Thesis (Ph. D.)--University of Chicago, 1916. / "Private edition, distributed by the University of Chicago Libraries, Chicago, Illinois." "Reprinted from the Botanical gazette, Vol. LXXI, No. 4, April 1921." "Literature cited": p. 286-288.

Th. doct.-ing.--Nutr., sci. de l'aliment., biochim. appl.--Nancy--I.N.P.L., 1980.

Interaction between orchids and fungi belongs to little understood aspects of orchid biology. This thesis investigated an identity of mycorrhizal and other fungal symbionts of several European orchid species and also an influence of these fungal symbionts on ecology, distribution, and evolution of the studied orchid species. Diverse methodological approaches were used including in situ seed germination, culture-dependent and -independent techniques for fungal isolation and identification, molecular phylogenetics, stable isotope analyses, and transmission electron microscopy.

M.Sc. (Botany) / Seed dormancy in Cyclopia spp. (Fabaceae) was investigated using seed from the seeder C. subternata and the resprouter C. intermedia obtained from the Southern Cape region. Seed of both species exhibited seed coat imposed dormancy which could be broken by scarification of the seed coat. However, in addition to an impermeable seed coat, seeds from C. intermedia also exhibit an embryo imposed dormancy which could be broken by cold treatment. Treatment of the seeds with gibberellic acid (GA3 ) , cytokinin (BA) and ethylene could be substituted for the cold treatment. The ethylene sensitivity of the seeds could be enhanced with short-chain saturated fatty acids (octanoic acid) which further stimulated germination. The effect of plant-derived smoke was also investigated and it appears that, in combination, ethylene and short-chain saturated fatty acids present in the smoke stimulate germination of the seeds. Treatment of the seeds with norbornadiene (NBD) before the above treatments resulted in the inhibition of germination, indicating that germination of the seeds of Cyclopia spp. is primarily controlled by the action of ethylene. The interaction between cold treatment, GA3 , BA and ethylene during germination of the seeds will be discussed.

No description available.

Including peanut (Arachis hypogaea L.) in crop rotations is common for eastern Virginia and the Carolinas, as it thrives in the long growing season and sandy soils. Boron (B) is widely deficient, and is more prone to leeching in sandy soils. Applied B has difficulty reaching growing points as B has reduced phloem mobility in peanuts. Current B fertilization recommendations are based on only three studies from the early 70s. Many changes have been made in cultivar breeding since then. This research examines if recommended B application rates and times are still necessary for optimal yield, plant health and seed quality for current cultivars. Two experiments in seven fields compared four total amounts of B applied (0, 0.3, 0.6, and 1.1 kg ha-1), and application time (planting; beginning peg, R2; full seed, R6; planting and R2; planting and R6), and runner and Virginia market types, newer and obsolete cultivars, with or without B fertilization. Leaf B was elevated only directly after fertilization (p=0.004, p<0.001), and in relation to total B applied (p<0.001), but seed B content was unaffected. Yield was not impacted by B rate or application time. Yield was higher (p=0.012) for newer cultivars when B fertilized, but no different than obsolete cultivars with B. Seed from obsolete cultivars had higher (p=0.010) B, no difference between market types or B fertilization. Germination of all seed was 97%. Based on this research, it is not necessary to apply B for optimal yield, plant health and seed quality for current cultivars. / Master of Science in Life Sciences

Members of the Bacillus genus, when faced with unfavorable environmental conditions such as depletion of nutrients, undergo an asymmetric division process ultimately leading to the formation of an endospore. In some instances, the spore serves as the infectious agent of an associated disease; such is the case with the spore of Bacillus anthracis and the disease anthrax. Spores are resistant to a variety of unfavorable environmental conditions including traditional decontamination techniques. Spore resistance is due to the formation of specialized structures that contribute to spore dormancy through several mechanisms, including maintenance of the dehydrated state of the spore core. Spore germination is a rapid process resulting in the irrevocable transformation of the non-metabolizing dehydrated spore into a vegetative outgrowing bacterium. The exact mechanism by which individual proteins function in the germination pathway remains unknown. In this study, we have focused on the roles of putative ion transporters and other germination-active proteins in affecting spore formation and germination. Metal ions can activate enzymes during the sporulation process and/or be factors in spore resistance properties. In B. subtilis, six proteins within the spore membrane proteome (ChaA, YcnL,YflS, YloB, YugS, ZnuA) are similar to components of known cation transport systems. These proteins may play roles in the accumulation of ions during sporulation and/or the release of ions during germination. Multiple mutants altered in the putative ion transporter genes were generated, and the effects of these mutations were analyzed. All strains containing a yloB deletion showed a decrease in heat resistant cfu/ml, and >40% of the spores appeared phase dark during microscopy, indicating the formation of unstable spores. Studies were conducted to quantify the amounts of individual ions in phase-bright spores using atomic emission spectroscopy and to analyze the rate at which ions are released from germinating spores. The transport of Ca2+ from mother cell to forespore during sporulation seems to be affected in the yloB deletion mutant. This Ca2+ deficit apparently renders the spores unstable, heat sensitive, and partially germination defective, suggesting that a high-affinity transporter for Ca2+ is nonfunctional. To better understand the underlying mechanisms of germination, a high-throughput genetic screening method called transposon sequencing was used. This analysis identified genes that had not been previously implicated in germination. To investigate their functions, a number of functional assays of all the Ger mutant strains were performed that indicated a delay in stage I of germination. The mutant strains showed significant reduction in germination efficiency with L-valine: about 50% of the population failed to initiate germination suggesting a defect in the GerA-mediated response. The expression of gerA was studied using a lacZ transcriptional fusion followed by quantitative western blot analyses to determine abundance of GerA in mutant strains. The mutants were classified based upon normal or decreased gerA transcription and normal or reduced GerA protein. Further work involves understanding the functions of the identified genes and their correlation to the GerA receptor. Insight into ion transporters of spore-forming bacteria and understanding the germination apparatus may lead to promising new applications, detection methods, or therapeutics for spores, and may allow the development of better spore decontamination procedures. / Doctor of Philosophy / Bacillus subtilis is an ubiquitous bacterium that is capable of forming endospores when faced with unfavorable environmental conditions. Spores are highly resistant to heat, radiation, lack of nutrients, desiccation and oxygen deprivation. They lack metabolism, which effectively keeps them in a state of suspended animation until germinated. They may remain stable and viable in this state for extremely long periods of time. Several important pathogenic bacteria are spore formers. This leads to difficulty in their environmental eradication and the treatment of patients. Germination allows spores to resume metabolism and reestablish a vegetative state. Certain key molecules activate the germination process. Each species of spore-forming bacteria has a specific set of these molecules called germinants that will enable the spore to exit its dormant state. The work presented focuses on the understanding of the germination apparatus of Bacillus subtilis, which may provide a model to understand the germination of other spore formers and help to improve methods of decontamination.

This investigation was concerned with determining the interaction of microwaves with germinating seeds. This study covers two different approaches. The preliminary efforts covered the response of germinating seeds to treatment by microwaves and heat. The second phase of the investigation used microwaves as a probe to determine some of the processes of early seed germination. The preliminary investigation measured the internal metabolic process by ATP production. Leakage of ions and organic material from germinating seeds indicated that membranes are a target of microwaves and heat. Electron photo-micrographs showed an increase in damage to membranes as heat and microwave treatments were increased. The second phase of this investigation was concerned with determining some of the biological activity at the initiation of germination of wheat seeds, Triticum aestivum L., using a resonating microwave cavity oscillating at 9.3 GHz as a probe. Direct current conductivity measurements were also made on the seeds as a means of confirming the observations made with the microwave cavity. There was no observable difference between treatment by UHF or heat in the ultrastructure of germinating seeds. A dielectric response far above that of free water was found as live seeds of wheat began to imbibe water. This effect was assumed to be due to the release of ions, because conductivity increased as corresponding quantities of water were imbibed; and both conductivity and dielectric response decreased as imbibition progressed. Although dead seeds also imbibe water, they do not show this decrease in dielectric response. The dielectric response of live seeds was reduced after the initial imbibition, showing that water became tightly bound as imbibition progressed. The dielectric response of actively growing shoots from the seeds was much less than that of the seeds themselves. The large quantity of water in the shoots is assumed to be immobile, being tightly bound within the membranes, enzymes, and organelles.

L'alliage de première génération (AM1) est un superalliage base-nickel utilisé par la Snecma pour élaborer des aubes de turbine monocristallines de géométrie complexe capables de résister aux conditions extrêmes de température et de pression. Cependant, lors du procédé de solidification, le contrôle du flux de chaleur est difficile pour des raisons de complexité de la géométrie, de la mise en grappe des pièces ou de la cinétique de solidification de l'alliage. Par conséquent, le risque de germination parasite peut avoir lieu dans le liquide surfondu. Pour comprendre l'origine de la germination parasite, il est important d'identifier avec précision la variation des isothermes dans la pièce au cours de la solidification pour localiser les zones de surfusion critiques. Pour ce faire, nous avons prédit par simulation numérique la germination et la croissance des grains au cours de la solidification. Nous avons implémenté dans le module CAFE du code Procast un algorithme de couplage permettant de tenir compte de la transformation liquide→solide dans la résolution du problème thermique. Ce couplage a permis de prédire le phénomène de recalescence qui témoigne de la germination parasite. La conversion enthalpie→température dans ce couplage tient compte de plusieurs chemins de solidification qui dépendent du taux de refroidissement à chaque nœud du maillage éléments-finis. Ces chemins de solidification sont tabulés grâce à un nouveau modèle de microségrégation conçu pour les alliages multicomposés en solidification dendritique colonnaire et équiaxe. Ce modèle est basé sur les équations de conservation de la masse totale et de la masse des solutés moyennées sur un volume représentatif. Dans ce modèle, la diffusion des espèces chimiques est contrôlée dans toutes les phases. Le modèle est aussi couplé avec un logiciel de calcul thermodynamique et un modèle de cinétique de croissance dendritique conçu pour les alliages multicomposés. Les prédictions du modèle retrouvent d'expériences menées sur l'AM1. / AM1 is a nickel-based superalloy that Snecma relies on to elaborate single crystal turbine blades having complex geometry and high resistance to extreme conditions of temperature and pressure. However, controlling heat flux during solidification process is difficult because of many reasons such as the complex geometry, the way of clustering parts and the superalloy solidification kinetics. Consequently, stray grain nucleation can occur in the undercooling liquid. Therefore, it is important to precisely identify critical undercooled zones during solidification. To do this, a new coupling algorithm is integrated in Procast software through its CAFE module. This coupling considers liquid→solid transformation in solving thermal problem. Thus, predicted recalescence during stray grain nucleation can be observed. Enthalpy→temperature conversion is based on tabulated solidification paths depending on cooling rate computed at each Finite Element node. Solidification paths are calculated using a new microsegregation model based on total mass and solute mass conservation equations over a representative volume element. It includes both finite diffusion in phases and growth kinetics for multicomponent alloys. It is also coupled with a thermodynamic software for equilibrium computation. The microsegregation model fits experimental data provided by quenching tests on AM1 superalloy.

Thèse (M.Ress.Min.) -- Université du Québec à Chicoutimi, 2005. / Bibliogr.: f. [85]-95. Document électronique également accessible en format PDF. CaQCU