This thesis presents the results of an investigation into the uptake and distribution of cadmium (Cd) in two cultivars of potato (Solanum tuberosum L.) shown to contain different concentrations of Cd in the tuber at maturity. An initial glasshouse trial sought to determine whether differences in tuber Cd between these two cultivars resulted from differences in uptake from the soil, or were due to differences in the allocation of Cd to the various tissues within the plant. Total uptake of Cd from the soil did not differ between cultivars, nor did the yield of tubers. However, there were marked differences in Cd distribution within the plant. Most of the differences in tuber Cd concentration could be accounted for by a large (3-fold) retention of Cd in the roots of cultivar Wilwash. The concentration of Cd in the shoots of Wilwash was also higher than of Kennebec, although to a lesser extent than the roots. Further studies were conducted to trace the pathways of Cd uptake and movement within the plant. A split-pot trial, involving long-term growth of potatoes in 109Cd-labelled soil, was undertaken to determine the overall pattern of Cd distribution and the importance of the root system in supplying Cd to the tubers. The root system of the potato plant is different to many plants, in that the main root system (basal roots) is augmented after tuber initiation by roots extending from the stolon and from the tuber itself. The basal roots were found to be the dominant source of Cd to all tissues and accounted for approximately 85 % of tuber Cd. The remaining tuber Cd was sourced directly from the stolon and tuber roots. However, there was no evidence of a direct link between the main (basal) root system and the stolons. Although Cd was found to accumulate in the periderm of the tubers, there was no uptake into the tuber tissue itself. Isotopic studies were undertaken to investigate the short-term movement of newly absorbed Cd in the xylem and the phloem. Cadmium was found to be highly mobile in both the xylem and phloem, with added Cd being rapidly assimilated into all tissues following both root and foliar application. Newly absorbed Cd was rapidly sequestered by the stems when applied to either the soil or to a source leaf, suggesting that the stems may act as a transitional storage pool when rapid turnover of nutrients and other mineral elements is required during tuber bulking. Inhibition of Cd uptake by zinc (Zn), has been proposed as a method for reducing the concentration of Cd in various agricultural crops, including potatoes. The ability of Zn to reduce Cd uptake was found to be highly dependent upon cultivar and on the concentration of Cd in the external medium. Although competition between Zn and Cd was found for cultivar Wilwash when the external concentration of Cd was low, when the concentration of Cd in the external media was high, increasing Zn served to increase Cd uptake. Both synergistic and competitive responses were also noted for cultivar Kennebec. However, the patterns of response were opposite to those evident in Wilwash. The complexity of these interactions highlighted the possible shortcomings in using soil applied Zn to limit Cd uptake by potatoes. / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2004.

This thesis presents the results of an investigation into the uptake and distribution of cadmium (Cd) in two cultivars of potato (Solanum tuberosum L.) shown to contain different concentrations of Cd in the tuber at maturity. An initial glasshouse trial sought to determine whether differences in tuber Cd between these two cultivars resulted from differences in uptake from the soil, or were due to differences in the allocation of Cd to the various tissues within the plant. Total uptake of Cd from the soil did not differ between cultivars, nor did the yield of tubers. However, there were marked differences in Cd distribution within the plant. Most of the differences in tuber Cd concentration could be accounted for by a large (3-fold) retention of Cd in the roots of cultivar Wilwash. The concentration of Cd in the shoots of Wilwash was also higher than of Kennebec, although to a lesser extent than the roots. Further studies were conducted to trace the pathways of Cd uptake and movement within the plant. A split-pot trial, involving long-term growth of potatoes in 109Cd-labelled soil, was undertaken to determine the overall pattern of Cd distribution and the importance of the root system in supplying Cd to the tubers. The root system of the potato plant is different to many plants, in that the main root system (basal roots) is augmented after tuber initiation by roots extending from the stolon and from the tuber itself. The basal roots were found to be the dominant source of Cd to all tissues and accounted for approximately 85 % of tuber Cd. The remaining tuber Cd was sourced directly from the stolon and tuber roots. However, there was no evidence of a direct link between the main (basal) root system and the stolons. Although Cd was found to accumulate in the periderm of the tubers, there was no uptake into the tuber tissue itself. Isotopic studies were undertaken to investigate the short-term movement of newly absorbed Cd in the xylem and the phloem. Cadmium was found to be highly mobile in both the xylem and phloem, with added Cd being rapidly assimilated into all tissues following both root and foliar application. Newly absorbed Cd was rapidly sequestered by the stems when applied to either the soil or to a source leaf, suggesting that the stems may act as a transitional storage pool when rapid turnover of nutrients and other mineral elements is required during tuber bulking. Inhibition of Cd uptake by zinc (Zn), has been proposed as a method for reducing the concentration of Cd in various agricultural crops, including potatoes. The ability of Zn to reduce Cd uptake was found to be highly dependent upon cultivar and on the concentration of Cd in the external medium. Although competition between Zn and Cd was found for cultivar Wilwash when the external concentration of Cd was low, when the concentration of Cd in the external media was high, increasing Zn served to increase Cd uptake. Both synergistic and competitive responses were also noted for cultivar Kennebec. However, the patterns of response were opposite to those evident in Wilwash. The complexity of these interactions highlighted the possible shortcomings in using soil applied Zn to limit Cd uptake by potatoes. / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2004.

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

Micrografting was used to study the restoration of symplasmic transport at the graft union and to examine the long-distance transport of macromolecules between scion and rootstock. New techniques were established, such as correlative imaging and single-cell analysis in microfluidic devices, to study graft development both in vivo and in vitro. Imaging of Arabidopsis homografts showed that a symplasmic domain develops in the callus stele whose function may be to contain the spread of auxin into the surrounding ground tissue. It was demonstrated, also, that recent reports of organelle transfer at the graft union cannot be explained by the formation of secondary plasmodesmata (PD) at the graft interface. While fused calli did not exchange organelles in vitro, large aggregates of the SIEVE-ELEMENT OCCLUSION RELATED protein fused to YFP (SEOR-YFP; 112 kDa) were unloaded from mature sieve tubes into living cells of the graft partner in vivo, suggesting that vascular remodelling may be a prerequisite for the exchange of organelles at the graft interface. Fusion proteins expressing organelle-targeting signals were found to translocate across the graft junction, unloading into cell files adjacent to the root protophloem. The phloem mobility of a given fusion protein was assessed using bioinformatic and statistical analysis of publicly available data. The size of a protein and its relative abundance in CCs both emerged as defining factors for subsequent phloem transport. The recipient tissue for phloem-unloaded macromolecules was identified as the phloem-pole pericycle (PPP). This cell layer is required to remove macromolecules from the terminus of the protophloem. Induced callose deposition at the PD that connect protophloem SEs to the PPP caused a restriction in unloading and a subsequent arrest in root growth. A non-cell autonomous protein of CC origin, NaKR1-1, is proposed to affect the unloading of macromolecules either by increasing the size exclusion limit (SEL) of PD within the PPP or by enabling a build-up in pressure at the protophloem terminus, due to SUC2 activity, thus allowing phloem unloading.

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Agradecemos a compreensão. on 2017-04-06T14:47:38Z (GMT) / Submitted by LAUDECIR LEMOS RAIOL JÚNIOR null (laudecir_junior@yahoo.com.br) on 2017-04-07T14:14:25Z No. of bitstreams: 1 Tese_Laudecir_Lemos_Raiol_Júnior.pdf: 1991949 bytes, checksum: ea284fe5c7ae6d63472b72e4fc5c107e (MD5) / Approved for entry into archive by LUIZA DE MENEZES ROMANETTO (luizamenezes@reitoria.unesp.br) on 2017-04-10T18:46:59Z (GMT) No. of bitstreams: 1 raioljunior_ll_dr_jabo.pdf: 1991949 bytes, checksum: ea284fe5c7ae6d63472b72e4fc5c107e (MD5) / Made available in DSpace on 2017-04-10T18:46:59Z (GMT). No. of bitstreams: 1 raioljunior_ll_dr_jabo.pdf: 1991949 bytes, checksum: ea284fe5c7ae6d63472b72e4fc5c107e (MD5) Previous issue date: 2017-01-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Huanglongbing (HLB), causada pela bactéria Candidatus Liberibacter asiaticus (Las) que coloniza o floema das plantas cítricas, é considerada a doença mais grave e destrutiva dos citros. Aspectos da patogenicidade de Las ainda não estão compreendidos, dificultado pela condição não cultivável do patógeno. Entender como Las se movimenta internamente na planta para colonizar os diferentes tecidos é fundamental para o controle do HLB e a busca de materiais com potencial de resistência. O objetivo desse trabalho foi caracterizar a movimentação de Las em plantas de citros. Nos experimentos plantas de laranjeiras foram inoculadas por enxertia de segmentos de ramos de plantas infectadas de 2 - 3 cm de comprimento. Para estudo da velocidade de movimentação de Las nos vasos do floema, foi utilizado duas metodologias. A primeira envolveu poda sequencial do caule a diferentes distâncias do ponto de inoculação e avaliação de amostras de folhas seis meses após a inoculação. Já na segunda metodologia foi realizado a coleta de amostras de anéis de casca do caule a diferentes distâncias do ponto de inoculação e de raízes fibrosas. Foi avaliado também a influência de novos fluxos de crescimentos na movimentação de Las. Lotes de plantas foram podadas na parte aérea ou no sistema radicular para indução do crescimento. Plantas não podadas foram usadas como controle. Foram amostradas folhas que surgiram na planta após a inoculação, folhas velhas, anel de casca e raízes fibrosas a partir de 15 dias após a inoculação. E para o estudo do padrão de movimentação de Las nas plantas, foram utilizadas plantas aneladas totalmente, parcialmente e não aneladas no caule e inoculadas no topo ou na base do caule para avaliar se Las precisa passar pela raiz para colonizar outros pontos da copa. Os resultados permitiram concluir que a velocidade média necessária para Las atingir a raiz de 95% das plantas, localizada 85 cm abaixo do local de inoculação, foi estimado variando entre 2,9 a 6,9 cm dia-1. Foi observado também que fatores ambientais influenciam a velocidade de movimentação da bactéria na planta. No experimento para avaliar a influência das regiões de crescimento, parte aérea ou sistema radicular, na movimentação de Las, a maior probabilidade de detecção da bactéria foi observada em tecidos das regiões que foram estimulados a crescer através da poda, quando comparados com as plantas não podadas. Com relação aos tecidos amostrados, anéis de casca do caule foram as que apresentaram maiores porcentagens de detecção de Las. Além disso, as plantas em que foram estimulados o crescimento do sistema radicular apresentaram 90% a mais de probabilidade de se encontrar Las nas raízes em relação a amostras de casca do caule ou folhas. Os resultados sugerem que a bactéria precisa passar pela raiz para atingir outros pontos da copa. No entanto, esse fator não foi totalmente esclarecido porque o anelamento das plantas provocou acúmulo de amido e alteração no fluxo da seiva, que pode ter influenciado na movimentação da bactéria. / Huanglongbing (HLB), caused by the bacteria Candidatus Liberibacter asiaticus (Las) which colonizes the phloem of citrus plants, is considered the most serious and destructive disease of citrus. Las pathogenicity aspects are not yet understood, hampered by non-cultured condition of the pathogen. Understanding how Las moves within the plant to colonize the different tissues is fundamental for HLB management and searching for materials with resistance potential. The objective of this research was to characterize the movement of Las in citrus plants. In the experiments orange plants were inoculated using grafting segments from infected plant branches 2-3 cm long. To study the speed of Las movement in phloem, two methodologies were used. The first involved sequential pruning of the stem at different distances from the inoculation site and evaluation of leaf samples six months after inoculation. In the second methodology was collected the ring samples of stem bark at different distances from the point of inoculation until the ground level and fibrous roots. It was also evaluated the influence of the growth flows in the Las movement. Lots of plants were pruned in the aerial part or in the root system to induction of growth. Unpruned plants were used as controls. The plants were evaluated by sampling young leaves, mature leaves, stem bark and roots every 15 days from inoculation. For the study of the movement pattern of Las in the plants, we used totally, partially and non-girdling plants and inoculated at the top or base of the stem to evaluate if Las must pass through the root to colonize other points of the canopy. The results allowed to conclude that the average speed required for Las to reach the 95% root of the plants, located 85 cm below the inoculation site, was estimated varying from 2.9 to 6.9 cm day-1. It was also observed that environmental factors influence the speed of the bacterium movement in the plant. In the experiment to evaluate the influence of the growth regions, aerial part or root system, in the movement of Las, the highest probability of detection of the bacteria were observed in tissues from the regions that were stimulated to grow through pruning, when compared with unpruned plants. Regarding the sampled tissues, stem bark rings were the ones with the highest percentages of Las detection. Furthermore, the growth of the root system increased the possibility of finding Las in roots samples by 90% than in other sampled tissues. The results suggest that the bacteria must pass through the root to reach other parts of the canopy. However, this factor was not fully understood because the plants girdling caused starch accumulation and change in the sap flow, which may have influenced the movement of the bacteria.

Zea mays plants kept at ambient (ca 375ppm) and elevated CO₂ (ca 650 to 700ppm) were used to examine the possibility of a symplasmic loading, unloading and transport pathway in dark-adapted and illuminated (200μmolm⁻²sec⁻¹ ) sink and source leaves. 5,6-carboxyfluorescein diacetate was introduced into the mesophyll cells and symplasmic transfer observed 3h after application. In sink and source leaves exposed to ambient CO₂ and illuminated at 200 molm-2sec-1, the fluorescence front was observed approximately 3cm from the point of application, while in dark-adapted plants, the fluorescence front was observed approximately 1cm from the point of application. Under elevated CO₂ conditions the fluorescence front in illuminated plants appeared to transport faster moving approximately 5cm from the point of application, and in dark-adapted plants, only 3cm from the point of application. Based on the increase in 5,6-CF accumulation under elevated CO₂ conditions, the present study suggests that there was an increase in capacity for assimilate loading and transport under elevated CO₂ conditions. In source leaves, 5,6-CFDA was taken up into the mesophyll cells, loaded symplasmically and transported basipetally. In sink leaves 5,6- CFDA was taken up from basal mesophyll and after symplasmic loading, was transported acropetally where it was offloaded into the younger immature sink region. Transport in the sieve tubes was confirmed by using aniline blue, which was applied 3h after 5,6-CF transport. Aniline blue coupled with 5,6-CF transport studies showed that the sieve tubes of both cross and longitudinal veins are involved in symplasmic unloading, loading and transport processes in sink and source leaves. Apoplasmic uptake of 5,6-CFDA by cut leaves showed that after apoplasmic transport via the transpiration stream, 5,6-CFDA was offioaded to the xylem parenchyma where it was metabolically cleaved , releasing fluorescent 5,6-CF into the xylem parenchyma. Transverse sections cut after 3h of uptake were observed after 120 and 180 min suggesting that a retrieval of solutes occurs from the xylem to the xylem parenchyma, bundle sheath, phloem parenchyma and to the th in-walled sieve tubes. It was not possible to determine if the thick-walled sieve tubes were involved or if they took up 5,6-CF. Given the available data on loading and offioading of assimilates in sink and source leaves respectively, this study demonstrated that a slow symplasmic pathway exists from the mesophyll to the phloem, and that offloading from the phloem in sink leaves can occur via a symplasmic route.

The relationship between leaf architecture, vein anatomy and phloem ultrastructure, and that of possible routes from mesophyll cells to phloem and potential phloem loading method was investigated using species adapted to the southern African climate. The research was based on the hypothesis of Gamaiei and Van Bel, using nothern hemisphere species only (Gamalei 1985a, b, 1989, 1991, VanBeletal. 1988, Van Bel 1992, 1994, 1996, Van Bel & Gamalei 1991, 1992, Gamalei et al. 1992, 1994, 1996, Van Bel 1992a-c, 1993a, b, 1996). The thesis commenced with a survey ofleafarchitecture of the Ranunculaceae, Apocynaceae and Asclepiadaceae. Anatomical and ultrastructural studies followed. Leaf architecture was described according to Hickey (1973). Within the Ranuncuiaceae, leaf architecture was found to be marginally actinodromous. Venation pattern consisted of a widely spaced reticulum of delicate veins, especially in Ranunculus. Leaf architecture of the Apocynaceae was described as pinnate, camptodromous and brochidodromous. The Asclepiadaceae showed less uniformity in terms of leaf architecture, being pinnate and camptodromous, with mostly brochidodromous and, unexpectedly, eucamptodromous patterns of secondary venation. A predominantly common leaf architecture supported the move to amalgamate the two families. As the less advanced eucamptodromous arrangement could represent a more primitive branch of this huge family, the phylogenetic classification of the new amalgamated family is eagerly awaited for discussion. Allocation of vein order allowed comparisons between species and families to be drawn. Reticulum density and vein order anatomy was used to indicate potential routes from mesophyll to phloem. A definite contrast was obvious between the loose arrangement of mesophyll and veins in the mesic Ranunculus, and the close mesophyll and dense venation of the xeric apocynate and asclepiad species, and was related to habitat. Ultrastructural characteristics of companion cells, together with plasmodesmatal abundance, were considered especially important for the determination of minor vein configuration. Descriptions of plasmodesmatal distribution did not consider functional status. In this thesis, vein structure and ultrastructure were considered in relation to phloem loading, not as a demonstration thereof. All three families were designated minor vein configuration type 2a. Two interesting examples that did not adhere to the familial norm, viz. few plasmodesmata and normal companion cells, occurred in the Asclepiadaceae. Secamone alpinii had abundant aggregated plasmodesmata, forming a potential symplasmic continuum from mesophyll to companion cells. The question of plasmodesmatal functionality remained open. Ceropegia carnosa showed folding of the companion cell membrane, but no accompanying wall ingrowths. The folds were suggested to increase surface area for apoplasmic phloem loading in the noted absence of plasmodesmata. Loading routes and methods suggested were based on anatomical and ultrastructural evidence only. Whilst these results were supported by published data for other species of these families, the prediction of the Gamalei and Van Bel hypothesis did not hold true. The relatively primitive Ranunculaceae were expected to have the least advanced type 1 minor vein configuration, with abundance plasmodesmata providing a symplasmic phloem loading pathway. The relatively advanced Apocynaceae and Asc1epiadaceae were predicted to have the most progressive minor vein configuration, type 2b, with specialised transfer cells to maximise apoplasrnic uptake. As families with type 2a minor vein configurations, the Ranunculaceae were more advanced than expected and the Apocynaceae and Asc1epiadaceae less so.

Systemic acquired resistance (SAR) is a defense response induced by an initial localized infection that leads to the generation of long-distance immune signals that travel to distant leaves to provide enhanced resistance to subsequent infections. The lipid transfer protein (LTP) DEFECTIVE IN INDUCED RESISTANCE1 (DIR1) travels via the phloem from induced to distant leaves during SAR and may chaperone several long-distance signal candidates. In this thesis, the role of DIR1 during SAR is explored by examining the route of DIR1 movement, investigating the conservation of DIR1 structure and function, and by identifying DIR1-interacting proteins. I demonstrate that Arabidopsis plant lines with restricted cell-to-cell movement through plasmodesmata are negatively impacted in long-distance DIR1 movement, suggesting that cell-to-cell movement is important for DIR1 to access distant leaves. To elucidate the molecular function of DIR1, orthology analysis was performed with putative DIR1 orthologs. Structurally important amino acid residues that contribute to the hydrophobicity of the LTP cavity were identified, supporting the idea that DIR1 binds a hydrophobic ligand during SAR. RNAi-mediated knockdown of the DIR1 paralog DIR1-like did not impact the SAR response, supporting the idea that DIR1- like plays a lesser role in SAR. In addition, targeted protein-protein interaction assays determined that LTP1 and LTP2 interact with DIR1, and SAR phenotypic analysis of an ltp2-1 mutant supported a role for LTP2 in SAR. Lastly, a comparative proteomics approach identified several proteins with differential abundance in phloem exudates collected during the induction of SAR. Of these proteins, m-type thioredoxins, a major latex protein-like protein, and the UV-B photoreceptor UVR8 were essential for the manifestation of SAR. Together, these data provide insight into DIR1 function by identifying the importance of cell-to-cell movement through plasmodesmata, the DIR1 hydrophobic cavity, and DIR1-interacting proteins for DIR1-mediated SAR. In addition, this work identifies new phloem-localized proteins that contribute to the SAR response, providing fundamental knowledge on protein composition within the phloem during biotic stress. / Dissertation / Doctor of Philosophy (PhD)

[Truncated abstract] The phloem long distance translocation system is not only involved in the transport of nutrients and photo-assimilates to different organs of the plant, but it also appears to be important for the transport of information molecules including growth-regulators, proteins and RNA. Translocation of signals appears to be involved in the coordination of developmental processes and also in the response of the plant to environmental cues. Much of the information about macromolecules in phloem comes from analyses of exudates collected from the stylets of sap sucking insects or from incisions made to the vasculature. Among the legumes, members of the genus Lupinus exude phloem 'freely' from incisions made to the vasculature at most organs of the plant. This feature was exploited in this study to document some of the macromolecules present in exudate of L. albus and which might represent potential mobile signals. Phloem exudate was collected mainly from the sutures of developing pods and from inflorescence racemes. Two-dimensional polyacrylamide gel electrophoresis and tandem mass spectrometry were used to identify 83 proteins in exudate. Analysis of a cDNA library constructed from exudate identified 609 unique transcripts. Both proteins and mRNA were classified into functional groups. The largest group was related to general and energy metabolism, suggesting some metabolic activity probably to support the sieve element (SE). Other significant functional groups were represented by proteins and transcripts involved in protein synthesis, turnover and sorting, and in redox homeostasis. Proteins in these categories could play a role in maintaining the functions and stability of proteins in SE. Macromolecules involved in signalling such as transcripts encoding proteins mediating calcium levels and the Flowering locus T (FT) protein were also identified in phloem exudate of L. albus. FT protein has been recently identified as a mobile signal that induces flowering. ... The hen1 mutant accumulates low, sometimes even undetectable levels of miRNA due to the lack of methylation. No translocation of the five miRNA assayed under nutrient replete (non stress) conditions was observed. Translocation of miR395 in response to sulphur (S) deficiency was also investigated, and while conclusive evidence of translocation was not obtained, the data suggested some movement from roots to shoots (possibly in xylem) of a signal in response to S-deficiency. Future work is required to provide greater insight into the translocation path and identity of this S-deficiency signal. This study suggests that not all miRNA identified in phloem exudates are mobile, which raises the question about their biological relevance in SE and how they reached this location (e.g. through the action of a non-selective transport mechanism). However, there is also the possibility that miRNA are translocated only in response to specific internal or external cues not tested in this study. This is the first study that provides information on macromolecules present in the phloem exudate of a member of the Fabaceae. The information obtained from this work, provides a basis for future studies in the identification of potential mobile signals that may play a role in a communication network that traffics information around the plant, regulating its various developmental processes and responding to environmental cues.

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.