A billion tons per year of genetically modified corn residues are soil incorporated having both direct and indirect effects on the belowground environment, soil carbon (C) sequestration, and nutrient cycling. If Bt genetic modification has non-target effects on corn stover structural/non-structural carbohydrate and nitrogen (N) concentrations, then the degradation rate of Bt-corn stover may be different than that of non-Bt isolines, possibly influencing soil C storage and N mineralization. Thus, this research focused primarily on the comparison of C and N mineralization of corn stover in soil as affected by Bt-trait, plant portion, water-availability and HFC-trait; and secondarily on the existence of Bt-related variations in the chemical structure of corn residues that might affect the degradation rate of stover in soil and consequently the soil C and N dynamics. A laboratory experiment was conducted under non-limiting N conditions with stover of Bt/non-Bt isogenic pairs of two varieties, a ?high fermentable corn? (HFC) line harvested at Snook, Texas and a non-HFC corn line harvested at the irrigated field of Snook and the non-irrigated field of College Station, Texas. The stover was partitioned into three plant portions, incorporated into a Weswood soil and incubated during 223 days. Results showed that the differences observed in the degradation in soil of Bt vs. non-Bt corn stover were dependent on environmental conditions (irrigated vs. non-irrigated settings) and hybrid variety (HFC vs. non-HFC hybrid lines). The structural composition of corn plants was affected by the Bt-trait, HFC-trait, irrigation and their interactions. Variations in the biomass fractions of the initial stover of Bt and non-Bt hybrids had minimum to non-impact on soil C and N concentrations measured at the end of the 223-day incubation period. Lignin concentration was affected by a Bt-trait*variety interaction. There were no significant differences in lignin concentration between non-Bt/Bt-corn derived stovers of the non-HFC variety irrespective of irrigation regime but Bt-hybrids of the HFC variety contained more than twice as much lignin as the non-Bt isogenic plants. The effects of higher lignin concentration on C mineralization rate appeared to be offset by an increased lignin degradability inherent in HFC-trait. Overall, results indicated that the cultivation of Bt-modified maize lines is not likely to have significant effects on soil C or N dynamics compared with the cropping of non-Bt hybrids.

Graduation date: 2003

Cadmium (Cd) is a toxic metal known to accumulate in and have adverse effects on the olfactory systems of fish. The objective of this project was to investigate the effect of cadmium on zebrafish larvae, specifically the effects on the olfactory system at cellular and functional levels. Zebrafish larvae (72 hours post fertilization) were exposed to sublethal concentrations of cadmium (0.5, 1, 5, and 10 µM) for 96 h. Whole-body cadmium accumulation during this exposure period as quantified using GFAAS (graphite furnace atomic absorption spectroscopy) was found to increase with both exposure length and concentration. Using a transgenic strain of hsp70/eGFP (heat shock protein 70/enhanced green fluorescent protein reporter gene) zebrafish, dose-dependent induction of the heat shock response was observed in the olfactory epithelium. Expression of hsp70/eGFP in the olfactory epithelium was a highly sensitive biomarker for the effects of cadmium in the olfactory system with a lowest observed effects concentration (LOEC) of 0.5 µM Cd. Strong induction of the transgenic reporter gene correlated closely with cell death (LOEC of 5 µM Cd) and histological alterations (LOEC of 1 µM Cd) in the olfactory epithelium of zebrafish larvae following cadmium exposure. Additionally, loss of sensory cilia from the surface of the olfactory epithelium was observed in larvae exposed to 5 and 10 µM Cd. Furthermore, behaviour tests to assess olfactory function revealed sensory deficits, likely due in part to the cadmium-induced degeneration of the olfactory epithelium (p<0.05 for 1 µM; p<0.001 for 5 and 10 µM Cd). <p>To determine if cadmium was entering the cells of the olfactory epithelium by acting as a calcium (Ca) antagonist, zebrafish larvae were co-exposed to 1, 5, or 10 µM Cd with 1 or 5 mM Ca for 96 h. Whole-body cadmium accumulation as quantified using ICP-MS (inductively coupled plasma mass spectrometry) was decreased in larvae co-exposed to cadmium and calcium. Additionally, induction of the heat shock response was reduced in the presence of increasing calcium co-treatment. These ameliorating effects of calcium were further revealed in cell death and histological analyses of the olfactory epithelium. Also, larvae co-exposed to cadmium and calcium exhibited greater olfactory sensory function compared to larvae exposed to cadmium only. Significant increases in aversion response were observed in larvae exposed to 5 µM Cd with 1 and 5 mM Ca (p<0.05). These results indicate that cadmium gains entry to the olfactory epithelium via calcium uptake systems, wherein it causes damage to the olfactory system and can lead to sensory impairment.

El Decabromodifenil èter (BDE-209) és un retardant de la flama àmpliament utilitzat i font de preocupació a causa de la toxicitat mostrada per altres Difenil Èters Polibromats (PBDEs). La presència de PBDEs en la llet materna fa preocupant la seva exposició durant el desenvolupament. Pensem que l’exposició primerenca a BDE-209 pot produir efectes a llarg termini i interactuar amb factors genètics, com el genotip de l’ApolipoproteinaE. Ratolins portadors de les diferents isoformeshumanes de l’ApoE foren tractats amb una dosi oral aguda de 0, 10 o 30 mg / kg de BDE-209 en el dia postnatal 10 i van ser avaluats per neurocomportament durant el desenvolupament, a l'edat adulta i la vellesa. L’exposició a BDE-209 indueix un retard en el desenvolupament físic i neuromotor i en la compactació de la mielina en els ratolins ApoE2, disminueix els nivells de tiroxina lliure en les femelles adultes i disminueix l'activitat en ratolins ApoE4. Els efectes més consistents durant tota la vida s'observen en ratolins ApoE3 i consisteixen en problemes d'aprenentatge als 4 mesos, i problemes d'aprenentatge i memòria i un augment de l'ansietat als 12 mesos. / Decabromodiphenyl Ether (BDE-209) is a flame retardant widely used and source of concern because ofthe toxicity showed by other Polibrominateddiphenyl ethers (PBDEs). The presenceof PBDEs in human’s breast milkmakes worrying its exposure during development. We hypothesised that an early exposure to BDE-209 can induce long-term impairments and interact with genetic factors, such as ApolipoproteinE genotype. Mice carrying the different Human ApoE isoforms treated with an acute oral dose of 0, 10 or 30 mg/kg of BDE-209 on postnatal day 10 were assessed for neurobehaviourduring development, in young adulthood and old age. BDE-209 exposure inducesadelay in physic and neuromotordevelopment and in myelin compaction in ApoE2 mice, decreases the levels of free thyroxin in adult femalesand decreases activity in ApoE4 mice. The most consistent effects across the lifespan are observed in ApoE3 mice and consist of impaired learning at 4 months, and impaired learning and memory and increased anxiety at 12 months.

Cadmium (Cd) is a toxic metal known to accumulate in and have adverse effects on the olfactory systems of fish. The objective of this project was to investigate the effect of cadmium on zebrafish larvae, specifically the effects on the olfactory system at cellular and functional levels. Zebrafish larvae (72 hours post fertilization) were exposed to sublethal concentrations of cadmium (0.5, 1, 5, and 10 µM) for 96 h. Whole-body cadmium accumulation during this exposure period as quantified using GFAAS (graphite furnace atomic absorption spectroscopy) was found to increase with both exposure length and concentration. Using a transgenic strain of hsp70/eGFP (heat shock protein 70/enhanced green fluorescent protein reporter gene) zebrafish, dose-dependent induction of the heat shock response was observed in the olfactory epithelium. Expression of hsp70/eGFP in the olfactory epithelium was a highly sensitive biomarker for the effects of cadmium in the olfactory system with a lowest observed effects concentration (LOEC) of 0.5 µM Cd. Strong induction of the transgenic reporter gene correlated closely with cell death (LOEC of 5 µM Cd) and histological alterations (LOEC of 1 µM Cd) in the olfactory epithelium of zebrafish larvae following cadmium exposure. Additionally, loss of sensory cilia from the surface of the olfactory epithelium was observed in larvae exposed to 5 and 10 µM Cd. Furthermore, behaviour tests to assess olfactory function revealed sensory deficits, likely due in part to the cadmium-induced degeneration of the olfactory epithelium (p<0.05 for 1 µM; p<0.001 for 5 and 10 µM Cd). <p>To determine if cadmium was entering the cells of the olfactory epithelium by acting as a calcium (Ca) antagonist, zebrafish larvae were co-exposed to 1, 5, or 10 µM Cd with 1 or 5 mM Ca for 96 h. Whole-body cadmium accumulation as quantified using ICP-MS (inductively coupled plasma mass spectrometry) was decreased in larvae co-exposed to cadmium and calcium. Additionally, induction of the heat shock response was reduced in the presence of increasing calcium co-treatment. These ameliorating effects of calcium were further revealed in cell death and histological analyses of the olfactory epithelium. Also, larvae co-exposed to cadmium and calcium exhibited greater olfactory sensory function compared to larvae exposed to cadmium only. Significant increases in aversion response were observed in larvae exposed to 5 µM Cd with 1 and 5 mM Ca (p<0.05). These results indicate that cadmium gains entry to the olfactory epithelium via calcium uptake systems, wherein it causes damage to the olfactory system and can lead to sensory impairment.

A billion tons per year of genetically modified corn residues are soil incorporated having both direct and indirect effects on the belowground environment, soil carbon (C) sequestration, and nutrient cycling. If Bt genetic modification has non-target effects on corn stover structural/non-structural carbohydrate and nitrogen (N) concentrations, then the degradation rate of Bt-corn stover may be different than that of non-Bt isolines, possibly influencing soil C storage and N mineralization. Thus, this research focused primarily on the comparison of C and N mineralization of corn stover in soil as affected by Bt-trait, plant portion, water-availability and HFC-trait; and secondarily on the existence of Bt-related variations in the chemical structure of corn residues that might affect the degradation rate of stover in soil and consequently the soil C and N dynamics. A laboratory experiment was conducted under non-limiting N conditions with stover of Bt/non-Bt isogenic pairs of two varieties, a ?high fermentable corn? (HFC) line harvested at Snook, Texas and a non-HFC corn line harvested at the irrigated field of Snook and the non-irrigated field of College Station, Texas. The stover was partitioned into three plant portions, incorporated into a Weswood soil and incubated during 223 days. Results showed that the differences observed in the degradation in soil of Bt vs. non-Bt corn stover were dependent on environmental conditions (irrigated vs. non-irrigated settings) and hybrid variety (HFC vs. non-HFC hybrid lines). The structural composition of corn plants was affected by the Bt-trait, HFC-trait, irrigation and their interactions. Variations in the biomass fractions of the initial stover of Bt and non-Bt hybrids had minimum to non-impact on soil C and N concentrations measured at the end of the 223-day incubation period. Lignin concentration was affected by a Bt-trait*variety interaction. There were no significant differences in lignin concentration between non-Bt/Bt-corn derived stovers of the non-HFC variety irrespective of irrigation regime but Bt-hybrids of the HFC variety contained more than twice as much lignin as the non-Bt isogenic plants. The effects of higher lignin concentration on C mineralization rate appeared to be offset by an increased lignin degradability inherent in HFC-trait. Overall, results indicated that the cultivation of Bt-modified maize lines is not likely to have significant effects on soil C or N dynamics compared with the cropping of non-Bt hybrids.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 160-187).

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 115-132).

Thesis (Ph. D.)--University of Chicago, Committee-on-Developmental Biology, 2002. / Includes bibliographical references. Also available on the Internet.

Thesis (M. Sc.)--York University, 1998. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 144-164). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ39236.