais no desenvolvimento dos sintomas. Inicialmente, foi avaliada a agressividade de três isolados do biótipo-S no MT, sendo que um isolado de Tiradentes apresentou maior agressividade, com maior incidência dos sintomas, maior engrossamento do caule, redução na altura das plantas, aumento no número de lóculos nos frutos e redução na biomassa radicular. Mutantes com alterações na percepção para auxina (diageotropica e entire) e uma linha transgênica expressando uma citocinina oxidase de Arabidopsis (35S::AtCKX2) diferiram para o engrossamento do caule e distribuição do número de lóculos nos frutos em relação ao MT. A linha transgênica 35S::AtCKX2 diferiu significativamente de MT com menor incidência de infecção. O engrossamento do caule associa-se ao aumento na área do córtex e, principalmente do xilema e floema. A aplicação exógena de citocinina sintética benzil-adenina (BA) e da auxina sintética ácido naftaleno acético (ANA) em MT evocam sintomas similares aos de plantas infectadas com M. perniciosa. Linhas transgênicas repórter de sinalização por citocinina (ARR5::GUS) ou auxina (DR5::GUS) indicaram sinalização diferencial por citocinina a 24 h e 36 h após inoculação (HAI) e 48 HAI por auxina. A infecção por M. perniciosa aumentou os níveis de ácido jasmônico, ácido salicílico (AS) e auxina em MT entre 5 d a 30 DAI, com maior incremento aos 5 DAI, enquanto que o nível de ácido abscísico aumentou aos 20 d e 30 DAI, e AS foi o único detectado em micélio dicariótico do biótipo-S. Genes de biossíntese de citocinina (IPT), ativação (LOG), degradação (CKX) e resposta à citocinina (ARRs e CRF) e auxina (AUX/IAA, ARFs, SAUR e GH3) foram induzidos em MT inoculado de 12 h a 5 DAI, mas com maior acúmulo de transcritos aos 30 DAI. M. perniciosa induziu maior expressão desses genes citados e de biossíntese auxina, nos momentos iniciais da interação (12 h a 5 DAI) em 35S::AtCKX2 do que no MT. O efeito da infecção em aumentar o número de lóculos nos frutos parece ser independente ou downstream a mutação fasciated, Mouse ears e ovate. A mutação Lanceolate parece ter um papel na redução do efeito da infecção em aumentar o número de lóculos. Os resultados obtidos sugerem que a infecção pelo M. perniciosa em MT altere os níveis/sinalização dos hormônios vegetais, principalmente auxina e citocinina, provocando o engrossamento do caule (aumento no xilema, floema e córtex), redução no crescimento e na biomassa radicular e aumento no número de lóculos nos frutos / Moniliophthora pernicisa is the causal agent of witches\' broom disease in cocoa (Theobroma cacao). The disease symptoms comprise loss of apical dominance, thickening and proliferation of axillary shoots, shift from inflorescence into vegetative meristem, parthernocarpy and necrotic lesions on fruits, suggesting a host hormonal imbalance. The availability of an isolated of S-biotype M. perniciosa, which colonizes tomato, enabled the utilization of the miniature tomato (Solanum lycopersicum) cultivar \'Micro-Tom\' (MT) as a suitable model to study the pathosystem M. perniciosa x S. lycopersicum. In addition to the characteristic symptoms of the infection in MT, the availability of mutants and transgenic lines introgessed into MT, with changes in plant metabolism and hormonal sensitivity, enable the investigation of the role of plant hormones in the development of symptoms. Initially, we evaluated the aggressiveness of three S-biotype M. perniciosa isolates. The isolate \'Tiradentes\' showed greater aggressiveness infecting MT, with higher plant infection incidence, greater stem thickening, reduction in plant height, increase in fruit locule number and reduction in root dry weight. Mutants with altered auxin perception (diageotropica e entire) and the transgenic line expressing a cytokinin oxidase gene of arabidopsis (35S::AtCKX2) differed in stem thickening and fruit locule number distribution, as compared to MT. The transgenic line 35S::AtCKX2 differed significantly from MT, showing lower incidence of infection. The thickening of the stem may be related with an increase in area of the cortex, especially xylem and phloem. The exogenous application of synthetic cytokinin benzyl adenine (BA) and auxin naphthalene acetic acid (NAA) in MT induces similar symptoms to plants infected with M. perniciosa. Cytokinin (ARR5::GUS) and auxin (DR5::GUS) signaling reporter transgenic lines revealed differential cytokinin signaling 24 h e 36 h hours after inoculation (HAI) and differential auxin signaling in 48 HAI. Infection of MT by M. perniciosa increased the content of JA, SA and auxin during the development of symptoms from 5 d to 30 DAI, with greater increase at an early stage of symptoms development (5 days after inoculation - DAI), whereas abcisic acid content increased in 20 and 30 DAI, and only AS was detected in dicariotic mycelium of the S-biotype M. perniciosa. Cytokinin biosynthesis (IPT), activating (LOG), and breakdown (CKX) genes and response to cytokynin genes (ARRs e CRF) and auxin (AUX/IAA, ARFs, SAUR e GH3) were induced in MT infected in 12 h a 5 DAI, with greater accumulation of transcripts in 30 DAI. M. perniciosa induced higher levels of IPT, LOG, CKX, ARRs, and CRF genes and auxin biosynthesis genes at an ealry stage of infection (12 h a 5 DAI) in 35S::AtCKX2, as compared to MT. The effect of the infection on increasing fruit locule number seems to be independent or downstream fasciated, Mouse ears and ovate mutation. Lanceolate mutation seems to play a role in reducing M. perniciosa ability of increasing fruit locule number. The results suggest infection of MT by S-biotpye M. perniciosa alters levels/signaling of the hormones, especially auxin and cytokinin, inducing stem thickening (increasing xylem, phloem and cortex), reduction in plant height, root dry weight and increase in fruit locule number

L'interférence ARN est un ensemble de mécanismes de régulation essentiel pour denombreux processus au cours du développement. Ces mécanismes sont caractérisés par lʼinhibition séquence-spécifique de lʼexpression de gènes via lʼaction de petites molécules dʼARN. Parmi les différentes voies de l'interférence ARN, la voie des trans-acting siRNAs dérivés du précurseurTAS3,qui combine des caractéristiques des voies des miRNAs et siRNAs, est spécifique des plantes et en contrôle divers aspects essentiels du développement. Dans cette voie, AGO7, un membre de la famille des protéines ARGONAUTE, interagit spécifiquement avec miR390 pour cibler et cliver le transcrit TAS3 amorçant ainsi la production de tasiARFs par lʼaction de SGS3, RDR6 et DCL4. Cette voie est conservée chez toutes les plantes terrestres. Par leur activité de répression sur des membres des facteurs de réponse à l'auxine ARF2, ARF3 et ARF4, les tasiARFS contrôlent la transition de phase et la régionalisation des feuilles. Notre laboratoire et dʼautres ont montré que TAS3 était également exprimé dans la racine dʼArabidopsis, posant la question du rôle joué par la voie TAS3dans le développement des racines. Nous avons établi que la voie TAS3, par lʼaction des tasiARFs, joue un rôle essentiel dans le contrôle de la croissance des racines latérales. Nous avons démontré que la voie TAS3 agit en aval de lʼauxine pour maintenir la correcte zone et abondance des facteurs de réponse à l'auxine, ARF2, ARF3 et ARF4. De plus nous avons élucidé un ensemble complexe de rétroactions de ces ARFs sur lʼexpression de miR390. Bien que les mécanismes de la voie TAS3 ont été identifié par divers screen génétiques, notre connaissance de lʼorganisation subcellulaire de cette voie reste essentiellement méconnue. Pour cette raison, nous avons choisi dʼétudier la localisation subcellulaire de la voie TAS3, en nous focalisant sur AGO7 qui en constitue un composant spécifique. Nous avons montré que AGO7, RDR6 et SGS3 sʼaccumulent dans des focicytoplasmiques spécifiques, les siRNA bodies. Nous avons observé une colocalisation entre cessiRNA bodies et des marqueurs des stress granules ainsi qu'une protéine virale associée aux membranes. Finalement nous avons démontré lʼimportance de la localisation cytoplasmique dʼAGO7pour la biogenèse des tasiARFs. Notre travail a permis de mieux comprendre les mécanismes de lʼaction de la voie TAS3 au cours du développement dʼArabidopsis. / RNA silencing is a regulatory mechanism essential for many processes during development. This mechanism is characterized by the sequence-specific inhibition of gene expression by small RNA molecules. Among the several pathways of RNA silencing, the TAS3 trans-acting small interfering RNA (ta-siRNA) pathway, which combines features of both micro (mi)RNA and siRNA pathways, is unique to plants and controls several key aspects of plant development. In this pathwayAGO7, a member of the ARGONAUTE family of RNAse, interacts specifically with miR390 to target and cut the TAS3 transcript, priming it for production of tasiARFs by SGS3, RDR6 and DCL4 action. This pathway is conserved across all land plants. By their repressing activity on Auxin Response Factors members, ARF2, ARF3 and ARF4, the tasiARFs control phase change and leaf patterning. Our lab and others have shown that TAS3 is also expressed in the root of Arabidopsis, raising the question of the role played by the TAS3 pathway in root development. We have shown that theTAS3 pathway, through the tasiARFs action, plays an essential role in the control of lateral rootgrowth. We have demonstrated that the TAS3 pathway acts downstream of auxin, to maintain the proper zonation and abundance of the Auxin Response Factors ARF2, ARF3 and ARF4. In addition,we unravelled a complex set of feedbacks of these ARFs on miR390 expression. Although the mechanisms of TAS3 processing have been identified through various genetic screens our knowledge of the subcellular organization of this pathway remains essentially unknown. For this reason we have chosen to study the subcellular localization of the TAS3 pathway, and focused on AGO7 which represents a specific element of this pathway. We have shown that AGO7, RDR6 and SGS3 accumulate in cytoplasmic foci, dubbed siRNA bodies. We have observed colocalization between these siRNA bodies and markers of the stress granules and a membrane-associated viral protein. Finally we have demonstrated the functional relevance of the cytoplasmic localization of AGO7 for the biogenesis of tasiARFs. Our work has led to a better understanding of the mechanisms underlying the action the TAS3 pathway during the development of Arabidopsis.

Made available in DSpace on 2016-04-28T14:58:35Z (GMT). No. of bitstreams: 1 2005-Cleiton Mateus Sousa.pdf: 885284 bytes, checksum: 42cf8890c05e973310a56f9182c0e1e0 (MD5) Previous issue date: 2005-01-20 / Gerberas are cut flowers with large color diversity and good durability. The use of growth regulators on in vitro propagation is related to the capacity to induce proliferation of sprouts and differentiation of roots. However, citokinins in excess can induce the formation of abnormal plant, with reduced acclimatization potential. The mineral and organic composition of media culture plays an important role during the process. The objective of this dissertation was to adjust protocols for in vitro propagation of Gerbera jamesonii. The following aspects were evaluated: (i) the effect of the inflorescence developmental stage on the performance of in vitro culture initiated from chapters (ii) gerbera varieties (iii) growth regulator balance and (iv) the effect of salt concentration of MS medium on the proliferation of in vitro sprouting and rooting and acclimatization of three varieties of gerbera. For variety Phanter, the regeneration of explants prepared from inflorescences depended on its stage of development. Explants prepared from young chapters showed better results. The concentration and source of citokinin, and the concentration of salts in MS medium influenced the proliferation of sprouts in explants of variety Ornela. BAP was more efficient than kinetin on proliferation of sprouts. Concentrations above 2.0 mg.L-1 of BAP induced the formation of plants with undesirable characteristics during in vitro multiplication, while this was not observed in the presence of the same kinetin in larger concentration (4.0 mg.L-1). The combinations of 0.5 mg.L-1 BAP with the different levels of IBA showed the best results for multiplication and production of sprouts, with potential for acclimatizing variety Ornela. The presence of BAP inhibited the differentiation of roots, while the same was not observed in largest concentration of kinetin. The concentration of salts below 50% limited the proliferation of sprouts in variety Ornela. The varieties Capuccino, Mirage and Ornela, when maintained in the same balance of BAP and IBA, showed divergences in results for number of sprouts; when acclimatized, they presented high survival rates. Difficulties on in vitro gerbera propagation were mostly found on the regeneration phase and on the formation of sprouts in explants prepared from chapters. For the other phases, no major difficulties were detected. / As g?rberas s?o flores de corte que apresentam diversidade na colora??o e boa durabilidade. O uso de fitorreguladores na propaga??o de plantas in vitro esta relacionado com a capacidade de induzir a prolifera??o de brotos e a diferencia??o de ra?zes. No entanto, citocininas em excesso podem induzir a forma??o de pl?ntulas anormais e com baixo potencial para serem aclimatadas. Al?m disso, a composi??o mineral e org?nica do meio de cultura apresenta importante papel durante o processo. O objetivo deste trabalho foi ajustar protocolos para a propaga??o massal in vitro de variedades de Gerbera jamesonii. Avaliou-se: o efeito do est?dio de desenvolvimento de infloresc?ncias na implanta??o de culturas in vitro a partir de cap?tulos; variedades; balan?os de fitorreguladores; concentra??o dos sais do meio MS na prolifera??o de brotos e enraizamento in vitro e a aclimatiza??o de tr?s variedades de g?rbera. A regenera??o de explantes preparados a partir de infloresc?ncias depende do est?dio de desenvolvimento das mesmas. Explantes preparados a partir de cap?tulos jovens apresentaram melhores resultados. A prolifera??o de brotos em explantes de g?rbera, variedade Ornela foi influenciada tanto pela concentra??o quanto pela fonte de citocinina, assim como pela concentra??o dos sais do meio MS. A mol?cula BAP mostrou ser mais eficiente que kinetina para induzir a prolifera??o de brotos. BAP acima de 2,0 mg.L-1 induziu a forma??o de plantas com caracter?sticas indesej?veis durante a multiplica??o in vitro, enquanto isto n?o foi observado mesmo na maior concentra??o de kinetina (4,0 mg.L-1). As combina??es de 0,5 mg.L-1 de BAP com os diferentes n?veis de AIB (0; 0,05 e 0,5 mg.L-1) apresentaram os melhores resultados para a multiplica??o e produ??o de brotos in vitro com potencial para serem aclimatados da variedade Ornela. Somente o BAP inibiu a diferencia??o de ra?zes. A concentra??o dos sais abaixo de 50% limitou a prolifera??o de brotos na variedade Ornela. As variedades Capuccino Mirage e Ornela, quando mantidas no mesmo balan?o de BAP e AIB apresentaram resultados divergentes quanto ? prolifera??o de brotos, e na aclimatiza??o apresentaram alta taxa de sobreviv?ncia. Na propaga??o in vitro de g?rbera, somente na fase de implanta??o das culturas in vitro que verificou-se dificuldade de regenera??o e na forma??o de brotos em explantes preparados a partir de cap?tulos. Nas demais fases, as variedades estudadas apresentaram facilidade e resultados bastante promissores.

Made available in DSpace on 2017-07-10T17:37:29Z (GMT). No. of bitstreams: 1 Celestina_A_Klahold.pdf: 398778 bytes, checksum: 232e5d7155574fb19e80293436725f73 (MD5) Previous issue date: 2005-05-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Soybeans is a crop of prominence in the national grain production. The production growth and the increasing in the productivity capacity of soybeans are connected to the scientific and technological advances in the productive sector. One of theses advances is the biostimulants uses. Thus this paper aimed to verify the effect of the biostumulant Stimulate® applied via seed and the leaves pulverization and the combination of these two ways in the development and yield of the soybeans. The experiment was performed in vases with a plastic cover umbrella kind, with sides open up to 2,5 m of height in the region called Linha São Domingos a region in Toledo Municipality, Paraná. Randomized block experimental design was used with four blocks with the treatments obtained through the combination of different biostimulant doses applied, via leaves and seeds. During the experiment four plant collections were done per treatment: 15 DAE (days after emergence) (stage V3), 58 DAE (stage R2), 73 DAE (stage R3) and 129 DAE (stage R9). Through the results it was possible to conclude that the applications of Stimulate® via seed did not promote the alterations in the evaluated variables at the 15 and 58 DAE in the soybeans crop. At the 73 DAE the application of the biostimulant Stimulate® via seed, via leaves and in the combination of the two ways resulted in positive effects on the dry mass of the flowers, dry mass of the root, ratio root/shoot and the number of leaves. The application of the biostimulant promoted increments to the numbers of beans, grains and the production per plant, highliting the treatments 3 (0,0 mL 0,5 Kg-1 (AS) + 0,150 mL L-1 (APF)), 5 (3,0 mL 0,5 Kg-1 (AS) + 0,0 mL L-1 (APF)), 8 (3,0 mL 0,5 Kg-1 (AS) + 0,225 mL L-1 (APF)) and 10 (5,0 mL Kg-1 (AS) + 0,075 mL L-1 (APF)). The increasing in the number of grains and the beans per plant resulting of the application of the biostimulant led to a lower mass of 100 grains, probably because of the partition of the photoassimilates among the physiological sink. / A soja é uma cultura que se destaca pela produção nacional de grãos. O crescimento da produção e o aumento da capacidade produtiva da soja estão aliados aos avanços científicos e tecnológicos no setor produtivo. Um destes avanços é o uso dos bioestimulantes. Desta forma este trabalho teve como objetivos verificar o efeito do biestimulante Stimulate®, aplicado via semente e pulverização foliar e combinação destas duas formas no desenvolvimento e produtividade da soja. O experimento foi realizado em uma propriedade agrícola da linha São Domingos, município de Toledo-PR. Este foi conduzido em vasos, sob cobertura plástica do tipo guarda chuva , com as laterais abertas até 2,5m de altura Utilizou-se delineamento experimental de blocos casualizados, com quatro blocos, sendo os tratamentos obtidos através da combinação da aplicação de diferentes doses do bioestimulate, via semente (0, 3 e 5mL 0,5Kg sementes-1) e via foliar (0,0; 0,075; 0,150 e 0,225 mL L-1). Durante o experimento foram realizadas quatro coletas de plantas por tratamento: aos 15 DAE (dias após emergência) (V3), 58 DAE (R2), 73 DAE (R3) e 129 DAE (R9). Através dos resultados, pode-se concluir que as aplicações de Stimulate® via semente não promoveram alterações nas variáveis avaliadas aos 15 e 58 DAE para a cultura da soja. Aos 73 DAE, a aplicação do bioestimulante Stimulate® via semente, via foliar e nas duas formas combinadas, resultaram efeitos positivos sobre a massa seca de flores, massa seca da raiz, razão raiz/parte aérea e número de flores. A aplicação de bioestimulante proporcionou incrementos quanto ao número de vagens, número de grãos e produção por planta, podendo-se destacar os tratamentos 3 (0,0 mL 0,5 Kg-1 (AS) + 0,150 mL L-1 (APF)), 5 (3,0 mL 0,5 Kg-1 (AS) + 0,0 mL L-1 (APF)), 8 (3,0 mL 0,5 Kg-1 (AS) + 0,225 mL L-1 (APF)) e 10 (5,0 mL 0,5 Kg-1 (AS) + 0,075 mL L-1 (APF)). O aumento no número de grãos e vagens por planta resultante da aplicação de bioestimulante resultou em menor massa de 100 grãos, devida provavelmente à partição de fotoassimilados entre os drenos fisiológicos.

J'étudie la formation du système vasculaire des feuilles des plantes à l'aide de modèles mathématiques. L'hypothèse de canalisation d'une phytohormone, l'auxin, stipule que l'auto activation de son transport entre les cellules crée des chemins préférentiels qui se différencieront plus tard en système vasculaire. J'entreprends une analyse numérique de modèles de canalisation sur une grande matrice et parviens à créer des motifs branchés dans lesquels circule l'auxin. Une analyse de stabilité d'un modèle simplifié nous éclaire sur les raisons de la formation de ces motifs et l'impossibilité de créer un réseau réticulé. La majorité des plantes ayant un système vasculaire réticulé, je modifie le modèle de façon à obtenir ce type de réseau. En ajoutant une variable biologiquement plausible je parviens à créer un réseau réticulé dans lequel l'auxin circule uniformément. Enfin, je discute des relations entre la formation du système vasculaire et de la spirale de phyllotaxie.

Several mechanisms have been proposed to explain the process of vein pattern formation in plant tissues. The most widely accepted amongst biologists is the canalization hypothesis, derived from pea root and stem experiments. According to this hypothesis, a signal, thought to be the phytohormone auxin, is transported polarly from cell to cell from the shoot to the root and is canalized progressively into narrow channels of high auxin fluxes that later differentiate to become vascular tissue. In this project, we set out to test whether auxin canalization drives vein pattern formation, using Arabidopsis thaliana mutants with increased auxin transport (max4-1, max3-9, max2-1 and max1-1). We predicted that the mutants would have distinct vein patterns and especially different angles between the primary and secondary veins, compared to the wild type. First rosette leaves of 15 plants per genotype were harvested for analysis each day from 7 to 17 days after sowing, giving a total of eight hundred twenty-five leaf samples to analyze. Venation patterns were extracted and analyzed using custom-made software written with Matlab. Overall, compared with the wild type, mutants with the highest auxin transport (max4-1 and max3-9) had different vein patterns at early developmental stages, confirming a role for auxin transport in vein patterning. However, veins of mutants and wild type connected at similar angles, which is not consistent with the auxin canalization hypothesis, as originally formulated.

Several mechanisms have been proposed to explain the process of vein pattern formation in plant tissues. The most widely accepted amongst biologists is the canalization hypothesis, derived from pea root and stem experiments. According to this hypothesis, a signal, thought to be the phytohormone auxin, is transported polarly from cell to cell from the shoot to the root and is canalized progressively into narrow channels of high auxin fluxes that later differentiate to become vascular tissue. In this project, we set out to test whether auxin canalization drives vein pattern formation, using Arabidopsis thaliana mutants with increased auxin transport (max4-1, max3-9, max2-1 and max1-1). We predicted that the mutants would have distinct vein patterns and especially different angles between the primary and secondary veins, compared to the wild type. First rosette leaves of 15 plants per genotype were harvested for analysis each day from 7 to 17 days after sowing, giving a total of eight hundred twenty-five leaf samples to analyze. Venation patterns were extracted and analyzed using custom-made software written with Matlab. Overall, compared with the wild type, mutants with the highest auxin transport (max4-1 and max3-9) had different vein patterns at early developmental stages, confirming a role for auxin transport in vein patterning. However, veins of mutants and wild type connected at similar angles, which is not consistent with the auxin canalization hypothesis, as originally formulated.

Plants often live in association with growth-promoting bacteria, which provide them with several benefits. One such benefit is the lowering of plant ethylene levels through the action of the bacterial enzyme 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase that cleaves the immediate biosynthetic precursor of ethylene, ACC. The plant hormone ethylene is responsible for many aspects of plant growth and development but under stressful conditions ethylene exacerbates stress symptoms. The ACC deaminase-containing bacterium Pseudomonas putida UW4, isolated from the rhizosphere of reeds, is a potent plant growth-promoting strain and as such was used, along with an ACC deaminase minus mutant of this strain, to study the role of ACC deaminase in plant growth-promotion. Also, transgenic plants expressing a bacterial ACC deaminase gene were used to study the role of this enzyme in plant growth and stress tolerance in the presence and absence of nickel. Transcriptional changes occurring within plant tissues were investigated with the use of an Arabidopsis oligonucleotide microarray. The results showed that transcription of genes involved in hormone regulation, secondary metabolism and the stress response changed in all treatments. In particular, the presence of ACC deaminase caused genes for auxin response factors to be up-regulated in plant tissues suggesting a de-repression of auxin signaling in the absence of high levels of ethylene. Also, transgenic plants had longer roots and grew faster than the non-transformed plants and genes involved in the stress response and secondary metabolism were up-regulated. Plants inoculated with bacteria had lower levels of secondary metabolism gene expression and slightly higher stress response gene expression than uninoculated plants. Yet, inoculation with the ACC deaminase-expressing bacterium caused less up-regulation of plant genes involved in stress and defense responses and the down-regulation of genes involved in nitrogen metabolism in comparison to plants inoculated with the ACC deaminase minus mutant. Nickel stress caused the down-regulation of genes involved in photosynthesis and carbon fixation and the up-regulation of genes involved in stress responses, and amino acid and lipid breakdown suggesting energy starvation. When transgenic plants expressing ACC deaminase in the roots were exposed to nickel stress, plant stress symptoms were significantly lower and biomass was significantly higher suggesting that lowering the level of ethylene relieved many of the stress symptoms. In fact, genes involved in photosynthesis, secondary metabolism and nitrate assimilation were up-regulated in transgenic plants compared with non-transformed plants in the presence of nickel, suggesting that ACC deaminase is effective at reducing the severe effects of this metal stress.