Thesis (Ph. D.)--University of Wisconsin--Madison, 1940. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [39-40]).

Methods were devised for the isolation and pure culture in defined mineral medium of Closteriurn ehrenbergii Menegh (Chlorophyceae). The effect of pH, type of nitrogen source, nitrate concentration, total hardness, and various buffers on growth were investigated. Best growth rates were obtained at pH 8 to 9, but good growth was observed even at pH 9.4. Nitrate, ammonia, or urea nitrogen could be utilized, but at concentrations greater than 10-2M urea was toxic to growth. At higher concentrations of ammonia and nitrate longer lag phases of growth were obtained but eventual higher cell yields were obtained. Good growth rates were obtained with Tris-(hydroxymethyl)-aminomethae buffer at up to l0-2M; higher concentrations were inhibitory.

Additions of copper were shown to affect cell morphology, growth rates and nutrient uptake in Closterium moniliferum. These parameters are interrelated in the total life cycle of the organism. It was found that the timing of events in the life cycle, including sexual reproduction, could be changed when copper was added. When increasing concentrations of copper were added to the growth medium, Closterium moniliferurn exhibited a stimulatory, inhibitory, or toxic dose-response typical of organisms to trace metals. The stimulatory effect, occurring at pCu* 14.4, was demonstrated by an early increase in cell number, increased nitrate uptake, and early onset of sexual reproduction. The inhibitory effects of greater concentrations of copper (pCu* 12.1) were a longer lag phase, decreased nitrate uptake, and later onset of sexual reproduction. Light micrographs and scanning electron micrographs of normal and aberrant cells demonstrated the effect of copper on morphology. It was demonstrated that the sexual phase in some srains of Closteriurn moniliferurn could be triggered by changes in the amount of nitrogen in the medium. Although it was expected that each cell would have a minimal cell quota (Q nitrogen/cell) before sexual reproduction occurred, work here demonstrated that Q was not the critical factor in the initiation of the process. Sexual reproduction occurred at Q = .05 micromoles nitrogen/cell up to .21 micromoles nitrogen/cell. Neither was cell density in batch cultures the critical factor. Sexual reproduction occurred in the range of 400 cells/ml up to 6100 cells/ml. Different nitrogen sources gave different responses in the onset of sexual reproduction. Nitrate depletion. not ammonia, appears to be the critical component in induction of sexual reproduction. The actual effect of metals like copper on the population dynamics of Closterium moniliferum in natural environments is yet to be determined. The stimulatory effect on nitrate uptake by copper, and its accompanying earlier formation of zygotes, may have survival value for the organism since the zygotes become thick-walled and are not as subject to environmental perturbations as vegetative cells.

Physiologic responses to Gibberellic Acid (GA), I-Naphthalene Acetic Acid (NAA), Benzylaminopurine (BAP), and Abscisic Acid (ABA). suggest that Oosterium monilfferum has the ability to utilize these plant growth factors. The growth promoters NAA and GA both increased growth when added to the media. The cell division regulator BAP (a synthetic cytokinin). also had a promotive effect on growth. Abscisic acid was found to be inhibitive to growth.

La saline de Sfax est un environnement thalasso halin (milieu salé alimenté par de l’eau de mer) riche en plancton malgré la contrainte du sel et l’intensité lumineuse élevée. Cette richesse est due à ses facteurs physico-chimiques particuliers. L’analyse STATICO a mis en évidence que l’azote et le phosphore peuvent influencer la distribution du phytoplancton en plus de la salinité qui domine dans ce milieu particulier. En se basant sur ce dernier paramètre, nous avons pu regrouper les espèces selon leur tolérance au sel. Afin de mieux comprendre le comportement du phytoplancton, trois espèces autotrophes Dunaliella salina (Chlorophycée), Cylindrotheca closterium (diatomée) et Phormidium versicolor Cyanophycée) ont été isolées, identifiées puis cultivées en batch dans de l’eau de mer artificielle sous trois niveaux d’éclairement et en présence de trois concentrations en NaCl. La croissance, l’activité photosynthétique ainsi que l’activité enzymatique anti-oxydante ont été mesurées. L’appareil photosynthétique de la Chlorophycée et de la cyanobactérie est moins affecté que celui de la diatomée qui est irréversiblement altéré aux forts éclairements et à la plus forte salinité; l’activité antioxydante n’a été détectée que sous l’éclairement le plus élevé et la synthèse des pigments caroténoïdes, qui sont des anti-oxydants non enzymatiques, est fortement activée surtout chez D.salina. La salinité et le niveau d’éclairement inter-réagissent sur la physiologie des trois espèces qui possèdent des mécanismes de résistance aux stress plus ou moins efficaces, d’où des résistances différentes aux contraintes du milieu selon les espèces. / The saltern of Sfax is a thalasso haline environment (salt medium supplied with sea water) plankton-rich despite the high salinity and the high light intensity. This richness is due to its physico-chemical characteristics. The STATICO analysis shows that nitrogen and phosphorus can influence the distribution of the phytoplankton in addition to salinity that dominates in this peculiar medium. Basing on this parameter, we could group the species according to their salt tolerance. To better understand the behavior of the phytoplankton, three autotrophic species Dunaliella salina (Chlorophyceae) Cylindrotheca closterium (diatom) and Phormidiumversicolor (Cyanophycea) were isolated, identified and grown in batch in artificialseawater in the presence of three NaCI concentrations and under three irradiations. Growth, photosynthesis and antioxidant enzyme activity were measured. The photosynthetic apparatus of the Chlorophyceae and the cyanobacteriumwas less affected than the diatom’s one that was irreversibly altered under high illumination and the highest salinity ; the antioxidant activity was only detected in cells grown under the highest irradiance and the synthesis of carotenoid pigments, that are non-enzymatic antioxidants,was strongly activated especially in D.salina. Salinity and light inter-reacted on the physiology of the three species that possess resistance mechanisms to stresses more or less effective, resulting in different resistance to environmental stresses depending on species.

The phytohormone auxin is an important morphogen with an essential role in the development of land plants, where mechanisms of its action are well described. However, its role in green algae is poorly understood. Land plants are part of the phylum Streptophyta together with six closely related groups of predominantly freshwater green algae (charophytes). So far, the knowledge about the evolutionary origins of auxin action mechanism is mainly based on genomic information, and much less on experimental findings. In this work, the presence of auxin, its precursor, and catabolism products were shown in representative species of charophytes with varying levels measured compounds both produced endogenously and into the culture media. Thus, we gained a comprehensive insight into the possible strategies of auxin homeostasis across the non-land plant streptophytes. Also, an effect of exogenous auxin on the cell morphology and culture growth of the desmid Closterium was investigated. Image analysis of IAA-treated cells revealed a rather pleiotropic effect on cell morphology. The culture growth was inhibited by IAA. Additionally, IAA induced malformations in cell shape, and the extent of this phenomenon across individual cultures was dependent on the culture growth status. Lastly, we optimized the method of...

Microphytobenthos (MPB), a mixed community of microscopic, photosynthetic organisms, algae and cyanobacteria, inhabiting the top few millimetres of bottom sediment, is a key component of intertidal mudflats. It accounts for a significant proportion of estuarine primary production, forms the base of the food chain and influences sediment distribution and resuspension (through production of extracellular polymeric substances (EPS)). Diatoms dominate the microphytobenthos community in the mid-latitudes of the Northern Hemisphere. Estuarine sediments, are a sink for metal contaminants derived from fluvial, marine and atmospheric sources. Whilst metal releases to estuaries have declined in recent years due to increased regulation and declining industrial activity, metals previously discharged and which are now locked up in saltmarsh sediments remain a concern. For example, there are indications that saltmarshes are already being eroded, due to climate change related sea level rise, in some locations. This erosion may result in the redistribution of historically contaminated sediment to locations, such as the mudflats, where it is more available to biota, such as the MPB. In addition to causing redistribution, climate change effects, such as increasing temperatures and storminess, may also alter the bioavailability of metals to MPB. Increased concentrations of metals within the MPB could potentially increase their transfer to higher organisms through the food chain with potential impacts for biota. Whilst planktonic algae have been well studied with respect to metal uptake from the water column, there has been little research involving MPB and uptake of metals from sediment. The extent to which contaminant uptake by microphytobenthic algae occurs and under what conditions is therefore poorly understood. The research presented uses laboratory, mesocosm and field studies, to gain an understanding of processes governing metal bioavailability and mechanisms for uptake from sediment to the diatoms of the MPB under the complex and variable conditions of intertidal mudflats. A laboratory study using a single diatom species Cylindrotheca closterium found that uptake of cadmium (Cd) varied with sediment properties revealing the importance of sediment particle size and organic matter content in metal bioavailability to diatoms. Additionally, this study showed that the presence of diatoms altered Cd partitioning between sediment, overlying and pore water. Specifically there was an increase in Cd in the overlying and pore water when diatoms were present, indicating that diatoms mobilise metals from the sediment to the water column potentially increasing metal bioavailability to other biota. A study was conducted using an intertidal mesocosm to increase the realism of the study system and examine uptake to a natural MPB community. Diatoms were found to have higher concentrations of all the metals analysed (except tin) than other types of algae (filamentous and sheet macroalgae), confirming their importance as a study organism with respect to metal uptake and potential mobilisation through the food chain. Sediment disturbance was shown to increase metal uptake (iron, aluminium, vanadium and lead) from the sediment to algae. This is of concern due to predicted increases in storminess which are likely to increase sediment disturbance, with the likelihood that uptake of metals to diatoms will increase in the future. However, there were also indications of an antagonistic effect of temperature on disturbance, whilst disturbance increased bioavailability and uptake, increasing temperatures reduced uptake of some metals. This highlights the importance of considering the effects of multiple stressors in complex systems. Field studies showed that concentrations of some metals were related to their position on the mudflat whilst others were related to sampling date, indicating that there may be seasonal controls, such as to the presence of greater diatom biomass in spring and autumn, on metal uptake from the sediment. The research conducted has increased understanding of metal uptake to microphytobenthic diatoms from sediment and the influence they have in transferring metals from sediment to water, however the research also raises a number of new questions. For example, there appeared to be a link between sediment organic matter content and bioavailability of metals to diatoms, although the relative contribution of the diatoms, other algae, cyanobacteria and EPS to the sediment organic matter warrants further investigation. Furthermore, it has shown that the use of laboratory and mesocosm studies for this type of research can produce similar outcomes to those observed in the field but under more controlled and easily manipulated conditions, although field studies will continue to be vital in improving understanding of metals availability and transfer.