1980-1989 Dissertations (MU)
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This collection contains the dissertations submitted to the Graduate School by doctoral degree candidates at the University of Missouri in the years 1980-1989. These copies were digitized from print copies at MU Libraries.
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Item Factors influencing off-farm employment and land-use intensity in Korea : a simultaneous equations approach(University of Missouri--Columbia, 1984) Suh, Chong Hyuk; Osburn, Donald D.Major policy issues in Korea pertain to increases in domestic food production though intensive land use, and the improvement of farm household income by enhancing off-farm employment. This study examined the interrelationships between off-farm employment participation and land use cropping intensity. A farm survey of 3,333 farm households and secondary data were used. An integrated model of off-farm work activities and land-use intensity determination was developed. The statistical models used were a single equation regression model to estimate farm earnings function, and a simultaneous equations model contained one qualitative dependent variables to estimate a joint determination of off-farm employment and land-use cropping intensity functions. Two statistical estimation methods -- the two-stage least square (2SLS) analogue and the iterative nonlinear three-stage least square (NL3S) estimations -- were applied to estimate a simultaneous equations model. As measures of land-use intensity, the land equivalent ratio and the multiple cropping index were used. Major finding from the analyses are as follows: The results from the statistical estimation show that off-farm employment participation is negatively (statistically significant) related to farm earnings. In other words, trade-offs exist between farm earnings and off-farm employment. Also, a strong positive relationship between land-use cropping intensity and farm earnings were observed. Simultaneous equations estimations, compared to single equation estimation, provided a stronger negative interrelationship between land-use cropping intensity and off-farm employment participation. The simultaneous estimation results confirmed the consistency of the model developed for this study. In conclusion, two important policy issues presently pursued by Korean agriculture -- improvement of farm income through off-farm employment and increases in food production by intensive land use -- contain inherent goal conflicts between them. Potential policy measures that can minimize the conflicts are increased resources devoted to farmers education and farm mechanization activities.Item Effect of morphactins, TIBA and ethrel on the wood anatomy of Hibiscus lasiocarpus (Malvaceae)(University of Missouri--Columbia, 1982) Rodriguez, Kyrsis Raquel; Cumbie, Billy G.The morphactins IT-3456 and hydroxyfluorene carboxylic acid; TIBA and ethrel were found to affect the normal development of the wood of Hibiscus lasiocarpus Cav. In all cases the process of xylogenesis was affected throughout the stem. The reduction in size of the vessel elements caused by IT-3456, TIBA and ethrel was so dramatic that their width, at the treatment areas, is close to that of the fibers. The morphactin hydroxyfluorene carboxylic acid caused a complete inhibition of the vessel element production at the treatment point. This inhibition was temporary and vessel element production was restored after a period of time. Except for TIBA, all the substances tested affected the apical meristems of the stems. IT-3456 and ethrel had an inhibitory effect while hydroxyfluorene carboxylic acid had a promoting effect in the growth in length of the experimental stems. In all cases the development of non-especialized cells like those of the parenchyma tissue was disrupted. The main targets of these substances seem to be the apical and lateral meristems of the stem as well as, any other non-especialized cell present.Item The secretory-excretory system of the nematode Caenorhabditis elegans(University of Missouri--Columbia, 1983) Nelson, F. Kenneth; Riddle, Donald L.The secretory-excretory system of C. elegans, reconstructed from serial-section electron micrographs of larvae, is composed of four cells, whose nuclei lie on the ventral side of the pharynx and adjacent intestine. (1) The first of these, the pore cell, encloses the terminal one-third of the excretory duct which leads to an excretory pore at the ventral midline. This cell, a modified hypodermal cell, secretes the cuticle that lines the excretory duct within the pore cell. Laser ablation of this cell seriously disrupts osmoregulation of the nematode. (2) The second cell, the duct cell, surrounds the duct with a lamellar membrane from the origin of the excretory duct at the excretory sinus to the pore cell boundary. Laser ablation of the duct cell nucleus results in disruption of osmoregulation and prevents the secretion of the duct cuticle within the duct cell. (3) The third cell, the large H-shaped excretory cell, extends bilateral canals anteriorly and posteriorly nearly the entire length of the worm. The excretory sinus within the cell body joins the lumena of the canals with the origin of the duct. Like the pore and duct cell, the excretory cell is essential for osmoregulation. (4) The fourth cell, the binucleate, A-shaped gland cell extends bilateral processes anteriorly from cell bodies located just behind the pharynx. These processes are fused at the anterior tip of the cell, where the cell enters the circumpharyngeal nerve ring. The processes are also joined at the anterior edge of the excretory cell body, where the excretory cell and gland are joined to the duct cell at the origin of the duct. Secretory granules may be concentrated in the gland near this secretory-excretory junction. The dauer larva (a developmentally arrested third-stage larva) uniquely lacks secretory granules, and the gland cytoplasm is displaced by a labyrinth of large, transparent spaces. Exit from the dauer stage results in the return of active secretory morphology in fourth stage larvae. The gland cell is not involved in osmoregulation, in growth control, in fertility, in longevity, or dauer larva formation.Item Pheromone, food, and temperature : environmental cues controlling development of the Caenorhabditis elegans Dauer larva(University of Missouri--Columbia, 1983) Golden, James W.; Riddle, Donald L.Development of the Caenorhabditis elegans dauer larva is influenced by the relative strengths of at least three environmental cues: a pheromone, food, and temperature. The fatty acid like pheromone enhances dauer larva forma�tion and inhibits recovery, and its concentration apparently serves as a measure of the population density. A labile, hydrophillic food-signal has effects opposite those of the pheromone, and its concentration provides a measure of the food-supply. The cues have been used in the analysis of dauer larva formation and recovery of the wild-type strain N2 and mutants affected in dauer larva formation. Dauer-inducing conditions produce a prolongation of the second intermolt period and morphologically distinguishable second stage larvae, called L2d. Unlike L2 larvae, L2d larvae have the potential to form either L3 or dauer larvae, depending on the environmental cues. Worms become committed to non-dauer development around the LI molt when grown in the absence of exogenous pheromone. Commitment to dauer larva formation occurs just before the second molt, at which time a few worms complete development into dauer larvae even if transfered to fresh medium. Incubation temperatures above 20�C enhance wild-type dauer larva formation in the presence of added pheromone, and temperature-shift studies place the temperature-sensitive period around the first molt. Some dauer-constitutive mutants overrespond to the pheromone, and apparently enhance the expression of the wild-type temperature-sensitive process. Two temperature-sensitive dauer-constitutive alleles, daf-4(m72) and daf-7(m62), are suppressed by the amber suppressors up-7(st5), indicating they are nonsense alleles and presumably produce a nonfunctional, rather than temperature-sensitive, gene product.Item Identification, characterization and regulation of Type II estrogen receptors in cultured human pituitary cells(University of Missouri--Columbia, 1981) Carlo, Mayra; Wyche, James H.The presence of estradiol receptors in the cytosol and pellet fractions of homogenized 18-54, SF cells was investigated. Using the protamine sulfate precipitation assay we have demonstrated that these cells, like other cell lines, seem to lack type I estrogen receptors in the cytoplasm but that these are present in the pellet fraction. The cells have what we have called type II-like receptors in the cytoplasm and presumably in the nucleus. The type II receptors in the cytosol and pellet fraction of homogenized 18-54, SF cells seem to differ in binding parameters, specificity and, probably other characteristics. The cytosol receptor is most probably a protein or contains a protein moiety susceptible to proteolytic degradation. It also seems to have an SH-group essential for binding. The regulation of the type II-like receptors in the cytosol is most likely different and independent of the regulation of type I receptors. Both type II receptors may be involved in the regulation of prolactin secretion by steroids and steroid-related compounds.