Thesis (M.Sc.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: leaf 115-122.

Thesis (M.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 119-125). Also available in electronic format on the Internet.

Thesis (Ph.D.)--Michigan State University. Biochemistry and Molecular Biology, 2008. / Title from PDF t.p. (viewed on July 7, 2009) Includes bibliographical references. Also issued in print.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2002. / Includes bibliographical references (leaves 238-266). Also available in electronic version. Access restricted to campus users.

Thesis (MScAgric)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Lemons with an elongated fruit shape achieve premium prices in certain discerning markets. Factors influencing the fruit shape of lemons were investigated to fmd means to produce a crop with a higher percentage of elongated lemons. Intra-plant factors were investigated to understand the variation in fruit shape within a single tree and even within the same fruit cluster. Bearing position (leafy vs. leafless inflorescences) and position in the canopy (inside vs. outside) were taken into consideration, along with the number of seeds, number of segments and rind thickness in the center of the fruit as well as stem- and stylar-ends. Bearing position and position in the canopy had no effect on fruit shape, while the number of seeds was positively correlated with elongated lemons. Rootstocks were evaluated to determine the influence of rootstock type on fruit shape. Twelve rootstocks were evaluated in total, at Addo, Citrusdal and Nelspruit. At all three locations rootstock type had no or little influence on fruit shape. Different scions were also evaluated at both Addo and Citrusdal to determine whether a certain scion characteristically produces elongated fruit. A total of 20 different scions were evaluated, and as opposed to rootstocks, there were larger variations between scions. Of the commercially-produced scions, 'Fino' lemon had the least variation, producing elongated lemons more consistently than 'Lisbon' and 'Eureka' lemons. Of the other scions, 'Cicily' lemon produced fruit with the smallest L:D ratio, while 'Vema' lemon was the scion producing fruit with the largest L:D ratio. 'Vema' lemon is, however, not an attractive fruit, having a thick rough rind. In the case of grapefruit, unwanted "sheepnosed" fruit with thick rinds are common in areas with a low winter temperature at night. 'Eureka' lemon fruit from six different climatic areas were compared to evaluate the difference in fruit shape. Cooler areas, such as Vaalharts, had more elongated fruit than areas with a higher winter temperature, such as Nelspruit. Altering lemon fruit shape was also attempted by chemical manipulation, usmg gibberellin, cytokinin or auxin containing products. Promalin® (GA4+7, BA), Accet" (GA4+7, BA), Corasil E® (2,4-D), Provide® (GA4+7) and ProGibb® (GA)) were sprayed at different times and different concentrations. Promalin'" was partly successful in altering fruit shape, but these changes were not large enough from a commercial point of view. Promalin'" also resulted in a lower percentage fruit set. Accel'", Corasil E®, Provide® and ProGibb® were not successful in altering fruit shape favorably, with Corasil E® having a strong thinning effect. / AFRIKAANSE OPSOMMING: Fakore wat die verlenging van suurlemoene beïnvloed Suurlemoene met 'n verlengde vrugvorm behaal hoë pryse in sekere markete. Faktore wat die vrugvorm van suurlemoene beïnvloed is bestudeer om praktyke te vind wat die produksie van verlengde suurlemoene kan verhoog. Intra-plant faktore is bestudeer om die variasie in vrugvorm binne 'n enkele boom en ook in dieselfde vrugtros te verstaan. Dra-posisie ("wit" en "groen" blomme) asook posisie in die boom (binnevrugte vs. buitevrugte ) is in aanmerking geneem. Die invloed van die hoeveelheid sade en segmente per vrug, asook skil dikte in die middle van die vrug en aan stingel- en kelkkant is ook bestudeer. Dra-posisie en posisie van vrug in die boom, het geen invloed op vrugvorm gehad nie, terwyl die hoeveelheid sade per vrug die beste met vrugvorm gekorreleer was. Die invloed van onderstam tipe op vrugvorm is ook geëvalueer. Vrugvorm van twaalf onderdstamme in totaal is te Addo, Citrusdal en Nelspruit ondersoek. By al drie areas is klein verskille in vrugvorm van verskillende onderstamme opgemerk. Saam met die onderstamme is 20 seleksies te Addo en Citrusdalondersoek, om te bepaal of 'n sekere seleksie 'n karakteristieke verlengde vrugvorm openbaar. In teenstelling met onderstamme, is groter variasie tussen seleksies gevind. Vandie kommersiële kultivars, het 'Fino' suurlemoen die minste variasie openbaar en deurgans verlende vrugte gelewer, terwyl 'Lisbon' en 'Eureka' suurlemoene groter variasie gehad het. Vandie ander seleksies, het 'Cicily' suurlemoen geneig om vrugte met die kleinsteL:D verhouding te lewer, terwyl'Vema' suurlemoen deurgans vrugte met 'n groter L:D verhouding gelewer het. 'Vema' suurlemoen is egter nie 'n aantreklike vrug nie, aangesien dit 'n dik skil het. In die geval van pommelos word ongewenste vrugte met 'n "skaapneus" vorm algemeen aangetref in areas met 'n lae mininmum winter temperatuur. Vrugvorm van 'Eureka' suurlemoene van ses verskillende klimaats areas is vergelyk. Koeler areas, soos Vaalharts, het meer verlengde vrugte gehad, terwyl Nelspruit met 'n hoër winter temperatuur, ronder vrugte produseer het. Daar is ook gepoog om suurlemoen vrugvorm te manipuleer d.m.v. chemiese bespuitings. Ouksiene, gibbereliene en sitokiniene asook kombinasies daarvan, is gebruik. Promalin® (GA4+7, BA), Accel® (GA4+7,BA), Corasil E® (2,4-D), Provide® (GA4+7) en ProGibb® (GA3) is by verskillende tye en verskillende konsentrasies gespuit. Promalin® was gedeeltelik suksesvol in verlenging van vrugte, maar die veranderinge was te klein uit 'n kommersiële oogpunt. Promalin® het ook tot uitdunning van vrugte gelei. Accel", Corasil E®, Provide® en ProGibb® was nie suksesvol in verandering van suurlemoen vrugvorm nie. Corasil E®het tot strawwe vruguitdunning gelei.

The literature on the effects of phytohormone on algae is clouded with contradictory reports. Reports have been published which substantiate and deny the effects of phytohormones in enhancing the growth and developmental processes in algae. The overall aim of this study was to investigate the response, if any, of the phytohormones indole-3-acetic acid (IAA), gibberellic acid A3 (GA) and kinetin on the physiology of the green alga, Scenedesmus quadricauda. Results obtained for the uptake of 14^C-IAA an(j l4C-kinetin by Scenedesmus strongly support the presumption that the alga does not absorb the hormones. The retention of the phytohormones by the alga is due to adsorption, and is independent of hormone concentration. Most of the label was adsorbed by the outer pectic layers of the cell wall.

A multiplicação de orquídeas in vitro vem sendo utilizada há algum tempo com objetivo de elevar a taxa de multiplicação, além de eliminar patógenos e reduzir gastos na produção. Esta ferramenta de trabalho vem sendo rotineiramente utilizada no nosso laboratório, ao longo de mais de duas décadas em nosso laboratório, em pesquisas básicas de fisiologia e de aprimoramento da técnica de clonagem, principalmente de orquídeas. Neste caso,o uso da técnica visa a obtenção de maior estabilidade genética dos regenerantes em cultivos de longa duração. Plantas do gênero Catasetum apresentam atividade indeterminada do meristema apical caulinar quando incubadas no escuro, originando em pouco tempo longos estolões com crescimento indeterminado, comportamento raro no reino vegetal. Cada nó do caule estiolado possui uma gema lateral que, quando isolada e incubada no claro, forma rapidamente uma planta completa, facilitando a micropropagação. Outras espécies de orquídeas valorizadas na floricultura não apresentam tal facilidade na multiplicação, mostrando-se recalcitrantes à micropropagação, como é o caso do gênero Dendrobium (Orchidaceae). O objetivo deste estudo foi obter uma melhor compreensão dos mecanismos fisiológicos envolvidos no estiolamento de plantas Dendrobium \"Second Love\", que apresenta crescimento caulinar limitado quando sob ausência de luz, buscando compreender os efeitos do escuro e dos hormônios etileno e giberelina, bem como do radical livre óxido nítrico e gás carbônico na atividade dos meristemas apicais e laterais dessa orquídea. Como objetivo complementar, buscou-se estimular um estiolamento mais pronunciado, visando com isto um aumento potencial na formação de gemas laterais, paralelamente à quebra da dominância apical e o crescimento subsequente dos estolões. As plantas de Dendrobium utilizadas faziam parte do nosso estoque de germoplasma in vitro. Após 120 dias de incubação no claro, as plantas foram transferidas para o escuro e tratadas com diferentes concentrações de ácido giberélico (GA), paclobutrazol (PA - inibidor de biossíntese de giberelina), etileno, 1-metilciclopropeno (1-MCP - inibidor da ação do etileno) e óxido nítrico (NO). Análises mensais dos teores de etileno e CO2 acumulados nos frascos foram realizadas por meio de cromatografia gasosa durante três meses. Após 30, 60 e 90 dias de tratamento no escuro, quantificou-se o número de gemas laterais presentes nos estolões, o número de gemas laterais e apicais que se desenvolviam, o tamanho dos estolões formados, bem como os respectivos valores de massas fresca e seca destes. Por fim, buscou-se avaliar ainda a importância da incubação na penumbra e no escuro sobre o crescimento caulinar, o número de gemas laterais e o desenvolvimento destas após três meses de cultivo. O crescimento no escuro dos caules das plantas de Dendrobium \"Second Love\" mostrou-se extremamente lento e limitado quando comparado ao das plantas de Catasetum fimbriatum. No entanto, quando tratadas com 1.000 μM de óxido nítrico, verificou-se ao final do terceiro mês que o número de gemas laterais era cinco vezes maior do que nas respectivas plantas controle. O tratamento com 10 ppm de etileno apresentou um aumento significativo no número de gemas e de estolões laterais, quando comparados ao controle a partir do segundo mês de incubação. Quanto ao tamanho do estolão apical, os tratamentos com 5 e 50 μM de GA não apresentaram nenhum efeito promotor sobre alongamento caulinar. Mesmo não apresentando a retomada da atividade meristemática apical, o tratamento com 5 μM de PA liberou um número maior de estolões laterais que o controle. Plantas tratadas com 1.000 ppm de NO, a partir do segundo mês de incubação, apresentaram um número elevado de estolões laterais, além dos mesmos apresentarem-se significativamente maiores. O tratamento com 100 ppm de 1-MCP apresentou o mesmo fenótipo das plantas tratadas no claro, ou seja, não estiolaram mesmo sob a ausência de luz. Quanto à emissão de etileno, observou-se que o tratamento com 1-MCP acarretou um aumento significativo na emissão deste gás pela planta, alcançando valores vinte vezes maiores do que no tratamento controle. Já a emissão de CO2 foi menor no tratamento claro quando comparada a maioria dos outros tratamentos no escuro. Os tratamentos em maiores concentrações de GA e NO pareceram promover algum tipo de estresse na planta (evidenciado pela necrose dos tecidos), demonstrando que a espécie em questão pode ser sensível à níveis elevados destas substâncias / In vitro multiplication has been used for some time in order to improve multiplication rate, eliminate pathogens and reduce the production costs. This working tool has been routinely used in our laboratory for over than two decades of basic research in plant physiology and enhancement of cloning technique, especially orchids, aiming to obtain greater genetic stability of regenerants in long term crops. Genus Catasetum present indeterminate shoot apical meristem activity when incubated in the dark, resulting, in a short period of time, long stolons with indeterminate growth: rare behavior in the plant kingdom. Each etiolated steam node has a lateral bud that, when isolated and incubated in light, quickly forms a complete plant, facilitating micropropagation. Other species of valued orchids in floriculture, such as genus Dendrobium (Orchidaceae), have no such facility in multiplication, being recalcitrant to micropropagation. The goals of this study were to gain a better understanding of the physiological mechanisms involved in plant etiolation in Dendrobium \"Second Love\", which has limited stem growth when in dark: and to understand the effects of dark, gibberellin and ethylene (plant hormones), as well as the free radical nitric oxide and carbon dioxide in the activity of apical and lateral meristems of the orchid. As a complementary objective, we tried to stimulate etiolation, aiming to potentially increase lateral buds formation and to break apical dominance with a subsequent stolons growth. Dendrobium plants used in this work were part of our in vitro germplasm stock. After 120 days of incubation in light, the plants were transferred to dark and treated with different concentrations of gibberellic acid (GA), paclobutrazol (PA - gibberellin biosynthesis inhibitor), ethylene, 1-methylcyclopropene (1-MCP - ethylene action inhibitor) and nitric oxide (NO). During a three months period, monthly analyzes of the accumulated levels of ethylene and CO2 in the flasks were performed using gas chromatography. After 30, 60 and 90 days of dark treatment the number of lateral buds presented in stolons, the number of developed lateral and apical buds, the size of formed stolons, and the respective amounts of fresh and dry mass were quantified. Finally, we evaluated the importance of incubation to steam growth in low light and in the dark, and the number of lateral buds and their development after three months of incubation. The Dendrobium \"Second Love\" steam growth in dark is extremely slow and limited when compared to Catasetum fimbriatum plants. However, after three months of treatment with 1.000 μM nitric oxide it was found to have five times more lateral buds than the respective control treatment plants. The treatment with 10 ppm ethylene showed a significant increase in the number of buds and lateral stolons compared to the control treatment from the second month of incubation. Treatments with 5 and 50 μM of GA had no promoting effect on the apical stolon stem elongation. Although not presenting the resumption of apical meristem activity, 5 μM of PA treatment has released a greater number of lateral stolons than the control treatment. Plants treated with 1000 ppm of NO, from the second month of incubation, showed a higher number of lateral stolons, moreover they were significantly larger. Treatment with 100 ppm 1-MCP had the same phenotype as plants treated in light: in other words, they did not etiolate even in light absence. Regarding the ethylene emission, we observed that the treatment with 1-MCP caused a significant increase in the emission of this gas by the plant, reaching values twenty times higher than the control treatment. CO2 emission was lower in light treatment when compared to most of the other treatments in dark. Treatments at higher concentrations of NO and GA seemed to foster some sort of plant stress (evidenced by tissue necrosis), demonstrating that the specie in question may be sensitive to high levels of these substances

Philosophiae Doctor - PhD / Plant natriuretic peptides (PNPs) are a novel class of extracellular, systemically mobile molecules that elicit a number of plant responses important in homeostasis and growth. Natriuretic peptides were first identified in vertebrates where they play a role in the regulation of salt and water balance. Subsequent experimental investigations have identified the presence of a natriuretic peptide hormone system in plants. While PNPs have been implicated in various physiological responses such as stomatal guard cell movements and regulation of net water uptake, its biological role has remained elusive. Here we have used co-expression and promoter content analysis tools to understand the biological role of the Arabidopsis thaliana PNP (AtPNP-A). The analysis of AtPNP-A and its co-expressed genes revealed that genes annotated as part of the systemic acquired resistance (SAR) pathway were over-represented, thus suggesting that AtPNP-A may function as a component of plant defense responses and specifically, SAR. The results further show that AtPNP-A shares many characteristics with pathogenesis related (PR) proteins in that its transcription is strongly induced in response to pathogen challenges, thus implying a newly described role for AtPNP-A in pathogen attack. Additional tissue expression analysis also indicated distinct localization of PNP activity in sepals and transcriptional meta-analysis showed that AtPNP-A may play a role in starch breakdown. Therefore, together with the finding that AtPNP-A plays a role in regulating phloem transport, we also hypothesize that AtPNP-A may play a role in phloem unloading in sepals to assist processes such as seed formation in plants. In plants, the second messenger, guanosine 3’,5’-cyclic monophosphate (cGMP) mediates a whole range of important processes including salinity tolerance, disease resistance, drought tolerance and responses to light. Since PNPs regulate water and salt homeostasis via a cGMP-dependent signaling pathways, it is thus important to analyse the transcriptome induced by the second messenger (cGMP) in Arabidopsis thaliana to give a better understanding of its mechanism of action. This study was also supplemented by the analysis of the gibberellic acid (GA) dependent transcriptome, since cGMP also plays a role its transcription pathway. This data analysis, together with promoter content investigation, revealed that genes upregulated after cGMP treatment and down-regulated in the GA insensitive mutant (ga1-3) were enriched with a GA response element (GARE), while no GARE enrichment were observed in genes up-regulated in the ga1-3 mutant. These findings suggest that GARE is indicative of GA-induced and cGMP-dependent transcriptional up-regulation. Gene ontology analysis confirmed previous reports that cGMP is involved in ion homeostasis and indicated that the transcriptional cGMP response is bi-polar in the sense that both genes up- and down-regulated in response to cGMP is involved in cation transport. Additionally, ab initio analysis of genes transcriptionally dependent on cGMP identified CHX8 as a hub gene and promoter content of CHX8 co-expressed genes show enrichment of the GARE motif. The fact that CHX8 has its highest expression levels during male gametogenesis and pollen tube growth, together with our findings, suggest that GA-induced and cGMP- dependent genes may play a key role in ion and water homeostasis in the male gametophyte. Finally, we propose that the type of analysis undertaken here can yield new insights into gene regulation networks and inform experimental strategies to unravel complex transcription regulatory systems under different developmental and stimulus specific conditions. / South Africa

Plant natriuretic peptides (PNP) are novel peptides which, like in vertebrates, have been shown to have a function associated with water and salt homeostasis. Two PNP-encoding genes have been identified and isolated from Arabidopsis thaliana, namely; AtPNP-A and AtPNP-B. In this study, the focus was on PNP-B, which has not been extensively studied. Bioinformatic analysis was done on the AtPNP-B gene. This included the bioinformatic study of its primary structure, secondary structure, tertiary structure, transcription factor binding sites (TFBS) and its relation to other known proteins. The AtPNP-B gene was shown to be a 510 bp long, including a predicted 138 bp intron. AtPNP-B was also shown to have some sequence similarity with AtPNP-A and CjBAp12. The TFBS for AtPNP-B and OsJPNP-B were compared and they comprised of TFBS that are related to water homeostasis and pathogenesis. This suggested two possible functions; water stress and homeostasis and a pathogenesis related function for PNP-B. Following bioinformatic analysis, the heterologous expression of the AtPNP-B was attempted to investigate whether the AtPNP-B gene encoded a functional protein and to determine the functional role of PNP-B. However, expression was unsuccessful. An evolutionary study was then carried out which revealed that there were some plants without the intron such as, rice, leafy spurge, oilseed rape, onion, poplar, sugar cane, sunflower and tobacco. These plants would therefore be used for expression and functional studies in the future. The evolutionary studies also revealed that PNP-B had a relationship with expansins and the endoglucanase family 45. Other PNP-B related molecules were also obtained from other plant genomes and therefore used in the construction of a phylogenetic tree. The phylogenetic tree revealed that AtPNP-B clustered in the same group as CjBAp12 while AtPNP-A had its own cluster group. There were also other PNP-B like molecules that clustered in the same group as expansins (α- and β-). Thus, we postulate that, like PNP-A, PNP-B also has a possible function in water and salt homeostasis. However, due to the clustering iii of AtPNP-B into the same group as CjBAp12, a possible role of PNP-B in pathogenesis-related response is also postulated.

Many of the anabolic effects of growth hormone (GH) are indirect, occurring through GH-stimulated production of insulin-like growth factor-I (IGF-I) by the liver. As well as being GH regulated, plasma IGF-I concentrations have been demonstrated to be dependent upon protein nutrition, with low protein diets being associated with reduced plasma IGF-I concentrations. This effect cannot be reversed by GH, suggesting that liver sensitivity to GH is impaired. To investigate the mechanisms through which protein supply affects GH sensitivity, primary cultures of ovine hepatocytes were grown in defined media. In a first experiment the media contained various fractions (0.2, 1.0, 5.0) of portal vein amino acid concentrations in fed sheep. In the second 24h incubation period, unstimulated IGF-I secretion was highly sensitive the concentration of amino acids in the media, with significantly greater release of basal IGF-I in 5x compared to either 1x (P<0.05) or 0.2x amino acid containing media. In a second series of experiments the effects of specific amino acid depletions was examined. Methionine depletion of 0.2x portal amino acid concentrations ablated the GH response second 24h of culture without affecting basal IGF-I release. By comparison ³H-leucine incorporation into secreted protein, following 20 hours of culture in defined media was significantly reduced in 0.2x aa (P<0.01) and 1.0x aa (P<0.05) media compared with 5.0x aa media, however secretory protein synthesis was unaffected by methionine depletion to 0.2x portal concentrations. The results suggest that amino acid availability regulates both basal and GH stimulated IGF-I release in ovine hepatocytes. Furthermore reducing methionine concentrations in the culture media to 0.2x portal concentrations diminishes GH response without compromising protein secretion.