Master of Science, Miami University, 2009, Botany

Plants respond to different qualities and quantities of light through photoreceptors, which lead to a cascade of genes being turned on and off. Phytochrome A is a photoreceptor that is active in plant development from seed germination to flowering and triggers the phytochrome A pathway. The SPA1 protein is specific to the phytochrome A pathway and is a negative regulator of phyA. By exposing plants to various light treatments, we found spa1 plants have enhanced positive phototropic responses of roots to red light. We also report that red and green light pulses interrupt phototropic responses of hypocotyls to blue light via SPA1. From these findings, we conclude that PHYA is responsible for positive phototropic responses of roots, and that the SPA1 protein is a key protein in crosstalk between photoreceptor pathways.

Committee: John Z. Kiss PhD (Advisor); Richard Moore PhD (Committee Member); Michael Vincent PhD (Committee Member) Subjects: Botany

Master of Science, University of Toledo, 2022, Biology (Ecology)

Atmospheric carbon dioxide (CO2) concentrations are increasing and may exceed 800 ppm by 2100. This is increasing global mean temperatures and the frequency and severity of heatwaves. Recently, it was shown for the first time that the combination of chronic warming and elevated carbon dioxide (eCO2) caused extreme upward bending during growth (i.e., hyponasty) of leaflets and leaf stems (petioles) in tomato (Solanum lycopersicum), which reduced growth. However, that study examined only two levels of CO2 (400, 700 ppm) and temperature (30, 37oC) at the young vegetative plant stage. Further, they did not investigate underlying mechanisms for this warming + eCO2-induced hyponasty, which is likely to involve the plant hormones auxin and ethylene, based on their role in thermal hyponasty. In this study, warming + eCO2 hyponasty was evaluated in tomato across a range of temperatures and CO2 concentrations, and at multiple life stages. Ethylene tomato mutants were examined to explore the potential role of these hormones in warming + eCO2 hyponasty. Lastly, other species were examined to test the hypothesis that warming + eCO2 hyponasty is restricted to compound-leaved species in this family. At eCO2 (800 ppm), petiole angle increased ca. linearly as temperature increased from 30-38oC. Under heat stress (HS, 38°C), petiole angle increased at all eCO2 concentrations compared to ambient (600/800/1000 vs. 400 ppm). All life stages examined (juvenile, pre-reproductive, and flowering) had increased petiole angle in leaves developed during warming + eCO2, such that most leaves exhibited hyponasty in juvenile plants but only young leaves did so in adults (previously fully-developed leaves were unaffected). Ethylene-insensitive (nr) and -constitutive (epi) mutants displayed similar changes in petiole angle with warming + eCO2 compared to the non-mutant reference (cv. Celebrity), indicating that ethylene is not a main component of the mechanism of this hyponastic response. (open full item for complete abstract)

Committee: Scott Heckathorn Dr. (Committee Chair); Heidi Appel Dr. (Committee Member); Jennifer Boldt Dr. (Committee Member) Subjects: Agriculture; Agronomy; Biology; Botany; Climate Change; Ecology; Environmental Science; Forestry; Morphology; Physiology; Plant Biology; Plant Sciences

Master of Science, Miami University, 2011, Botany

Roots of Arabidopsis thaliana grow toward gravity, positive gravitropism. In addition, these roots exhibit negative phototropism relative to blue light and positive phototropism relative to red light. Our studies investigated the importance of phytochromes, the red-light photoreceptors, for root and shoot gravitropism and phototropism. We used two transgenic lines, one which was deficient in phytochrome in the roots (M0062/UASBVR) and the other was deficient in phytochrome in the cotyledons (CAB3::pBVR). The transgenic lines were grown in either light or dark conditions to determine whether roots directly perceive light signals or if the signal is perceived in the shoot and then transmitted to the root. Kinetics of tropistic curvature and growth were assayed by standard methods or with a computer-based feedback system. We found that the perception of red light occurs directly in the root and that signaling also may occur from root to shoot in gravitropism.

Committee: John Kiss PhD (Advisor); Michael Vincent PhD (Committee Member); Martin Stevens PhD (Committee Member) Subjects: Biology; Botany; Molecular Biology; Plant Biology