Fluorescence (F), DCMU-enhanced fluorescence (F^DCMU) and a ratio of these two measurements (F ratio) were found to be useful indicators of light history but not physiological condition of natural phytoplankton assemblages. Changes in the fluorescence properties of unialgal continuous and batch cultures at different growth rates and following nutrient addition were observed only during nutrient starvation. Nutrient deficiency in Lake Ontario was not revealed either by seasonal patterns of fluorescence or by short term changes in the F ratio following nutrient additions. This result however is not conclusive evidence of nutrient sufficiency because of the insensitivity of the fluorescence ratio as an indicator of growth rate. The depression of F and F^DCMU observed in surface waters of Lake Ontario occurred during conditions of high light and low mixing rates. The result suggests that ''photoinhibition" of photosynthesis as measured by conventional primary productivity techniques, may occur in nature only under these particular conditions. A general relationship between temperature gradients or water column stability and the difference in fluorescence between 1 and 10 meters was observed. This relationship was due to both vertical structure in the assemblage and the physiological effect of light on fluorescence. Diurnal patterns of fluorescence were found to be due to the physiological effect of light on fluorescence rather than a circadian rhythm. The physiological effect was dependent on both the duration and intensity of exposure of the cells to light as well as the sensitivity of the assemblage to light. Differences were associated with seasonal changes in species composition with spring and winter populations exhibiting the greatest sensitivity. / Thesis / Master of Science (MSc)

This study has investigated the involvement of photosynthetic electron transport chain on the regulation of gene expression of methionine sulfoxide reductase (UfMSR) in the marine macroalga Ulva fasciata Delile.UfMSRA is from copper stress and UfMSRB ir from hypersalinity stress. UfMSRA is similar to Arabidopsis AtMSRA4 and UfMSRB is similar to AtMSRB1. UfMSRA is specific to the MetSO S-enantiomer and UfMSRB catalytically reduces the MetSO R-enantiomer. Both enzymes are required, since in the cell oxidation of Met residues at the sulfur atom results in a racemic mixture of the two stereoisomers. UfMSRA and UfMSRB transcripts were increased by white light, blue light and red light with the maximum at 1 h following a decline, but kept constant in the dark. The magnitude of UfMSRA and UfMSRB transcript increase showed a positive linear correlation to increasing light intensity from 0-1200 u mole¡Pm-2¡Ps-1. The treatment with linear electron transport chain inhibitors, hydroxylamine, 3-(3,4-dichlorophenyl) -1,1-dimethylurea (DCMU), 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) and stigmatellin, effectively inhibited PS II activity under 300 u mole¡Pm-2¡Ps-1 irradiance. DBMIB and stigmatellin can increase UfMSRA transcript that was reversed by 2,6-dichlorophenolindophenol (DCPIP), a PS I electron donor. It indicates that the block of electron transport of the downstream of cytochrome b6f indeuces UfMSRA gene expression. Hydroxylamine, DCMU and DBMIB decreased UfMSRB transcript that was not reversed by DCPIP while stigmatellin increased UfMSRB mRNA level, reflecting a role of reduced state with Qo site located at cytochrome b6f on the induction of UfMSRB gene expression. The cyclic electron transport chain inhibitors, antimycin A that inhibited photosynthetic electron transport, can inhibit the increase of UfMSRA and UfMSRB transcripts by irradiance. UfMSRA and UfMSRB gene expression were both modulated by cyclic electron transport chain and linear electron transport chain. These results reveal that photosynthetic electron transport chain modulates UfMSRA and UfMSRB gene expression by change its redox state.

The pathway of seawater ammonium assimilation and influence of light on amino acid synthesis remain unresolved in cnidarian symbioses. Labeled ammonium (10 μM 15NH4Cl) in seawater was used to trace the pathway of the incorporation into amino acids in host tissue, Zoanthus sp., and zooxanthellae, Symbiodinium microadriaticum. Freshly isolated zooxanthellae were exposed to 20 μM 15NH4Cl with coral homogenate to evaluate the role of host factors on amino acid synthesis. High performance liquid chromatography and mass spectrometry was used to measure percent labeling and concentrations of amino acids. In zooxanthellae, ammonium was assimilated into glutamine likely via glutamine synthetase and into glutamate via glutamine 2-oxoglutarate amidotransferase. Interrupting photosynthesis with DCMU did not inhibit glutamine and tryptophan synthesis however reduced the 15N-enrichment of glutamate, aspartate, and ornithine in zooxanthellae, as well as arginine, ornithine, and lysine in host tissue. Coral homogenate had little effect on the 15N-enrichment of glutamine, aspartate, and alanine in freshly isolated zooxanthellae. Evidence is presented to support the uptake of ammonium ions and data shows that glutamine and not glutamate is translocated to the coral host.

Chlamydomonas reinhardtii can utilize CO2 for autotrophic growth (HSM plus 5% CO2) or acetate for mixotrophic growth (TAP). This study was to elucidate the differential regulation of methionine sulfoxide reductase (MSR) gene expression between HSM plus 5% CO2 and TAP cultured cells, and also to determine the difference of gene expression in response to high light (1,000 £gE m-2 s-1). The role of photosynthetic electron transport (PET) in the regulation of MSR gene expression was also examined by the use of PET inhibitors. High light inhibited PSII activity (Fv/Fm and Fv'/Fm') of HSM plus 5% CO2 and TAP cultured cells., while the responses of CrMSR gene expression in mixotrophically grown cells were different from autotrophically grown cells, High light increased the expression of CrMSRA1, CrMSRA2, CrMSRA3, CrMSRA5, CrMSRB1.2, and CrMSRB2.1, but inhibited the expression of CrMSRA4 and CrMSRB2.2 in autotrophically grown cells. The expression of CrMSRA3, CrMSRA5, and CrMSRB2.1 in mixotrophically grown cells was increased by high light but that of CrMSRA1, CrMSRA4, and CrMSRB2.2 was inhbited. The number of MSR isoform that was up-regulated by high light was greater in autotrophically grown cell than that in mixotrophically grown cells. Using the PET inhibitors (3-(3,4-dichlorophenyl)-1,1- dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB)), most of the CrMSRA expression was regulated by reduced QA for autotrophically grown cells while reduced PQ was the main site for mixotrophically grown cells by high light. The expression of CrMSRB in autotrophically grown cells was mainy modulated by QA (-) or Cytb6f (-), while that was not affected by PET, except a role of Cytb6f (-) on the high light-induced CrMSRB2.2 expression. We fouind that CrMSRB gene expression in autotrophically grown cells was highly affected by PET but not for micotrophically grtown cells. The present result that H2O2 did not accumulate in autotrophically and mixotrophically grown cells suggests that H2O2 may be not involved in the regulation of high light regulation of CrMSR gene expression. The present study shows that the mRNA expression of CrMSR isoforms in Chlamydomonas was diffrerentially regulated between autotrophically and mixttrophically grown cells. The relationship between the utilization of different C source and CrMSR gene expression will be discussed.

Methionine sulfoxide reductase A (MSRA) and MSRB are responsible for the repairing of methionine-R-sulfoxide (Met-S-SO) and methionine-S-sulfoxide (Met-R-SO) back to me-thionine, respectively. Five MSRA isoforms and four MSRB isoforms are discovered in the unicellular green alga Chlamydomonas reinhardtii. Whether high light regulates CrMSR ex-pression via photosynthetic electron transport (PET) was examined. By checking the se-quence of PCR product of each isoform, quantitative real-time primers were designed for discrimination of isoform expression. Light ≥ 300 £gE m-2 s-1 and PET inhibitors inhibited PSII activity (Fv/Fm, Fv´/Fm´) and photosynthetic O2 evolution rate, particularly 1,000 £gE m-2 s-1, in which it did not recover after 3 h. A transfer to dark decreased CrMSRA2, CrMSRA3, CrMSRB1.1, CrMSRB1.2, CrMSRB2.1 mRNA levels but increased CrMSRA4 mRNA levels. When exposed to 50, 300, 600, or 1,000 £gE m-2 s-1, CrMSRA2, CrMSRA3, CrMSRA5, CrMSRB1.1, CrMSRB2.1 and CrMSRB2.2 mRNA levels increased as light ≥ 300 £gE m-2 s-1, and concomitantly CrMSRA4 mRNA level decreased. Changes in mRNA levels increased as light intensity increased. The treatment of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) in 1,000 £gE m-2 s-1 inhibited high light effect, and the treatment of 2,5-dibromo-3-methyl-6- isopropyl-p- benzoquinone (DBMIB) in 50 £gE m-2 s-1 increased CrMSRA3, CrMSRA5 and CrMSRB2.2 mRNA levels but decreased CrMSRA4 mRNA level. The application of phena-zine methosulfate (PMS), an electron donor to P700+ that promotes cyclic electron transport, in 300 £gE m-2 s-1 enhanced the increase of CrMSRA3 and CrMSRA5 mRNA levels by high light but inhibited the decrease of CrMSRA4 mRNA level, reflecting a role of cyclic PET. The above results let us to draw a conclusion that plastoquinone as reduced status mediates the expression of CrMSRA3, CrMSRA4, CrMSRA5 and CrMSRB2.2 by high light. The im-plication of linear electron transport and cyclic electron transport on the regulation of CrMSR gene expression will be discussed.We speculated that the high light up-regulation of CrMSR mRNA expression offers the resistance of Chlamydomonas to photooxidative stress.