Thesis (M.Sc.) -- University of Adelaide, Dept. of Botany, 1979.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

I have isolated and characterized a recessive mutation in the Forked (FKD) gene that results in the abnormal initiation of vascular bundles in the foliar organs, such that the apices of the vascular bundles initiate freely. Once initiated, the development of Fkd vascular bundles is like wild type, generating an open vascular pattern of similar complexity to the closed venation pattern of wild type. Despite the significant alteration in the vascular pattern, Fkd plants are morphologically indistinct from wild type. fkd mutants do not show altered sensitivity to the effects of auxin and show additive phenotypes with auxin response mutants, suggesting the FKD is part of a pathway acting independently of auxin. The similarity of the open vascular pattern of Fkd plants to that of ancestral vascular plants suggests that acquisition of this pathway may have been critical in the evolution of the closed vascular pattern. / x, 55 leaves : ill. ; 28 cm.

The development of leaf vascular patterns is a highly regulated process. The plant hormone auxin is critical for vascular patterning: auxin canalization is proposed to cause files of cells to accumulate higher auxin levels and develop into veins. Thus, the response of cells to auxin and transport of auxin are critical to establish proper cell fate. We have characterized a mutation in the Arabidopsis thaliana gene name AUTOBAHN (ABN). abn leaves produce leaves that proliferate disorganized, overlapping veins parallel to the midvein with no differentiation of higher order veins. abn leaves show no normal aspects of the secondary auxin response though double mutant analysis suggest that ABN functions independently of previously characterized auxin response pathways. Wild type plants grown on an influx inhibitor phenocopy abn suggesting that abn is defective in carrier-mediated auxin influx. / x, 69 leaves : ill. ; 28 cm.

The complex vasculature seen in the vascular plants provides a scaffolding of structural support and is responsible for the movement of water, minerals, photosynthate and some hormones. The auxin canalization model proposes that a positive feedback mechanism causes auxin-transporting cells to become vascular cells. We have isolated a leaf-patterning mutant, unhinged (unh), which shows a simplified leaf vascular pattern with more freely ending veins and fewer secondary veins. Expression of the ATHB8::GUS reporter construct indicates that the UNH gene acts prior to procambial patterning of the first presumptive secondary veins. Expression of the auxin responsive reporter gene DR5::GUS is reduced in unh leaves and roots, indicating that UNH may be involved in auxin signaling. Increasing the level of auxin in unh leaves through the addition of auxin transport inhibitors, low concentrations of 2,4-dichlorophenoxyacetic acid, and through introducing unh into mutants in which auxin transport is defective partially rescues the unh phenotype, supporting this hypothesis. The unh mutation maps to a 60kb region near the top of chromosome IV. No other leaf vascular mutant or auxinassociated mutant have been reported in this area, thus UNH represents a novel component of leaf vascularization and auxin signaling. / xi, 65 leaves : ill. (some col.) ; 29 cm.

Thesis (MSc)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--Washington State University, August 2006. / Includes bibliographical references (p. 82-98).

Thesis (PhD (Biochemistry))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The sugarcane stalk, besides being the main structural component of the plant, is also the major storage organ for carbohydrates. Sucrose forms the bulk of stored carbohydrates. Previous studies have modelled the sucrose accumulation pathway in the internodal storage parenchyma of sugarcane using kinetic models cast as systems of ordinary differential equations. Typically, results were analysed with methods such as metabolic control analysis. The present study extends those original models within an advection-diffusion-reaction framework, requiring the use of partial differential equations to model sucrose metabolism coupled to phloem translocation. Let N be a stoichiometric matrix, v a vector of reaction rates, s a vector of species concentrations and r the gradient operator. Consider a coupled network of chemical reactions where the species may be advected with velocities, U, or diffuse with coefficients, D, or both. We propose the use of the dynamic system, s + r (Us) + r (Drs) = Nv; for a kinetic model where species can exist in different compartments and can be transported over long distances in a fluid medium, or involved in chemical reactions, or both. Darcy’s law is used to model fluid flow and allows a simplified, phenomenological approach to be applied to translocation in the phloem. Similarly, generic reversible Hill equations are used to model biochemical reaction rates. These are also phenomenological equations, where all the parameters have operationally defined interpretations. Numerical solutions to this formulation are demonstrated with time-courses of two toy models. The first model uses a simple “linear” pathway definition to study the impact of the system geometry on the solutions. Although this is an elementary model, it is able to demonstrate the up-regulation of photosynthesis in response to a change in sink demand. The second model elaborates on the reaction pathway while keeping the same geometry definition as the first. This pathway is designed to be an abstracted model of sucrose metabolism. Finally, a realistic model of sucrose translocation, metabolism and accumulation is presented, spanning eight internodes and four compartments. Most of the parameters and species concentrations used as initial values were obtained from experimental measurements. To analyse the models, a method of sensitivity analysis called the Fourier Amplitude Sensitivity Test (FAST) is employed. FAST calculates the contribution of the possible variation in a parameter to the total variation in the output from the model, i.e. the species concentrations and reaction rates. The model predicted that the most important factors affecting sucrose accumulation are the synthesis and breakdown of sucrose in futile cycles and the rate of cross-membrane transport of sucrose. The models also showed that sucrose moves down a concentration gradient from the leaves to the symplast, where it is transported against a concentration gradient into the vacuole. There was a net gain in carbohydrate accumulation in the realistic model, despite an increase in futile cycling with internode maturity. The model presented provides a very comprehensive description of sucrose accumulation and is a rigorous, quantitative framework for future modelling and experimental design. / AFRIKAANSE OPSOMMING: Benewens sy strukturele belang, is die suikerrietstingel ook die primêre bergingsorgaan vir koolhidrate. Die oorgrote meerderheid van hierdie koolhidrate word as sukrose opgeberg. Studies tot dusver het die metabolisme rondom sukroseberging in die parenchiem van die onderskeie stingellitte as stelsels gewone differensiaalvergelykings gemodelleer. Die resultate is ondermeer met metaboliese kontrole-analise geanaliseer. Hierdie studie brei uit op die oorspronklike modelle, deur gebruik te maak van ’n stromings-diffusie-reaksie-raamwerk. Parsiële differensiaalvergelykings is geformuleer om die metabolisme van sukrose te koppel aan die vloei in die floëem. Gestel N is ’n stoichiometriese matriks, v ’n vektor van reaksiesnelhede, s ’n vektor van spesie-konsentrasies en r die differensiaalvektoroperator. Beskou ’n netwerk van gekoppelde reaksies waar die onderskeie spesies stroom met snelhede U, of diffundeer met koëffisiënte D, of onderhewig is aan beide prosesse. Dit word voorgestel dat die dinamiese stelsel, _s + r (Us) + r (Drs) = Nv; gebruik kan word vir ’n kinetiese model waar spesies in verskeie kompartemente kan voorkom en vervoer kan word oor lang afstande saam met ’n vloeier, of kan deelneem aan chemiese reaksies, of albei. Darcy se wet word gebruik om die vloeier te modeller en maak dit moontlik om ’n eenvoudige, fenomenologiese benadering toe te pas op floëem-vervoer. Eweneens word generiese, omkeerbare Hill-vergelykings gebruik om biochemiese reaksiesnelhede te modelleer. Hierdie vergelykings is ook fenomenologies van aard en beskik oor parameters met ’n duidelike fisiese betekenis. Hierdie omvattende raamwerk is ondermeer gedemonstreer met behulp van numeriese oplossings van twee vereenvoudigde modelle as voorbeelde. Die eerste model het bestaan uit ’n lineêre reaksienetwerk en is gebruik om die geometrie van die stelsel te bestudeer. Alhoewel hierdie ’n eenvoudige model is, kon dit die toename in fotosintese as gevolg van ’n verandering in metaboliese aanvraag verklaar. Die tweede model het uitgebrei op die reaksieskema van die eerste, terwyl dieselfde stelselgeometrie behou is. Hierdie skema is ontwerp as ’n abstrakte weergawe van sukrosemetabolisme. Ten slotte is ’n realistiese model van sukrosevervoer, metabolisme en berging ontwikkel wat agt stingellitte en vier kompartemente omvat. Die meeste parameters en konsentrasies van biochemiese spesies wat as aanvanklike waardes in die model gebruik is, is direk vanaf eksperimentele metings verkry. Die Fourier Amplitude Sensitiwiteits-Toets (FAST) is gebruik om die modelle te analiseer. FAST maak dit moontlik om die bydrae van parameters tot variasie in modeluitsette soos reaksiesnelhede en die konsentrasies van chemiese spesies te bepaal. Die model het voorspel dat sintese en afbraak van sukrose in ’n futiele siklus, asook transmembraan sukrosevervoer, die belangrikste faktore is wat sukrose-berging beïnvloed. Die model het ook getoon dat sukrose saam met ’n konsentrasiegradiënt beweeg vanaf die blare tot by die stingelparenchiem-sitoplasma, van waar dit teen ’n konsentrasiegradiënt na die vogselholte (vakuool) vervoer word. Volgens die realistiese model was daar ’n netto toename in die totale hoeveelheid koolhidrate, ten spyte van ’n toename in die futile siklus van sukrose in die ouer stingellitte. Die model wat in hierdie proefskrif voorgestel word verskaf ’n uitgebreide, omvattende beskrywing van sukroseberging. Voorts stel dit ’n rigiede kwantitatiewe raamwerk daar vir toekomstige modellering en eksperimentele ontwerp.

The plant hormone auxin is involved in a wide range of developmental phenomena in plants. It carries out many of its effects through a signalling network involving the regulation of specific genes, including those involved in its own polar transport between cells. These transporters are able to be redistributed between cell faces, causing the asymmetric auxin transport that is a key requirement for the formation of vein patterns in leaves. In this thesis I describe the development of a biochemical kinetics-based model of auxin signalling and transport in a single cell, which displays biologically plausible responses to auxin application. The single-cell model then serves as the basis for a multicell model of auxin-mediated vein formation at a very early stage of leaf formation in Arabidopsis thaliana. / ix, 73 leaves : ill. ; 29 cm.

Thesis (M.S.)--State University of New York at Binghamton, Department of Biological Sciences, 2007. / Includes bibliographical references.