The sensitivitiy of several species of marine phytoplankton to copper was investigated. No specific trends were found with respect to any general differences between diatoms and dinoflagellates or between different sized cells. Further investigation using a single bioassay species, Nitzschia lonqissima, indicate it to be very sensitive to cupric ion activity. Several physiological systems appear to be affected to different degrees, with cell division being more affected than photosynthetic pigment production or ¹⁴C uptake. The activity of the enzyme nitrate reductase is greatly increased by the addition of low concentrations of copper. / Science, Faculty of / Zoology, Department of / Graduate

Mn was found to reduce the toxicity of Cu to the marine diatom Thalassiosira pseudonana (clone 3H) in the chemically well defined medium Aquil (Morel et al., 1979), verifying the results of Sunda and Huntsman (1983). A cation-exchange resin technique developed by Zorkin (1983) was modified for use in natural seawater samples to estimate the biologically active Cu and Mn. Seawater samples taken from the bottom waters of a local fjord were found to support better growth of the test organism than samples from shallow waters, although the concentration of the biologically active Cu as estimated by the resin technique was similar for samples collected from all depths. The biologically active Mn concentration was found to be higher in the bottom water samples, indicating that the bioassay organism was probably responding to the interaction between the ionic forms of Cu and Mn, rather than to changes in the biologically active Cu concentration. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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.

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Copper toxicity was investigated using the green alga, Selenastrum capricornutum. Two major areas were investigated: the forms of copper which are toxic to growth of the alga and factors that can change the concentration of free copper, Cu2+ (aq), in the growth medium during the logarithmic growth of the organism. This research has shown that S. capricornutum is sensitive to the free Copper ion, Cu 2+ (aq), irrespective of the total copper concentration.

A positive relationship between foliar copper levels and fruit firmness in apricots was established in the late 1980’s. A review of the literature and discussions with both national and international researchers led to research upon the influence of foliar applied copper on fruit quality. Studies were initiated using cherries, which in addition to being a soft fruit also suffer from rain induced fruit cracking. Results of initial studies suggested that the treatment should be applied to other fruit crops to determine if similar responses occur in these. To this end two further experiments were conducted on apples. As a result of this research, a practical means of reducing rain induced damage to cherries was developed. This finding has major ramifications for all cherry growing regions of the world. / Doctor of Philosophy (PhD)

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Magister Scientiae - MSc (Biodiversity and Conservation Biology) / Heavy metal accumulation in arable land as a result of mining activities, pesticides and fertilisers has become a global concern. Steinkopf and Concordia in the Northern Cape are well-known for subsistence farming, but just as well-known for the nearby copper mining industry. Very little research has been done on heavy metal toxicity in these areas, thus it was of importance to assess the wheat cultivars (Triticum aestivum) historically used in the study areas, to ensure the viability of wheat farming. The nine wheat cultivars screened were Flameks, Knoppies, Rooiwol, Rooigys, Yecoro Royo, Charchia, Witwol, Kariega and Losper. A comparative study was done by determining the concentration levels of Cu, Fe, Zn, Mn, K, Mg, Ca, Na, N and P in the roots and shoots of sensitive and tolerant wheat cultivars. It was established that Witwol and Rooigys were the most tolerant to these adverse conditions. Kariega and Rooiwol were most sensitive. Their tolerance was achieved by excluding copper from the roots and limiting the translocation of copper to the shoots. This trend to exclude copper uptake in Witwol and Rooigys, warrants further investigation on a molecular level to explain these adaptive mechanisms. / South Africa

The green alga, Selenastrum capricornutum Printz, was used in an algal bioassay to determine the toxic properties of copper in various natural lake waters of Oregon. Lake water was collected and brought back to the laboratory where it was treated with various copper concentrations and inoculated with a cell suspension of the test alga. Growth of the alga was determined by direct cell counts. The copper ion activity, pH, and absorbance of the test cultures were also determined. The growth of the alga was ·found to depend upon the water tested and also upon the copper concentration used.

Heavy metal accumulation in arable land as a result of mining activities, pesticides and fertilisers has become a global concern. Steinkopf and Concordia in the Northern Cape are well-known for subsistence farming, but just as well-known for the nearby copper mining industry. Very little research has been done on heavy metal toxicity in these areas, thus it was of importance to assess the wheat cultivars (Triticum aestivum) historically used in the study areas, to ensure the viability of wheat farming. The nine wheat cultivars screened were Flameks, Knoppies, Rooiwol, Rooigys, Yecoro Royo, Charchia, Witwol, Kariega and Losper. A comparative study was done by determining the concentration levels of Cu, Fe, Zn, Mn, K, Mg, Ca, Na, N and P in the roots and shoots of sensitive and tolerant wheat cultivars. It was established that Witwol and Rooigys were the most tolerant to these adverse conditions. Kariega and Rooiwol were most sensitive. Their tolerance was achieved by excluding copper from the roots and limiting the translocation of copper to the shoots. This trend to exclude copper uptake in Witwol and Rooigys, warrants further investigation on a molecular level to explain these adaptive mechanisms.