Soil salinity and heat stress are two major abiotic stresses affecting plant growth and yield. Transcription factors (TFs) are key regulators in stress responses. They link stress sensing with many tolerance mechanisms by translating stress signals into changes in gene expression that ultimately contribute to stress tolerance. The NAC (NAM, ATAF and CUC) TF family have been found to be involved in responses to biotic and abiotic stresses. In this PhD project, the role of NAC TFs in response to heat and salt stress was studied in the model system Arabidopsis thaliana (Arabidopsis), and in two agriculturally relevant species, Solanum lycopersicum (tomato) and Chenopodium quinoa (quinoa). Plants have the ability to acquire thermotolerance if they are pre-exposed to a mild, non-lethal high temperature. The maintenance of acquired thermotolerance for several days is known as thermomemory. Here we investigated the role of NAC TFs in thermotolerance. The expression profiles of 104 Arabidopsis NAC TFs were measured and compared between primed and unprimed plants. Some NACs with a distinctive expression pattern in response to thermopriming were selected for further phenotypic analysis. Knock-out (KO) mutants of the ATAF1 gene showed an enhanced thermomemory phenotype compared with wild type plants (WT) and from this work, the functions of the ATAF1 gene were studied further. RNAseq co-expression analyses of ATAF1 overexpressor and ataf1 KO plants found that ANAC055 expression was co-regulated with that of ATAF1. JUBGBRUNNEN1 (JUB1) is another NAC TF involved in responses to heat, drought and salinity. In this study, the role of AtJUB1 overexpression in salinity was investigated in tomato plants. AtJUB1 overexpression resulted in higher proline levels and improved maintenance of water content and biomass in AtJUB1-overexpressing plants grown hydroponically under salinity compared with WT plants. Quinoa has recently gained much attention because of its high nutritional value and high tolerance to several stresses including drought and salinity. NAC TFs are hypothesized to play a major role in quinoa’s tolerance to abiotic stresses. In this study, the NAC TFs family were identified and investigated in the genome of quinoa. 107 NAC TF genes were identified and their transcriptional responses to different stresses including salt, drought and heat were investigated.

No description available.

Unprecedented population losses of the staghorn coral, Acropora cervicornis, since the 1970s have been attributed primarily to disease. Although a positive linear relationship between disease prevalence and increased water temperature has been described, the pathogen(s) causing disease and whether they are spread through the water or vectors is still poorly understood. Additionally, an increase in disease outbreaks and severity has provided an urgent need to identify natural genotypic resistance to disease in Caribbean acroporids. Studies to date have explored a variety of pathogen transmission methods, but prior to this study, there has been no examination of differences among common techniques. I investigated pathogen transmission and resistance to development of the disease known as rapid-tissue loss (RTL) in 11 different genotypes by comparing two common transmission methods (direct contact vs. waterborne). Additionally, I investigated changes in tissue condition over a 9-day acclimation period to determine the potential effect of acclimation on disease susceptibility. Overall, disease was significantly higher in the direct contact treatment, though resulting disease varied greatly by genotype, with only one genotype appearing resistant to developing disease. Acclimation time influenced tissue condition with a significant decline in condition occurring from day zero to day two, but significant improvements in surface body wall parameters were observed from days two to nine. These results highlight the differences between disease transmission methods and demonstrate the importance of selecting an appropriate transmission method and acclimation period for future studies.

Long-term, repeated exposures to cold might lead to cold adaptation. The study examined, in a small homogeneous group of non-acclimatised men, the inter-individual response to a short-term, high-intensity cold acclimation regimen. In particular, six young (24 - 28 years), healthy men performed 5 daily, whole-body (immersed to the chest for up to 120-min) immersions in 14°C water, during which their thermo-effector responses were evaluated. The study also sought to determine whether, or to what extent, any thermoregulatory modifications induced by the repeated severe cold stress would be transferred to acute moderate cold stress immersions (i.e., “transfer” adaptation). Thus, a few days before and after the acclimation protocol, subjects’ thermoregulatory function was assessed during whole-body immersions in 21°C water. During all immersions, thermal (rectal and skin temperatures), cardiorespiratory (oxygen uptake, mean arterial pressure, heart rate) and perceptual (thermal sensation and comfort, pain, affective valence) responses were monitored. The 5-day cold acclimation regimen caused a hypothermic adaptation, which was characterised by: i) a reduction in the cold-induced elevation of endogenous heat production (i.e., oxygen uptake), which was mainly ascribed to a delay in the activation of shivering, ii) an attenuation in the cold-induced increase of arterial pressure and heart rate, and iii) the alleviation of thermal discomfort. Aside from the blunted pressor response, these thermo-adaptive modifications seemed to be transferrable during exposure to a moderate cold stimulus as well. Still, during both cold provocations, the thermoregulatory adjustments were described by a large inter-individual variability, regarding the direction and the magnitude of the response.

No description available.

No description available.

In this study, the biodegradation potential of MTBE in uncontaminated and previously contaminated aquifer sediments under aerobic conditions was investigated. Laboratory microcosms were constructed using aquifer samples collected from three different areas of a shallow gasoline-contaminated aquifer in eastern Fairfax Co., Va in the Atlantic Coastal Plain province. Uncontaminated aquifer samples were collected upgradient of the plume, and contaminated aquifer samples were collected in the source area and in an area downgradient of the source. Biodegradation of MTBE was observed in microcosms that contained previously contaminated aquifer sediments. More complete degradation was observed in aquifer sediments containing a low level of petroleum contamination than in heavily contaminated aquifer sediments. Biodegradation of MTBE appeared to be limited by a lack of oxygen in heavily contaminated soils. When degradation was discernible it appeared to follow a first order pattern with a rate constant (l) of between 0.037 and 0.066 d-1, following a lag period of 20 to 40 days. In microcosms containing lightly contaminated aquifer material, MTBE was respiked during active metabolism, and degradation occurred with no lag or acclimation period. Results indicated that little or no degradation occurred in the microcosms containing uncontaminated soil. The results of this research suggest that the availability and level of petroleum hydrocarbon compounds influence indigenous microorganisms capable of degrading MTBE. / Master of Science

Estrous synchronization (ES) protocols enhances profitability of beef cow-calf operations by improving percentage of cows pregnant early in the breeding season and increasing kg of calf weaned per cow exposed. Many factors, however, influence the fertility of cattle enrolled to ES protocols. The overall goal of this work was to determine the influences of estrus expression and timing of artificial insemination (AI), as well as temperament on fertility of Bos taurus beef females exposed to ES protocols. Multiparous cows (n = 1,676) were enrolled to the 7-d CO-Synch+ Controlled internal drug releasing device (CIDR) protocol and cows expressing estrus were inseminated. Cows not expressing estrus received a gonadotropin-releasing hormone injection and were either inseminated immediately or delayed by 8 hours. Pregnancy rates were greater for cows expressing estrus to the protocol. Delaying AI for 8 hours in cows that failed to express estrus did not improve pregnancy rates. The effects of temperament on fertility of beef heifers enrolled to the 7-d CO-Synch+CIDR protocol were investigated. Heifers (n = 297) had temperament assessed by chute score and exit velocity, and classified as adequate or excitable. Hair and blood were collected for cortisol evaluation. Pregnancy rates were greater for adequate temperament heifers. Circulating cortisol concentrations were greater for excitable heifers, and overall plasma and hair cortisol concentrations were reduced from the start of the protocol to the end. Heifers with adequate temperament have improved fertility and ES protocols acclimated heifers and reduced plasma and hair cortisol concentrations due to handling. / Master of Science / Infertility is a major issue that affects profitability of beef cow-calf producers. Estrous synchronization (ES) protocols are a tool that allow artificial insemination (AI) without estrus detection and increases the proportion of females pregnant at the start of the breeding season, providing a strategy to improve profitability. However, females enrolled in the ES protocol and that fail to express estrus have reduced pregnancy rates when compared to females expressing estrus. Furthermore, beef females with excitable temperament have reduced fertility when compared to females with adequate temperament. The effects of delaying insemination to 8 hours post injection of gonadotropin-releasing hormone for animals failing to express estrus during ES were determined in beef multiparous cows. Cows expressing estrus had greater pregnancy rates compared to cows not expressing estrus, and delayed insemination did not improve pregnancy rates. To determine the effects of temperament on fertility heifers were enrolled in an ES protocol and had temperament determined as adequate or excitable based on chute score and exit velocity. Hair and blood samples were collected for cortisol evaluation. Excitable heifers had reduced pregnancy rates and greater circulating cortisol concentrations, but hair cortisol did not differ between temperaments. Overall cortisol profiles indicate that heifers became acclimated to handling during ES protocol. Development of ES that maximizes estrus expression prior to AI and selection of cattle with adequated temperament can enhance profitability of cow-calf operations.

No description available.

Doctor of Philosophy / Department of Entomology / David C. Margolies and Yoonseong Park / Organisms are capable of sensing environmental conditions through diverse mechanisms. Transient receptor potential channels (TRPs) are a cation channel family that has been found to function in diverse sensing mechanisms. In this dissertation, I identified the function of several TRPs in thermosensing and mechanosensing in the red flour beetle, Tribolium castaneum. Candidate TRPs were chosen based on homology to TRPs found and studied in Drosophila melanogaster. To identify the function of candidate TRPs in T. castaneum, I suppressed the expression of target genes by RNA interference technique and investigated the phenotype of each treated beetle. Temperature is a major limiting environmental factor for organisms. I tested the function of candidate TRPs in thermotaxis (behavior) and thermal acclimation (physiology). Using bioinformatics approaches, I identified three candidate TRPs – painless, pyrexia, and trpA1 – involved in high temperature sensing. To test thermotactic behavior, I investigated beetle movement on a temperature arena with two separate temperature zones. Thermal acclimation was tested by pre-exposing beetles to either 42 °C for 10 min. When treated with double stranded RNA of TRPA1 (dstrpA1), the thermotactic response of beetles at 39 and 42 °C was reduced when compared to control groups. With pre-exposure at 42 °C, survivorship of dstrpA1-treated beetles significantly increased after one minute exposure at 52 °C compared to beetles that were not pre-exposed. With dspainless treatment, beetles showed lower response to thermal acclimation and lower long-term survivorship. Beetles treated with dspyrexia showed lower recovery after heat treatment without pre-exposure at 42 °C. To identify the function of candidate TRPs in mechanosensing, I evaluated dsRNA treated beetles for survival, walking behavior, and tonic immobility. Treatment with dsnompC and dstrpA5 resulted in failure in eclosion, causing 93 % mortality in both treatments. Survivors in dsnompC showed defects in elytra sclerotization. In dsnanchung and dsinactive treatments, adults showed abnormal walking behavior and reduced walking speed that were likely caused by defects of mechanosensing in folding of the joint between the femur and tibia. For tonic immobility, beetles with dsnanchung, dsinactive, dswaterwitch and dsick2 (insect cytokine 2) treatments showed increased sensitivity to mechanical stimulation leading to tonic immobility.