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Includes abstract. / Includes bibliographical references (leaves 89-94). / Eusocial insects, in particular ants, demonstrate great variability in their sociogenetic structure with regards to colony organization, queen number, queen mating frequency, levels of relatedness and worker reproduction. Within this study I perform an analysis on two groups of ant nests of the species Campo notus klugii, in order to investigate how the genetic structure may inform us of the sociogenetic structure of the species.

Includes bibliographical references. / Plants rely on an elaborate multi-layered defence system to perceive and effectively respond to disease causing pathogens. The defence-related cir1 (constitutively induced resistance 1) mutant was first isolated in an effort to identify components of the Arabidopsis thaliana defence system essential for resistance against pathogens. The cir1 mutant has previously been described as having increased resistance to the virulent bacterial pathogen Pseudomonas syringae pv. tomato DC3000 and oomycete pathogen Hyaloperonospora parasitica Noco2 and was shown to constitutively express salicyclic acid-, jasmonic acid/ethylene- and reactive oxygen intermediate-responsive genes. Genetic analysis and mapping studies of the mutation revealed that it is recessive and may be encoded by one of eight genes located within a 309.10 kb region on the lower arm of chromosome four.

Apparatus has been developed for the irradiation of V79-379A Chinese hamster lung fibroblast cells with 3.6 MeV protons from the Van de Graaff accelerator at the National Accelerator Centre in Faure. The original intention of this work was to investigate and measure a possible dose rate effect on the survival of V79 cells, in the dose range from zero to 25 Gy, at dose rates of about 3 Gy/s and 300 Gy/s. The survival curves initially obtained were anomalous in that they showed abnormally high levels of survival and a tendency to remain at a constant survival level for doses above 10 Gy. Systematic attempts to correct this observed anomaly, involved the following; apparatus improvements were made, a means of measuring the beam profile was devised, the current measuring device and the dosimetry were improved and a possible dose rate effect on intracellular oxygen was investigated. After these improvements, the anomalous effect was much reduced, but not entirely eliminated. The final results showed no significant difference between the survival of cells irradiated at dose rates of about 3 Gy/s and 300 Gy/s; qualitative differences were however noticeable. After correction for the effect of a non-uniform beam profile, the survival curves were significantly different to published work. This difference suggested a possible dose rate effect between dose rates of about 0.1 Gy/s and dose rates above 3 Gy/s.

Includes bibliographical references. / Polyphenols in plants are known to act as antioxidants, antimicrobials, antifungal, photoreceptors, visual attractors and as light screens. In this study polyphenols in angiosperms found in southern Africa and called resurrection (desiccation tolerant) plants were studied. These plants are Myrothamnus flabellifolius, Xerophyta viscosa, Xerophyta humilis, Xerophyta schlecterii, Xerophyta villosa. Craterostigma wilmsii, Craterostigma plantagineum, Craterostigma pumilum and Eragrostis nindensis. These plants are able to tolerate water stress without undergoing permanent damage. During drying these plants are subjected to different stresses and one such stress is oxidative stress. It has been suggested that polyphenols function as stress protectants in plant cells by scavenging reactive oxygen species (ROS) produced during a period of oxidative stress. In this study the total phenolic content and the related antioxidant capacity of the plants leaf extracts were analysed.

Bibliography: leaves 147-152. / Brain Factor 1 (BF-1), a winged helix transcription factor, displays a restricted pattern of expression within the developing forebrain, playing a critical function in the regulation of neuronal progenitor cell proliferation and differentiation within the developing forebrain. The molecular mechanisms by which BF-1 carries out its function remain to be elucidated. Hence, this study aimed to investigate and characterise the molecular mechanisms by which BF-1 function is regulated during neuronal development.

Plants have evolved a complex system of defence to prevent pathogen establishment. The Arabidopsis thaliana cir1 (constitutively induced resistance 1) mutant displays enhanced resistance to infection by the virulent bacterial pathogen Pseudomonas syringae and constitutively expresses a number of defence genes. Evidence suggests that CIR1 is a negative regulator of plant immunity important in the absence of pathogen attack. Genetic mapping experiments indicate that cir1 is located on the lower arm of chromosome 4 of A. thaliana and may be one of 8 known genes in the region. Analysis of T-DNA knockouts of these 8 genes suggests that AT4G11100 is the mostly likely candidate for CIR1. This project established that the disease resistance phenotype of cir1 is temperature dependent and linked to reduced plant growth. Genetic crosses between cir1 and at4g11100 T-DNA knockout mutants revealed that the mutants complement and therefore AT4G11100 is not CIR1. However, like cir1, the at4g11100 T-DNA knockout mutants display enhanced disease resistance. Over expression of AT4G11100 leads to increased susceptibility to infection by Pseudomonas syringae (Pst) and reduced induction of the salicylic acid defence gene PR2 following Pst infection, suggesting that AT4G11100 may too be a negative regulator of immunity. Additionally, a plant line with exceptionally high AT4G11100 expression levels displayed distinct leaf morphology, possibly implicating AT4G11100 in leaf development.

Directional cell migration, chemotaxis, requires a polarized cell morphology in which the cell extends pseudopodia at the front and contracts the rear to move towards a stimulus. PI(4,5)P2 levels set up a threshold for the activity of signaling molecules at the rear and the leading-edge of a cell. To further demonstrate the importance of plasma membrane (PM) PI(4,5)P2 in maintaining cell morphology during chemotaxis, we used a mutant strain of the eukaryotic model system, Dictyostelium discoideum. This mutant strain lacks the type I PIP5 kinase, which is the main enzyme synthesizing PI(4,5)P2. These cells, designated pikI-, have highly reduced PI(4,5)P2 levels and higher Ras GTPase activity compared to wildtype cells. Leading-edge biosensors diffuse to the cytosol when the pikI- round-up and translocate back to the PM when the cells spread. These observations propose that PI(4,5)P2 levels elevate as cells round-up and decrease as cells spread. This interesting phenotype resembles the front and rear of a migratory cells. Interestingly, pikI- resemble similar cell morphology and biosensors dynamics observed when we use an inducible system to deplete PM PI(4,5)P2 levels. We, also, observed the dynamics of a biosensor for an F-actin polymerization protein called formin A (ForA). ForA has been shown to localize at a polarized cell’s rear and in the cleavage furrow of dividing cells. In addition, ForA have a PI(4,5)P2 binding motif and binds to PI(4,5)P2 preferentially in vitro. Our results support a role for PI(4,5)P2 in regulating ForA with the plasma membrane. Taken together, we proposed that local levels of PI(4,5)P2 contribute to the electrostatic interactions of regulatory proteins controlling actin dynamics and membrane protrusions. PM PI(4,5)P2 below a threshold activate regulatory proteins that excite the signaling that promotes protrusions, while below threshold levels would inhibit those proteins activity. The change in PI(4,5)P2 levels would be predicted to affect the membrane’s charge, which in turn changes the interaction and disassociation of many anionic regulatory proteins involved in the signaling pathway and cytoskeletal rearrangements. Additionally, we show for the first time, a correlation between the PM PI(4,5)P2 threshold and rates of phosphatidylserine (PS) exposure in cancer therapeutics. Receptor-mediated cell stimulation triggers PS exposure to the outer leaflet of the plasma membrane. Interestingly, pik1- and cells using an inducible system to deplete PM PI(4,5)P2 levels depicted the same responses. In addition to PI(4,5)P2, PS exposure affects the membrane’s charge which impacts the signaling molecules activity in the pathway. Altogether, PI(4,5)P2 and PS are proposed to be novel therapeutic targets in cancer treatments. Chemotaxis is a feature of metastatic cancer cells and is regulated by various regulators including actin cytoskeleton. Actin cytoskeleton reorganization during chemotaxis is regulated by actin-binding proteins including those that interact with the PM PI(4,5)P2. Energy production regulates cell migration as well, through glycolysis pathway. A previous study proposed that actin reorganization releases Aldo A enzyme which enters glycolysis, through activating PI3K signaling pathway. However, the mechanism of action remains unclear. We speculate that local PI(4,5)P2 levels regulate Aldo Activity through regulating actin-severing proteins activity including cofilin and gelsolin, and actin polymerizing protein including ForA. PI(4,5)P2 levels below a threshold release actin-severing proteins to the cytosol triggering the severing of actin and the release of Aldo A. while, above PI(4,5)P2 threshold activates and localizes for a on the PM promoting the F-actin polymerization and the sequester of Aldo A into F-actin. The goal of this work is to discover a new model for actin cytoskeleton regulation during migration, as its linkage to glycolysis and metabolism has important implications for cancer.

Dans cette thèse, nous enrichissons et appliquons la théorie des processus de Poisson spatiaux pour résoudre certains problèmes issus de la conception et du déploiement des réseaux cellulaire. Cette thèse comporte deux parties principales. La première partie est consacrée à la résolution de quelques problèmes de dimensionnement et de couverture des réseaux cellulaires. Nous calculons la probabilité de surcharge de systèmes OFDMA grâce aux inégalités de concentration et aux développements d'Edgeworth, pour lesquels nous prouvons des bornes d'erreur explicites, et nous l'appliquons à résoudre un problème de dimensionnement. Nous calculons également la probabilité d'outage et le taux de handover pour un utilisateur typique. La seconde partie est consacrée à l'étude de différents modèles pour la consommation d'énergie dans les réseaux cellulaires. Dans le premier modèle, l'emplacement initial des utilisateurs forme un processus de Poisson ponctuel et à chaque utilisateur est associé un processus d'activité de type ON-OFF. Dans le second modèle, l'arrivée des utilisateurs constitue un processus de Poisson en espace et en temps, une dynamique connue sous le nom de dynamique de Glauber. Nous étudions également l'impact de la mobilité des utilisateurs en supposant que les utilisateurs se déplacent de manière aléatoire pendant leur séjour. Nous nous intéressons dans toutes ces situations, à la distribution de l'énergie consommée par une station de base. Cette énergie est divisée en deux parties: la partie additive et la partie diffusive. Nous obtenons des expressions analytiques pour les moments de la partie additive ainsi que la moyenne et la variance de l'énergie totale consommée. Nous trouvons une borne d'erreur pour l'approximation gaussienne de la partie additive. Nous prouvons que la mobilité des utilisateurs a un impact positif sur la consommation d'énergie. Il n'augmente ni ne réduit l'énergie consommée en moyenne, mais réduit sa variance à $0$ en régime de mobilité élevé. Nous caractérisons aussi le taux de convergence en fonction de la vitesse des utilisateurs. / Nowadays, cellular technology is almost everywhere. It has had an explosive success over the last two decades and the volume of traffic will still increase in the near future. For this reason, it is also regarded as one cause of worldwide energy consumption, with high impact on carbon dioxide emission. On the other hand, new mathematical tools have enabled theconception of new models for cellular networks: one of these tools is stochastic geometry, or more particularly spatial Poisson point process. In the last decade, researchers have successfully used stochastic geometry to quantify outage probability, throughput or coverage of cellular networks by treating deployment of mobile stations or (and) base stations as Poisson point processes on a plane. These results also take into account to impact of mobility on the performance of such networks. In this thesis, we apply the theory of Poisson point process to solve some problems of cellular networks, in particular we analyze the energy consumption of cellular networks. This thesis has two main parts. The first part deals with some dimensioning and coverage problems in cellular network. We uses stochastic analysis to provide bounds for theoverload probability of OFDMA systems thanks to concentration inequalities and we apply it to solve a dimensioning problem. We also compute the outage probability and handover probability of a typical user. The second part is dedicated to introduce different models for energy consumption of cellular networks. In the first model, the initial location of users form a \PPP\ and each user is associated with an ON-OFF process of activity. In the second model, arrival of users forms a time-space \PPP. We also study the impact of mobility of users by assuming that users randomly move during its sojourn. We focus on the distribution of consumed energy by a base station. This consumed energy is divided into the additive part and the broadcast part. We obtain analytical expressions for the moments of the additive part as well as the mean and variance of the consumed energy. We are able to find an error bound for Gaussian approximation of the additive part. We prove that the mobility of users has a positive impact on the energy consumption. It does not increase or decrease the consumed energy in average but reduces its variance to zero in high mobility regime. We also characterize the convergent rate in function of user's speed.

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