Grown for its distinctive foliage, Strobilanthes dyerianus is a popular bedding and container plant. A problem in production is that over-wintered stock plants often flower. Once the plant becomes reproductive, stem elongation slows and floral buds arise from every node, rendering the plants useless for propagation. The objectives of this research were to examine the effectiveness of manipulating environmental factors and the application of ethephon on preventing floral bud initiation, as well as determine optimal nitrogen rate for stock plant culture. The first experiment was performed in a glass greenhouse and ran 11 weeks, utilizing 8 h, 10 h, 12 h and a 4 h night interruption photoperiod treatments to determine critical photoperiod. None of the photoperiod treatments were significant for inhibiting flowering and there was a positive correlation between plant size and flowering. A second experiment was performed in growth chambers to create three photoperiods (8 h, 12 h and 16 h) with two temperature regimes (24C day/ 21C night and 17C day/ 14C night) for a total of six treatments. Neither photoperiod nor temperature inhibited bud initiation, and there was no correlation between plant size and flowering. The third experiment examined potential use of ethephon to maintain vegetative plants. Six rates of ethephon (0, 150, 300, 450, 600 or 750 mg·Lˉ¹) were applied at three frequencies (weekly, biweekly and monthly) over an eleven week period. Floral initiation was not totally inhibited, but flowering was highly correlated to plant size. Additionally, plant growth response to nitrogen was examined to determine the optimal rate for stock plant production. Plants were treated with 0, 100, 200, 300 or 400 mg·Lˉ¹ N from a 15 N – 2.2 P – 12.4 K fertilizer at each irrigation for eight weeks. There were no differences among plant quality ratings for plants receiving 100, 200, 300 or 400 mg·Lˉ¹ N, and plants grown with 200 mg·Lˉ¹ N had the largest leaf area and shoot dry weight. / Master of Science

The gaseous plant hormone ethylene is a small molecule that regulates developmental change. Research was conducted in three areas: sensitivity, synthesis, and alterations to synthesis. Vegetative pea plants were more sensitive than radish plants to atmospheric ethylene. Light intensity did not affect ethylene sensitivity. Ethylene synthesis rates were measured for unstressed cotton, corn, soybean, and tomato plants. The per-plant ethylene synthesis rate ranged from 0.1-80 pmol plant-1 s-1. However, when normalized to net photosynthetic rate, this range was 1-4 µmol of ethylene synthesis per mol of CO2 uptake. Diurnal cycles in ethylene synthesis were present in all crops studied. These cycles were disrupted by drought stress and were attenuated when synthesis rates underwent large changes. Drought stress decreased synthesis in cotton. Flooded corn and soybean had increased synthesis. Blocked perception had no effect on ethylene synthesis or net photosynthetic rate in healthy unstressed plants.

Catalysts consisting of silver on α-Al₂O₃, α-SiC, and β-SiC supports were synthesized and tested for catalytic performance in the gas-phase direct oxidation of ethylene to ethylene oxide. For this study, which used no promoters, ethylene oxidation selectivity of SiC-supported catalysts ranged from 10 to 60% and conversion from 0-4.5%. Silicon carbide supported catalysts exhibited poor performance except for a surface-modified β-SiC-supported catalyst, which demonstrated conversion and selectivity similar to that of an α-Al₂O₃-supported catalyst. This Ag/β-SiC catalyst was further investigated with a kinetic study, and the reaction orders were found to be 0.18 with respect to ethylene and 0.34 with respect to oxygen. The kinetic results were consistent with Langmuir-Hinshelwood rate expressions developed from single-site and dual-site reaction mechanisms. Gold nanoparticles on titanium oxide and titania-silica supports are active for the formation of propylene oxide by the oxidation of propylene with hydrogen and oxygen mixtures. This study investigates the effect of cyanide treatment on gold supported on titanosilicate zeolite supports (Au/TS-1). Catalysts treated with weak solutions of sodium cyanide resulted in preferential removal of small gold particles, while catalysts treated with strong solutions resulted in dissolution of the gold and re-precipitation as gold (+1) cyanide. X-ray absorption spectroscopy demonstrated that catalysts which produce propylene oxide in the presence of hydrogen and oxygen mixtures had supported gold (+3) oxide nanoparticles of 3 nm size after synthesis, which were reduced to gold metal at reaction conditions. Samples treated with strong solutions of sodium cyanide resulted in supported gold (+1) cyanide particles of large size, 9-11 nm. These particles did not produce propylene oxide but, surprisingly, showed high selectivity toward propylene hydrogenation. Increasing gold (+1) cyanide particle size resulted in a decrease in hydrogenation activity. TS-1 and Au/TS-1 surfaces were studied with laser Raman spectroscopy. Surface fluorescence was substantially reduced with a low-temperature ozone treatment, allowing observation of titanosilicate framework bands. Hydrocarbon vibrations are observed for TS-1 and Au/TS-1 under propylene. Density functional theory models indicated that propylene adsorbed to a metal site along the Ï bond would show a Raman spectrum very similar to gas-phase propylene except for out-of-plane C-H vibrations, which would be moved to higher energy. This adsorption spectrum, with out-of-plane vibrations shifted to higher energy, was observed for both TS-1 and Au/TS-1. Langmuir adsorption isotherms were generated for both TS-1 and Au/TS-1, and a scaling factor derived from propylene uptake experiments allowed these isotherms to be scaled to propylene coverage of titanium. / Ph. D.

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

published_or_final_version / Botany / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

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