Der Ansatz der Arbeit lässt sich auf zwei Gebiete aus der Blickbewegungsforschung zurückführen. Einerseits basieren die Studien auf Experimenten zum remote distractor effect, andererseits auf Untersuchungen beim Lesen bzw. der Wahrnehmung komplexer Szenen. Innerhalb beider Ansätze findet eine Analyse der Auswirkungen unterschiedlichen Reizmaterials (z.B. Texte oder Bilder) auf die Fixationsdauer statt. Aktuelle Erklärungsansätze werden im Bezug zu den gefundenen Ergebnissen dargestellt und kritisch bewertet. Anhand der Ergebnisse einer Voruntersuchung wird vorgeschlagen, die gefundenen Effekte im Rahmen der Orientierungsreaktion (OR) zu betrachten. In einer Serie von vier Untersuchungen wird dargelegt, dass die Dauer von Fixationen auch durch externe Ereignisse moduliert wird. In der ersten Untersuchung wurden die zeitlichen Aspekte des Distraktoreffekts untersucht. Dafür erschienen Distraktoren mit verschiedenen Latenzen nach Fixationsbeginn. Zusätzlich wurde untersucht, welche Auswirkungen unterschiedliche Distraktormodalitäten (visuell und akustisch) zeigen. Die Ergebnisse demonstrierten eine deutliche Verlängerung der jeweils vom Distraktor betroffenen Fixation für alle Latenzen. Für Distraktoren beider Modalitäten zeigte sich eine vergleichbare Verlängerung betroffener Fixationen. Bei der zweiten Untersuchung wurde für visuelle Distraktoren geprüft, inwieweit sich die vorgeschlagene Interpretation im Rahmen der OR bestätigen lässt. Dafür wurde der Effekt hinsichtlich einer Habituation untersucht. Für die Studie wurden Distraktoren mit zwei verschiedenen Latenzen auf umweltbezogenen vs. retinal fixierten Koordinaten präsentiert. Die Ergebnisse zeigten, dass eher Störungen auf gleichen retinalen Positionen eine Abnahme des Effektes zur Folge haben (also habituieren). Für Distraktoren auf konstanten Bildpositionen konnte keine systematische Abnahme des Distraktoreffektes gemessen werden. Für die dritte Untersuchung wurden Augenbewegungen und blickkontingente ereigniskorrelierte Potentiale (EKP?s) parallel aufgezeichnet. Bisher liegen keine Erkenntnisse vor, wie anhand von Parametern der Augenbewegungen Habituation nachweisbar ist, die Abnahme der N1-Komponente der EKP?s hingegen gilt als etablierter Nachweis einer Habituation. Die Ergebnisse zeigten, neben der Verlängerung der Fixationsdauer für visuelle und akustische Distraktoren, eine deutliche Auswirkung auf die N1-Komponente. Bei der Prüfung der Habituation über die betrachteten Bilder zeigte sich eine Verringerung des Effektes in der Fixationsdauer und der N1-Komponente. Auf Schwierigkeiten in Bezug auf den Nachweis einer ausgeprägten Habituation wurde an entsprechender Stelle hingewiesen. Die letzte Studie (N=1) testete, ob sich die Neuinterpretation des Effektes mit neurophysiologischen Erkenntnissen vereinbaren lässt. Bei dem Probanden wurde aufgrund eines Unfalls eine Schädigung des frontalen Augenfeldes (FEF) angenommen. Es wurden Distraktoren links, rechts, ober- und unterhalb des Fixationsorts dargeboten. Beim ersten Versuch, 12 Monate nach dem Unfall, zeigte sich für Distraktoren links des Fixationsortes keinerlei Verlängerung der betroffenen Fixationen. Beim zweiten Versuch, acht Monate später, zeigte sich der Distraktoreffekt auf allen Positionen. Dies lässt sich als Unterstützung der Annahme einer Schädigung der FEF interpretieren, da sich in verschiedenen Studien selbst bei operativer Entfernung der FEF eine deutliche Verringerung der entstandenen Defizite nach einigen Wochen zeigte. Mögliche Alternativen der dargestellten Interpretation wurden an entsprechender Stelle diskutiert. Diese Untersuchungen bestätigen, dass sich ereignisbezogene Verlängerungen der visuellen Fixationsdauer mit dem Rahmenkonzept der OR in Verbindung bringen lassen. Es gilt jedoch zu berücksichtigen, dass eine Reihe weiterer Einflussfaktoren an der Modulation des Effektes beteiligt sind, obwohl es sich offenbar um eine Reaktion subkortikalen Ursprungs handelt.

β-N-methylamino-L-alanine (BMAA) is one of the more recently discovered bioactive compounds produced by cyanobacteria. BMAA is a non-protein amino acid reported present in human brain tissues of patients deceased from a neurodegenerative disease, such as Alzheimer´s disease or amyotrophic lateral sclerosis (ALS). This observation in combination with its neurotoxic effects in eukaryotes (in vivo and in vitro) and its potential to incorporate into (human) proteins, causing protein aggregation, suggests BMAA as a possible causative environmental agent for neurodegenerative diseases. Due to the ubiquitous nature of cyanobacteria with a wide occurrence in both aquatic and terrestrial environments, BMAA could be globally spread. Hence, investigations of a possible coupling between BMAA and neurodegeneration are urgently needed as well as to identify sources of BMAA in Nature. The aim of this thesis was to examine the potential occurrence of BMAA in bloom forming cyanobacteria of the Baltic Sea and its possible transfer to other organisms of this ecosystem. Of importance was also to reveal any likely routes for human BMAA exposure in the Baltic Sea region and to further investigate BMAA as a triggering agent for neurodegenerative diseases. Acknowledged difficulties of analysing BMAA in biological samples also inferred method development as part of the experimental studies. Investigating the role of BMAA in its producers was another purpose of the thesis, which may be crucial for future management of BMAA-producing cyanobacteria. By screening natural populations of the major filamentous bloom forming cyanobacteria of the Baltic Sea, we discovered the presence of BMAA throughout the entire summer season of two consecutive years, using a highly specific analytical method (liquid chromatography-tandem mass spectrometry; LC-MS/MS). BMAA was found to bioaccumulate in zooplankton and fish, as well as in mussels and oysters from the Swedish west coast. To improve the understanding of BMAA analyses in natural samples, the formation of carbamate adducts in the presence of bicarbonate was examined. Using two derivatization techniques in combination with LC-MS/MS, we could show that BMAA detection was not hindered by carbamate formation. Exogenously added BMAA inhibited nitrogen fixation in the model cyanobacterium Nostoc sp. PCC 7120, which was also hampered in growth and displayed signs of nitrogen starvation. Finally, BMAA was detected in cerebrospinal fluid in three of 25 Swedish test individuals, and represents the first confirmation of BMAA in the human central nervous system using LC-MS/MS as the primary analytical method. However, the association of BMAA to neurodegenerative diseases could not be verified as BMAA was present in both control individuals (two) and in one ALS-patient. Nevertheless, the finding of a known neurotoxic compound in the human central nervous system is alarming and potential consequences should be investigated. The discovery of the neurotoxic compound BMAA in Baltic Sea organisms, and in the central nervous system of humans potentially consuming fish from this ecosystem is concerning and warrants continued investigations of BMAA occurrence and human exposure. Further knowledge on the function and regulation of BMAA may help in developing strategies aiming to minimise human exposure. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.</p>

No description available.

In this study several free-living diazotrophs (FLD) were isolated and screened for their nitrogen fixing ability on a range of crops grown in greenhouse, hydroponics and field trials. Rhizosphere isolates of free-living diazotrophs (FLD) may be effective biofertilizer inoculants, and may improve plant health where crops are grown with little or no fertilizer, as is the case in the Developing World. FLD isolates from rhizospheric soils in KwaZulu-Natal were assessed by growing them on N-free media, which is a key isolation method. They were then evaluated for their nitrogenase activity by quantifying ethylene production from acetylene by gas chromatography (GC). The free living isolates that produced greater quantities of ethylene were detected by an acetylene reduction assay (ARA). These were further assessed for colony formation on N-free media with different carbon sources, and at a range of temperatures (20, 25 and 300C) and pH values (6.0, 7.0 and 8.0). Isolates G3 and L1 were identified using DNA sequencing by Inqaba Biotechnical Industries (Pty) Ltd as Burkholderia ambifaria Coenye et al, and Bacillus cereus Frankland, respectively. These isolates grew significantly better on an ethanol medium, at temperatures of 20, 25 and 300C and pHs of 6.0, 7.0 and 8.0. Isolates B3 (Burkholderia sp.) and D6 (Bacillus cereus Frankland) also grew well on an ethanol medium, but only at 200C and at a pH of 6.0 and 7.0, respectively, while Isolate E9 (Burkholderia cepacia Frankland) grew well on an ethanol medium only at 300C, and pH 6.0 and 7.0. Temperature and pH strongly influence FLD growth on N-free media using different carbon sources. Further trials were conducted to screen the best isolates under greenhouse condition, using both seed treatments and drenching application techniques onto several crops. The drenching application resulted in an increase in the growth and N-total of all the evaluated crops, relative to an unfertilized control. Growth and N-total of maize and sorghum increased with seed treatments, but did not increase the growth of lettuce and zucchini. Drenching of FLD isolates at 106cfu ml-1, applied on weekly basis, resulted in an increase in the growth of lettuce. Increased doses and frequency of application of the FLD bacteria resulted in a decrease in lettuce growth. This led to the conclusion that application of FLD bacteria at high doses and short intervals may create a situation where the applied FLD bacteria and the resident rhizosphere microbes compete for root exudates. High doses at low frequencies and low doses at high frequencies may be more effective on lettuce. Inoculation of Isolate L1 (B. cereus) at 106cfu ml-1 or in combination with Eco-T® (Trichoderma harzianum Rifai), significantly increased growth of lettuce. This result may have been due to nitrogen fixation, or to secretion of growth promoting substances by both the FLD and T. harzianum, and to biocontrol effects of Eco-T®. Application of Isolate L1 (B. cereus) at 106cfu ml-1 with or without Eco-T® was an effective tool for enhancing plant growth and nitrogen fixation. An FLD, Isolate L1 (B. cereus), was applied to lettuce plants together with a complete hydroponics fertilizer at 25% strength (Ocean Agriculture 3:1:3 (38) Complete), with the N level at 25mg l-1. These plants grew significantly better than the control plants grown on 25% of normal NPK fertilization, or with an inoculation of L1 alone. This indicates that it may be possible to integrate FLD applications with the application of low levels of commercial fertilizers, which is what resource poor farmers can afford. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

1. For the first time detailed phytosociological measurements, using objective methods have been made in a large number of lowland successional stands throughout eastern Canada. 2. Soil and soil surface organic matter samples were collected on a volume-weight basis for all stands studied. An increased use of bulk-density sampling methods is advocated as they allow the conversion of all nutrient percentage and parts per million analyses to actual weights par unit area profile depth, as was done in the present work. [...]

Diatoms play a fundamental role in marine food webs, and significantly contribute to global primary production and carbon sequestration into the deep ocean. In many offshore areas of the open ocean, iron (Fe) input is low, and its availability often limits phytoplankton biomass. Recently, gene sequences encoding ferritin, a nearly ubiquitous iron storage and detoxifying protein, have been identified in pennate diatoms such as Pseudo-nitzschia, but not in other Stramenopiles (which include centric diatoms, brown algae and some protist plant parasites) or Cryptophyte relatives. Members of this genus readily bloom upon addition of iron to Fe-limited waters, and are known to produce the neurotoxin domoic acid. Until now, the reason for the success of pennate diatoms in the open ocean was uncertain; however, expressing ferritin would allow pennate species to store Fe after a transient input, using it to dominate Fe stimulated algal blooms. Here, the ferritin gene was cloned from the coastal pennate diatom Pseudonitzschia multiseries, overexpressed in Escherichia coli, and purified using liquid chromatography. The ferritin protein sequence appears to encode a non-heme, ferritinlike di-iron carboxylate protein, while gel filtration chromatography and SDS-PAGE indicate that this ferritin is part of the 24 subunit maxi-ferritins. Spectroscopically monitoring the addition of Fe(II) to a buffered ferritin solution shows that the P. multiseries protein demonstrates ferroxidase activity, binding iron and storing it as Fe(III) in excess of 600 equivalents per protein shell. In keeping with the typical stoichiometry of the ferroxidase reaction, oxygen (O₂) is consumed in a 2 Fe:O₂ratio while hydrogen peroxide is produced concurrently. iii Diatoms evolved from secondary endosymbiosis involving eukaryotic red algae; however, a broad phylogenetic comparison suggests that P. multiseries ferritin was likely acquired via lateral gene transfer from cyanobacteria – not from its ancestral endosymbionts. Until recently, no other ferritins have been identified in diatoms, and the protein characterized here is unique in that it seems to be derived from a prokaryotic organism yet it occurs in a marine eukaryote. These findings have direct implications for the success of pennate diatoms in both Fe rich coastal waters and upon Fe addition in the open ocean.

Medicago truncatula est une Légumineuse établissant une interaction symbiotique avec une bactérie tellurique de la famille des Rhizobiacées, Sinorhizobium meliloti. Cette interaction induit l'organogénèse racinaire d'un nouvel organe, la nodosité dans laquelle s'établit un microenvironnement propice à la différenciation de S. meliloti en bactéroïde fixateur du diazote atmosphérique. Ce dernier réduit ainsi le N2 atmosphérique en ammonium, assimilé ensuite par la plante hôte. Cette réduction étant très endergonique M. truncatula fournit aux bactéroïdes des substrats carbonés issus de la photosynthèse. Cependant, cette interaction n'est pas pérenne, du fait de la mise en place d'un processus de sénescence ; processus conduisant à la lyse des bactéroïdes et des cellules hôtes végétales. Cependant, à l'heure actuelle, ce processus de rupture symbiotique reste largement méconnu. Afin de mieux caractériser ce processus de sénescence, nous avons développé de nouveaux outils cytologiques permettant par microscopie confocale de suivre in vivo la viabilité, mais également le fonctionnement des bactéroïdes au sein de la cellule hôte végétale. Ces nouvelles approches cytologiques pourraient ainsi offrir de nouvelles perspectives pour une caractérisation plus précise du déroulement du processus de sénescence nodositaire. Dans le cadre de ce travail de thèse, nous avons également cherché à déterminer l'implication de deux cystéines protéases dans la mise en place du processus de sénescence nodositaire. Une des caractéristiques de ce processus de sénescence est une hausse de l'activité protéolytique, notamment des activités cystéine protéases. L'analyse transcriptomique par cDNA-AFLP du processus de sénescence nodositaire (Van de Velde et al. 2006) a pu mettre en évidence 508 gènes différentiellement exprimés dont deux cystéines protéases, MtCP6 et MtVPE. L'analyse spatio-temporelle de MtCP6 et MtVPE, par fusion transcriptionnelle avec le gène rapporteur GUS, a permis de mettre en évidence l'induction de ces deux gènes lors du processus de sénescence nodositaire aussi bien développementale qu'induit par un traitement abiotique ou lors d'une interaction symbiotique non efficace. De plus, nous avons pu démontrer, par génétique inverse, que la diminution de l'expression de ces deux protéases retarde la mise en place du processus de sénescence, alors que leur expression précoce conduit à la promouvoir. Enfin, l'étude par microscopie confocale de la localisation subcellulaire de ces protéases par fusion traductionnelle avec la GFP, démontre leur adressage aux bactéroïdes. Nos données tendent donc à démontrer le rôle clef de MtCP6 et de MtVPE dans le processus de sénescence nodositaire, où ces protéases pourraient participer directement au déclenchement d'une dégradation des bactéroïdes.

En prenant pour acquis qu'il existe bel et bien une relation entre droit d'auteur et évolution médiatique, nous avons tenté d'expliciter cette relation en nous penchant sur le cas des artistes interprètes et exécutants. Ainsi, en mettant à contribution l'une des théories de la communication, la médiologie, nous avons, d'une part, identifié ce que l'on appelle, en jargon médiatique, un média dominant; d'autre part, nous avons caractérisé la mentalité médiatique qui en découle. Enfin, nous avons examiné le droit d'auteur à la lumière de ces caractéristiques afin de déterminer quelle place revenait à l'artiste interprète et exécutant dans un contexte médiatique précis. Plus spécifiquement et conformément à la démarche que nous venons de décrire, la première partie de ce mémoire a donc porté sur l'influence d'un premier média dominant, l'imprimerie. Le statisme et la fixité exigés par la prédominance de ce média a naturellement orienté notre analyse vers l'importance de la fixation en droit d'auteur. Comme la fixation revêt une place de choix en droit d'auteur, la prestation artistique, qui ne répond pas à ce critère, est reléguée au régime des droits voisins. Puis, avec l'avènement d'un second média dominant, le média de réseaux, c'est une toute autre ère qui s'ouvre, celle de la dématérialisation. La fixation devient alors un critère en pleine perte de vitesse. Malgré tout, la communauté internationale continue de croire que la prestation artistique relève du régime des droits voisins Cependant, le Traité de l'OMPI octroie aux artistes interprètes et exécutants plus de droits. Serait-ce le premier signe d'une éventuelle accession des artistes interprètes et exécutants au régime de droits d'auteur? / If we assume that copyright laws and the evolution of media are linked, our analysis of performance artists attempts to clarify this relationship. Using mediology as a tool for communication theory, we first identified a dominant media, or what is referred as a «mediasphere» in mediology. Next, we qualified its resultant mentality. Finally, we used these characteristics to examine copyright laws in an effort to determine the position of performers in a given mediasphere context. More specifically, the first part of this thesis focuses on the influence of the print as a dominant medium. The prevalence of this medium demands a level of statism and fixity which prompts us to analyze the importance of fixation in copyright laws. Considering the predominance of fixation in copyright laws and the transitory nature of the artistic performance, performers are only granted neighboring rights, not copyrights. Nowadays, the emergence of the electronic medium seems to give way to a new mediasphere in which dematerialisation is the key. Therefore, fixation as a criterion for determining whether or not to copyright a work of art is slowly losing its significance. Despite this fact, the international copyright community continues to believe that performers should be protected by neighboring rights. However, the WIPO Treaty of 1996 grants performers greater rights. Is this the first sign ofperformers gaining potential access to authorship? / "Mémoire présenté à la Faculté des études supérieures en vue de l'obtention du grade de Maître en droit (LL.M.)"

<p><font face="TimesNewRomanPSMT"> <p align="left">Natural radioactivity studies have been carried out to study the textural characteristics, heavy mineral composition, provenance, sediment transport, and depositional environment of beach placer deposits. The naturally occurring radionuclides such as properties of beach sands, which reflect the geological characteristics such as transport and sorting processes and the depositional environment. The present work focuses on the radiometric characteristics of beach sand deposits along the west coastof South Africa. Beach sands samples were collected at the Melkbosstrand (MBS) and Ouskip (OSK) beach. The activity concentrations of these radionuclides were determined by high-resolution gamma-ray spectrometry using a high-purity germanium (HPGe) detector in a low-background configuration.</p> </font></p>

A large proportion of the world’s nitrogen needs is derived from symbiotic nitrogen fixation (SNF), which contributes substantially to agricultural sustainability. The partnership between legumes and rhizobia result in the formation of specialised structures called root nodules. Within these nodules SNF is supported by the sucrose transported from the leaves to the nodules for respiration. The end products of SNF in soybean (Glycine max (L.) Merr.) root nodules, namely ureides, are transported to the upper parts of the plant to supply nitrogen. Symbiotic nitrogen fixation provides a vital advantage for the production of soybean compared with most grain crops in that soybean fixes the nitrogen required for its growth and for the production of the high-protein content in seed and oil. The process of SNF is dramatically affected by drought, salt, cold and heavy metal stresses. Since SNF is such an important yield-determining factor, a lack in understanding these complexes inevitably delays progress towards the genetic improvement of soybean genotypes and also complicates decisions with regard to the suitability of certain genotypes for the various soybean producing areas in South Africa. The largest soybean producing areas in South Africa are situated at high altitudes, with minimum daily temperatures which can be critically low and impeding the production of soybean. Soybean is chilling sensitive, with growth, development and yield being affected negatively at temperatures below 15°C. Dark chilling (low night temperature) stress has proved to be one of the most important restraints to soybean production in South Africa. Among the symptoms documented in dark chilling sensitive soybean genotypes are reduced growth rates, loss of photosynthetic capacity and pigment content, as well as premature leaf senescence and severely inhibited SNF. Existing knowledge about stress-induced nodule senescence is based on fragmented information in the literature obtained in numerous, and often diverse, legume species. The precise nature and sequence of events participating in nodule senescence has not yet been fully explained. The main objectives of this investigation were to characterise the natural senescence process in soybean nodules under optimal growth conditions and to characterise the alteration of the key processes of SNF in a chilling sensitive soybean genotype during dark chilling. Moreover, to establish whether recovery in nodule functionality following a long term dark chilling period occured, or whether nodule senescence was triggered, and if sensitive biochemical markers of premature nodule senescence could be identified. A known chilling sensitive soybean genotype, PAN809, was grown under controlled growth conditions in a glasshouse. To determine the baseline and change over time for key parameters involved in SNF, a study was conducted under optimal growing conditions over a period of 6 weeks commencing 4 weeks after sowing. The cluster of crown nodules were monitored weekly and analysis included nitrogenase activity, ureide content, respiration rate, leghemoglobin content, sucrose synthase (SS) activity and sucrose content. Further investigations focused on induced dark chilling effects on nodule function to determine the alterations in key parameters of SNF. Plants were subjected to dark chilling (6˚C) for 12 consecutive nights and kept at normal day temperatures (26˚C). The induced dark chilling was either only shoot (SC) exposure or whole plant chilling (WPC). These treatments were selected since, in some areas in South Africa cold nights result not only in shoot chilling (SC) but also in low soil temperatures causing direct chilling of both roots and shoots. To determine if premature nodule senescence was triggered, the recovery following 12 consecutive nights of chilling treatment was monitored for another 4 weeks. It was established that the phase of optimum nitrogenase activity under optimal growing conditions occurred during 4 to 6 weeks after sowing where after a gradual decline commenced. This decline was associated with a decline in nitrogenase protein content and an increase in ureide content. The stability of SS activity and nodule respiration showed that carbon-dependent metabolic processes were stable for a longer period than previously mentioned parameters. The negative correlation that was observed between nitrogenase activity and nodule ureide content pointed towards the possible presence of a feedback inhibition trigger on nitrogenase activity. A direct effect of dark chilling on nitrogenase activity and nodule respiration rate led to a decline in nodule ureide content that occurred without any limitations on the carbon flux of the nodules (i.e. stable sucrose synthase activity and nodule sucrose content). The effect on SC plants was much less evident but did indicate that currently unknown shoot-derived factors could be involved in the minor inhibition of SNF. It was concluded that the repressed rates of respiration might have led to increased O2 concentrations in the nodule, thereby inhibiting the nitrogenase protein and so the production of ureides. It was found that long term chilling severely disrupted nitrogenase activity and ureide synthesis in nodules. Full recovery in all treatments occurred after 2 weeks of suspension of dark chilling, however, this only occurred when control nodules already commenced senescence. This points toward reversible activation of the nitrogenase protein with no evidence in support of premature nodule senescence. An increase in intercellular air space area was induced by long term dark chilling in nodules, specifically by the direct chilling of nodules (WPC treatment). The delayed diminishment of intercellular air space area back to control levels following dark chilling may be an important factor involved in the recovery of nitrogenase activity because enlarged air spaces would have favoured gaseous diffusion, and hence deactivation of nitrogenase, in an elevated O2 environment (due to supressed nodule respiration rates). These findings revealed that dark chilling did not close the diffusion barrier, as in the case of drought and other stress factors, but instead opened it due to an increase in air space areas in all regions of the nodule. In conclusion, this study established that dark chilling did not initiate premature nodule senescence and that SNF demonstrated resilience, with full recovery possible following even an extended dark chilling period involving low soil temperatures. / Thesis(PhD (Botany))--North-West University, Potchefstroom Campus, 2013