Dans l’histoire évolutive des végétaux, la polyploïdisation a été un phénomène récurrent qui a façonné les génomes, aurait contribué à l’avènement de grandes étapes évolutives et aurait favorisé la survie de nombreuses lignées lors de crises écologiques majeures. Le principal mécanisme d’apparition d’espèces polyploïdes est la polyploïdisation sexuelle, qui implique la formation de gamètes 2n résultant de modifications de la division méiotique. Récemment plusieurs mutants produisant des taux élevés de gamètes 2n ont été identifiés chez A. thaliana. Chez cette espèce, la perte de fonction du gène AtPS1 conduit à la mise en place de fuseaux parallèles en méiose II et celle du gène AtCYCA1;2/TAM à l’omission de la seconde division méiotique. L’objectif de cette thèse a été de déterminer des facteurs et mécanismes responsables de la formation de gamètes 2n, en utilisant le rosier comme modèle végétal. Ces travaux ont permis : (i) d’identifier un facteur abiotique, la température élevée, comme inducteur de production de forts taux de gamètes 2n, (ii) de montrer que la fenêtre de sensibilité à ce facteur est restreinte à la méiose et (iii) de révéler que ces gamètes 2n produits sont principalement issus de la mise en place de fuseaux parallèles en méiose II. Afin de déterminer les mécanismes moléculaires à l’origine de leur formation, deux gènes candidats, RhPS1 et RhCYCA1 ont été identifiés chez Rosa. L’analyse de leur expression a révélé : (i) en condition non inductible, leur forte expression dans les étamines au stade méiose et (ii) la répression rapide de leurs niveaux de transcrits en condition d’induction de gamètes 2n. La fonction méiotique du gène RhPS1 a été validée par complémentation du mutant atps1-1 d’A. thaliana et par l’obtention d’une lignée rosier transgénique p35S::ARNi-RhPS1. Compte tenu de ces résultats, l’étude de la polyploïdisation et de ses mécanismes peut désormais être replacée dans le contexte actuel de changement climatique. / In the evolutionary history of plants, polyploidization has been a recurring phenomenon that has shaped the genomes, might have contributed to the occurrence of major evolutionary step and might have facilitated the survival of many plant families during major ecological crises. The main mechanism of polyploidization is sexual polyploidization, which involves the formation of 2n gametes resulting from meiotic division changes. Recently, mutants highly producing 2n gametes have been isolated in A. thaliana. Loss of AtPS1 gene function leads to parallel spindles orientation in meiosis II and loss of AtCYCA1;2/TAM gene function leads to the omission of the second meiotic division. The aim of this PhD project was to identify factors and mechanisms responsible for the 2n gametes formation, using Rosa as a model. This work permitted to: (i) discover an abiotic factor, high temperature, that can induce a high production of 2n gametes, (ii) show that the sensitivity window to this factor is narrow and restricted to meiosis and (iii) reveal that 2n gamete production in inductive condition, results from parallel spindle orientation in meiosis II. To determine molecular mechanisms responsible for their formation, two candidate genes, RhPS1 and RhCYCA1 were identified in Rosa. Analysis of their expression revealed: (i) their high expression level in stamens at meiosis stage in non-inductive condition and (ii) the rapid repression of their transcript levels under inductive condition. Meiotic gene function of RhPS1 was validated by complementation of atps1-1 mutant and by generating a rose transgenic line p35S:: RNAi-RhPS1. According to these results, polyploidization and its mechanisms can now be replaced in the context of the current climate.

M.Tech (Department of Information technology, Faculty of Applied and Computer Science), Vaal University of Technology. / The advancement of technology, particularly in the area of mobile computing, revolutionizes the way business is done in many industries such as the education sector, government sector, financial institutions, retail sector and the way people conduct their daily activities. The current technology provides influential tools for organisations and can significantly influence their operation, structure and approach. The development of mobile computing has created a new innovation for various industries by increasing the availability, frequency and speed of communication between the organisations and the individuals. However, users’ perceptions can play an important role towards the adoption of these new developments. The overriding purpose of this study was to investigate the users’ perceptions on the security of mobile computing in South Africa for adoption of e-applications. The literature review was concentrated on the process of progressive development occurring during the study. To accomplish that goal it became necessary to reach some essential objectives i.e. investigating the users’ perceptions models in literature. For the purpose of the study, it was important to propose a research framework for users’ perceptions on the security of mobile computing with the potential for the adoption of e-applications in South Africa. The research evaluated the proposed framework to establish if there is any relationship between the e-application adoption factors. Furthermore, the hypotheses were tested to determine which factors would influence the adoption of e-applications in South Africa. Technology Adoption Model 2 (TAM2) and Diffusion of Innovation (DOI) provide the theoretical basis for explaining how users perceive e-application services that they access and operate through mobile computing. To achieve that, a quantitative study was conducted with South African residents, with respect to mobile security perceptions; 476 valid questionnaires were received from the participants who were selected non-randomly. Questionnaires were developed from the proposed research framework derived from DOI and TAM2 and the items were adopted from other prior technology adoption studies. Through the use of the survey instrument developed for this study, data were collected in order to address the importance of this study based on the problem statement posed in the first chapter of this dissertation. The valid questionnaires were analysed by using the Statistical Package for the Social Sciences (SPSS), Version 24.0. Reliability analysis, principal component analysis, correlations and multiple linear regression tests were conducted. Among other things this study made sure that ethical considerations are adhered to. The findings revealed positive relationships between perceived usefulness of security mechanisms, perceived ease of use of security mechanisms, subjective norm on security mechanisms, relative advantage of security mechanisms, compatibility of security mechanisms, complexity of security mechanisms, aesthetics of security mechanisms interface and intention to adopt e-applications. Furthermore, subjective norm on security mechanisms was strongly correlated to intention to adopt e-applications, complexity of security mechanisms strongly correlated to perceived usefulness of security mechanisms, relative advantage of security mechanisms and aesthetic of security mechanisms interface strongly correlated to perceived usefulness of security mechanisms. In addition, subjective norm of security mechanisms strongly influence intention to adopt eapplications in South Africa. Also, aesthetics of security mechanisms interface strongly influence both perceived usefulness of security mechanisms and perceived ease of use of security mechanisms. The reason behind it may be interpreted as users nowadays seeing the beauty as the platform to attract and encourage them to use e-applications. Finally, the proposed model analysis and survey evaluation will enable South African organizations to make informed decisions about the use of e-applications services. These findings contribute to a road map for the education sector, government sector, financial institutions, and retail sector as well as to encourage their customers or clients to adopt e-applications.