Fósforo (P) é um dos principais nutrientes que limitam a produção vegetal. Em arabidopsis, sua deficiência reduz o comprimento da raiz principal e aumenta o número e a densidade de raízes laterais. O isolamento e caracterização de mutantes têm ajudado a elucidar a função de genes envolvidos na superação da deficiência de P. Este estudo objetivou fazer a caracterização de respostas morfo-fisiológicas dos mutantes de Arabidopsis thaliana p9, p23 e p37 a suprimentos contrastantes de P, bem como avaliar interações nutricionais de P com outros nutrientes. Este trabalho foi desenvolvido em colaboração com a University of California at Davis, Davis - Califórnia, EUA. Todos os estudos foram conduzidos em câmara de crescimento. Entre os estudos conduzidos citam-se: efeito de formulações de meios de cultura na arquitetura radical; caracterização morfo-fisiológica dos mutantes; transferência de plantas entre meios de cultura com contrastes de P e nitrogênio (N); respostas as interações nutricionais P x Fe e P x N. A maioria das avaliações centraram-se no desenvolvimento do sistema radical, porém em alguns estudos, analisou-se a expressão de genes de resposta à limitação por P. A presença de ácidos nucléicos no meio de cultura reduz o desenvolvimento radical dos três mutantes, sobretudo em p9. A ausência de Fe no meio permite resgate do fenótipo radical de COL em p9, enquanto a supressão de N possibilita resgate do fenótipo em p23 e p37, independente da condição de P. A inibição radical em arabidopsis causada pelo Fe é agravada sob deficiência de P. Parte do fenótipo radical dos mutantes pode ser causada por defeitos na síntese e/ou sinalização de auxinas ou citocininas. As mutações de p9 e p23 foram localizadas no braço superior do cromossomo 1, próximas ao marcador F23M19 onde se obteve as menores taxas de recombinação (0,0% - p9Ler e 7,8% - p23Ler). / Phosphorus (P) is one of the main limiting nutrients to plant production. In arabidopsis, P deficiency reduces the primary root length and increases the number and the density of lateral roots. Isolation and characterization of mutants have contributed to better understanding the function of several genes involved in overcoming P starvation. This study has had as objective figure out morpho-physiological response of the p9, p23 and p37 Arabidopsis thaliana mutants in different P supply conditions, as well as evaluates and identify nutritional interactions between P and other nutrients. This work was developed in a collaborative work with the University of California at Davis, Davis - California, U.S.A. All studies were carried out in growth chamber. Among the conducted studies there are: effect of media on the root arquitecture; morphological and physiological characterization of the mutants; studies with plant transference from media with different P and nitrogen (N) levels and check for nutritional interactions between P x Fe and P x N. Most of the evaluations were focused on root development. However, in some studies we also analyzed the expression of genes related to P limitation. The presence of nucleic acids in the growth media reduces root development of the three mutants, particularly in p9. The absence of Fe in the media rescues the COL root phenotype in p9, while N suppression rescues that phenotype in p23 and p37, regardless of the P condition. The root inhibition in arabidopsis caused by Fe is stronger under P deficiency. Part of the mutant root phenotype might be caused by defects in the synthesis and/or signaling of auxins or cytokinins. The p9 and p23 mutations were mapped to the upper arm of chromosome 1, next to marker F23M19 for which the lowest recombination ratios were obtained (0.0% - p9Ler and 7.8% - p23Ler).

<p>The flower is debatably the most complex of the plant organs, composed of far more tissues than any other plant organ system, and, as such, the molecular mechanisms that govern tissue specification and development have only just begun to be explored. One tissue that has seen little research is the stigma. The stigma is the apical-most part of the gynoecium and is designed to trap pollen grains on specialized cells called stigma papillae and provide the means for them to germinate. Using a forward genetic screen, many mutants which exhibit defects in stigma development were identified. The identification of the genes with the causative mutations will uncover new genes involved in stigma development which can be linked to previously discovered genes to build a more comprehensive gene regulatory network of stigma specification. Over the course of the screen, a new mutant, <i>lily</i>, was identified which has open buds throughout most of flower development. This valuable genetic tool allows microscopy and chemical applications at younger stages than emasculation allows. Here, <i>lily</i> was used to show the importance of reactive oxygen species in stigma specification and identity maintenance. In addition to specification, the morphological differentiation of stigma papillae was investigated. Using reverse and chemical genetics, live-imaging, and morphometrics, it was found that stigma papillae grow via an anisotropic diffuse growth mechanism. Collectively, these findings constitute a substantial breaking of ground for stigma research, providing a solid foundation for future investigation.</p>

Wong, Hon-Kit. / Thesis submitted in: December 2003. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 119-139). / Abstract in English and Chinese. / Thesis committee --- p.i / Statement --- p.ii / Abstract --- p.iii / Acknowledgement --- p.vii / General abbreviations --- p.ix / Abbreviations of chemicals --- p.x / List of figures --- p.xii / Table of contents --- p.xvi / Chapter 1 --- Literature review --- p.1 / Chapter 1.1 --- Nitrogen assimilation and regulation in plants --- p.1 / Chapter 1.2 --- Asparagine metabolism and its gene regulation in plants --- p.2 / Chapter 1.2.1 --- A brief introduction of asparagine --- p.2 / Chapter 1.2.2 --- Asparagine synthetase gene family in A. thaliana --- p.3 / Chapter 1.2.3 --- Reciprocal regulation of ASN1 and ASN2 gene --- p.3 / Chapter 1.2.4 --- Primary structure difference of ASN1 and ASN2 protein --- p.4 / Chapter 1.2.5 --- "ASN1 overexpressor support the notion that it is a major gene regulating the free asparagine levels in plant tissues, while ASN may play different physiological function(s)" --- p.2 / Chapter 1.2.6 --- Evidence support ammonium-dependent AS in plant --- p.6 / Chapter 1.3 --- Ammonium toxicity and mechanism of ammonium toxicity to plant --- p.7 / Chapter 1.3.1 --- Ammonium toxicity --- p.7 / Chapter 1.3.2 --- Mechanism of ammonium toxicity --- p.9 / Chapter 1.4 --- "Relationship among asparagine, ammonium, and stress physiology" --- p.12 / Chapter 1.4.1 --- Ammonium accumulates under stress conditions --- p.12 / Chapter 1.4.2 --- Asparagine accumulates under stress conditions --- p.14 / Chapter 1.5 --- Relationship of asparagine metabolism and photorespiration --- p.17 / Chapter 1.5.1 --- A brief introduction of photorespiratory pathway --- p.17 / Chapter 1.5.2 --- Involvement of Asn in the photorespiration nitrogen cycle --- p.18 / Chapter 1.5.3 --- Reassimilation of ammonium released from photorespiration --- p.19 / Chapter 1.5.4 --- Photorespiration and stress physiology --- p.21 / Chapter 1.6 --- Role of amino acids in abiotic stress resistance --- p.23 / Chapter 1.6.1 --- Overview --- p.23 / Chapter 1.6.2 --- Proline accumulation and plant adaptation to water deficits and salinity stress --- p.24 / Chapter 1.6.3 --- Role of amino acids as precursors of quaternary ammonium compounds serving as compatible osmolytes --- p.28 / Chapter 1.7 --- A brief history of protoplast transient expression systems --- p.35 / Chapter 1.8 --- Advantages of mesophyll protoplast transient expression systems --- p.37 / Chapter 1.9 --- Hypothesis and main idea of this study --- p.38 / Chapter 2 --- Methods and Materials --- p.39 / Chapter 2.1 --- Materials --- p.39 / Chapter 2.1.1 --- Plants --- p.39 / Chapter 2.1.2 --- Bacterial strains and plasmid vector --- p.39 / Chapter 2.1.3 --- Primer used --- p.39 / Chapter 2.1.4 --- Chemicals and reagents used --- p.40 / Chapter 2.1.5 --- Solution used --- p.40 / Chapter 2.1.6 --- Commercial kits used --- p.40 / Chapter 2.1.7 --- Equipment and facilities used --- p.40 / Chapter 2.2 --- Methods --- p.41 / Chapter 2.2.1 --- Growth medium and condition --- p.41 / Chapter 2.2.1.1 --- Normal growth condition --- p.41 / Chapter 2.2.1.2 --- Growth medium and stresses treatments --- p.41 / Chapter 2.2.1.3 --- Plant growth in Azaserine medium --- p.43 / Chapter 2.2.2 --- Biochemical Assay --- p.44 / Chapter 2.2.2.1 --- Ammonium assay --- p.44 / Chapter 2.2.2.2 --- Ammonium extraction for ammonium assay --- p.46 / Chapter 2.2.2.3 --- Soluble protein determination --- p.46 / Chapter 2.2.2.4 --- Detection of chlorophyll content --- p.47 / Chapter 2.2.3 --- Molecular techniques --- p.47 / Chapter 2.2.3.1 --- Bacterial cultures for recombinant DNA --- p.47 / Chapter 2.2.3.2 --- Recombinant DNA techniques --- p.48 / Chapter 2.2.3.3 --- Transformation of DH5a Competent cell --- p.48 / Chapter 2.2.3.4 --- Gel electrophoresis --- p.49 / Chapter 2.2.3.5 --- DNA and RNA extraction from plant tissues --- p.50 / Chapter 2.2.3.6 --- Generation of cRNA probes for Northern blot analyses --- p.52 / Chapter 2.2.3.7 --- Northern blot analysis --- p.53 / Chapter 2.2.3.8 --- PCR techniques --- p.54 / Chapter 2.2.3.9 --- Sequencing --- p.55 / Chapter 2.2.4 --- Genetic techniques --- p.56 / Chapter 2.2.4.1 --- Backcross of Azaserine resistant mutant --- p.56 / Chapter 2.2.4.2 --- Phenotype screening of backcross progenies --- p.56 / Chapter 2.2.5 --- Transient gene expression --- p.57 / Chapter 2.2.5.1 --- Protoplast isolation from Arabidopsis leave --- p.57 / Chapter 2.2.5.2 --- Protoplast transformation --- p.58 / Chapter 2.2.5.3 --- Gus protein extraction from protoplasts --- p.59 / Chapter 2.2.5.4 --- Gus assay --- p.60 / Chapter 2.2.5.5 --- MU calibration standard --- p.60 / Chapter 2.2.5.6 --- Sample assay --- p.60 / Chapter 3 --- Result --- p.61 / Chapter 3.1 --- Expression of ASN2 and ammonium assay in Arabidopsis thaliana under various stress conditions and senescence --- p.61 / Chapter 3.1.1 --- Ammonium assay of wild type seedlings under stress conditions --- p.61 / Chapter 3.1.2 --- Kinetic studies of ASN2 expression under different stresses treatments --- p.65 / Chapter 3.1.3 --- Ammonium assay of wild type seedlings under stress conditions --- p.70 / Chapter 3.2 --- NH4+ regulation on expression of ASN2 promoter --- p.73 / Chapter 3.2.1 --- The cloning ASN2 promoter --- p.73 / Chapter 3.2.1.1 --- Defining of ASN2 promoter region --- p.73 / Chapter 3.2.1.2 --- PCR amplification of ASN2 promoter from genomic sequence --- p.77 / Chapter 3.2.1.3 --- Cloning ASN2 promoter into transient gene expression vector (pBI221 vector) --- p.80 / Chapter 3.2.2 --- Transient gene expression --- p.84 / Chapter 3.2.2.1 --- Arabidopsis leave mesophyll protoplasts isolation --- p.84 / Chapter 3.2.2.2 --- Transformation and GUS expression assay --- p.87 / Chapter 3.3 --- Characterization ASN2 transgenic plants under stress conditions --- p.91 / Chapter 3.3.1 --- Construction of ASN2 transgenic plants --- p.91 / Chapter 3.3.2 --- Characterization of ASN2 transgenic plants --- p.93 / Chapter 3.3.2.1 --- Ammonium assay of ASN2 transgenic plant under different concentration of ammonium --- p.93 / Chapter 3.3.2.2 --- Ammonium assay of ASN2 transgenic plant under high light irradiance --- p.93 / Chapter 3.4 --- Characterization of mutant plants (AzaR) that showed altered ASN2 expression --- p.97 / Chapter 3.4.1 --- Phenotype of azaserine resistant mutant --- p.97 / Chapter 3.4.2 --- ASN2 expression level up-regulated in azaserine resistant mutant --- p.99 / Chapter 3.4.3 --- Checking for linkage between azaserine resistance and ASN2 overexpression --- p.101 / Chapter 3.4.4 --- Crossing the mutant with Landsberg for mapping the azaserine resistant mutant --- p.106 / Chapter 4 --- Discussion --- p.108 / Chapter 4.1 --- ASN2 may relate to ammonium metabolism --- p.108 / Chapter 4.2 --- ASN2 transgenic plants and their response under stresses conditions --- p.111 / Chapter 4.3 --- ASN2 promoter studies by transient gene expression method --- p.112 / Chapter 4.3.1 --- Identification of promoter region --- p.113 / Chapter 4.3.2 --- Isolation of protoplasts from Arabidopsis leaf --- p.114 / Chapter 4.3.3 --- Studies of ASN2 promoter transient gene expression in A thaliana protoplasts --- p.114 / Chapter 4.4 --- Azaserine Resistant Mutant --- p.115 / Chapter 4.4.1 --- Overexpression of ASN2 gene in Azaserine resistant mutant and checking for linkage --- p.115 / Chapter 4.4.2 --- Cross of Azaserine Resistant mutants with Lersberg ecotype for mapping --- p.116 / Chapter 5 --- Conclusion and prospective --- p.118 / References --- p.119 / Appendix --- p.140

胞吐作用定義為囊運小泡將物質運輸到質膜或細胞外空間的轉運過程。其中關鍵的一步發生在同源SNARE 蛋白介導的膜融合之前，即將胞吐囊泡瞄向並靶定在適當的質膜位點。先前在酵母和哺乳動物中的研究表明，一個名為exocyst 的蛋白質複合體在這一關鍵步驟發揮作用。exocyst 蛋白複合體最早在酵母發現，之後這個複合體也在哺乳動物中被發現。這個複合體包含8 個不同的亞基：SEC3，SEC5，SEC6，SEC8，Sec10，Sec15，Exo70 和Exo84。Exocyst 同源蛋白也已在植物中發現。相比酵母和動物，exocyst 在植物體內的功能還鮮為人知，尤其是在胞吐運輸過程中的作用 。通過瞬時表達熒光蛋白標記的擬南芥同源的exocyst 蛋白Exo70：AtExo70E2 以及使用這個同源物的特異抗體，我們在擬南芥和煙草BY－2 懸浮培養細胞中發現了一種新的細胞器，並命名為exocyst 陽性細胞器（EXPO）。這種細胞器分別位於質膜或是細胞質中。由於它未能與任何傳統的細胞器標記物重合，或是被布雷菲爾德菌素A，渥曼青黴素和刀豆素A 影響，以及不能與FM4-64 重合，我們判斷這些細胞器不定位於常規的分泌或胞吞途徑中。對於快速冷凍樣本進行的免疫電子顯微鏡顯示EXPO 的雙膜性質，同時也發現了陽性標記的位於質膜外的單膜囊泡的存在。與此同時，在野生型細胞中也發現了同樣結構的細胞器。EXPO和自噬體非常相似， 都有兩層膜。然而，EXPO 不能被的自噬標記物（AtAtg8e）所標記。同時，在營養脅迫條件下，EXPO 的數量也沒有增加。因此，EXPO 代表著植物所特有的一種非常規分泌形式。 / 此外，通過在擬南芥原生質體內進行瞬時表達，我進一步證實在AtExo70E2 存在的條件下， 一些exocyst 成員可以被招募到EXPO 。AtExo70E2 的旁系同源物AtExo70A1 是在這方面物法取代AtExo70E2 的作用。蛋白蛋白相互作用分析證實了AtSec10 或AtSec6 與AtExo70E2 之間的相互作用。 AtExo70E2，而不是它在酵母或是動物中的同源蛋白，可以誘導EXPO 在動物細胞中的形成。反之，人或是酵母Exo70 同源蛋白都不能誘導EXPO 在植物細胞中的形成。這些結果表明AtExo70E2 在EXPO 形成過程中的特定的以及至關重要的作用。 / Exocytosis defines the process in which vesicles transport substances to the plasma membrane (PM)/extracellular space of the cell. One key step of exocytosis is the targeting and docking of the exocytic vesicles to the appropriate PM sites, which is prior to membrane fusion mediated by soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE). Previously studies have demonstrated that a protein complex called exocyst complex is involved in this key step in yeast and mammals. The exocyst complex, containing eight different subunits: Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70 and Exo84, was first identified in yeast and subsequently in mammals. Exocyst homologs have also been found in plants. In comparison to its yeast and animal counterparts, little is known about the function of exocyst proteins in plants especially in the process of exocytosis. By using both antibodies specific for one of the orthlogs of exocyst protein: AtExo70E2 as well as transiently-expressed fluorescently-tagged constructs for this exocyst subunit, a novel organelle termed exocyst-positive organelle (EXPO) was identified in suspension cultured Arabidopsis and tobacco BY-2 cells. These organelles were located to both the plasma membrane and cytosol. Based on their failure to overlap with any conventional organelle markers or response to brefeldin A (BFA), wortmannin or concanamycin A (ConcA) treatments, as well as their inability to take up the endocytic dye FM4-64, these organelles were thus not lie on the conventional secretory or endocytic pathways of plant cells. Immunogold electron microscopy (EM) of cryofixed samples revealed the double membrane nature of EXPO and also produced labeling of large single-membrane bound vesicles outside of the PM. These structures were also identified in wild type cells. EXPO and autophagosomes are similar in that both have two boundary membranes. However, EXPO did not label positively with YFP-AtAtg8e, a standard marker for autophagosomes, nor did the number of EXPO increase when the cells were subjected to nutrient stress. Therefore, EXPO represents a form of unconventional secretion unique to plants. / Further studies demonstrated that a number of exocyst subunits can be positively recruited to EXPO in the presence of AtExo70E2 by performing transient expression in Arabidopsis protoplasts. The paralog AtExo70A1 is unable to substitute for AtExo70E2 in this regard. Protein-protein interaction assay have confirmed the interaction between AtExo70E2 and AtSec6 and AtSec10. AtExo70E2, but not its yeast counterpart, is also capable of inducing EXPO formation in animal cells. Inversely, neither human nor yeast Exo70 homologs are able to cause the formation of EXPO in Arabidopsis protoplasts. These results point to a specific and crucial role for AtExo70E2 in EXPO formation. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Ding, Yu. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 101-118). / Abstracts also in Chinese. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgements --- p.v / Table of Contents --- p.vii / List of Tables --- p.x / List of Figures --- p.xi / List of Abbreviations --- p.xiv / Chapter CHAPTER 1 --- p.1 / General Introduction --- p.1 / Chapter 1.1 --- The secretory system in eukaryotic cells --- p.2 / Chapter 1.2 --- Exocytosis and exocyst complex --- p.6 / Chapter 1.3 --- Project Objectives --- p.7 / Chapter CHAPTER 2 --- p.9 / Exocyst-positive organelles (EXPOs) mediate unconventional protein secretion in plant cells --- p.9 / Chapter 2.1 --- Abstract --- p.10 / Chapter 2.2 --- Introduction --- p.11 / Chapter 2.3 --- Materials and Methods --- p.12 / Chapter 2.4 --- Results --- p.20 / Chapter 2.4.1 --- Expression pattern of different AtExo70 paralogs with fluorescent tag in Arabidopsis protoplasts --- p.20 / Chapter 2.4.2 --- The organelles labeled by AtExo70E2 are distinct from well known endomembrane markers --- p.23 / Chapter 2.4.3 --- The AtExo70E2 positive organelles do not lie on the secretory or endocytic pathways --- p.27 / Chapter 2.4.4 --- Arabidopsis Exo70E2-specific antibodies confirm identity of AtExo70E2-positive organelles --- p.31 / Chapter 2.4.5 --- AtExo70E2 positive organelles are true and novel double membrane organelles --- p.33 / Chapter 2.4.6 --- EXPO are not autophagosomes but sequester cytosolic proteins to release them into the apoplast --- p.41 / Chapter 2.5 --- Discussion --- p.53 / Chapter 2.5.1 --- EXPO: novel organelles labeled by exocyst --- p.53 / Chapter 2.5.2 --- EXPO and autophagosome: same or not? --- p.55 / Chapter 2.5.3 --- EXPO: the evidence of unconventional secretion in plant cells --- p.56 / Chapter 2.6 --- Perspectives --- p.56 / Chapter CHATER 3 --- p.58 / AtExo70E2 is essential for exocyst subunit recruitment and for EXPO formation in both plants and animals --- p.58 / Chapter 3.1 --- Abstract --- p.59 / Chapter 3.2 --- Introduction --- p.60 / Chapter 3.3 --- Materials and Methods --- p.62 / Chapter 3.4 --- Results --- p.70 / Chapter 3.4.1 --- AtExo70E2 is required for the membrane recruitment of a number of exocyst subunits --- p.70 / Chapter 3.4.2 --- AtExo70E2 is required for the recruitment of some other, but not all, AtExo70 subunits --- p.74 / Chapter 3.4.3 --- AtExo70A1 is unable to recruit other exocyst subunits --- p.74 / Chapter 3.4.4 --- FRET and BiFC confirm interactions between AtExo70E2 and other exocyst subunits --- p.80 / Chapter 3.4.5 --- Arabidopsis Exo70E2 can also induce EXPO formation in animal cells --- p.84 / Chapter 3.4.6 --- Neither human nor yeast Exo70 can induce EXPO in plant protoplasts --- p.84 / Chapter 3.4.7 --- EXPO induced by AtExo70-GFP expression in HEK cells do not colocalize with standard organelle markers --- p.87 / Chapter 3.4.8 --- Electron microscopy confirms the presence of EXPO-like, double membrane structures in HEK cells after expression of AtExo70E2-GFP --- p.87 / Chapter 3.5 --- Discussion --- p.91 / Chapter 3.5.1 --- Plant exocyst and the discovery of EXPO --- p.91 / Chapter 3.5.2 --- AtExo70E2 is a key player in exocyst recruitment onto EXPO --- p.93 / Chapter 3.5.3 --- AtExo70E2 expression as a signal for EXPO formation --- p.96 / Chapter 3.6 --- Perspectives --- p.100 / References: --- p.101 / Chapter List of publications derived from this Ph.D. thesis research --- p.119

No description available.

Wong Lee. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 152-169). / Abstracts in English and Chinese. / Thesis Committee --- p.i / Abstract --- p.ii / 摘要 --- p.iv / Acknowledgements --- p.v / Abbreviations --- p.vi / List of Figures --- p.vii / List of Tables --- p.ix / Table of Contents --- p.xi / Chapter 1 --- Literature Review --- p.1 / Chapter 1.1 --- GS-GOGAT cycle in plants and bacteria --- p.2 / Chapter 1.2 --- Roles of PII in regulation of glutamine synthetase in E. coli --- p.4 / Chapter 1.2.1 --- Regulation of GS in E. col --- p.4 / Chapter 1.2.2 --- Transcriptional regulation --- p.5 / Chapter 1.2.2.1 --- The glnALG operon / Chapter 1.2.2.2 --- Intracellular signal through PII and Utase-UR / Chapter 1.2.2.3 --- NRI/NRII as two-component system / Chapter 1.2.3 --- Post-translational regulation by adenylylation and deadenylylation --- p.11 / Chapter 1.2.3.1 --- Role of PII in adenylylation/deadenylylation / Chapter 1.2.4 --- Cumulative Feedback Inhibition --- p.15 / Chapter 1.3 --- PII in other bacteria --- p.15 / Chapter 1.4 --- PII in other higher organisms --- p.20 / Chapter 1.5 --- "PII protein is conserved in enteric bacteria, cyanobacteria, archaea, algae and higher plants" --- p.23 / Chapter 1.6 --- Nitrogen assimilation in higher plants --- p.25 / Chapter 1.6.1 --- Nitrogen uptake --- p.25 / Chapter 1.6.2 --- Primary nitrogen assimilation --- p.28 / Chapter 1.6.3 --- Nitrogen transport and interconversions --- p.28 / Chapter 1.6.4 --- Nitrogen flow --- p.29 / Chapter 1.6.5 --- Molecular regulation of nitrogen assimilation and possible roles of PII in plants --- p.30 / Chapter 1.7 --- Hypothesis of this study --- p.33 / Chapter 2. --- Materials and Methods --- p.35 / Chapter 2.1 --- Materials --- p.35 / Chapter 2.1.1 --- Plant materials --- p.35 / Chapter 2.1.2 --- Equipment and facilities used --- p.35 / Chapter 2.1.3 --- Growth media --- p.37 / Chapter 2.1.4 --- Buffers and solutions used in RNA extraction --- p.38 / Chapter 2.1.5 --- Buffers and solutions used in Northern blot analysis --- p.41 / Chapter 2.1.6 --- Molecular reagents and synthetic oligonucleotides used in the preparation of DIG-labeled probes --- p.45 / Chapter 2.1.7 --- Chemicals used in BioRad Protein Assay --- p.48 / Chapter 2.1.8 --- Chemicals and apparatus used in chlorophylls extraction and quantitation --- p.49 / Chapter 2.1.9 --- Buffers and solutions used in the glutamine synthetase enzyme extraction and assay --- p.49 / Chapter 2.2 --- Methods --- p.50 / Chapter 2.2.1 --- Plant growth --- p.50 / Chapter 2.2.2 --- RNA extraction --- p.52 / Chapter 2.2.3 --- Northern blot analysis --- p.54 / Chapter 2.2.4 --- Chlorophyll extraction and quantitation --- p.61 / Chapter 2.2.5 --- Root length measurement --- p.61 / Chapter 2.2.6 --- Total glutamine synthetase enzyme assay --- p.61 / Chapter 2.2.7 --- Measurement of total nitrogen in seeds --- p.64 / Chapter 2.2.8 --- Recording growth and development --- p.64 / Chapter 3. --- Results --- p.65 / Chapter 3.1 --- Overexpression ofPII and truncated PII mRNA in transgenic plants --- p.65 / Chapter 3.2 --- General growth characteristics of PII transgenic plants when grown on soil --- p.70 / Chapter 3.3 --- Physiological changes in the PII and truncated PII transgenic lines --- p.72 / Chapter 3.3.1 --- Fresh weight of the young seedlings --- p.73 / Chapter 3.3.2 --- Chlorophyll contents of shoots --- p.75 / Chapter 3.3.3 --- Root lengths --- p.88 / Chapter 3.3.4 --- Carbon and nitrogen status of seeds --- p.94 / Chapter 3.4 --- Expression of nitrogen assimilatory genes in PII and truncated PII transgenic lines --- p.96 / Chapter 3.4.1 --- Nitrate reductases --- p.96 / Chapter 3.4.2 --- Glutamine synthetases --- p.99 / Chapter 3.4.3 --- Asparagine synthetases --- p.107 / Chapter 3.5 --- Total glutamine synthetase enzyme activity --- p.117 / Chapter 4. --- Discussion --- p.126 / Chapter 4.1 --- Overexpressing PII and truncated PII in the transgenic plants --- p.126 / Chapter 4.2 --- The overall growth and development --- p.135 / Chapter 4.3 --- Chlorophyll --- p.135 / Chapter 4.4 --- Root length --- p.137 / Chapter 4.5 --- Expression of nitrogen assimilatory genes --- p.138 / Chapter 4.5.1 --- Genes encoding nitrate reductase --- p.138 / Chapter 4.5.2 --- Genes encoding glutamine synthetase --- p.140 / Chapter 4.5.3 --- Genes encoding asparagine synthetase --- p.141 / Chapter 4.6 --- Overall GS enzyme levels in the rosette leaves --- p.144 / Chapter 4.7 --- N/C ratio of the seed storage --- p.146 / Chapter 4.8 --- Proposed model for the roles of PII --- p.147 / Chapter 4.9 --- Conclusions --- p.149 / Chapter 4.10 --- Further studies --- p.150 / References --- p.152

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Intercellular signalling is essential for multicellular organisms to coordinate growth and development, and is mediated by a huge variety of proteins. Some signalling pathways rely on the proteolytic cleavage of membrane proteins by a relatively newly discovered process of regulated intramembrane proteolysis (RIP), the cleavage of proteins within a transmembrane domain. There are four classes of intramembrane cleaving proteases (ICliPs) – Rhomboids, Site-2-proteases, Signal peptide peptidases and γ-secretase. Of all the ICliPs studied to date, γ-secretase is unique, as it is comprised of a four-protein complex, and is only found in multicellular organisms. A vast amount of research is carried out on the γ-secretase complex, not just because of its role in developmentally important pathways, such as NOTCH signalling, but also due to its role in Alzheimer’s disease. The β-amyloid precursor protein (APP) is cleaved by γ-secretase, and defects in this process result in the release of abnormal peptides that form the senile plaques in the brains of Alzheimer’s disease patients. Homologues of the four components of γ-secretase (PRESENILIN (PS), NICASTRIN (NCT), ANTERIOR PHARYNX DEFECTIVE-1 (APH-1) and PRESENILIN ENHANCER-2 (PEN-2)) are found in plants. The aim of this thesis was to characterise the potential γ-secretase components in Arabidopsis thaliana, to determine whether they form a complex, and to analyse what role, if any, they play in plant signalling. The members of the putative Arabidopsis γ-secretase complex (AtPS1 and 2, AtNCT, AtAPH1 and AtPEN2) were identified through BLAST searches, and found to be uniformly expressed. Analysis of T-DNA insertion mutants in each of these genes, and combinations there of, revealed no gross morphological differences to wild type under normal growth conditions and when subjected to a range of stresses. Protein fusions to GFP under the control of the 35S promoter were constructed and stably transformed into plants. AtPEN2:GFP is expressed throughout the plant, and accumulates in BFA sensitive Golgi bodies in roots. AtPS1:GFP, only accumulates strongly in developing seeds. Native blue PAGE was used to look for high molecular weight complexes (HMW) containing AtPEN2:GFP and AtPS1:GFP. Both fusion proteins were found in similar sized HMW complexes. A variety of methods were used to look for substrates of the iv putative γ-secretase complex in Arabidopsis, and although no specific substrates were identified, a potential role in seed development has been established.

Philosophiae Doctor - PhD / Plants are continuously exposed to varying conditions in their environment, to which they have to adapt by manipulating various cellular processes. Environmental (abiotic) and pathogen (biotic) stress are challenges against which plants have to defend themselves. Many plant responses to stress stimuli are a result of cellular processes that can be divided into three sequential steps; namely signal perception, signal transduction m1d execution of a response. Stress signal perception is, in most of these cases, facilitated by cell surface or intracellular receptors that act to recognize molecules presented to the cell. In several cases, hormones are synthesized in response to stress signals and in turn these hormones are perceived by cellular receptors that trigger signal transduction cascades. Propagation of signal transduction cascades is a complex process that results from activation of various signaling molecules within the cell. Second messengers like calcium (Ca2+) and guanosine 3', 5'-cyclic monophosphate (cGMP) play a vital role in mediating many signal transduction processes. The result of these signal transduction cascades is, in most instances, expression of genes that contribute to the plant's ability to cope with the challenges presented to it. Plant natriuretic peptides (PNPs) are novel plant hormones that regulate water and salt homeostasis via cGMP-dependent signaling pathways that involve deployment of Ca2+. The aim of this study is to partially characterize a PNP and a guanylyl cyclase, both from Arabidopsis thaliana. Guanylyl cyclases synthesize cGMP from the hydrolysis of guanosine 5' -triphosphate (GTP) in the cell. The study also aims to investigate the effect of drought and salinity on cGMP levels in plants, using sorbitol to mimic the osmolarity/dehydration effect of drought and NaCl as a source of salinity stress and thus link NaCl and sorbitol responses to both AtPNP-A and cGMP up-regulation.

N-acylethanolamines (NAEs) are fatty acid derivatives that occur naturally in plant and animal systems. In mammals, they regulate physiological functions, including neurotransmission, immune responses, vasodilation, embryo development and implantation, feeding behavior, and cell proliferation. NAEs are metabolized by fatty acid amide hydrolase (FAAH), which belongs to the amidase signature family. It is hypothesized that putative FAAH functions as the catalyst in the metabolism of N-acylethanolamine in tomato plants. To test the hypothesis, FAAH protein homologs were identified in tomato via in silico analysis. Among the six homologs identified, FAAH1 and FAAH2 were selected for further validation. This study is focused on 1) in silico analyses of SlFAAH2, 2) quantification of transcript levels for SlFAAH2, 3) determination of FAAH activity at various developmental stages of tomato, and 4) isolation of and synthesis of SlFAAH2 cDNA for cloning. Putative SlFAAH2 showed high homology to Arabidopsis FAAH1. Transcript levels, as measured by qPCR using RNA extracted from various developmental stages, were highest at 0 days and lowest at 4 days. Enzyme activity at certain developmental stages coincided with SlFAAH2 transcript levels. In order to confirm that putative SlFAAH2 encodes for an enzyme that hydrolyzes NAEs, SlFAAH2 gene was isolated from total RNA of tomato, cDNA was synthesized by reverse transcription and the gene was amplified by PCR for further cloning in a heterologous expression system for biochemical characterization. To gain better molecular and biochemical understanding of FAAH and determine its broader functions, it is pertinent to characterize FAAH in other plant species.