Browsing by Subject "Growth (Plants)"
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Item Age Studies in the Rhizome of Ephedra Coryi(Texas Tech University, 1950-08) McLean, John DavidNot Available.Item Branch Abscission in the Joint-Fir, Ephedra(Texas Tech University, 1952-08) Cumbie, Billy GlennNot Available.Item Functional analyses of two arabidopsis apyrases(2007-12) Wu, Jian, 1975-; Roux, Stanley J.ATP can serve as a signal molecule in the extracellular space to regulate biological processes and physiological effects in plant and animal cells. In mammalian cells, the level of extracellular ATP (eATP) is regulated by ectoapyrases, which can hydrolyze extracellular ATP to ADP and ADP to AMP. In this dissertation, I describe the important role of two Arabidopsis apyrases in the regulation of plant growth. Seven apyrases have been identified in Arabidopsis thaliana. The genes for two of these seven apyrases, APY1 and APY2, which have high sequence similarity, were cloned and characterized previously. The function of APY1 and APY2 was analyzed by T-DNA insertional mutant lines. The double knockout (DKO) apyrase pollen displayed a complete block of pollen germination, which implicated this step as the cause of the lethality of apyrase double knockout mutants. The vast majority of the mutant pollen grains were identical to wild-type in their nuclear state, and were viable as assayed by metabolic activity and plasma membrane integrity. Pollen tube elongation was inhibited by suppression of apyrase activity using anti-apyrase antibodies or by chemical inhibitors of apyrases. Etiolated hypocotyls overexpressing APY1 (with expression driven by a constitutive Cauliflower Mosaic Virus (CaMV) 35S promoter) exhibited faster growth rates compared to wild-type plants. Because of the lethality of apy1apy2 double mutants, RNA interference (RNAi) was performed as an alternative approach to posttranscriptionally silence the expression of apyrases. The suppression of apyrases in the RNAi lines resulted in a dwarf phenotype in overall vegetative growth and dramatically reduced growth in primary root and etiolated hypocotyls. In addition, the RNAi mutant plants lacked a well-defined meristematic zone and had a greatly reduced elongation zone in the primary root. Previously, promoter-GUS fusions showed that high expression of apyrase was associated with areas of rapid growth and regions with high auxin levels. Abnormal auxin accumulation was found in the proximal regions of the primary roots of RNAi mutant plants, which demonstrated that the absence of apyrase results in disrupted auxin distribution. Other phenotypes in RNAi mutant plants, such as less lateral root formation and more adventitious roots, could also be associated with abnormal auxin distribution. The investigation of the subcellular localization of apyrases showed that some fraction of apyrase was localized on cell periphery. These results suggest that the expression of APY1 and APY2 is essential for plant growth. They favor the hypothesis that Arabidopsis apyrases, like their homologs in animals, control the levels of ATP in the extracelluar space, and this control allows them to act as key regulators in growth.Item Influence of biosolids application on growth, nitrogen uptake, and photosynthesis of two desert grasses(Texas Tech University, 1999-12) Mata-Gonzalez, RicardoThis research is an evaluation of the effects of different rates and dates of biosolids application, as well as irrigation levels on biomass production, nitrogen absorption, and gas exchange characteristics of blue grama {Bouteloua gracilis) and tobosagrass {Hilaria mutica) in the Chihuahuan Desert, Individuals of blue grama and tobosagrass were transplanted into pots and grown under greenhouse conditions, Biosolids were applied in March (spring application) or Jime (summer application) at rates of 0, 7, 18, 34, and 90 dry Mg ha"'. Plants were irrigated at 40 or 80% soil field capacity. Treatments were combined in a factorial experiment and plants were arranged in a completely randomized block design. Application of biosolids produced an increase in available soil nitrogen, which favored an increase in shoot biomass of blue grama and tobosagrass. As biosolids rates and irrigation levels increased, biomass allocation increased in the shoots of the grasses. As biosolids rates and irrigation levels decreased, biomass allocation to the roots increased. Spring application of biosolids promoted greater soil nitrogen availability and higher plant growth than summer application of biosolids. Biosolids promoted higher nitrogen uptake and higher nitrogen concentrations in the shoots. Higher plant nitrogen concentrations were particularly favored by biosolids application when irrigation was not a limiting factor. Plant nitrogen concentrations were not strongly correlated with photosynthetic rates in both species. Leaf area, nitrogen concentrations, and photosynthesis rates in tobosagrass irrigated at 80% field capacity increased as biosolids rates increased. Increasing rates of biosolids in tobosagrass under the low irrigation level and in blue grama irrespective of irrigation level produced increases in leaf area, which corresponded with decreases in stomatal conductance and photosynthetic rates. Except for tobosagrass at high levels of irrigation, blue grama and tobosagrass seemed to have a mechanism of stomatal regulation to avoid excessive water loss in response to increments in leaf area.Item Influence of Ethrel on Phenological Development in Mesquite(Texas Tech University, 1972-12) Parsons, David LNot Available.Item Ionic balance and transpiration rates in Atriplex halimus L(Texas Tech University, 1973-12) Miller, Don RayMissingItem Localization of glutathione-s-transferase and its effect on seedling development(Texas Tech University, 1998-12) Lodhi, Sundus AminaPlants have evolved various defense mechanisms that include antioxidants (easily oxidizable compounds of small molecular weight) and antioxidant enzymes to combat the effects of reactive oxygen species produced by abiotic and biotic stress. One such enzyme family is glutathione-S-transferase (GST). These enzymes detoxify various electrophilic and hydrophobic compounds via conjugation to the thiol group of glutathione (GSH), an antioxidant molecule that is abundantly present in plant cells. Tobacco plants transformed with NtI07, a cDNA clone that encodes a GST with glutathione peroxidase activity, have been shown to have increased tolerance to salt and temperature stress, as well as to have increased levels of oxidized glutathione (Roxas et al., 1997). Although GST has been established as an effective enzyme to protect seedlings under stressful conditions, exactly how the plant system is affected remains to be completely understood. We have attempted to examine the effects of glutathione on seedling growth by using the specific glutathione synthesis inhibitor, buthionine sulfoximine (BSO). Results indicated that glutathione is required for normal seedling growth, and seedlings treated with BSO had higher lipid peroxidation levels than controls. Although we observed that exogenous glutathione also had an inhibitory effect on growth, seedlings treated with glutathione did not show higher levels of lipid peroxidation. Seed storage protein mobilization patterns in GST-overexpressing and wildtype seedlings have also been investigated under normal and stress conditions. We found that GST-overexpressing seedlings mobilized their storage proteins more slowly than did wildtype under normal conditions, however the mobilization in the transgenic seedlings was less affected under salt stress than it was in wildtype. Knowledge about the localized activity of GST could also help elucidate the mechanism of stress resistance. We used polyclonal antibodies raised against the protein to localize GST in two-week old tobacco seedlings and found the primary localization to be in the nucleus of both transgenic and wildtype seedlings, indicating that GST may be involved in protection against DNA damage.Item Relation of soil moisture to growth responses in apple trees(Texas Tech University, 1941-05) Elle, George ONot availableItem Seeded bermudagrass establishment using subsurface drip irrigation(Texas Tech University, 2003-08) Weeaks, Justin DThroughout most of the .Southwest water is becoming limited. Innovative methods to conserve water loss during irrigation arc being evaluated and implemented in many parts of the U.S. No research to date has indicated whether seeded bermudagrass can be established by using subsurface drip irrigation (.SDI). In two experiments, seeded bemiudagrass was successfully established using SDI. Treatments consisted of tubing spaced at 30, 46, and 61 cm. Emitter spacing was equal to distance between lateral lines. The control treatment consisted of pop-up sprinklers. Salinity accumulation is a concern when irrigating turfgrass in areas of poor water quality and low annual rainfall. Salinity accumulation was visible at the soil surface during establishment in 2001, but turfgrass showed no visible signs of stress due to salinity. Salinity accumulation was greater in most months at the 0-15 cm depth in both years compared to the 15-30 cm depth. In establishment periods with significant rainfall, salinity accumulation is still possible but not seen at the soil surface in 2002. This research documents the ability to successfully establish seeded bermudagrass using SDI. Full turfgrass coverage (> 90%) for the control plots in 2001 was around 8.5 weeks and the SDI treatments had complete coverage in 10 weeks. Turfgrass coverage for all treatments in 2002 was 9 weeks. Experiment II had a slightly faster establishment rate due to greater rainfall and different soil characteristics than that of Experiment I. Root count and depth of roots for both years showed roots to 61 cm depth in all treatments. A general trend of higher salinity accumulation midpoint of tubing was seen in Experiments I and II. However, after significant rainfall, salinity accumulation returned to concentrations comparable to initial soil salinity in both years. This is important because roots are finding water below the SDI tubing, which was buried at IS cm. Root number in both years was sufficient to provide a healthy turfgrass. Subsurface drip irrigation is a successful method of establishing seeded bermudagrass.Item The Effects of Certain Plant Growth Stimulants as Seed Treatments on the Germination and Yield of Cotton and a Grain Sorghum(Texas Tech University, 1944-07) Ayres, Cecil INot Available.Item The effects of changing water availability on the photosynthetic response of plants in the sotol-grasslands of Big Bend National Park, Texas(Texas Tech University, 2003-08) Walker, Erin MThe Hadley Climate Model 11 predicts that Big Bend National Park will receive a 25% increase in both summer and winter rainfall over the next 100 years and that seasonal rainfall patterns will shift from frequent, small storm events to fewer, large storm events. The physiological responses of sotol {Dasylirion leiophyllum) and sideoats grama (Bouteloua curtipendula) to future predicted rainfall patterns were examined over the summer of 2002 through the winter of 2003 in the sotol-grasslands of the Pine Canyon Watershed in Big Bend National Park. Stomatal conductance and photosynthesis were measured for plants that received a 25% increase in seasonal precipitation in either the summer, winter, both the summer and winter, or that received no increase in seasonal rainfall. Stomatal conductance and photosynthesis were also measured for plants that received small, frequent rainfall pulses, rainfall pulses of moderate size and frequency, and large, infrequent rainfall pulses. The 25% increase in seasonal rainfall had no effect on stomatal conductance and photosynthesis for either D. leiophyllum or B. curtipendula, but manipulating rainfall pulses size and frequency did affect the physiological response of the two species. The increase in stomatal conductance and photosynthesis for D. leiophyllum when it received larger, less frequent rainfall pulses, and the favorable response of 5. curtipendula to rainfall pulses of moderate size and frequency suggests that the response of both species is dependent on their rooting habit. Because of its shallow roots, B. curtipendula relied on numerous small pulses to maintain soil water availability in the upper-most soil layers, whereas D. leiophyllum required larger pulses that percolate into its deeper root zone. These results suggest that both species will have a favorable response to the future rainfall patterns predicted by the Hadley Climate Model II.Item The Origin and Development of the Diaphragm at the Base of the internode of Ephedra Coryi(Texas Tech University, 1950-08) Widmoyer, Fred BNot Available.Item Vascular differentiation in embryos and seedlings(Texas Tech University, 1970-08) Mathews, Robert EldonNot availableItem Weed management with the computer-based Herbicide Application Decision Support System (HADSS) program(Texas Tech University, 2001-05) Lyon, Leanna L.Field experiments were initiated in 1999 and continued in 2000 to evaluate the Cotton Herbicide Application Decision Support System (HADSS®) program in Texas Southern High Plains cotton production. Weed management systems in the irrigated experiment were evaluated in a natural infestation of Palmer amaranth (Amaranthus palmeri S. Wats) and devil's-claw [Proboscidea louisianica (Mill.) Thellung], while the dryland experiment had Palmer amaranth, devil's-claw, and silverieaf nightshade {Solanum elaeagnifolium Cav.). Weed management systems evaluated were: (1) a preplant incorporated (PPI herbicide followed by (fb) postemergence HADSS® recommendations (PPI fb POST HADSS®); (2) postemergence HADSS® recommendations alone (POST HADSS®); and (3) Texas Agricultural Experiment Station (TAES) recommendations for the Texas Southern High Plains. All weed management systems were evaluated in glyphosate [A/-(phosphonomethyl) lycine]-tolerant, bromoxynil 3,5-dibromo-4-hydroxybenzonitrile)-tolerant, and conventional cotton varieties and each system was compared to an untreated and weed-free check in each variety. Weed control was evaluated approximately two weeks after each treatment and at harvest and cotton lint yields and net returns over weed control costs were determined for each weed management system.