Dissertation (PhD) -- University of Stellenbosch, 2004. / ENGLISH ABSTRACT: In most plants the efficiency of sucrose production and the systemic distribution thereof are the major determinants of growth, development and yield. The factors governing sugar partitioning co-ordinate its distribution in response to intrinsic and environmental signals. These factors include sugar transporters and invertases as well as metabolites, including sucrose and glucose, which function as signalling molecules to modulate gene expression. The genetic transformation of plants and the subsequent development of transgenic lines with disturbed sugar metabolism have made an unprecedented impact on the study of sugar translocation and -partitioning. For instance, the transformation of plants with a yeast-derived invertase targeted to different subcellular compartments has led to the elucidation of several key aspects of sugar metabolism, including phloem loading mechanisms, the regulation of photosynthesis by sugars, the importance of sugar-metabolism compartmentation with regards to sucrose biosynthesis, storage and distribution, as well as the role of cell-wall invertase in phloem unloading and sink strength. In this study, a similar strategy of transgenic plant analysis was employed to expand our insight into the regulation of sugar partitioning. The yeast-invertase Suc2 gene, from Saccharomyces cere visiae , was overexpressed in either the cytosol, vacuole or apoplast of transgenic tobacco plants. These transgenic lines displayed varying increases in invertase activity, altered sugar levels and consequently disturbed sink-source interactions and sugar partitioning. Transgenic lines overproducing the yeast-derived invertase in either the vacuole (Vac-Inv) or apoplast (Apo-Inv) were utilised to analyse the effect of the altered sugar levels in sink and source organs on the expression of sugar transporters, as well as the endogenous cell wall invertase and inhibitors in these plants. Transcript levels of the sucrose transporter NtSUT1 and hexose transporter NtMST1 encoding genes increased significantly in the source leaves and roots of Vac-Inv lines, whereas increased NtMst1 transcript levels were also detected in the roots of Apo-Inv lines. The increased mRNA levels could be correlated to the altered invertase activities and sugar levels in these tissues. It is concluded that NtSUT1 and NtMST1 are differentially regulated by sucrose and/or hexose content on a transcriptional level. Furthermore, the regulatory effect of the altered sugar levels on transporter expression depended on the subcellular compartment in which the yeast invertase was expressed. It would seem that the subcellular compartmentation of sugar metabolism is also fundamental to the regulation of sugar partitioning. The transcription levels of the endogenous cell wall invertase (CWt) and cell wall invertase inhibitor (Cwi-Inh) genes were examined in the various tissues of Apo-Inv and Vac-Inv lines at both the vegetative and flowering growth stages. In comparison with the control lines, the various tissues of the Apo-Inv and Vac-Inv lines displayed altered Cwi and Cwi-Inh expression levels, depending on the sink-source status and growth stage. However, no obvious correlation between the Cwi and Cwi-Inh expression levels and soluble sugar content of these tissues was found. It is suggested that the post-transcriptional and post-translation control of these proteins by sugars might play an important role in their regulation. Analysis of the Cwi:Cwi-lnh mRNA ratio and growth observations of the various tissues of control as well as Apo-Inv and Vac-Inv lines indicated that this transcription ratio could be an accurate indicator of the sink strength of sink organs. In addition, the influence of sink-source interactions on sugar partitioning was investigated. Reciprocal grafting between Apo-Inv and control lines resulted in scions with an altered sucrose metabolism in either the sink or source organs. These scions were subjected to biomass distribution, soluble sugar quantification and C4C]- radiolabelling experiments. The latter revealed an unaltered state of sugar partitioning from the above-ground tissues of the Apo/GUS scions and a significant shift in sugar partitioning towards the roots of the GUS/Apo scions in comparison to the control GUS/GUS scions. Phenotypic changes, opposite to those observed in Apo-Inv lines expressing the heterologous invertase in both sink and source organs, could initially be observed in the GUS/Apo and Apo/GUS scions. However, no significant differences in phenotype or biomass distribution could be observed between the mature GUS/Apo, Apo/GUS and GUS/GUS scions seven weeks postgrafting. This inconsistency between phenotype and sugar partitioning might be explained by an increase in the respiration rate of the tissues as supported by the soluble sugar content. These results highlight the complexity and adaptability of sucrose metabolism and sugar partitioning. In addition, it confirms that sugar partitioning can be modulated by sink-source interactions and emphasise the importance of invertases in the regulation of sugar partitioning through its ability to alter sink strength. This study forms part of the rapidly expanding initiative to unravel the control mechanisms of sugar partitioning. The results obtained in this study confirmed again that the introduction and expression of a single heterologous gene in transgenic plants could provide significant insight into the regulation of this process. It was shown here that the expression of sugar transporters is closely regulated by sugar levels and therefore fulfils a vital function in sugar sensing and consequently the regulation of sugar partitioning. The data presented in this study also demonstrated the intricate and flexible nature of the relationship that exists between sugar metabolism, partitioning and growth phenomena. / AFRIKAANSE OPSOMMING: Die doeltreffendheid van sukroseproduksie, tesame met die sistemiese verspreiding daarvan, is die vernaamste faktore wat die groei, ontwikkeling en opbrengsvermoë van die meeste plante bepaal. Die faktore wat suikerverdeling beheer, funksioneer om suikerverspreiding te koordineer in reaksie op beide inherente- en omgewingsseine. Hierdie faktore sluit suikertransporters en invertases in, asook metaboliete soos sukrose en glukose wat funksioneer as seinmolekule in die modulering van geenuitdrukking. Die genetiese transformasie van plante en die gevolglike daarstelling van transgeniese lyne met veranderde suikermetabolismes het 'n beduidende inwerking op die bestudering van suikervervoer en -verdeling gehad. Byvoorbeeld, die transformasie van plante met 'n gis-invertase geteiken na verskillende sub-sellulêre kompartemente, het tot die toeligting van verskeie aspekte van suikermetabolisme gelei, insluitende dié van floëemladingsmeganismes, die regulering van fotosintese deur suikers, die belang van kompartementalisering ten opsigte van sukrosebiosintese, -opberging en -verspreiding, en die rol van selwand-invertases in floëemontlaaiing en swelgpuntkrag. In hierdie studie is van soortgelyke transgeniese plantontledings gebruik gemaak om 'n dieper insig tot die regulering van suikerverdeling te verkry. Die gis-invertase Suc2 geen, afkomstig van Saccharomyces cerevisiae, is ooruitgedruk in óf die sitosol, vakuool óf apoplastiese ruimte van transgeniese tabakplante. Hierdie transgeniese lyne het wisselende toenames in invertase-aktiwiteite en veranderde suikervlakke getoon, asook gevolglike versteurde bron-swelgpunt interaksies en suikerverdeling. Transgeniese lyne met ooruitdrukking van die gis-invertase in óf die vakuool (Vac-Inv) óf die apoplast (Apo-Inv) is gebruik om die gevolg van die veranderde suikervlakke in bron- en swelgpuntorgane op die uitdrukking van suikertransporters, asook die endogene selwand-invertase en invertase-inhibitor in hierdie plante te bepaal. Transkripsievlakke van die sukrosetransporter NtSut1 en die heksosetransporter, NtMst1, het beduidend toegeneem in die bron-blare en wortels van die Vac-Inv lyne; 'n toename in NtMst1 transkripsievlakke is ook in die wortels van Apo-Inv lyne bevestig. Die toenames in boodskapper RNA kon gekorreleer word met die veranderde invertase-aktiwiteite en suikervlakke in hierdie weefsels. Die gevolgtrekking word gemaak dat NtSUT1 en NtMST1 differensieël gereguleer word op transkripsionele vlak deur die sukrose en/of heksose inhoud van weefsels. Meer nog, die regulerende effek van die veranderde suikervlakke op transporteruitdrukking het afgehang van die subsellulêre kompartement waarin die gis-invertase uitgedruk is. Dit wil dus voorkom dat die subsellulêre kompartementalisering van suikermetabolisme fundamenteel tot die deurgee en waarneming van suikerseine is, met In gevolglike eweneens belangrike rol in die regulering van suikerverdeling. Die transkripsievlakke van beide die endogene selwand-invertase (CWI) en die selwand-invertase-inhibitor (CWI-Inh) enkoderende gene is in verskeie weefsels van die Apo-Inv en Vac-Inv lyne, tydens beide die vegetatiewe- en blomstadia, bestudeer. Die onderskeie weefsels van die Apo-Inv en Vac-Inv lyne het, in vergelyking met die kontrole lyne, veranderde Cwi en Cwi-inh transkripsievlakke getoon wat bepaal is deur bron-swelgpunt status en groeistadium. Geen duidelike korrelasie kon tussen beide Cwi en Cwi-inh uitdrukkingsvlakke en oplosbare suiker inhoud gevind word nie. Daar word voorgestel dat post-transkripsionele en posttranslasionele beheer deur suikers 'n belangrike rol in die regulering van hierdie proteïne speel. Bestudering van die Cwi:Cwi-lnh mRNA verhouding, asook groei verskynsels van die onderskeie weefsels van kontrole en Apo-Inv en Vac-Inv lyne, dui daarop dat hierdie transkripsievlak-verhouding moontlik 'n akkurate aanwyser van die swelgpuntkrag van 'n swelgpuntorgaan kan wees. Voorts is die invloed van bron-swelgpuntorgaan interaksies op suikerverdeling ondersoek. Omgekeerde enting tussen Apo-Inv en kontrole lyne het entlote met gemodifiseerde suikermetabolisme in óf hul bron- óf hul swelgpuntorgane tot gevolg gehad. Hierdie entlote is aan biomassaverspreidings-, oplosbare suiker kwantifisering en C4C]-radiomerking eksperimente onderwerp. Hierdie resultate het gewys dat, in vergelyking met die kontrole (GUS/GUS) ente, daar geen verandering in die status van suikerverdeling vanaf die bogrondse plantdele in die Apo/GUS ente is nie, maar wel 'n beduidende verskuiwing in suikerverdeling na die wortels van die GUS/Apo ente. Fenotipiese veranderinge, wat teenoorgesteld van dié teenwoordig in die Apo- Inv lyne waar die heteroloë invertase in beide bron en swelgpuntorgane uitgedruk word, is aanvanklik in die GUS/Apo en Apo/GUS ente waargeneem. Geen verskille in fenotipe of biomassa-verspreiding kon egter sewe weke na die entings prosedures tussen die GUS/Apo, Apo/GUS and GUS/GUS ente gevind word nie. Dit mag verduidelik word deur 'n moontlike toename in respirasietempo in die betrokke weefsels; die oplosbare suikervlakke wat in die verskillende ente aangeteken is ondersteun dié moontlikheid. Hierdie resultate as geheelonderstreep die kompleksiteit en aanpasbaarheid van suikermetabolisme en -verdeling. Verder bevestig dit dat suikerverdeling beïnvloed kan word deur bron-swelgpunt interaksies, asook die belang van invertases in die regulering van suikerverdeling gegewe die vermoë om swelgpuntkrag te verander. Hierdie studie vorm deel van 'n vinnig groeiende inisiatief om die beheermeganismes van suikerverdeling te ontrafel. Die resultate verkry in hierdie studie bekragtig die belang van rekombinante DNA tegnologie in die bestudering van fundamentele plantprosesse. Die invoeging en uitdrukking van 'n geteikende gisinvertase in transgeniese plante het gelei tot veranderde suikervlakke en bronswelgpunt interaksies in hierdie lyne met die gevolglike ontginning van waardevolle inligting ten opsigte van die regulering van suikerverdeling in reaksie tot interne seine. Daar is aangetoon dat suikertransporters onlosmaakbaar gekoppel is aan die deurgee en waarneming van suikerseine, spesifiek op die vlak van transkripsionele regulering, en dus ook die regulering van suikerverdeling. Voorts wys die resultate op die komplekse en aanpasbare aard van die verhouding wat bestaan tussen suikermetabolisme, -verdeling en groeiverskynsels.

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蛋白質分泌及胞吐作用是指蛋白質在內質網(ER)中合成後前往質膜(PM) ， 隨後， 被分泌到達細胞外的過程。 而細胞分泌路徑是指蛋白質途經數個含有膜包被的細胞器後運送到细胞之外。 這些細胞器，包括內質網， 高爾基體， 反式高爾基網絡(TGN) 及質膜。 分泌蛋白分泌出细胞之外後， 在细胞外基質中進行其功能。 / 為達到這項研究的目的，我們結合了細胞、分子和生物化學上的方法， 來對蛋白質運輸路徑及參與蛋白質分泌的細胞器進行研究。首先，通過MALDI-MS/MS對煙草懸浮BY-2細胞中的原態分泌性蛋白質進行分析。第二，把已識別的分泌蛋白包括陽離子過氧化物酶同工酶40K（40K）和N1過氧化物酶（N1），透過轉基因細胞的GFP融合表達方式、及應用特異性抗體於免疫螢光和膠體金免疫電鏡上的測定來對其特性作進一步分析。 第三，總合以上的研究，煙草懸浮BY-2細胞的典型蛋白質分泌路徑次序為質網 - 高爾基體 - 反式高爾基網絡 - 質膜。 / Protein secretion or exocytosis is the process by which proteins synthesized in the endoplasmic reticulum (ER) travel to the plasma membrane (PM) for their subsequent secretion outside of the cell. The secretory pathway responsible for protein secretion contains several membrane-bounded organelles such as the ER, Golgi apparatus, trans-Golgi Network (TGN), and PM. The secreted proteins move outside of the cell and perform their functions in the extracellular matrix. / The general objective of this study was to examine the transport pathways and organelles involved in protein secretion in plant cells using a combination of cellular, molecular and biochemical approaches. First, major native secreted proteins in suspension cultures of tobacco BY-2 culture cells were identified via MALDI-MS/MS analysis. Second, the identified secreted proteins, cationic peroxidase Isozyme 40K (40K) and peroxidase N1 (N1), were further characterized by examining the GFP fusion expression of transgenic cell lines and by generating specific antibodies in immunofluorescent and immunogold electron microscope (EM) studies. Third, throughout all of these studies, a typical ER-Golgi-TGN-PM pathway was mapped for protein secretion in tobacco BY-2 cells. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Lam, Chun Kok. / "December 2012." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 79-84). / Abstracts also in Chinese. / Thesis /Assessment Committee --- p.i / Statement --- p.i / Abstract --- p.ii / 摘要 --- p.iv / Acknowledgements --- p.v / List of Abbreviations --- p.xiii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1. --- Secreted protein --- p.1 / Chapter 1.2. --- Secretory Pathway --- p.1 / Chapter 1.3. --- Protein secretion --- p.2 / Chapter 1.4. --- Plant Peroxidases --- p.3 / Chapter 1.5. --- Project Objective --- p.4 / Chapter 1.6. --- Significance --- p.4 / Chapter Chapter 2 --- Materials and Methods --- p.6 / Chapter 2.1. --- Mass spectrometry analysis --- p.6 / Chapter 2.2. --- Generation of 40K/N1-GFP construct --- p.7 / Chapter 2.2.1. --- For transient expression --- p.7 / Chapter 2.2.2. --- For stable expressing constructs --- p.7 / Chapter 2.3. --- Transient expression of 40K/N1-GFP --- p.7 / Chapter 2.4. --- Generation of transgenic cell lines --- p.8 / Chapter 2.5. --- Fluorescence microscopic screening --- p.9 / Chapter 2.6. --- Generation and characterization of antibodies specific for 40K/N1 peroxidase --- p.9 / Chapter 2.7. --- Confocal immunofluorescence studies --- p.10 / Chapter 2.8. --- (TIRF) Total internal reflection fluorescence microscopy --- p.11 / Chapter 2.9. --- Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blot analysis --- p.11 / Chapter 2.10. --- Drug Treatment --- p.12 / Chapter 2.10.1. --- Dexamethasone (dex) --- p.12 / Chapter 2.10.2. --- Brefeldin A (BFA)/Concanamycin A (ConcA) --- p.12 / Chapter 2.11. --- Salt treatment (plasmolysis) --- p.13 / Chapter 2.12. --- EM (electron microscopy) study --- p.13 / Chapter Chapter 3 --- Results --- p.14 / Chapter 3.1. --- Protein secretion from tobacco BY2 cells --- p.14 / Chapter 3.2. --- Western blot analysis --- p.15 / Chapter 3.3. --- Protein expression in tobacco plant tissues --- p.15 / Chapter 3.4. --- EM labeling on the wild type BY-2 cells --- p.16 / Chapter 3.5. --- Localization in the tobacco root tip apoplast --- p.17 / Chapter 3.6. --- 40K/N1 peroxidase transient/stable cell line expression --- p.18 / Chapter 3.7. --- Time course study of 40K/N1 peroxidase-GFP cell line expression after induction --- p.18 / Chapter 3.8. --- Plasmolysis (salt treatment analysis) --- p.20 / Chapter 3.9. --- Brefeldin A (BFA) and concanamycin A (ConcA): Trafficking through the Golgi and TGN --- p.20 / Chapter 3.10. --- Examining exocytosis by total internal reflectance fluorescence (TIRF) --- p.22 / Chapter 3.11. --- Immunolabeling study --- p.23 / Chapter 3.12. --- EM study on transgenic 40K & N1 peroxidase-GFP cell lines --- p.24 / Chapter Chapter 4 --- Discussion --- p.26 / Chapter 4.1. --- Trafficking from the ER to the extracellular matrix --- p.26 / Chapter 4.2. --- Secretion through PM by exocytosis --- p.28 / Chapter 4.3. --- Time required for the secretory pathway --- p.29 / Chapter 4.4. --- Similarities of 40K and N1 --- p.30 / Chapter 4.5. --- Future perspectives --- p.30 / References --- p.79

Endocytosis is essential for eukaryotic cells. However, relatively little is known about the endocytic pathway and its molecular machinery in plant cells. In this research, a highly conserved membrane protein called secretory carrier membrane protein 1 (SCAMP) from rice (Oryza sativa) (OsSCAMP1) was employed as a tool to study the plant endocytosis. Toward this goal, I have generated polyclonal antibodies specific to SCAMP and transgenic tobacco BY-2 cell lines expressing yellow fluorescence protein (YFP)-SCAMP fusion. Confocal microscopy study showed that SCAMP localized to both plasma membrane (PM) and motile organelles. Further drug treatment and uptake studies demonstrated that these organelles are early endosomes distinct from Golgi and prevacuolar compartment (PVC), because they colocalized with the endosomal marker FM4-64. Immunogold electron microscopy study with SCAMP antibodies has identified the early endosome (EE) as a vesicular tubular membrane organelle, which resembles the structure of trans-Golgi network (TGN). These results indicate that the secretory and endocytic pathways are merged at the TGN which may serve as the sorting station for both pathways. / Since brefeldin A (BFA) induced both TGN and Golgi to form similar aggregates or BFA compartments in tobacco BY-2 cells, studies were also performed to sort out these BFA-induced compartments. Here I have demonstrated that the BFA-induced compartments derived from Golgi and TGN are physically distinct where the TGN aggregates were usually found to be surrounded by the Golgi aggregates in the same cells in both confocal immunofluorescent and immunogold EM studies. Furthermore, the internalized endosomal marker FM4-64 was found to colocalize with the TGN-derived BFA compartments but separated from the Golgi aggregates, whereas the endocytosis inhibitor tyrphostin A23 prevented TGN but not Golgi from forming BFA compartments. Therefore, the secretory Golgi organelle is functinally distinct from the endocytic TGN/EE in their responses to BFA treatment in plant cells. / The possible roles of SCAMPs in cytokinesis were also investigated. In transgenic tobacco BY-2 cells expressing the TGN/EE marker SCAMP-YFP, SCAMPs were found to be concentrated in the developing cell plate together with the internalized endosomal marker FM4-64 under confocal microscopy and this was further confirmed by immunogold electron microscopy studies with SCAMP antibodies. These results have demonstrated that SCAMPs, TGN and endocytosis are all involved in the cell plate formation during cytokinesis in plant cells. / Lam, Sheung Kwan. / Adviser: Jiang Liwen. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3266. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 176-191). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Foliar application of the phytotoxic herbicide diquat dibromide was made to twenty tuliptree seedlings actively growing under field conditions on October 6, 1973, at the Purdue Davis farm in Randolph County, Indiana. Herbicidal extraction was accomplished by two extraction procedures: Langlois, et. al., (1963), and a method described in the Pesticide Analytical Manual (9/1/67). Herbicidal application methods utilized two concentrations and three time periods for translocation to occur.Results from the herbicidal application to the tuliptree seedlings indicate that diquat dibromide is present in all parts of the seedling trees within a two hour time period, and that relative amounts of diquat per plant organ are time dependent.Ball State UniversityMuncie, IN 47306

Bibliography: leaves 151-184 / vi, 184 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Botany, 1990

The symbiotic unit of an arbuscular mycorrhizal fungus and its host is able toachieve and maintain far higher inflow of nutrients than non-mycorrhizal roots. The colonization strategy of the mycobiont within the plant is intrinsic to the symbiosis with respect to both structural adaptations and nutrient exchange. An investigation into the effect of Glomus etunicatum colonization on the structure and phloem transport in Eragrostis curvula (Umgeni) allowed for greater insight into the dynamic of the symbiosis. The combined use of stains (such as Trypan Blue, Chlorazol Black, Safranin and Fast Green), and techniques, (such as freeze-microtome transverse sectioning and permanent slide preparations) contributed to a successful general observation of an intermediate colonization strategy using light microscopy methods. However, clarity into structural detail of mycorrhizal forms required electron microscopy studies. The SEM method used with freeze fracture was a relatively quick and simple method allowing for the observation of surface and internal features. The TEM method allowed for highresolution images providing insight into the variations in the apoplasmic compartmental form, and how this may relate to the function of the symbiosis with regard to fungal coils or arbuscules. The apoplasmic nature of mycorrhizas was substantiated and no symplasmic connections were found between symbionts. Fluorescence studies demonstrated that 5,6-carboxyfluorescein was transported through the phloem into the roots of E. curvula, but remained predominantly in the root phloem. Unloading only occurred in optimal nutrient exchange areas of meristimatic lateral or apical growth regions. It was not possible, using fluorescence techniques and related equipment available, to conclusively establish if there were symplasmic connections between the mycobiont and its host or if bidirectional transfer of nutrients occurred at the same interface.

Call number: LD2668 .T4 1985 J36 / Master of Science

[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.

Call number: LD2668 .T4 1985 M444 / Master of Science