<p> A new two-capillary absolute viscometer for the measurements of the viscosity of gases down to cryogenic temperatures and for moderate pressures up to 200 atm has been developed and described in this thesis.</p> <p> An experimental determination of the absolute viscosity of nitrogen at atmospheric pressure and in the temperature range 97.41-297.88°K is also reported. The maximum error of the smoothed data is believed to range from ±1% at highest temperatures to ±1.6% at the least favourable lowest temperatures.</p> <p> Data obtained in this work and those of previous workers have been correlated using integral equations postulated by Chapman-Enskog collision theory of dilute gases.</p> <p> Furthermore, viscosity measurements have been carried out for nitrogen at 42 and 84 atm and are presented in the thesis to confirm the applicability of the viscometer for high pressure work.</p> / Thesis / Master of Engineering (MEngr)

This thesis is an investigation of photoperiodic injury (PI) in tomato plants and practices to alleviate the problem. PI is a physiological disorder characterized by chlorosis and necrosis of leaves when plants are grown under either long photoperiods or non-24 h light/ dark cycles. Solanum lycopersicum L. (tomato) is particularly susceptible to PI. Our group has shown a correlation between PI and altered circadian expression patterns for the nitrate assimilatory enzymes nitrate reductase (NR) and nitrite reductase (NiR) in tomato, resulting in accumulation of the toxic metabolite nitrite, particularly at specific times of day (TOD) when the NiR/NR activity ratio is low. We hypothesized that accumulation of nitrite and PI can be alleviated by altering nitrate nutrition at specific times of day and the use of an air temperature differential. The tomato cultivars ‘Micro Tom’ (PI-tolerant) and ‘Basket Vee’ (PI-susceptible) were grown under various photoperiod regimes to determine: (1) if a positive correlation exists between PI and nitrite accumulation as determined by visual assessment, and chlorophyll and nitrite quantification; (2) if 24 h light affects the diel pattern of nitrate uptake in a way that favours PI through measurements of nitrate depletion; and (3) if PI can be alleviated by altering nitrate nutrition at two specific TOD when tomato is susceptible to nitrite accumulation. A positive correlation was found between nitrite accumulation and PI. Nitrate uptake experiments showed that the nitrate uptake rate per se is not responsible for PI in tomato, but maintenance of circadian nitrate uptake patterns even in 24 h light in combination with a loss of the circadian patterns for NR and NiR activities could contribute to PI. Nitrite accumulation and PI was decreased by utilizing a nutrient solution containing 25% total nitrogen at two specific 4 h periods in the day when tomato is susceptible to nitrite accumulation. We call this new technique TOD fertigation. Time-of-day fertigation in combination with a 6 oC temperature differential further reduced nitrite accumulation and PI. These findings showed the response of greenhouse tomatoes to supplemental lighting and the potential for increasing the photoperiod threshold for PI. / The Mexican Council for Science and Technology (CONACYT); The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)

Bacterial endophytes are the organisms that live inside the plant for a full or a part of their life cycle. Endophytic bacteria have captured the interest of agriculture industry due to their plant beneficial properties, such as synthesis of phytohormones, solubilization of soil nutrients, and alleviation of biotic and abiotic stresses. Several studies have reported that stress tolerant endophytic bacteria can work with a similar performance as non-stressed conditions when inoculated to the plants under stressed conditions. Combination of abiotic stresses such as salinity, drought and low nitrogen stress can have additive or agonistic effects on bacterial and plant growth, and their interactions. However, very few studies have reported the impact of combined stress on endophytic bacterial assisted plant growth promotion. Therefore, understanding the underlying mechanisms of endophytic bacterial assisted plant’s tolerance abiotic stresses may provide the means of better exploiting the beneficial abilities of endophytic bacteria in agricultural production. Thus, the aim of this thesis was to study the stress tolerance mechanisms, beneficial characteristics, and plant growth promotion characteristics of endophytic bacteria under individual and combined abiotic stresses. Transcriptome analysis of endophytic bacteria revealed that tolerance mechanisms to deal with one kind of stress is different than concurrent stresses. Salinity and drought stress largely modulated the genes involved in flagellar assembly and membrane transport, showing reduced motility under stress conditions to preserve the energy. Additionally, bacterial endophyte that can fix nitrogen was studied with maize plant growth promotion under drought and low nitrogen stress conditions. The results suggested that diazotrophic bacterial endophyte can promote plant growth under moderate individual and combined stress conditions. Plant growth promoting endophytic bacteria can be utilized as an efficient tool to increase crop production under individual and concurrent abiotic stresses.