• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 326
  • 19
  • 8
  • 4
  • 1
  • Tagged with
  • 631
  • 631
  • 226
  • 149
  • 144
  • 120
  • 93
  • 76
  • 75
  • 71
  • 68
  • 59
  • 59
  • 54
  • 41
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
131

The Vascular Flora of the Eagletail Mountain Region

January 2012 (has links)
abstract: This study identifies the flora of the Eagletail Mountain Region, an area covering approximately 100,600 acres, located in west-central Arizona that includes the Eagletail Mountains, Granite Mountains, portions of the Harquahala Valley, and Cemetery Ridge near Clanton Well. The region is located about 129 km (80 mi) west of Phoenix and 24 km (15 mi) south of Interstate 10. Plants were collected over a six-year period, beginning September, 2004 and ending May, 2010, including two wet winters and two wet summers. A total of 702 collections were made covering 292 species that represented 63 families. Additional information on the region included in the thesis are: 1) an analysis of the climate, based on 20 years of rainfall records; 2) a description of the geology and its influence on plant distribution; 3) a prehistory and history identifying archeological sites; 4) an analysis of food plants used by the Native Americans that suggests how they were able to live in the region; 5)a paleo-botanical history based on an evaluation of pack-rat midden collections from mountain ranges around the region; 6) a comparison of the trees, shrubs, and perennials of the Eagletail Mountain Region with those of the Sierra Estrella and Kofa Mountains; and 7) a survey of non-native species. The habitats that the plants occupied based on climate and soils included were: 1) the bottoms and sides of sandy/ gravelly washes, 2) bajada slopes-volcanic soils, 3) bajada slopes-granitic sandy soils, 4) slot canyons/rock outcrops, 5) desert pavement, and 6) open valleys. Each habitat has its own characteristic species composition and distribution. / Dissertation/Thesis / M.S. Biology 2012
132

SIR2 DEACETYLASE ENZYME AND ITS POSSIBLE ROLE IN PATHOGEN INFECTION

Chand Thakuri, Bal Krishna, Kumar, Dhirendra 04 April 2018 (has links)
Silent Information Regulator 2 (SIR2) have a phylogenetically conserved catalytic domain from bacteria to humans. It catalyzes NAD+ dependent deacetylase activity post-translationally on acetylated lysine residues present in the protein. Because SIR2 are NAD+ dependent, its activity gets influenced by the change in the level of NAD+. SIR2 is responsible for calorie restriction and increased replicative yeast lifespan. It breakdown high energy bond in nicotinamide adenine dinucleotide (NAD), and the synthesis of O-acetyl-ADP-ribose which is a novel product. Lysine de/acetylation of histone molecule plays a significant role in chromatin dynamics in eukaryotes, but little is known in term of non-histone molecule modification by SIR2 enzyme especially in the case of the plant. SIP-428 is one of the SABP2 interacting protein (SIP) that exhibit SIR2 deacetylase activity. SABP2 is one of the essential components of salicylic acid (SA) signaling pathway that converts inactive methyl salicylate (MeSA) to active SA to induce local as well as SAR. AtSRT2, an Arabidopsis homolog of SIP-428 negatively regulate the basal resistance. Although catalytic domain is conserved, functional divergence has been reported in the case of SIR2 homologs. Presence of acetylated lysine residue in many cellular and organellar proteins implicated the possible physiological and metabolic role of SIP-428. Our result demonstrated SIP-428 exhibited NAD+ dependent deacetylase activity, but its lysine residue found to be acetylated, which raises the possibility of a post-translation regulatory mechanism that modulates the activity of SIP-428. SIP-428 have non-histone substrate, the negative regulator of basal resistance, and SAR. To understand better about the role of SIP-428 in plant physiology how it plays a vital role in SABP2 signaling pathway we will be using transgenic tobacco plant with altered expression of SIP-428 (Silence and inducible overexpression). Verified T3 generation of silence line and T2 generation of overexpression were created. These transgenic plant will be used to answer the possible link between SIP-428 and SABP2 in response to pathogen infection.
133

Planting Density Effects on the Growth of Dune Grasses.

Kirschner, Audrey 01 January 2019 (has links)
Coastal dune vegetation plays a key role in dune formation and stabilization through sediment trapping and erosion control. To restore degraded dunes, revegetation of dune building species is critical. Planting density has been found to effect growth of marsh species, with closer plantings alleviating stress through facilitation. As coastal dunes are high stress environments, it is expected that dune species may also exhibit facilitative interactions based on the Stress Gradient Hypothesis. Therefore, planting grasses in clumped configurations may lead to more successful dune revegetation. The objective of this research was to determine how planting density affects the growth of two dominant dune grasses along the US Atlantic coast, Ammophila breviligulata and Uniola paniculata, through field surveys of natural distribution, density, and a manipulation study of planting densities. Natural distribution differed between the two species with A. breviligulata occurring at lower dunes and U. paniculata occurring at higher dunes. Ammophila breviligulata occurred more densely than U. paniculata. Planting density of U. paniculata had an effect on growth parameters (shoot length, stem number, and ramet number) but not survival with dispersed plantings (50 cm apart) having higher growth than clumped plantings. The effect of density planting on growth parameters may impact dune building processes. Sparsely planted U. paniculata may have greater sediment capture compared to densely planted U. paniculata due to greater stem number and biomass resulting in taller, steeper dunes.
134

Modification, Verification of Sequence and Optimization of Expression of P297F an Inactive Mutant of Flavonol Specific Glucosyltransferase from Grapefruit (CP3GT)

Fox, Sarah 01 May 2020 (has links)
Citrus fruits are widely consumed and can offer various health benefits. One enzyme found in grapefruits, Citrus paradisi flavonol specific 3-O-glucosyltransferase (CP3GT), catalyzes the addition of glucose to one specific flavonoid class and at only one site. These flavonoids are plant secondary metabolites that can be used in a variety of plant functions including signaling and protection. The only class of flavonoids that CP3GT glucosylates is flavonols, and this specificity is of interest to study for potential benefits in biotechnology and enzyme modeling. In order to study this enzyme and its structure, a variety of mutants were created using site-directed mutagenesis. One mutant, P297F, exhibited a loss of function. This mutant was previously studied by inserting a thrombin cleavage site, extracting the plasmid expressing the mutation and sequencing it. The gene sequence was previously verified to be in frame and contain the needed thrombin cleavage site to remove tags used for protein purification and identification. The plasmid was then linearized, and transformed into yeast. After this, conditions for protein expression were tested over a 72-hour period. The protein was found to have optimal expression at 50 hours with a constant temperature of 28 °C and methanol concentration of 0.5 %. However, numerous protein expression experiments indicated very low protein expression. For this reason, the P297F gene was amplified through colony PCR, extracted and sent for sequencing to verify the transformation of the gene into yeast and identify possible reasons for low protein production. Analysis of this sequencing data showed a single nucleotide addition early in the tag sequence causing a frameshift after this location. Reanalysis of the previous plasmid sequencing data showed this same mutation, indicating improper conclusions were drawn. Efforts should be made to identify a plasmid without the mutation or correct the frameshift mutation so that the tag sequence produces the correct amino acids.
135

Formation and Control of Chlorophyll, Solanine Alkaloids, and Sprouts of Potato (Solanum tuberosum L.) Tubers and Carbonyl Compound of Tomato (Lycopersicon esculentum mill.) Fruits

Jadhav, S. J. 01 May 1973 (has links)
Part 1. Formation and control of chlorophyll, solanine alkaloids, and sprouts of potato (Solanum tuberosum L.) tubers Incorporation of radioactive carbon from acetic acid-2-14C (sodium salt), β-hydroxy-β-methylglutaric acid (HMG)-3-14C, L-leucine-U-14C, L-alanine-U14C, and D-glucose-U-14C into the predominant glycosidic steroidal alkaloids, &alpha-chaconine of potato sprouts was 4.88, 9.0, 15, 24, and 20 times less than that of mevalonic acid (MVA=2-14C (DBED salt), respectively. The efficiency ratio revealed that β-hydroxy-β-methylglutaric acid (HMG)-3-14 was incorporated via acetate or acetoacetate. The distribution of radioactivity originated from D-glucose-U-14C was nearly nine times higher in the glycoside moiety than that in the aglycone part of the glycoalkaloids. Apparently, Alar( succinic acid 2,2-dimethylhydrazide), Ethrel or Ethephon (2-chloroethylphosphonic acid), and Telone (1 ,3-dichloropropene and related chlorinated hydrocarbons) significantly reduced the rate of incorporation of β-hydroxy-β-methylglutaric acid (HMG)-3-14C into the alkaloids. A catalytic conversion of solanidine and UDP-glucose-U-14C to β-glucoside by the enzymatic system in a suspension of potato slices and the enzyme preparation from sprouts demonstrated the presence of β-glucosyltransferase in Solanum tuberosum L. Stepwise synthesis of α-solanine and α-chaconine from solanidine in potato tubers or sprouts seems possible. Formation of solanine alkaloids in peeled potato slices was stimulated when stored at 15 and 24 C in dark or light (200 foot-candles). The slices held under light developed nearly three to four times more alkaloids than those held in the dark. Significantly higher concentrations of solanine alkaloids were formed in the late stage (after 24 hours) than in the early stage of the storage period . Hence, it can be concluded that when potatoes are sliced for chips or French fries, they should be processed immediately, before the glycoalkaloids are synthesized in higher concentrations. Post-harvest application of chemicals, such as Phosfon (tributyl 2,4-dichlorobenzylphosphonium chloride), Phosfon-S (tributyl 2,4-dichlorobenzylammonium chloride), Amchem 72-A42 [2-(p-chlorophenylthio)- triethylamine], Amchem 70-334 or CPTA [2-(p-chlorophenylthio)-triethylamine hydrochloride], Nemagon (1,2-dibromo-3-chloropropane), and Telone (1,3-dichloropropene and related chlorinated hydrocarbons) at the concentrations of 250, 500, and 100 parts per million (ppm) in water; glycerin (10, 20, and 30 percent weight by volume [w/v] in water); and mineral oil (1.25, 2. 5, 5, 10, 15, 20, and 100 percent [w/v] in ether or petroleum ether) significantly inhibited the formation of chlorophyll and solanine alkaloids in the peripheral (periderm and outer parenchyma) zone of potato tubers exposed to a fluorescent light (200 foot-candles) for 6 or 7 days at 16 C and 60 percent relative humidity. The rates of inhibition increased with concentration of chemicals studied. A 10 percent solution of mineral oil was the minimum required concentration for effective control of chlorophyll and solanine alkaloids. The tubers dipped in 10 percent mineral did not develop chlorophyll on exposure to light (200 foot-candles) for 4 weeks, while the overall rate of inhibition of alkaloids was significantly high. In general, oil treatments were the most effective in controlling the formation of chlorophyll, solanine alkaloids, and sprout growth. Part II . Formation and control of carbonyl compounds of tomato (Lycopersicon esculentum Mill.) fruits Incubation of unsaturated fatty acids such as linoleic and linolenic acids with the crude soluble extract from tomato fruits produced carbonyl compounds. The enzyme preparations did not catalyze the conversion of saturated or monounsaturated fatty acids to carbonyls. Inability of potassium cyanide to inactivate the crude soluble extract proved that degradation of these fatty acids was mediated by lipoxidase and nonenzymatic oxidation by heme compounds was eliminated. These findings were supported by the fact that hydrogen peroxide, an inhibitor of lipoxidase enzyme, had inhibitory effects on the degradation of linoleic and linolenic acids by the tomato extract. Hexanal was found to be one of the products of the enzyme reaction. The identity of hexanal was confirmed by comparing the physical properties such as retention time, infra-red and ultra-violet absorption bands, and Rf value with those of an authentic sample . Biogenesis of hexanal from linoleic or linolenic acid was further substantiated by the use of uniformly labeled 14C isotopes of these fatty acids with the crude soluble extract, filtered homogenate, and tissue slices. Maximum activities (as evidenced by the production of carbonyls) were observed in the extract prepared with and incubated in a buffer medium of pH 7.5 (0.l M, Tris-HCl). The degradation of linoleic and linolenic acids was maximum at 30 C when incubated for 4 hours with 1 ml of the crude soluble extract. The enzymatic activity was enhanced by metal ions and compounds containing free -SH groups. Increase in the production of carbonyls by addition of citric and L-ascorbic acid may result from their metabolism. In general, ripe fruits contained greater enzymatic activities but smaller amounts of linoleic and linolenic acids than green fruits . The activity of the crude extract was increased by dialysis and the ammonium sulfate fractionation between 30 and 70 percent saturation. The rates of degradation of linoleic and linolenic acids catalyzed by the insoluble fractions of tomato extracts were more than those by the corresponding soluble fractions. Tomato fruits (green-wrap or large green) stored under hypobaric or sub-atmospheric pressures were analyzed for their volatiles after ripening. The concentrations of selected carbonyls (acetaldehyde, 2-methyl propanal, butanal, 3-methyl butanal, and hexanal) and some other volatiles decreased substantially with decrease in storage pressure.
136

The effect of antibiotics on thermophilic blue-green algae

Christenson, Erleen Blanche 01 January 1971 (has links)
The nature of the action of penicillin on the cell walls of bacteria is reviewed. The composition of bacterial cell walls is compared to cell walls of blue-green algae. The test organisms used were thermophilic: Anacystis nidulans grew optimally at 35⁰C, whereas Synechococcus lividus grew best at 45⁰ C. Growth was recorded by reading optical densities. Cells of these two thermophilic blue-green algae were treated with varying dosages of penicillin and streptomycin. Penicillin inhibited growth of Anacystis nidulans and Synechococcus lividus in concentrations of 3.0 Mg/ml and 0.03 Mg/ml respectively. However, when 0.3 Mg/ml of penicillin was added to Anacystis nidulans, an initial lag phase of growth was observed. Possible reasons for this lag are suggested and results of pertinent experiments are discussed. No similar lag was noted in Synechococcus lividus. Streptomycin inhibited growth of both species when present in 0.03 Mg/ml.
137

Observations on the establishment of seedlings of Phoradendron californicum on Prosopis juliflora

Null, Richard L. 01 January 1971 (has links)
The mistletoe Phoradendron californicum is a common parasite on the mesquite plant Prosopis juliflora. Seeds of the parasite are deposited upon the host plant by birds and perhaps other agents. Normally seedlings of the parasite become established when the elongating radicle of the embryo comes into contact with a host branch and forms a holdfast. From the underside of the holdfast the primary haustorium enters the host tissue and establishes the parasitic union. Later the aerial portion of the parasite develops. Some seeds of P. californicum follow a different sequence; they stimulate the host to produce gum in the tissue beneath the seed by apparent dissolution of cells. The exuded gum elevates the developing seed from the host branch preventing establishment of the host-parasite union. The possible significance of this apparent defense mechanism is discussed.
138

Mutual exclusion between Salmonberry and Douglas-fir in the Coast Range of Oregon

Still, Kenneth Ray 01 January 1972 (has links)
One serious problem faced by the forest industry in the Pacific Northwest is poor regeneration of commercial trees on land which is harvested and subsequently dominated by brush species. In Coastal Oregon, salmonberry is one of these brush species. Detailed investigations of field sites indicate that light intensity in the brush stands was low but sufficient for germination and early growth of Douglas-fir seedlings and soil moisture percentages and nutrient levels were high enough to support early Douglas-fir growth. Laboratory tests demonstrated the presence of leachable phytotoxins in the leaves of salmonberry. The hypothesis resulting from this study is that salmonberry releases a phytotoxin that in synergism with environmental stresses (i.e., light), suppresses germination and growth of Douglas-fir seedlings in the field.
139

A taxonomic study of the marine algae of Netarts Bay, Oregon

Kunert, Charles Jerome 01 January 1972 (has links)
Gathering taxonomic data is fundamental to any biological or ecological research. It was the intent of this paper to increase the storehouse of taxonomic information by studying the marine algae of one section of the Oregon coastline. Netarts Bay was chosen because of its accessibility and generally primitive nature. It is in an area of Oregon largely untouched by phycologists and so offered an opportunity for original research. Techniques of collecting and preserving specimens were kept as simple as possible, thus allowing a proportionately greater amount of the available time to be spent in the classification of the organisms. The body of this paper is, therefore, an annotated list of the algae collected and identified. A total of 78 species were identified, the majority belonging to the division Rhodophta (45 of the 78). An effort was made in collecting to be as thorough as possible. Algae ranging in habitat all the way from the spray zone to the depths of Netarts Bay were included. However, while the collection is comprehensive, because of the great size of the Bay it is undoubtedly incomplete. Only further research can identify which algae have been overlooked or omitted. Photographs are in evidence throughout much of the text. It is hoped that they will illustrate some of the forms which might be found only in this region and also, as accurately as possible, to aid in the identification of species elsewhere.
140

Community Assembly and Dynamics of the Forests of Powdermill Nature Reserve (Rector, PA)

Murphy, Stephen J. 11 October 2018 (has links)
No description available.

Page generated in 0.0694 seconds