This thesis provides new evidence which contributes to a clearer understanding of the mixing history of the lunar soil, the interactions of cosmic rays with the lunar surface and any temporal and spatial variations in cosmic ray intensity at the lunar surface. The bombardment of the lunar surface by cosmic rays produces secondary neutrons which are thermalised by the lunar soil. These thermal neutrons are captured by trace elements with large neutron capture cross sections such as cadmium, gadolinium and samarium. Measurements by thermal ionisation mass spectrometry of the changes in the isotopic abundances of cadmium, gadolinium and samarium due to neutron capture are presented in this thesis. Evidence is also presented of the first observations of mass fractionation in cadmium in lunar soils.Changes have been observed in samples from the Apollo 14, 16 and 17 missions. In 114 [superscript 114]Cd/[superscript 113]Cd changes of 0.3% to 0.5% have been observed in lunar samples 60501,105, 65701,23 and 72161,73, of 0.4% and 0.8% in [superscript 158]Gd/[superscript 157]Gd in samples 14163,848 and 60501,105 and of 0.8%, 1.2% and 0.06% in [superscript 150]Sm/[superscript 149]Sm in samples 14163,848 and 60501,105 and 74220,125 respectively. This is the first time that neutron capture has been detected in cadmium. Mass fractionation effects of 0.30%, 0.53% and 0.54% per mass unit have been observed in lunar samples 60501,105, 65701,23 and 72161,73, the first cadmium mass fractionation observed in lunar soils. The cause of elemental mass fractionation on the Moon is not yet understood. These new data from cadmium, a volatile element with a large mass range from [superscript 106]Cd to [superscript 116]Cd is a valuable contribution to the debate.Thermal neutrons are captured preferentially at resonance energies of 0.03 eV by [superscript 155]Gd and [superscript 157]Gd, at 0.09 ++ / eV by [superscript 149]Sm and at 0.178 eV by [superscript 113]Cd. A comparison of the changes in [superscript 114]Cd/[superscript 113]Cd, [superscript 156]Gd/[superscript 155]Gd, [superscript 158]Gd/[superscript 157] and [superscript 15O]Sm/[superscript149]Sm due to neutron capture can therefore indicate the relative energies of the neutrons.Previous work has compared changes in [superscript 158]Gd/[superscript 157]Gd and [superscript 150]Sm/[superscript 149]Sm, this work extends the comparison with the new measurements of the changes in 114 [superscript 114]Cd/[superscript 113]Cd, This thesis shows that the intensity of the thermal neutrons peaks at a higher energy than the <0.1 eV assumed by Lingenfelter et al. (1972). The capture rate for gadolinium calculated by Lingenfelter, has been shown to be too high, this thesis shows that if a modified energy spectrum is considered, biased towards higher energies, it will bring the calculated neutron capture rate by gadolinium closer to the measured rates.The concentrations of cadmium, gadolinium and samarium in nine lunar samples have been measured for the first time by high precision isotope dilution mass spectrometry. Cadmium in 10017,341, 14310,615, 15041,188, 15059,240, 60501,105, 65701,23, 72161,73 and 74220,125 is 10.0_+0.2, 1.51_+0.02, 32.8+_0.6, 34.9+_0.3, 112+_2, 68.3_+0.8, 57.0+_0.6 and 300+_7 ppb respectively. Gadolinium concentrations of 21+_7 ppm in 14163,848, 3.26+_0.05 and 5.8_+0.3 ppm in 60501,105, and 8.1+_0.2 and 8.6+_0.1 ppm in 74220,125 are presented. Samarium concentrations of 24.3_+0.4 and 29.8_+0.5 ppm were found in 14163,848, 2.68+_0.04 and 14+2 ppm in 60501,105, and 6.3+_0.1 and 6.8+_0.1 ppm in 74220,125.The concentrations of cadmium, gadolinium and samarium in the seven geochemical reference materials BCR-1, BHVO-1, BIR-1, DNC1, MAG-1, PCC-1 and W-2 are also presented, some measured for the first ++ / time by isotope dilution mass spectrometry.

This Ph. D. thesis presents results and conclusions from studies 1) investigating the interaction between metal and metalloid ions and thermophilic bacteria, and 2) characterizing microbial populations in a geothermally active habitat with relatively high concentrations of metalloid ions and compounds. In initial cadmium ion toxicity assays, the minimal inhibition concentration for 46 thermophilic bacteria of the genera Aneurinibacillus, Anoxybacillus, Bacillus, Brevibacillus, Geobacillus, and Thermus were determined. The highest tolerances to cadmium ions (Cd2+) in the range of 400 to 3200 micro;M were observed for species belonging to the genus Geobacillus. The thermophilic Gram-positive bacteria Geobacillus stearothermophilus and G. thermocatenulatus were selected to describe further biosorption reactions between cadmium ions and chemically reactive functional groups (potential ligands) within and onto the bacterial cell walls. Data obtained from electrophoretic mobility, potentiometric titration and cadmium ion adsorption experiments were used to quantify the number and concentrations of ligands and to determine the thermodynamic stability constants for the ligand-cation complexes. The first reported surface complexation models (SCMs) quantifying metal ion adsorption by thermophilic microorganisms predicted cadmium adsorption and desorption by both studied Geobacillus strains over a range of pH values and for different biomasses. The results indicated the functional group, with a deprotonation constant pK value of approximately 3.8, to be more dominant in cation biosorption accounting for 66 and 80% of all titrable groups for G. thermocatenulatus and G. stearothermophilus, respectively. The generated SCMs are different from model parameters obtained from mesophilic species that have been studied to date and might indicate a different biosorption behavior for both studied Geobacillus strains. Another objective of this thesis was to characterize microbial populations in the hot spring Champagne Pool, located in Waiotapu, New Zealand. The thermal spring is approximately 65 m in diameter and discharges water at 75eg; C and pH 5.5, which is oversaturated with arsenic and antimony compounds that precipitate and form orange deposits. Recovered nucleic acids and adenosine 5'-triphosphate (ATP) concentrations obtained for Champagne Pool water samples indicated low microbial density and were in good agreement with relatively low cell numbers of 5.6 plusmn; 0.5 x10^6 cells per ml. Denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene clone library analyses revealed the abundance of Sulfurihydrogenibium, Sulfolobus and Thermofilum-like populations in Champagne Pool. Two novel bacteria and one novel archaeon were successfully isolated with a distant phylogenetic relationship to Sulfurihydrogenibium, Thermoanaerobacter, and Thermococcus, respectively. Genotypic and metabolic characteristics differentiated isolate CP.B2 from described species of the genus Sulfurihydrogenibium. CP.B2 represents a novel genus within the Aquificales order, for which the name Venenivibrio stagnispumantis gen. nov., sp. nov. is proposed. V. stagnispumantis is a thermophilic, chemolithothrophic bacterium, that utilizes molecular hydrogen as electron donor and oxygen as electron acceptor and displayed growth in the presence of up to 8 mM NaAsO2 (As3+) and more than 20 mM Na2HAsO4.7H2O (As5+). However, growth was not observed when Na2HAsO4.7H2O and NaAsO2 were provided as the sole electron acceptor and donor pair. Arsenic resistance was conferred by the genes arsA and arsB

This thesis presents the results of an investigation into the uptake and distribution of cadmium (Cd) in two cultivars of potato (Solanum tuberosum L.) shown to contain different concentrations of Cd in the tuber at maturity. An initial glasshouse trial sought to determine whether differences in tuber Cd between these two cultivars resulted from differences in uptake from the soil, or were due to differences in the allocation of Cd to the various tissues within the plant. Total uptake of Cd from the soil did not differ between cultivars, nor did the yield of tubers. However, there were marked differences in Cd distribution within the plant. Most of the differences in tuber Cd concentration could be accounted for by a large (3-fold) retention of Cd in the roots of cultivar Wilwash. The concentration of Cd in the shoots of Wilwash was also higher than of Kennebec, although to a lesser extent than the roots. Further studies were conducted to trace the pathways of Cd uptake and movement within the plant. A split-pot trial, involving long-term growth of potatoes in 109Cd-labelled soil, was undertaken to determine the overall pattern of Cd distribution and the importance of the root system in supplying Cd to the tubers. The root system of the potato plant is different to many plants, in that the main root system (basal roots) is augmented after tuber initiation by roots extending from the stolon and from the tuber itself. The basal roots were found to be the dominant source of Cd to all tissues and accounted for approximately 85 % of tuber Cd. The remaining tuber Cd was sourced directly from the stolon and tuber roots. However, there was no evidence of a direct link between the main (basal) root system and the stolons. Although Cd was found to accumulate in the periderm of the tubers, there was no uptake into the tuber tissue itself. Isotopic studies were undertaken to investigate the short-term movement of newly absorbed Cd in the xylem and the phloem. Cadmium was found to be highly mobile in both the xylem and phloem, with added Cd being rapidly assimilated into all tissues following both root and foliar application. Newly absorbed Cd was rapidly sequestered by the stems when applied to either the soil or to a source leaf, suggesting that the stems may act as a transitional storage pool when rapid turnover of nutrients and other mineral elements is required during tuber bulking. Inhibition of Cd uptake by zinc (Zn), has been proposed as a method for reducing the concentration of Cd in various agricultural crops, including potatoes. The ability of Zn to reduce Cd uptake was found to be highly dependent upon cultivar and on the concentration of Cd in the external medium. Although competition between Zn and Cd was found for cultivar Wilwash when the external concentration of Cd was low, when the concentration of Cd in the external media was high, increasing Zn served to increase Cd uptake. Both synergistic and competitive responses were also noted for cultivar Kennebec. However, the patterns of response were opposite to those evident in Wilwash. The complexity of these interactions highlighted the possible shortcomings in using soil applied Zn to limit Cd uptake by potatoes. / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2004.

Les formes réactives de l'oxygène (FRO) ont été analysées dans différents compartiments cellulaires en utilisant des méthodes spectroscopiques (UV/VIS, fluorescence, infrarouge, résonance paramagnétique électronique). L'identité et les mécanismes catalytiques des enzymes qui produisent les FRO dans les membranes plasmiques (MP) et les mitochondries ont été étudiés, ainsi que le rôle protectif de l'oxydase terminale plastidiale (PTOX) des chloroplastes. Cd2+ s'est révélé être un inhibiteur de la NADPH oxydase des MP. In vivo Cd2+ inhibait la production extracellulaire de O2•- mais stimulait l'accumulation de H2O2. Dans des mitochondries isolées, Cd2+ a augmenté la production de FRO. Antimycin A a entraîné une élévation du H2O2 extracellulaire, confirmant que la mitochondrie est le site principal de production de l'H2O2 extracellulaire induite par Cd2+ in vivo. Une quinone réductase (QR) génératrice de FRO a été isolée des MP. La déprotonation pH-dépendante du quinole a produit des formes intermédiaires instables qui génèrent des FRO par réaction avec O2. Des espèces quinoniques ont été détectées dans la MP et pourraient servir de substrat aux QR in vivo. La protection de la chaine photosynthétique de transfert d'électron par la plastoquinol:O2 oxydoréductase a été étudiée chez des plantes PTOX+ surexprimant PTOX. En raison de leur réponse altérée en conditions de faible et forte intensité lumineuse, il a été proposé que pour fonctionner comme enzyme protectrice, PTOX est couplée à une SOD. Chez les lignées PTOX+, le niveau de SOD chloroplastique n'était pas plus élevé, limitant probablement leur capacité à détoxifier les taux élevés de O2•- généré.

La vacuole est un organite qui joue un rôle important dans de nombreux processus de la cellule végétale, et en particulier dans la protection contre les toxiques cellulaires. Parmi ceux-ci, le cadmium est un polluant courant qui affecte les fonctions physiologiques de la plante. La vacuole est connue pour sa capacité à séquestrer les ions métalliques présents dans le cytosol. Toutefois, les acteurs protéiques de cette compartimentation, et notamment les transporteurs, ne sont pas bien connus. Afin de mieux comprendre le rôle de cet organite dans les mécanismes de protection contre le stress métallique, nous avons mis en place une série d'outils d'analyse du protéome vacuolaire, dans le but de réaliser une caractérisation protéomique de référence de cet organite, utile pour l'étude de sa dynamique en conditions de stress. Mon travail a consisté dans un premier temps à mettre au point une méthode de purification de vacuoles à partir de cellules en culture d'Arabidopsis thaliana. La pureté des échantillons obtenus a été confirmée à l'aide de tests biochimiques (western-blots et mesures d'activités enzymatiques) et nous avons pu initier l'analyse par spectrométrie de masse des constituants protéiques de la membrane et de la fraction soluble de la vacuole. Celle-ci a permis d'identifier 689 protéines non-redondantes, dont 110 transporteurs. La localisation in vivo de 5 d'entre elles a été réalisée via l'expression in planta de ces protéines fusionnées à la GFP. Cette première approche protéomique a été complétée d'une étude plus approfondie du protéome vacuolaire, visant à en acquérir des notions quantitatives et organisationnelles. Pour cela, des gels d'électrophorèses bidimensionnelles (IEF / SDS-PAGE) ont été réalisés à partir de la fraction soluble des vacuoles. Les spots résolus ont été quantifiés via le logiciel d'analyse d'images PDQuest et identifiés par spectrométrie de masse. Cette étude a permis de mettre en évidence un certain nombre de protéines majeures de ce compartiment et a porté le nombre total de protéines vacuolaires identifiées par nos travaux à 709. Quelques protéines connues pour être cytosoliques ont toutefois été retrouvées, et une cartographie du protéome cytosolique a également été réalisée afin de la comparer avec celle du protéome soluble de la vacuole et tenter de mieux comprendre l'origine de ces protéines. Cette analyse a été complétée d'une expérience préliminaire de digestion de vacuoles intactes par la protéinase K. Les résultats obtenus suggèrent la présence de protéines à l'intérieur de la vacuole (probablement en cours de dégradation), et d'autres associées à la face externe du tonoplaste probablement de façon spécifique. Enfin, la présence de complexes protéiques a été évaluée à travers la réalisation d'électrophorèses en conditions non dénaturantes qui ont permis de retrouver des complexes connus (ATPase vacuolaire) mais aussi de mettre en évidence plusieurs complexes putatifs de protéines diverses (protéases, glycosidases ...). Un dernier aspect de mon travail a enfin consisté à développer un outil informatique d'exploitation de données d'analyses à haut débit. La confrontation, grâce à cette structure, des résultats de protéomiques vacuolaires et d'autres d'expression génique lors d'un stress cadmium ont permis d'identifier des protéines présentes dans (ou associées à) la vacuole dont le niveau de transcrit est modulé lors d'un stress. Ces analyses croisées ont notamment mis en évidence la protéine DWARF1, qui catalyse une étape de la biosynthèse des brassinostéroïdes, une classe d'hormones. L'étude de l'implication de cette hormone a alors montré que celle-ci est capable de moduler la tolérance au cadmium de plantules, très probablement via des mécanismes qui n'ont encore jamais été identifiés. L'ensemble de ce travail constitue une base pour l'étude ultérieure de la dynamique du protéome vacuolaire. Il propose des méthodes et des outils d'analyse, ainsi qu'une série de données de référence, pour mieux comprendre les processus vacuolaires de la détoxication métallique, et a d'ores et déjà permis de mettre en évidence des aspects nouveaux du fonctionnement de cet organite.

<p>Heavy metals polluting our environment cause concern for developing organisms. Among them, cadmium with extremely slow elimination from the body, causes lower birth weight in humans but has not been classify as a human teratogen. Studies in different laboratory animals have shown that cadmium indeed is a potent teratogen. Exposure to cadmium during early mouse embryonic stages (e.g. day 7-8 post-coitus) interferes with the closure of the anterior neural pore producing exencephalic embryos. The underlying mechanisms are not understood, but the heavy accumulation of cadmium in extra- and intraembryonic endoderm and chorioallantoic placenta, however not in the neuroepithelium, suggests that the effects on neural tube closure is due to indirect mechanisms. In this thesis, the disruption in the mouse embryo at the time of neural tube closure of the hierarchies of some signalling pathways and gene regulatory networks that control embryonic development has been studied after cadmium exposure. Cadmium was shown to cause DNA damage as measured by Comet assay, and to activate genes and proteins in the apoptotic pathways (<i>p53, p21, Bcl-2, Bax</i>, and caspase-3), increasing the number of apoptotic cells mostly in areas of physiological cell death, especially in the neuroepithelium. Many of these effects could be reversed by zinc pre-treatment, known to counteract the teratogenic effect of cadmium. Cadmium was also shown to affect Zn-transport and –regulatory proteins in the embryo, but perhaps more importantly in yolk sac placenta, and in the decidua (ZnT-1, MT-I, and ZIP-4). Using gene arrays, cadmium was found to considerably affect gene expression of rather few genes, such as those of metallothioneins and stress-related proteins, supporting in principle an extraembryonic site of action of cadmium. In addition, a number of genes expressed in the anterior visceral endoderm (<i>Hesx1, HNF3β, Cerl, Otx2</i> and <i>Sox2</i>) where cadmium accumulates, and known to signal to the anterior neuroepithelium, was affected by cadmium. This finding may suggest a new principle for chemical teratogenesis.</p>

Les xénobiotiques se trouvant dans l’environnement peuvent occasionner des effets délétères aux organismes vivants. Toutefois, nous sommes encore loin de connaître l’ensemble des mécanismes d’action des polluants et des réponses mises en place chez les organismes afin de survivre dans un environnement pollué. Dans ce travail, nous avons utilisé le crabe chinois, Eriocheir sinensis, comme modèle d’étude afin de mettre en évidence les réponses à un stress induit par le cadmium dissous dans le milieu aquatique. Nous avons focalisé notre attention sur la fonction d’osmorégulation. Différents types d’exposition ont été testés : une exposition « aiguë » (500 µg Cd l-1 de 1 à 7 jours) ; une exposition « chronique » (10 ou 50 µg Cd l-1 pendant 30 jours). On observe une diminution de la capacité d’hyper-osmorégulation suite à une exposition aiguë. Sous cette condition, les branchies antérieures sont endommagées et les activités de différentes enzymes diminuées. Par contre, le Cd semble sans effet sur les branchies postérieures. Il est par conséquent probable que les branchies antérieures auraient perdu leurs propriétés de perméabilité et laisseraient passer plus librement l’eau et/ou les ions. Une exposition chronique n’affecte pas l’osmorégulation. Cependant, une exposition chronique suivie d’une exposition aiguë montrent que le crabe s’acclimate, c’est-à-dire qu’il devient plus résistant au Cd. Chez ces crabes acclimatés, l’hépatopancréas est capable d’accumuler une plus grande quantité de Cd grâce, en partie du moins, à une teneur accrue en métallothionéines. L’analyse protéomique a permis d’observer que l’expression d’enzymes anti-oxydantes et de chaperonnes moléculaires est augmentée dans les branchies antérieures, suggérant que le Cd affecte les branchies en induisant des espèces réactives à l’oxygène et en oxydant les groupements sulfures des protéines. De plus, le potentiel de dégradation des protéines semble accru. Enfin, plusieurs enzymes impliquées dans différentes voies métaboliques sont sous exprimées, indiquant que le crabe entre dans un état compensatoire lui permettant de faire face à de fortes quantités de Cd. Ce travail démontre qu’une approche intégrative utilisant des analyses physiologiques, morphologiques, biochimiques et protéomiques, permet de caractériser l’état de stress dans lequel un organisme aquatique se trouve suite à différents types d’exposition à un xénobiotique. Même si une exposition chronique ne montre pas d’effet physiologique, elle peut toutefois induire des changements au niveau du protéome.

Heavy metals polluting our environment cause concern for developing organisms. Among them, cadmium with extremely slow elimination from the body, causes lower birth weight in humans but has not been classify as a human teratogen. Studies in different laboratory animals have shown that cadmium indeed is a potent teratogen. Exposure to cadmium during early mouse embryonic stages (e.g. day 7-8 post-coitus) interferes with the closure of the anterior neural pore producing exencephalic embryos. The underlying mechanisms are not understood, but the heavy accumulation of cadmium in extra- and intraembryonic endoderm and chorioallantoic placenta, however not in the neuroepithelium, suggests that the effects on neural tube closure is due to indirect mechanisms. In this thesis, the disruption in the mouse embryo at the time of neural tube closure of the hierarchies of some signalling pathways and gene regulatory networks that control embryonic development has been studied after cadmium exposure. Cadmium was shown to cause DNA damage as measured by Comet assay, and to activate genes and proteins in the apoptotic pathways (p53, p21, Bcl-2, Bax, and caspase-3), increasing the number of apoptotic cells mostly in areas of physiological cell death, especially in the neuroepithelium. Many of these effects could be reversed by zinc pre-treatment, known to counteract the teratogenic effect of cadmium. Cadmium was also shown to affect Zn-transport and –regulatory proteins in the embryo, but perhaps more importantly in yolk sac placenta, and in the decidua (ZnT-1, MT-I, and ZIP-4). Using gene arrays, cadmium was found to considerably affect gene expression of rather few genes, such as those of metallothioneins and stress-related proteins, supporting in principle an extraembryonic site of action of cadmium. In addition, a number of genes expressed in the anterior visceral endoderm (Hesx1, HNF3β, Cerl, Otx2 and Sox2) where cadmium accumulates, and known to signal to the anterior neuroepithelium, was affected by cadmium. This finding may suggest a new principle for chemical teratogenesis.

Mercury cadmium telluride is important in the detection of electromagnetic radiation in the eight to twelve micron atmospheric window for infrared imaging systems. High resolution infrared imaging systems use either large (256x256 element to 1024x1024 element) staring arrays or much smaller (1-6 element) scanned arrays in which the image is optically scanned across the detectors. In scanned arrays, high resolution and sensitivity may result in the scan direction not being parallel to the detector bias current. The response of an infrared detector to uniform illumination is investigated. It is found that variations in the detector thickness result in significant changes in output voltage. Scanned detectors are modeled in five different orientations; scan parallel to bias, scan opposite to bias, scan perpendicular to bias, and two orientations of the scan diagonal to the bias. The response is analyzed for two cases: 1) the size of the scanned radiation equal to the size of the detector and 2) when the pixel width is half of the width of the detector, but of equal length. Results of the simulation show that the fastest response occurs when the scan and bias are parallel. The largest response occurs when the scan direction is diagonal to the bias, but the response time is much slower than when the bias is parallel to the scan. Therefore, a tradeoff must be made between maximum signal and speed of response. Test detectors are being fabricated and will be tested at FLIR Systems Inc., Portland, Oregon, to confirm the model predictions. / Graduation date: 1992

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