Click Here to download Dr. Grzymski's thesis dissertation. It is approximately 4.2 MB.
Abstract
The function of marine diatom plastids were examined at three levels of metabolic complexity: ecosystem, cellular and sub-cellular. Trophic transfer efficiencies of two size classes of phytoplankton: diatoms and the less suitable autotrophic food source, cryptophytes were examined. Decreased diatom abundances caused by increasing Antarctic temperatures are negatively affecting krill abundance and result in a doubling in the carbon biomass that is either remineralized in the surface water or exported to deeper water. At the cellular level, carbon fixation and photosystem II (PSII) efficiency were examined in low light adapted cultures of the marine diatom Thalassiosira pseudonana (3H) under monochromatic wavelengths of ultraviolet radiation. Maximum damage to the quantum yield for stable charge separations was found in the UVB (280-320nm) wavelengths without background PAR light while the damage under PAR was 30% less. Various fluorescent transients were measured and the results indicate localized damage most likely on the acceptor side of the photosystem II reaction center. However, dark adapted measurements of fluorescence transients with and without DCMU do not result in similar functions. A strong correlation was found between the weightings of the induction curves without DCMU and carbon fixation. This was due to a loss of electron transport from the reaction center to plastoquinone. At the sub-cellular level, plastid structure and function was examined in the benthic foraminifera Nonionella stella. I characterize and identify the chloroplasts sequestered in the foraminifer inhabiting sediments collected off California from a water depth of about 600 m. Two unique sequences of diatoms were found in all samples examined: a diatom 16S rDNA sequence resembling Skeletonema costatum was the most prevalent and a diatom sequence resembling Odontella sinensis was also abundant. Three hypotheses on the possible function of sequestered chloroplasts in the deep sea are presented. Our results suggest that the potential for photo or chemoautotrophy is low and instead the chloroplasts are used to meet the nitrogen requirements of the host. The organism and its metabolic adaptations are presented as a modern analog of protistan evolution and the evolution of nitrogen metabolism.