La formation des fleurs comprend trois étapes successives. Tout d'abord, un méristème, contenant les cellules souches, se forme sur les flancs du méristème d'inflorescence. Puis, le méristème adopte une identité florale. Enfin, la morphogenèse florale permet le développement des différents organes floraux répartis en quatre verticilles. Ces étapes font intervenir des réseaux génétiques distincts. Le facteur de transcription LEAFY (LFY) est un régulateur majeur du développement floral chez les plantes à fleurs. Le but de ma thèse était de comprendre les fonctions précises de LFY au cours du développement floral, en particulier dans les étapes précoces du développement. Les études moléculaires de LFY chez la plante modèle A. thaliana ont permis de montrer que cette protéine a la capacité de se multimériser lors de sa liaison à l'ADN. En étudiant l'importance fonctionnelle de la dimérisation de LFY, j'ai pu mettre en évidence l'importante de cette propriété pour la régulation de ses gènes cibles, responsables de l'identité florale. De plus, en couplant des études génétiques, les études transcriptomiques et les données de liaisons à l'ADN à l'échelle génomique, j'ai mis en évidence un nouveau réseau de gènes régulé par LFY et impliqué dans le développement du méristème, avant sa détermination en fleur. Ces données ouvrent la perspective que cette nouvelle fonction de LFY est une fonction indépendante de sa fonction florale et déjà présente chez la plupart des plantes terrestres.LFY est hautement conservé chez toutes les plantes terrestres, mais ne fait pas partie d'une famille multigénique contrairement à la plupart des facteurs de transcription qui ont formé des familles multigéniques par duplication au cours de l'évolution. J'ai étudié l'évolution des propriétés de LFY, notamment sa capacité de se dimériser. Pour cela, nous nous sommes intéressés aux homologues de LFY et nous avons découvert que LFY était déjà présent chez les algues vertes multicellulaires. En étudiant l'interface de dimérisation chez les différents homologues de LFY, nous avons mis en évidence que l'acquisition de cette propriété a joué un rôle crucial dans l'évolution de la protéine.Enfin, je me suis intéressé au contrôle post-traductionnel de l'activité de la protéine LFY. Les résultats préliminaires sont présentés et permettent de penser que ce mode de régulation est important pour les fonctions de ce facteur de transcription unique. / Flower formation comprises three successive steps. First, a new meristem, containing stem cells, is formed on the flanc of the inflorescence meristem. Then, this meristem adopts a floral identity. Finally, floral morphogenesis occurs that allow the development of floral organs arranged into four distinct whorls. The LEAFY (LFY) transcription factor is a major regulator of floral development in flowering plants. The aim of my thesis was to precisely understand the roles of LFY during floral development, especially during early stages. Previous studies in the model plant A. thaliana demonstrate that LFY can multimerize upon binding to DNA. By studying the functional importance of the dimerization property of LFY, we were able to show that this property is important for the regulation of its target genes, including those responsible for floral identity. In addition, by combining genetic studies, transcriptomic datas as well as whole-genome LFY binding sites, we have shown that LFY controls a new network of genes which are directly involved in meristem formation, before its determination into flower. These data raise the prospect that this new function of LFY is in fact a non-floral function already present in most land plants.LFY is highly conserved in all land plants, but is not part of a multigene family in contrast to most transcription factors. I studied the evolution of LFY properties, including its ability to dimerize on specific DNA sequences. For this purpose, we looked for the ancestor form of LFY and found out that LFY was already present in multicellular green algae. By studying the dimerization interface in different counterparts of LFY, we demonstrate that the acquisition of this dimerization property has played a crucial role during the evolution of the protein.Finally, I studied the post-translational control of LFY activity which remains largely unknown. Preliminary results are presented and suggest that this mode of regulation is important for many functions of this orphan transcription factor.

LEAFY (LFY) est un facteur de transcription unique et très conservé chez les plantes terrestres. Il contrôle le développement floral chez les angiospermes (plantes à fleurs), mais son rôle est encore mal connu chez toutes les autres plantes terrestres à l'exception de la mousse Physcomitrella patens où l'orthologue de LFY (PpLFY) est requis pour la première division cellulaire du zygote. PpLFY ne reconnaît pas les mêmes séquences d'ADN que LFY d'Arabidopsis thaliana, malgré la très forte conservation de leurs domaines de liaison à l'ADN. LFY semble donc avoir changé de propriétés au cours de l'évolution ; l'objectif de ma thèse a été de déterminer si de tels changements s'étaient produits fréquemment chez les plantes terrestres, et de comprendre leur origine et leur impact sur la régulation des gènes cibles de LFY. Pour cela, j'ai étudié la spécificité de liaison à l'ADN des orthologues de LFY chez les grands groupes de plantes terrestres par des expériences de SELEX, et cette spécificité s'est révélée très fortement conservée, excepté dans le cas de PpLFY. Ces résultats nous ont permis de construire un modèle biophysique performant pour prédire la liaison de LFY à l'échelle génomique, ce que nous avons appliqué à l'étude de l'évolution de la régulation de quelques gènes clés par LFY. Nous avons ainsi pu prédire la régulation du gène floral AGAMOUS par LFY chez différentes espèces angiospermes, et nous avons pu montrer que LFY régulait très vraisemblablement les orthologues des gènes d'identité florale chez les gymnospermes, c'est-à-dire avant l'apparition de la fleur. La divergence de spécificité de PpLFY nous a poussés à étudier les gènes cibles de PpLFY : pour cela, j'ai initié des approches bioinformatiques et expérimentales chez P. patens. Enfin, pour comprendre comment ce changement de spécificité s'est déroulé au cours de l'évolution, nous nous sommes penchés sur l'ancêtre de LFY et avons découvert que LFY était déjà présent chez les algues vertes. Des études pour déterminer la spécificité ancestrale de LFY chez ces espèces ont été initiées. / LEAFY (LFY) is a unique transcription factor, highly conserved within land plants. LFY directly regulates a set of genes participating in floral development in angiosperms (flowering plants), but its role in the other groups of land plants is unknown, except in the moss Physcomitrella patens where the LFY ortholog (PpLFY) regulates the first cell division in the zygote. PpLFY does not bind to the same DNA sequences as LFY from Arabidopsis thaliana, in spite of the very high degree of conservation of their DNA binding domains. Thus, it appears that the properties of LFY have changed during evolution ; the goal of my thesis was to find out if such changes had occurred frequently in land plants, and what are their origins and consequences on target genes regulation. I performed SELEX experiments on LFY orthologs from all land plants, which revealed that their DNA binding specificty was highly conserved, except in the case of PpLFY. These results allowed us to build an accurate biophysical model to predict LFY binding on DNA fragments at a genomic level, which we applied on the evolution of the regulation of key target genes by LFY. We were able to predict the regulation of the floral gene AGAMOUS by LFY in various angiosperm species, et we could also show that LFY was very likely regulating gymnosperm orthologs of genes involved in floral organ identity, even before the appearance of the flower. The change in DNA binding specificity observed for PpLFY led us to study more precisely the consequences of this change for the regulation of target genes : for this, I initiated bioinformatic and experimental work in P. patens. Finally, to understand how this change in DNA binding specificity had occurred during evolution, we looked for the ancestor of LFY and found out that LFY already existed in green algae. We are currently investigating the ancestral specificity of LFY in these species.

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Food insecurity remains a major challenge affecting the rural poor households in South Africa. The consumption of green leafy vegetables is important to address micronutrients deficiency in rural communities and, at the same time, it contributes to fibre intake. This study investigated the people’s attitude towards the cultivation and utilisation of ILVs in rural communities. A cross-section survey study was conducted among 1 000 respondents in randomly selected households in communities. The majority of respondents were not willingly consuming ILVs. This is because most consumers were black and of the low-income group. ILVs that are consumed grow mainly in the wild. The regular consumption of these vegetables as indicated in this study is interesting, as this will help in mitigating micronutrient deficiency. Furthermore, these vegetables could be incorporated in formulated food to improve iron and zinc, especially in infant foods formulation. Based on the findings of this study it would be important to find ways of encouraging cultivation of ILVs for both nutrition and as income generating activities. / Business Management / M. Consumer Science

Most plant oxylipins, a large class of diverse oxygenated polyunsaturated fatty acids and their derivatives, are produced through the lipoxygenase (LOX) pathway. Recent progress in dicots has highlighted the biological roles of oxylipins in plant defense responses to pathogens and pests. In contrast, the physiological function of LOXs and their metabolites in monocots is poorly understood. We cloned and characterized three maize LOXs ZmLOX10 ZmLOX11 and ZmLOX12. Both ZmLOX10 and ZmLOX11 apeared to be 13-LOX, whereas ZmLOX12 is a unique 9-LOX. Whereas leaf was the preferential site of ZmLOX10 expression, ZmLOX11 was strongly expressed in silks. Induction of these ZmLOX10 and ZmLOX12 by wounding and defense-related compounds suggested their role in plant resistance mechanisms against pests and pathogens. Abscisic acid, however, was the only inducer of ZmLOX11 in leaves. Higher increase in ZmLOX10 transcripts in maize infected by fungus Cochliobolus carbonum implicated this gene in resistance responses to necrotrophic pathogens. In addition, ZmLOX10 was shown to be the first reported LOX to be regulated by a circadian clock. It was found that ZmLOX10 was also inducible by low temperatures. Phenotypical studies of wild type and mutant near isogenic lines showed that expression of ZmLOX12, specific to underground organs, was required for pathogenesis of F. verticillioides on maize mesocotyls.

Most plant oxylipins, a large class of diverse oxygenated polyunsaturated fatty acids and their derivatives, are produced through the lipoxygenase (LOX) pathway. Recent progress in dicots has highlighted the biological roles of oxylipins in plant defense responses to pathogens and pests. In contrast, the physiological function of LOXs and their metabolites in monocots is poorly understood. We cloned and characterized three maize LOXs ZmLOX10 ZmLOX11 and ZmLOX12. Both ZmLOX10 and ZmLOX11 apeared to be 13-LOX, whereas ZmLOX12 is a unique 9-LOX. Whereas leaf was the preferential site of ZmLOX10 expression, ZmLOX11 was strongly expressed in silks. Induction of these ZmLOX10 and ZmLOX12 by wounding and defense-related compounds suggested their role in plant resistance mechanisms against pests and pathogens. Abscisic acid, however, was the only inducer of ZmLOX11 in leaves. Higher increase in ZmLOX10 transcripts in maize infected by fungus Cochliobolus carbonum implicated this gene in resistance responses to necrotrophic pathogens. In addition, ZmLOX10 was shown to be the first reported LOX to be regulated by a circadian clock. It was found that ZmLOX10 was also inducible by low temperatures. Phenotypical studies of wild type and mutant near isogenic lines showed that expression of ZmLOX12, specific to underground organs, was required for pathogenesis of F. verticillioides on maize mesocotyls.

Biocontrol has been critized because the target effects of biocontrol introductions have not been studied rigorously. The objectives of this thesis were 1)to assess quantitatively the efficacy of a classical biocontrol agent after its release and 2)to suggest factors that affect the density and distribution of the biocontrol agent. In 1997, Aphthona lacertosa, a root-feeding flea beetle that is native to Europe, was released for the biological control of leafy spurge in Alberta. The beetles had established at more than 75% of the release sites that were monitored in 1999. In 2000, the peak abundance of A.lacertosa across release sites ranged from low (<10 beetles m-2) to high (>70 beetles m-2). Sites with high beetle densities had a significantly greater local (ie. within 5m of release point) reduction of leafy spurge than sites with low beetle densities. The density and distribution of A. lacertosa are affected by cumulative degree-days (CDD) at the release site and plant lacertosa are affected by cumulative degree-days (CDD) at the release site and plant morphology, respectively. Beetle population growth may be enhanced by releasing A. lacertosa at sites where there are more CDD. It is expected that high densities of A. lacertosa will effectively control leafy spurge populations. / 93 leaves : ill. (some col.) ; 29 cm.

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No. of bitstreams: 1 silva_phs_me_jabo.pdf: 1324447 bytes, checksum: 0a31631931bf7d8856203d7c9fcd70a5 (MD5) Previous issue date: 2017-11-07 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O nitrogênio é um elemento requerido em maior quantidade pela maioria das culturas e o segundo mais acumulado pela rúcula. Neste contexto, o trabalho foi realizado com o objetivo de avaliar o efeito de doses de nitrogênio no crescimento e na produtividade da rúcula. O delineamento experimental utilizado foi o de blocos casualizados, com quatro repetições. Foram avaliados seis tratamentos (0, 50, 100, 150, 200 e 250 kg ha-1 de N). A rúcula caracteriza-se por apresentar crescimento inicial lento, tendo maior exigência nutricional no final do ciclo, com isso, as melhores respostas foram obtidas aos 35 dias após a emergência. O teor máximo de nitrato estimado foi de 2,1 g kg-1 de massa seca obtido com aplicação da dose de 250 kg ha-1 de N, que corresponde a 146 mg kg-1 de massa fresca e está muito abaixo do limite máximo tolerável. As doses crescentes de nitrogênio pronunciaram-se positivamente sobre a altura de plantas, número de folhas, área foliar, massa fresca e seca da parte aérea. A máxima produtividade de rúcula (4,53 kg m-2) foi obtida com 223 kg ha-1 de nitrogênio. O teor de nitrato na dose que maximiza a produtividade não é uma característica que prejudica a qualidade da rúcula. / Nitrogen is an element required in greater quantity by most of the crops and the second most accumulated nutrient by rocket. In this context, this study aimed to evaluate the effect of different nitrogen rates on rocket growth and productivity. A randomized complete block design with four replications. Six treatments were evaluated (0, 50, 100, 150, 200 and 250 kg ha-1 of N). Rocket is characterized as a vegetable which presents slow initial growth, having a higher nutritional requirement at the end of its cycle. Therefore, the best plant responses in this study were obtained at 35 days after the emergence of seedlings. The maximum estimated nitrate content was 2.1 g kg-1 of plant dry mass obtained with the application of 250 kg ha-1 of N, which corresponds to 146 mg kg-1 of plant fresh mass. This is considered below the maximum tolerable limit. The increasing nitrogen doses in this study were positively correlated with plant height, number of leaves, leaf area, and fresh and dry mass of the crop canopy. Rocket maximum yield production in this study (4.53 kg m-2) was obtained with 223 kg ha-1 of N. The nitrate content in the dose which maximizes the productivity is not a characteristic that negatively affects rocket quality.

Orientador: Marcelo Carnier Dornelas / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-12T18:50:55Z (GMT). No. of bitstreams: 1 Cutri_Lucas_M.pdf: 1586936 bytes, checksum: 89c34c442b82fc8e799842fa98af8efe (MD5) Previous issue date: 2009 / Resumo: O gene LEAFY (LFY) específico de plantas, além de atuar na transição do meristema vegetativo para o reprodutivo, parece regular também a transição do desenvolvimento de produtos do meristema apical tão diversos quanto: folhasgavinhas; flores-gavinhas e inflorescências-flores solitárias, além de diminuir drasticamente o tempo necessário para que a planta passe da fase vegetativa para a fase reprodutiva. O gênero Passiflora é um candidato em potencial para o estudo da evolução da função biológica do gene LFY, por conter todas as estruturas morfológicas em que o referido gene atua. Neste estudo, foram analisadas duas espécies divergentes de Passiflora: Passiflora edulis var flavicarpa e Passiflora suberosa. O desenvolvimento reprodutivo de ambas foi caracterizado com o uso de microscopia óptica e de microscopia eletrônica de varredura. Análises moleculares da função do gene LFY também foram executadas nestas duas espécies. Isolou-se, via PCR, fragmentos potencialmente correspondentes a homólogos do referido gene em P. edulis e em P. suberosa. Estas seqüências gênicas, denominadas respectivamente PeLFY e PsLFY foram utilizadas em análises filogenéticas. O padrão de expressão de ambos os genes foi investigado em experimentos de RTPCR e hibridização in situ em diferentes tecidos durante o desenvolvimento das espécies de Passiflora estudadas Adicionalmente, foram obtidas plantas transgênicas de P. suberosa, contendo uma construção de superexpressão do gene LFY de Arabidopsis / Abstract: The LEAFY (LFY) gene is plant-specific, and besides playing a role in the transition of the vegetative to the reproductive meristems, it seems to regulate the development of different products of the shoot apical meristem (SAM) as leaves-tendrils, flowerstendrils, solitary flowers-inflorescences. It is also responsible for decreasing substantially the time needed for the transition from the vegetative to the reproductive phase. The genus Passiflora is a good model for the study of the evolution of the biologic function of the LFY gene, because it has all morphological structures in which this gene acts. In this study, two distinct species: Passiflora edulis var. flavicarpa and Passiflora suberosa had their reproductive development analyzed by optical microscopy and scanning electron microscopy. Molecular analyzes of LFY functions were also performed in both species. Fragments corresponding to homologs of the LFY gene were cloned from P. edulis and P. suberosa by PCR. These fragments were named PeLFY and PsLFY, respectively and were used in filogenetic analyzes. The expression patterns of these genes were investigated by RT-PCR and in situ hybridization in different tissues of the studied Passiflora species. Additionally, transgenic lines of P. suberosa were obtained that contained a construction that promoted the overexpression of the Arabidopsis LFY gene / Mestrado / Mestre em Biologia Vegetal

Phenolic compounds in African green leafy vegetables (GLVs) may have a significant impact on human health. However, there is little information on the phenolic composition, antioxidant properties, as well as biological and cellular protective effects of these vegetables. The effects of boiling and extraction solvent on these compounds and on their antioxidant properties are also unknown. Phenolic content, antioxidant activity and cellular protective effects of four African GLVs in comparison with spinach, an exotic GLV, was determined. African GLVs had appreciable levels of total phenolics and antioxidant activity and in higher quantities compared to spinach. Boiling decreased the antioxidant content and activity of these vegetables and 75% acetone was more effective in extracting antioxidants from the GLVs compared to water. GLVs with high levels of phenolics also contained higher levels of antioxidant activity, suggesting that phenolics are likely to have contributed to radical scavenging activity of these vegetable extracts, even though the degree of scavenging varied in each extract of the vegetable species. The flavonoid compositions of raw and boiled African GLVs and spinach were determined using high-performance liquid chromatography. Epicatechin and rutin were the most dominant flavonoids found in both water and 75% acetone extracts. Among water extracts, pumpkin contained higher concentrations of detected flavonoids, while among the acetone extracts, cowpea exhibited higher concentrations. The effect of boiling was dependent on the type of vegetable and the specific flavonoids. There were no major differences observed between the type of flavonoids detected in extracts of African GLVs and those in spinach. However, similar to the results of total phenolics and antioxidant activity, the 75% acetone extracts of African GLVs also exhibited higher amounts of flavonoids than spinach. The protective effects of GLVs against oxidative haemolysis were dependent on the type of vegetable species. Boiling had variable effects depending on the species. The highest level of protection of erythrocytes against oxidative damage was offered by amaranth extracts, while extracts of raw jute mallow contributed to the damage of erythrocytes. The highest antioxidant protection activity against oxidative damage in plasmid DNA was offered by extracts of jute mallow and lowest by spinach.<p. For the cell viability assays, GLVs were evaluated to determine their cytotoxicity levels and functional role in oxidative damage. The results of the long-term cell viability (i.e. MTT, NR and CV) assays indicated no cytotoxicity, while the short-term cell viability (i.e. DCF) assay indicated that all extracts of raw GLVs were significantly (p < 0.05) cytotoxic to SC-1 fibroblast and human adenocarcinoma colon cancer (Caco-2) cells than extracts of cooked samples, and the levels of toxicity in the extracts of spinach was higher than in African GLVs. These results indicate that there was an initial cytotoxic effect as extracts of raw GLVs were added to the cells. However, after about 72 h, the cells recovered from the initial shock and started proliferating as usual. In the presence of peroxyl radicals, extracts of African GLVs exhibited higher protective effects against oxidative damage in both types of cell cultures than extracts of spinach. These results indicate that these protective effects could be attributed to the presence of phenolics and antioxidant properties of these extracts. Although boiling reduced the antioxidant content and activity of African GLVs, the levels remained higher than in spinach. Boiling also decreased the cytotoxicity and cell damage caused by extracts of raw GLVs samples. African GLVs are consumed after boiling, and therefore the observed cytotoxicities might not be experienced in practical terms. African GLVs have therefore a potential to reduce the risk and development of diseases associated with oxidative stress in communities that consume these vegetables. / Thesis (PhD)--University of Pretoria, 2012. / Centre for Nutrition / PhD / Unrestricted