Plant Science & Landscape Architecture Theses and Dissertations
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Item The kinetics and quantum yield of photophosphorylation in Anacystis nidulans (Richt.) Drouet(1972) Owens, Olga v. H.; Krauss, Robert W.; Plant Physiology; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)The active metabolite, ATP, serves not only as a high energy intermediate but also as a controller of some enzymatic reactions. In plant cells, the larger part of the ATP is formed by photophosphorylation. In this paper the rates, the quantum yields, and the wavelength dependencies of photophosphorylation in the blue-green alga Anacystis nidulans are reported. A fluorometric method for determination of enzymatically produced NADPH from ATP was adapted for use on cell extracts. In the light, the ATP level was 0.15 to 0.25 µmoles/mg chl. In the dark, the ATP level was 70% of that in light. In both darkness and anaerobosis, the level was 20%. A return to the light restored the ATP level from both conditions. Dark, anaerobic cells were exposed to measured irradiancies of 710 nm and 620 nm. The rate of ATP formation was measured within the first few seconds and found to be directly proportional to absorbed intensity. Saturation of the rates occurred at an intensity one-tenth the optimum for oxygen production. Quantum requirements of 6-8 were similar for each of the two wavelengths. The system II inhibitor DCMU, had a greater effect at 620 nm that at 710 nm indicating an involvement of system II in photophosphorylation only at 620 nm. At low intensities and over long time periods white light failed to produce a saturating steady-state level of ATP indicating a simultaneous consumption of ATP. Measurements in short dark periods following marginal illumination showed consumption of ATP to be 2 to 4 times greater that production in weak light. Thus, the quantum requirement can be calculated to be 2. ATP formation, therefore, is not the limit ing factor in co2 fixation. The evidence is the high quantum yield of photophosphorylation and the unsaturation of co2 fixation at intensities at which ATP synthesis is saturated.Item A Revision of North American Melanthium L. (Liliaceae)(1978) Bodkin, Norlyn Lee; Reveal, James L.; Botany; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Melanthium L. (Liliaceae ) is a genus of perhaps eight species with the four species of North America distributed from central Iowa eastward to southern New York, south to northern Florida and eastern Texas. The type species , M. -virginicum L., is found over this entire range growing commonly in swamps , marshes and bogs. Melanthium latifolium Desr. , found mostly on rich wooded slopes, and M. parviflorum (Michx.) S. Wats. located at higher elevations, occur mainly in the mid-Appalachian mountains. Melanthium woodii (Robbins ex Wood) Bodkin, comb. nov., is known from rich deciduous slopes of the Ozark Plateaus where it is very local and rare, and from five small disjunct populations in three eastern states. The major decision made in this treatment is the maintenance of Melanthium as distinct from the heterogeneous genus Veratrum L. on the basis of leaf size and shape, inflorescence, features of the tepalular glands and claws, adnation of stamens to tepals and general habit of the plants. The numerous synonyms associated with the name Melanthium are treated and either included under that genus , or excluded and assign d to their proper genera. The four (tentatively) Asian species, all of southwestern China , are not discussed due to a paucity of recent material.Item Net Productivity of Emergent Vegetation at Horn Point Salt Marsh(1975) Cahoon, Donald Richard; Stevenson, John C.; Botany; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Analyses of monthly standing crop, daily rates of production, and variations in yearly productivity for 5 production for the Spartina patens/Distichlis spicata mixture were conducted over two consecutive growing seasons for a Chesapeake Bay brackish marsh. Regression models for plant height and dry weight biomass were generated for all that the relationship between height and dry weight within each species is the same for all seasons of the year except in the species Spartina alterniflora and Phragmites australis. Positive correlation coefficients ranged from .27 for S. alterniflora to .96 for P. australis with the other species having intermediate value. Overall, production at Horn Point is lower than most other values in the literature with the 2-year average for S. alterniflora (676 g/m2) being 1/2 the average for the Atlantic Coast but the 2-year average for S. patens (628 g/m2) being slightly higher than its Atlantic Coast average. On a square meter basis, the primary producers rank in the following order of importance for the two year average of standing crop: Typha angustifolia (985 g/m2), Phragmites australis (892 g/m2), S. alterniflora/Amaranthus cannabinus (676 g/m2), S. patens/D. spicata (628 g/m2), and Hibiscus moscheutos (531 g/m2). However, the most important zones in terms of areally weighted production (in metric tons) for 1973 at Horn Point Marsh are the S. patens/D. spicata (7.61), H. mocheutos (5.07), S. alterniflora/A. cannabinus (3.22), P. australis (0.659), and T. angustifolia/H. moscheutos (0.644). In the brackish marsh (S. patens/D. spicata) exclosure experiments demonstrated that almost 100% of the net primary production (NPP) passes through the detritus food chain but in the contiguous fresh marsh (H. moscheutos) 37% of the NPP is utilized by the grazing food chain. Underground production for S. patens/D. spicata was determined by an experimental approach involving transplantations of underground material and a dry weight shoot:root ratio of 1:16 was determined over a twelve month period. An efficiency rate for conversion of visible solar radiation to plant production in 1974 ranged from 0.11% for H. moscheutos in the Typha/Hibiscus zone to 1.12% for the Typha angustifolia/Hibiscus moscheutos mixture.Item A Study of the Soils Derived from Serpetinite and Associated Rocks in Maryland(1978) Rabenhorst, Martin Capell; Foss, John E.; Agronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Approximately 25,000 acres have been mapped as serpentinite-derived soils in Maryland. While fertility studies have been done in serpentine areas, little work has been undertaken concerning the genesis of these soils. The objectives of this study were: 1) characterize the properties of soils formed from serpentinite and associated mafic rocks; 2) apply the results of the characterization study to an understanding of the genesis of these soils; and 3) examine the mapping and classification of serpentine soils with reference to geologic mapping. In a reconnaissance effort, 48 sites were sampled and analyzed for extractable Mg, Ca, P, and K and for pH. From field observations and these data, seven locations were selected for profile descriptions and detailed sampling. Physical, chemical , and mineralogical analyses were conducted on these samples. All serpentine profiles showed weak to moderate expression of argillic horizons and as a result of high Mg saturation, are classified as Alfisols. Argillic horizons in the non-serpentine profiles were strongly developed. Serpentine minerals were generally abundant in the > 0.2 μm fractions of serpentinite-derived soils. These weather to form expansible 2:1 minerals in the finer fractions. Vermiculite and smectite were important in both serpentine and non-serpentine profiles. The presence of quartz, mica, and feldspar in the surface horizons of all profiles indicate that eolian additions have occurred in many counties in the Maryland Piedmont. Comparison of soil mapping with geologic mapping has revealed large acreages of serpentine soil units mapped over non-serpentine mafic rock . This demonstrates the need to better utilize available geologic information in soil mapping. Serpentinitic mineral families are not currently recognized in any soil series in Maryland. Three of the four serpentine profiles, however, contained high levels of serpentine minerals. There is, therefore, a need to recognize serpentinitic soil families in Maryland in order to better differentiate between soils formed from serpentinite or from non-serpentine mafic rocks.Item The State of Water and Cell Morphology In Deep Frozen Populus(1985) Hirsh, Allen Gene; Solomos, Theophanes; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md)By using differential scanning calorimetry, electron microscopy, light microscopy, and freezing survival experiments, it is shown that superhardy Populus balsamifera v. Virginiana (Sarg.) is capable of withstanding liquid nitrogen (LN 2) temperatures because of the formation during cooling, at a temperature of about -30°C and cooling rates less than 30°C/hr, of aqueous glasses in the intracellular solutions. In more detail, the major findings concerning the state of intracellular water are: (1) the bulk of the intracellular contents go through an equilibrium glass transition at about -28°C during slow (<5°C/hr) cooling; (2) smaller additional amounts of intracellular material go through equilibrium glass transitions at about -47°C and -70°C; (3) as a result of the resistance to homogeneous nucleation of these glass forming intracellular solutions when they are in equilibrium with extracellular ice at<.-20°c, cooling/warming at any combination of rates from 3°C/hr to 1200°C/min between -20°c and -196°C is non-injurious to fully hardened wood; (4) death associated with quench cooling in LN2 from -15°C is correlated with the devitrification, (cold crystallization) near -90°C upon warming of the very low temperature glass forming component, followed by further devitrification of the higher temperature components, especially between -30°c and -20°c; and (5) the vacuolar compartment appears least resistant to devitrification and capable of thereby causing death even when the cytoplasm resists devitrification. In addition, it was found that when fully superhardy wood is cooled slowly (3°C/hr) after being imbibed with water (doubling total water content) massive intracellular freezing occurs. Despite the fact that total tissue water of tender Populus (summer wood) is 2x that of the artifically water loaded hardy wood on a gram H20/gram dry weight basis, tender wood cooled at 3°C/hr to -50°c does not display intracellular freezing. It is killed by -2°C. It is shown that in both tender and hardy wood <10% of water is extracellular. Thus a significant excess of extracellular water appears to cause intracellular freezing and this may be a major reason for the large water loss seen in the fall 'hardening off' of most temperature zone woody plants. It is also shown that during slow cooling, the plasma membranes of both hardy and tender Populus cells stick to and collapse the cell wall, but that these membranes stay smooth in the case of superhardy cells and wrinkle markedly in the case of tender cells. Membrane-associated particles appeared to clump in the membranes of slowly cooled tender cells but not in the slowly cooled hardy cells.Item ENHANCING QUALITY OF LIFE ON URBAN RESIDENTIAL STREETS BY CREATING PLACES FOR PEOPLE AND TREES(2019) PARKER, PAMELA; Ellis, Christopher; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lower income urban rowhouse neighborhoods are often treeless with only narrow sidewalks separating the front door from the street. This thesis explores the opportunity to capitalize on the predicted shift from private automobile ownership to fleets of autonomous vehicles and the subsequent significant drop in parking demand. Space previously designated as parking lanes can be converted into continuous tree planting strips and social spaces along inner-city residential streets. In this thesis, I propose three streetscape models utilizing the space no longer needed for parking: 1) the James Street Private Model that designs a 10’ wide continuous tree planting strip, allowing trees, gardens and patios to be installed along the foot of the rowhouse steps; 2) the James Street Public Model that creates the same tree strip design but positions it between the sidewalk and the street; and 3) the Shared Street Model, set along a narrower alley street, that forms a meandering road shared with pedestrians, public spaces and trees. These streetscape improvements directly address the quality of life of the residents by enhancing their safety and security, physical surroundings, social relations and health.Item FUSARIUM SPECIES OF CUCUMIS MELO IN THE MID-ATLANTIC REGION OF THE US AND THEIR IMPACT ON SALMONELLA ENTERICA NEWPORT SURVIVAL AND INTERNALIZATION ON VARIOUS MELON CULTIVARS.(2019) Korir, Robert Cheruiyot; Everts, Dr. Kathryne L; Micallef, Dr. Shirley A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fruit rots caused by Fusarium spp. can lead to economic yield losses on melon (Cucumis melo). However, which Fusarium spp. are the most prevalent in Maryland and Delaware has not been documented. Several Salmonella enterica subsp. serovar Newport (S. Newport) outbreaks on melon have occurred over the past 25 years. Fusarium spp. infestation on melon have potential impact on survival and colonization of Salmonella. Our objectives were to identify Fusarium spp. infestations on melons within the Delmarva region, and evaluate their impact on survival and internalization of S. Newport on various melon cultivars. Fifty-six isolates were molecularly identified, according to Fusarium-ID online database, as Fusarium spp. (Fusarium fujikuroi-20, Fusarium proliferatum-18, Fusarium oxysporum-15, Fusarium graminearium-2, Fusarium verticilloides-1). Our findings revealed that most of the Fusarium isolates we collected were not pathogenic to melon fruit. We evaluated the impact of four Fusarium spp. (F. armeniacum, F. oxysporum, F. fujikuroi, and F. proliferatum) on S. Newport survival in five melon cultivars; ‘Arava’ (C. melo var. reticulatus, Galia), ‘Athena’ (var. reticulatus, muskmelon), ‘Dulce Nectar’ (var. inodorus, honeydew), ‘Jaune de Canaries’ (var. inodorus, Canary), and ‘Sivan’ (var. cantalupensis, Charentais). Impact of F. proliferatum on survival and interlization of S. Newport was evaluated on honeydew (smooth) and cantaloupe (netted) melons. Generally, Fusarium did not impact the survival of S. Newport, however greater survival of S. Newport was observed on the netted cultivars compared to the smooth surface melons. Fusarium fujikuroi significantly enhanced survival of Salmonella when inoculated on riper ‘Jaune de Canaries’ melons (above ¾ slip). However, when the experiments were replicated with less ripe (about ¾ slip) melon, F. fujikuroi did not significantly influence the growth of S. Newport. Salmonella Newport internalized in all treatments and the cantaloupe and honeydew melons, but variation in population levels were observed across the treatments. Overall, Fusarium proliferatum did not impact internalization of S. Newport on either melon type. This may be attributed to that Fusarium species used during this study were non-pathogenic. Salmonella Newport recovered gradually decreased with time. Fusarium species on melon, influence S. Newport colonization differently. Also, melon rind type affects the ability of S. Newport to survive and colonize differently.Item SPATIO-TEMPORAL ANALYSIS OF PHOTOTROPISM IN ARABIDOPSIS SEEDLINGS(2019) Pritchard, Candace; Murphy, Angus S; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Optimization of light capture during seedling development is a major determinant of plant fitness. As seedlings emerge from the soil, the processes of photomorphogenesis and phototropism optimize deployment of structures that capture light for photosynthesis. Photomorphogenesis produces hypocotyl thickening, cotyledon expansion, and chloroplast maturation. Concurrent phototropic responses initiated by blue light position the expanding cotyledons to maximize photosynthesis. The mechanisms underlying both processes have been explored for more than 140 years, but are still not fully understood. This dissertation seeks to provide a better understanding of phototropism by exploring the timing and localization of the constituent mechanisms downstream of the well-characterized perception of blue light by the PHOTOTROPIN photoreceptors. The experiments described herein characterize temporally and spatially distinct processes involved in asymmetric auxin accumulations that lead to differential hypocotyl elongation. To better identify the link between early perception and later auxin transport and elongation events, an open-air system was used to remove seedling hindrance and provide better spatio-temporal resolution. These experiments confirmed the more rapid bending conferred by loss of the ATP Binding Cassette class B (ABCB) 19 auxin efflux transporter and loss of differential elongation in the mid hypocotyl elongation zone in higher order pinformed mutants. However, apart from the enhancement of phototropic bending observed in abcb19 and pin4 mutants, no auxin transport mutants tested showed alterations in early phototropic responses, and no mutant exhibited a delay in the onset of phototropic bending. Recently identified CBC1 and CBC2 (CONVERGENCE OF BLUE LIGHT (BL) AND CO2 1/2) have been shown to act in downstream signaling during phot1-mediated regulation of stomatal conductance. Similarly, during phototropism cbc1cbc2 double mutants show early defects in phot1-mediated phototropism. Further, CBC1 and CBC2 have been shown to regulate S-type anion channels. Analysis of S-type anion channel mutants also reveals defects in early bending responses. These results point to blue light-dependent regulation of anion channel activity having an important role during the earliest stages of phototropism.Item A Study of Resistance to the Sweet Potato Wilt Pathogen, Fusarium oxysporum Schlecht f. batatis (Wr.) Snyder & Hansen, and of Histological Aspects of the Host-pathogen Complex(1963) Wells, John Milton; Kantzes, James G.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Research on Fusarium wilt of sweet potato, a vascular disease caused by Fusarium oxysporum Schlecht f. batatis (Wr.) Snyder & Hansen, was undertaken to determine the susceptibility of various sweet potato lines to Maryland isolates of the pathogen under field and greenhouse conditions. Highly resistant lines would be useful as sources of resistance to Fusarium wilt in sweet potato breeding programs. In 2 years of field and greenhouse trials, 94 different lines of sweet potato were inoculated with a composite spore and mycelial suspension of 5 Maryland isolates of F. oxysporum f. batatis. Results indicated that the following lines were highly resistant to the pathogen: the foreign plant introductions P.I. 153655 ("Tinian"), P.I. 153906, P.I. 153907, and P.I. 251602; the variety Pelican Processor; and the breeding selections B-6842 from the United States Department of Agriculture Plant Industry Station at Beltsville, Maryland, and T-7 from the Georgia Coastal Plain Agricultural Experiment Station at Tifton, Georgia. Greenhouse experiments showed that the host range of Fusarium oxysporum f. batatis should include an additional species of Morning Glory, lpomoea pandurata (L.) G. F. w. Mey. Furthermore, no symptoms of infection were obtained on various crop plants commonly grown in rotation on land used for sweet potato culture. Physiological studies in the laboratory and greenhouse indicated that no significant levels of fungitoxic substances were present in either uninoculated or inoculated ''Tinian" plants. Nor could a fungal metabolite be detected, under the existing experimental conditions, which was toxic to a susceptible variety of sweet potato (Porto Rico) but not to the resistant ''Tinian". A study was made of the basis for resistance of the foreign plant introduction "Tinian" (P. I. 153655). Histological examinations of serial stem sections of the susceptible sweet potato variety Porto Rico and of the resistant foreign plant introduction ''Tinian" were made from plants collected at 3-day intervals following inoculation with spores of the pathogen. It was found that "Tinian" responded to infection by the production of tyloses in advance of the fungus. Twelve days after inoculation, 75 - 88% of the vessels which were 22 - 32 mn above the invasion site at the base of the plant were completely filled with tyloses. This compared to only 0 - 3% in the uninoculated control plants. Furthermore, no mycelia or spores could be detected in tnis region but were present in 25 - 50% of tne vessels within 11 mm of tne invasion site. In the variety Porto Rico the occurrence of tyloses in the inoculated plants was not significantly greater than in the uninoculated controls, except near the invasion site where after 12 days 3 - 6% of the vessels contained small 1 tyloses. The pathogen was not limited, as in ''Tinian", to the immediate invasion site. Tnis suggests that tne production of tyloses in "Tinian may represent an important defense mechanism against Fusarium wilt.Item Nitrogen cycling by grass-brassica mixtures in the Mid-Atlantic(2019) Gaimaro, Joshua Ruben; Tully, Kate; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mixtures of cover crop species may be more effective than monocultures at internal nutrient cycling due to their ability to occupy different niches. Our study investigates nitrogen (N) cycling of radish (Raphanus sativus L.) and rye (Secale cereal L.) in monocultures and mixtures compared to a no cover crop control. The study was established on fine-textured soils near Laurel, MD where we estimated N leaching losses, quantified mineral soil N (to 60 cm), and cover crop biomass N for two years. Forage radish suppressed estimated N leaching in the fall, while cereal rye suppressed estimated N leaching in the spring. In this study, growing radish in a mixture with rye decreased the risk of N leaching losses and enhanced N cycling due to the difference in timing of N uptake and release. Our research indicates that grass-brassica mixtures are a flexible management tool for mitigating N leaching in the Mid-Atlantic.