Browsing by Subject "Plants -- Effect of stress on"
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Item Carbon and nitrogen assimilation during development of sorghum as related to genotype and water stress(Texas Tech University, 1985-05) Harden, Margarette LWater stress is a major deterrent of grain yield in much of the Great Plains and the world. Grain sorghum is more drought tolerant than other cereals and is grown on vast areas in West Texas. For sorghum to become a more important feed grain crop, then genotypes that are more water efficient and water stress tolerant must be developed. The purpose of this study was to determine the relative contribution of both carbon and nitrogen assimilated prior to flowering to the grain filling process as affected by water stress and genotypic differences. Sorghum genotypes differing in degree of leaf senescence during grain filling were grown in field studies with and without irrigation. At flowering the average sorghum plant had accumulated 63% and 70% of the total dry matter (DM) and nitrogen (N), respectively, of that present at physiological maturity. For the average sorghum plant, 15% and 40% of final grain DM and N, respectively, were due to reallocation from assimilates present at flowering. Significant differences in the assimilation and reallocation of DM and N in the sorghum plants occurred due to water stress and genotype. All water stressed plants relied more heavily on DM and N accumulated by flowering in leaves and stalks to fill the grain than nonstressed plants indicating the severe effect of stress on both photosynthesis and protein synthesis. Both genotypes used existing DM and N present at flowering in addition to absorbing more during grain filling. The senescent plants relied more heavily on reallocation of assimilates from stalks and leaves acquired by flowering to fill the grain than did the nonsenescent plants. Findings from this study should aid in understanding the effects of water stress and genotype selection upon the use of net assimilation and remobilization of DM and N in the grain filling process. The use of established reserves by the grain sorghum plant could be an important mechanism to allow plants to mature if no detrimental effects due to stalk or leaf remobilization occur.Item Characterization of intraspecific and interspecific populations of cotton and common cocklebur grown under two water regimes(Texas Tech University, 1985-12) Wells, Jerry WayneNot availableItem Development and fecundity of the southwestern corn borer (Lepidoptera, Pyralidae) as affected by plant water stress and a secondary host(Texas Tech University, 1985-12) Aslam, MuhammadNot availableItem Development of cotton callus initiation medium and in vitro screening for osmotic stress tolerance(Texas Tech University, 1987-05) Zimmerman, Thomas WAsceptic excised seed hypocotyls of the Gossypium hirsutum L. varieties Acala 1517-75, Coker 500, Dunn 120, Paymaster 303, and TMl, and the exotic cotton lines, Tl, T25, and T133, were cultured for 24 days on six media and two gelling agents, Difco bacto agar and Kelco Gelrite. Significantly more callus was initiated on media solidified with Gelrite than with agar. The Linsmaier and Skoog medium (21) supplimented with 30 g/1 glucose, 0.1 mg/1 BA, and 0.1 mg/1 2,4-D supported significantly more callus production than the other five media. Exotic cottons, representing the seven races, were subjected to polyethylene glycol (PEG) induced osmotic stress in vitro in modified Linsmaier and Skoog (21) medium. The PEG levels were 0, 10, 20, and 30% w/v representing osmotic stresses of -5, -10, -16, and -24 bars respectively- The rate of dry matter accumulation, measured as dry cell weight (DCW), varied among cotton lines at each PEG level. The differences in density, DCW divided by packed cell volume, among the cotton cell lines at the stress levels indicate osmotic adjustment by the cells.Item Establishment and stress tolerance of buffalograss(Texas Tech University, 1995-12) Gaitan-Gaitan, FernandoBuffalograss [Buchloe dactyloides (Nutt.) Engelm.j is a well adapted species and one of the most drought tolerant grasses native to the semi-arid Southern Great Plains. Successful establishment of buffalograss is often limited by date of planting, seeding rate and type of seed. Buffalograss response to drought stress is to enter dormancy with very rapid regrowth when water becomes available. Characterization of other phenotypic responses to drought have not been established due to the lack of a suitable drought stress tolerance test. This dissertation presents the results of several studies conducted at the Texas Tech Plant Laboratory in Lubbock, Texas during three years to determine the optimal planting dates as well as seeding rates and type of seed to use. A modified tray system was designed to test buffalograss seedlings at two drought stress levels. Results indicated that when the cultivars 'Comanche' and Texoka' were used, optimal dates to obtain turfs with good stand density and quality are from mid May to mid July. Caryopses always produced higher stand establishment two and four weeks after planting. Experiments conducted to determine the optimal seeding rates and type of seed using 'Comanche' buffalograss indicated that rates of 1125 to 1875 caryopses m^"^ gave optimum stand establishment and turf quality. Caryopses had a faster emergence and had less seedling mortality than burrs. However, final density and turf quality were not affected by type of seed and planting rate . A test to assess the drought tolerance of buffalograss seedlings was designed modifying a PEG-based tray system used to measure drought tolerance in forage grasses. The modified test uses variable day/night temperatures and an open container to allow constant air movement at leaf level. After tests were performed on over 1000 seedlings in each of four populations, no significant differences between drought stress levels or populations were found. Seedling survival ranged from 0.6 to 1.5 percent measured after plants were rewatered. The system proved to be useful for buffalograss seedling screening with adequate calibration for type of soil used and chamber conditions.Item Genotypic variability for rate and duration of grain fill in sorghum (Sorghum bicolor [L.] Moench) grown under two levels of water availability(Texas Tech University, 1983-06) Onwuka, Sebastine ObiNot availableItem Growth and development of cotton when released from osmotic stress(Texas Tech University, 1980-08) Prien, Samuel D.Not availableItem Oxidative stress responses in transgenic cotton that overexpresses superoxide dismutase(Texas Tech University, 1995-08) Payton, Paxton R.Transgenic cotton plants that express a chimeric gene encoding chloroplast-localized Mn superoxide dismutase (Chi MnSOD) from tobacco have been analyzed to determine whether they exhibit improved resistance to oxidative stress. The Chi MnSOD activity for the transgenic plants was several fold greater than that for wild-type plants as deduced from non-denaturing PAGE, and the total SOD activity was three-fold greater according to spectrophotometric enzyme assays. Also, transgenic plants exhibited ~30% greater ascorbate peroxidase activity and ~20% greater glutathione reductase activity. The immediate recovery of photosynthesis for attached leaves for the Chi MnSOD transgenic line K 10 exposed to 4°C and 1700 µmol/m^2/s was slightly better than that for wild-type leaves, especially after a 35 min exposure (significant to 0.05%). However, the recovery of photosynthesis for longer exposure times was comparable for Chi MnSOD transgenic and wild-type plants, including exposures of leaf discs in the lab to 1200 µmol/m^2/s and 7°C for 1 to 3 h. Resistance to light-mediated, paraquat-induced cellular damage was also slightly better for transgenic plants, but primarily at 0.3 µM paraquat. The oxidized/reduced ascorbate in unstressed, transgenic plants was similar to that in wild-type plants exposed for 1 h to high light and 8°C. While this stress nearly doubled the total glutathione and the percentage oxidized in wild-type plants, there was no effect of stress on these parameters in Chi MnSOD plants. However, their pre-stress levels were similar to those for stressed wild-type leaves. The activation state of stromal fructose 1,6-bisphosphatase (FBPase) was used as an indicator of the oxidative state of the chloroplast. The enzyme in wild-type and transgenic plants deactivated similarly following severe chilling stress (4°C and 1700 µmol/m^2/s). However, under milder stress conditions (10°C and 1200 |jmol/m^/s for 10 min), the activation state of FBPase in MnSOD plants was unaffected while it was significantly decreased in wild-type C-312 plants. It appears that the increase in MnSOD activity in chloroplasts is enough to provide some resistance to oxidative stress caused by chilling in high light. Furthermore, the pool sizes of ascorbate and glutathione may be factors restricting the oxidative stress defense response during severe chilling/high light stress of cotton plants that over-express MnSOD in their chloroplasts by limiting the ability of the Halliwell-Asada enzymes to compensate for the increased activity of SOD. This research was supported by USDA Plant Response to the Environment and the Texas Advanced Technology Program.Item Relative contribution of assimilates and turgor pressure to leaf area development(Texas Tech University, 1981-05) Yimbo, Peter OriwaNot availableItem Soil-plant water relations in the Altiplano of Peru(Texas Tech University, 1985-12) Aguirre, LucreciaThe growth patterns of key range species and forage production on two major range sites, and the influence of soil water on plant water status and growth were measured. The research was conducted at La Raya Research Station, Department of Cusco (highlands of southern Peru) during June 1984 to May 1985- Site II (light sandy loam soil) had higher mean forage production (2,417 kg/ha) than Site I (heavy sandy loam soil (1,436 kg/ha). Site I was dominated by Festuca dolichophylla and Muhlenbergia fastigiata. Vegetative composition included grasses, 87%, sedges and reeds, 7%, and forbs, 5%. Site II was dominated by F^. rigida and Stipa obtusa. The vegetation was composed of grasses, 93%, forbs, 6%, and sedges, 1%. Festuca dolichophylla and Festuca rigida started regrowing in September; although Festuca rigida grew at a faster rate than Festuca dolichophylla and produced a greater amount of dry matter, it started decreasing earlier (May-June) than Festuca dolichophylla (July). Soil water content increased as the wet season progressed. The soil water content was higher on Site I (heavy sandy loam) 26% than at Site II (light sandy loam) 20% from September to April. The greatest water content occurred in November (36% and 34%, Site I and Site II, respectively). The water content was lowest (10% and 8%, Site I and Site II, respectively) in September. Soil water potential averaged across month and time of day (dry season and early wet season) was higher on Site II (light sandy loam), -47 bars, than at Site I (heavy sandy loam), -54 bars. During the dry season, the potentials were -70 and -69 bars, on Site I and Site II, respectively. Plant water potentials also increased as the wet season progressed. Festuca dolichophylla had lower plant water potentials than Festuca rigida throughout the day. Festuca dolichophylla attained higher conductance rates than Festuca rigida during November; conductances at mid-day were 0.3727 and 0.2900 cm.sec respectively.Item The Effect of Water Stress on Sorghum Bicolor L. Moench: A Stereological Study of Bundle Sheath Cells(Texas Tech University, 1982-12) Vishnoi, UshaSorghum leaves from plants grown under irrigated and dryland field conditions were used. The leaves from stressed plants had smaller leaf areas and they were thicker than the leaves from nonstressed plants. The bundle sheath cells occupied about 13% of the leaf area in both nonstressed and stressed plants. Leaves from stressed plants had smaller but more numerous bundle sheath cells. It was concluded that the reduced leaf area in the stressed plants was due to a sensitivity of cell enlargement to water stress and that cell division was not affected. Stereological analysis of bundle sheath cells from nonstressed and stressed plants was used to study differences in the cell wall, cytoplasm, chloroplasts, starch granules, chloroplast lipid bodies, mitochondria and central vacuole. The total volumes showed a decrease in the cell wall, cytoplasm and central vacuole of the bundle sheath cells of stressed plants. In the same cells the chloroplasts were reduced in number but individual chloroplasts showed no change in volume. In stressed plants the starch granules were both smaller and fewer in number whereas the chloroplast lipid bodies were the same size but fewer in number. The mitochondria were both smaller and fewer in the leaves from the stressed plants. On a per leaf basis the chloroplasts were reduced both in volume and number but only mitochondrial volume was reduced.Item The effect of water stress on the leaf area of Cucumis melo(Texas Tech University, 1986-08) Matthews, Lisa RGreenhouse and field-grown Cucumis melo, cantaloupe vines were grown under irrigated and water stressed conditions. In addition, the stressed plants were rewatered after stress had resulted in a reduction in leaf area, providing a water stressed/recovered condition. The upper surface of the leaves was examined with a scanning electron microscope to determine if the primary cause of reduced leaf area was a decrease in cell number or cell size. The reduction in leaf area induced by water stress was due to a decrease in mitotic activity of the epidermal cells, which caused a reduction in the total number of cells per leaf. Leaves that first appeared during water stressed conditions exhibited the most severe decrease in cell division. Leaves that first appeared under irrigated conditions but developed under stressed conditions exhibited relatively normal cell division as well as normal leaf size. This indicated that most cell division occurred during and immediately following leaf initiation. Cell size did not appear to be affected by water stress, but was affected by the age of the leaf. There was a recovery of leaf area after the stressed plants were rewatered that resulted from a corresponding recovery of cell division and a concomitant increase in the total number of cells per leaf. This finding contradicts the majority of the literature which suggests that cell turgor is most affected by water stress which, therefore, causes a decrease in cell expansion. Measurements of plant water status of the greenhouse grown plants revealed an increase in diffusive resistance during water stress and a decrease in relative water content during water stress with a recovery of both upon rewatering. It is concluded that, under the conditions used in this study, cell division was more sensitive to water stress than was cell enlargement. Further, cell differentiation, as judged by the relative number of upper leaf surface cells, was found to be increased in the guard cells but unaltered in the epidermal cells and trichomes.Item The effects of leaf development and environmental stresses on the activity of glutathione reductase in crops(Texas Tech University, 1984-12) Gamble, Patricia ElaineNot availableItem The effects of various irrigation and nitrogen levels on gas exchange of cotton leaves(Texas Tech University, 1986-05) Favers, Kyle LeeNot availableItem Varietal interactions associated with different cultural practices in grain sorghum production(Texas Tech University, 1986-12) Ossoble, Aden AliNot availableItem Water stress and Russian wheat aphid interactions in wheat(Texas Tech University, 1995-12) Nalbant, DemetNot available