D. Tech. Biotechnology and Food Technology. / Assesses the symbiotic dependency of grain and shrub / tree legumes as well as shrub/tree legume species adaptation to different rainfall regimes within five agroecological zones in Botswana, leaves of the test species were sampled.

Mature microbial mats from sandy intertidal beaches of the Texas Gulf coast demonstrated substantial levels of nitrogenase activity. Two species of non-heterocystous cyanobacteria, a Hydrocoleum and a Microcoleus, dominated the upper green layer of mature mats. Subsurface layers of cyanobacteria, but not mature mats, appeared during dry seasons. These "proto-mats" contained almost exclusively Microcoleus and demonstrated neither nitrogenase activity nor detectable nitrogenase reductase (Fe-protein). Hydrocoleum, identified from its morphology and 16s rDNA, was isolated and cultivated as unialgal cultures. Similar diel patterns of nitrogenase activity and Fe-protein expression were found in intact mature mats and in isolated Hydrocoleum cultures. Primers and a probe specific for the Hydrocoleum nifH gene, along with q-rtPCR measurements, demonstrated similar levels, but slightly different patterns, of expression in intact mature mats and cultures of isolated Hydrocoleum. Increased levels of nifH transcripts and Fe-protein in Hydrocoleum cultures appeared before the end of the light period of a diel cycle, and the light period was required for nitrogenase activity in the subsequent dark period. Levels of nifH transcripts stayed very low and nitrogen fixation stopped when cultures were maintained under continuous darkness. The pattern of nitrogenase activity in Hydrocoleum cultures was not affected by elimination of ambient O₂, increasing or decreasing temperature in a range from 20 ˚C to 35 ˚C, or light intensity. However, the level of nitrogenase activity did vary with environmental conditions. Highest nitrogenase activities were observed when assays were conducted in an aerobic rather than an anaerobic environment, at 25 ˚C rather than a higher or lower temperature, and illuminated with bright (~ 900 [mu]E/m²s¹), rather than less intense light. Average levels of nifH transcripts were positively correlated with levels of nitrogenase activity. Isolated cultures of Hydrocoleum formed mat-like structures in undisturbed flasks, suggesting that Hydrocoleum may be an early colonizer of intertidal sand for mat formation. However, observations of subsurface proto-mats indicate that Microcoleus is more likely to serve as the foundation for cyanobacterial mats, with Hydrocoleum later providing structural integrity and nitrogen availability. A process of successional development of microbial mats from the South Texas Gulf Coast is hypothesized. / text

published_or_final_version / Surgery / Master / Master of Surgery

published_or_final_version / Orthopaedic Surgery / Master / Master of Philosophy

No description available.

No description available.

The agroforestry practice of establishing shelterbelts and/or windbreaks composed of tree and shrub species that include buffaloberry (Shepherdia argentea Nutt.), caragana (Caragana arborescens Lam.) and sea buckthorn (Hippophae rhamnoides L.) is widespread within Saskatchewan. Shelterbelts play major roles in reducing wind speed, trapping snow, improving land-use efficiency and increasing economic returns. However, the practice of alley cropping within Saskatchewan is not popular. Also, apart from the protective roles the tree species offer in shelterbelts, some species have atmospheric nitrogen (N2)-fixation capabilities through biological nitrogen fixation (BNF) that are potentially important. The simultaneous integration of trees and crops on the same land management unit may lead to competition between crops and trees for growth resources such as nutrients, soil moisture and incoming radiation, the latter leading to limited access of light for understory crops. Understanding the contributions of the trees in supplying nitrogen (N) through BNF and in modifying microclimatic conditions in the alleyways would generate information needed to know their impacts on yield and nutrition of associated crops. In order to assess the contribution of the tree species in supplying N and minimizing interspecific competition while maximizing the benefits of tree-based intercropping systems, the thesis quantified the BNF capabilities of each species under greenhouse conditions using 15N dilution techniques and assessed how much of the fixed N2 is transferred to associated triticale (Triticale hexaploide Lart.) and oats (Avena sativa L.) under field conditions. Growth and yield of oats was also studied by measuring photosynthetically active radiation (PAR) and soil moisture in a Manitoba maple (Acer negundo var. negundo L.) -oats alley cropping system at Indian Head, SK. The BNF results showed that each of the test species fixes a substantial amount of N and there was a high transfer of N to associated triticale and oats. Results from the interspecific interaction study also showed that soil moisture was the primary factor affecting oats yields followed by light, with the south-lying oat plants affected more than north-lying. It can be concluded that alley cropping systems can be a practical and beneficial agroforestry practice within Saskatchewan. However, the distance between tree rows should be wide enough to permit farm machinery operations.

No description available.

No description available.

In the N$ sb2$ fixing legume symbiosis, suboptimal root zone temperatures (RZTs) not only decrease N$ sb2$ fixation. but reduce the formation and development of nodules. The purpose of this thesis was to elucidate the mechanism by which suboptimal RZTs affect nodulation and nodule development in legumes, such as soybean (Glycine max (L.) Merr.) and to attempt to find ways to overcome this inhibition. Initial studies characterized the RZT response in soybean plants inoculated with Bradyrhizobium japonicum. In plants grown at RZTs from 25 to 17$ sp circ$C, the time between soybean inoculation with B. japonicum and the beginning of N$ sb2$ fixation increased by 2.5 days for every $ sp circ$C decrease, whereas below 17$ sp circ$C RZT each $ sp circ$C appeared to delay the onset of N$ sb2$ fixation by 7 days. RZTs less than 17$ sp circ$C strongly inhibited the nodulation process and, as a result also sharply decreased N$ sb2$ fixation per plant. The greater sensitivity below 17$ sp circ$C is due to events related to, or occurring before infection initiation. Coinoculation of soybean with B. japonicum and other microorganisms beneficial to legumes, either vesicular-arbuscular (VA) mycorrhizae or plant growth promoting rhizobacteria (PGPR), increased soybean nodulation and N$ sb2$ fixation, but these increases were temperature dependent. Vesicular-arbuscular mycorrhizal colonization had a negative effect on nodule establishment below 18.5$ sp circ$C RZT, but a positive one above this RZT. At each temperature tested some PGPR increased the amount of fixed N and number of nodules formed, whereas some decreased the level of these variables. The most stimulatory strain at each temperature was: 15$ sp circ$C-Serratia proteamaculans 1-102, 17.5$ sp circ$C - S. proteamaculans 1-102 and Aeromonas hydrophila P73, and 25$ sp circ$C - S. liquefaciens 2-68. / Because our research indicated that an event before infection thread initiation was most sensitive, and because the first known step in establishment of the symbiosis is production of a plant-to-bacterial signal molecules. I tested whether the poor nodulation at suboptimal RZTs was related to disruption of plant-to-bacterium signalling. Inocula bacteria were preincubated with genistein, a major isoflavonoid signal molecule in soybean. This shortened the period between inoculation and root hair curling, and hastened the onset of N$ sb2$ fixation under both controlled environment and field conditions. At 15 and 17.5$ sp circ$C RZTs, 20 and 15 $ mu$M genistein was found to reduce the inhibition of suboptimal RZTs, increase nodulation, and accelerate the onset of ${ rm N} sb2$ fixation. When applied to the plant rhizosphere in the field, genistein also reduced the inhibitory effects of cold spring soils on nodulation and N$ sb2$ fixation. Direct measurements of genistein accumulation in soybean roots indicated that, with decreasing RZTs, genistein accumulation decreased. B. japonicum USDA110 containing plasmid ZB977 with nodY-lacZ fusion genes incubated with genistein under different temperatures indicated that higher genistein concentrations and longer incubation times were required to activate the lacZ gene to a maximum level under low incubation temperature. Overall, these findings suggested that plant-to-bacteria signal molecules such as genistein may be an important limiting factor in the nodulation of legume plants at low RZT.