Dissertations / Theses: 'Plant response to light'

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Schwalb, Michael. "Measuring the short term plant photosynthetic response to varying light quality using light emitting diodes (LEDs)." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121207.

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Light emitting diodes (LEDs) emit narrow bandwidth light and have the potential to increase the spectral efficiency of supplemental lighting in greenhouses by optimizing spectral output for plant growth and yields. At the moment of writing, data describing the plant response to varying light quality and quantity was limited. The objective of this research was to examine photosynthetic response of plants to varying light quality and quantity and to gather photosynthetic response data that could be used to design an optimal spectrum for a prototype LED array for plant growth experiments. The action spectrum of tomato (Solanum lycopersicum), lettuce (Lactuca sativa) and petunia (Petunia × hybrida) seedlings was measured at three irradiances (30, 60 and 120 µmol m-2 sec-1) using LED arrays with peak wavelengths from 405nm – 700nm and a bandwidth of 25nm (full width at half maximum). The action spectrums for all plant species at all three irradiances were characterized by localized blue and red action peaks within the range of 430 to 449 nm and 624 to 660 nm respectively. A peak also occurred at 595 nm for 30 µmol m-2 sec-1. The photosynthetic response of tomato, lettuce and petunia to varying red (660nm) and blue (430nm) wavelengths with and without background broadband radiation was also measured. For all three species tested, with and without background radiation, the optimum photosynthesis range occurred within the red to blue ratio (r:b) range of 5:1- 15:1 except for petunia without background radiation for which the maximum occurred at 50:1. These results suggest that the optimal red to blue ratio for photosynthetic activity for tomato, lettuce and petunia occurred between a red to blue ratio of 5:1-15:1.
Les diodes électroluminescentes (DEL) émettent une lumière relativement monochromatique et pourraient accroître l'efficacité des lampes pour les serres commerciales en émettant des longueurs d'ondes optimisées pour le rendement des plantes. L'objectif de ce projet a consisté à examiner l'effet des longueurs d'ondes sur l'activité photosynthétique des plantes. L'activité photosynthétique des tomates (Solanum lycopersicum), laitues (Lactuca sativa) et pétunias (Petunia × hybrida) a été mesurée à trois puissances d'irradiation (30, 60 and 120 µmol m-2 sec-1) en utilisant des DELs avec une émission maximale entre 405 nm et 700 nm et une bande passante de 25 nm. La réponse photosynthétique maximale à chaque niveau d'irradiation se situait dans la portion bleu et rouge du spectre visible, soit respectivement entre 430 - 449 nm et 624 to 660 nm. Un maximum a aussi été observé à 595 nm à 30 µmol m-2 sec-1. L'effet de la proportion des longueurs d'onde bleue et rouge (émises par les DELs) sur l'activité photosynthétique des tomates, laitues et pétunias a aussi été mesuré avec et sans le rayonnement de fond. Pour chaque espèce, avec et sans le rayonnement de fond, la proportion optimale (en terme de rouge et bleu) pour l'activité photosynthétique se situait entre of 5:1- 15:1, sauf dans le cas du pétunia, pour lequel le maximum se situait à 50:1 sans rayonnement de fond. La proportion optimale pour l'activité photosynthétique a diminué avec le rayonnement de fond pour chaque espèce à chaque niveau d'irradiation.

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Choudhury, Feroza Kaneez. "Rapid Metabolic Response of Plants Exposed to Light Stress." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1157543/.

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Environmental stress conditions can drastically affect plant growth and productivity. In contrast to soil moisture or salinity that can gradually change over a period of days or weeks, changes in light intensity or temperature can occur very rapidly, sometimes over the course of minutes or seconds. So, in our study we have taken an metabolomics approach to identify the rapid response of plants to light stress. In the first part we have focused on the ultrafast (0-90 sec) metabolic response of local tissues to light stress and in the second part we analyzed the metabolic response associated with rapid systemic signaling (0-12 min). Analysis of the rapid response of Arabidopsis to light stress has revealed 111 metabolites that significantly alter in their level during the first 90 sec of light stress exposure. We further show that the levels of free and total glutathione accumulate rapidly during light stress in Arabidopsis and that the accumulation of total glutathione during light stress is dependent on an increase in nitric oxide (NO) levels. We further suggest that the increase in precursors for glutathione biosynthesis could be linked to alterations in photorespiration, and that phosphoenolpyruvate could represent a major energy and carbon source for rapid metabolic responses. Taken together, our analysis could be used as an initial road map for the identification of different pathways that could be used to augment the rapid response of plants to abiotic stress. In addition, it highlights the important role of glutathione in initial stage of light stress response. Light-induced rapid systemic signaling and systemic acquired acclimation (SAA) are thought to play an important role in the response of plants to different abiotic stresses. Although molecular and metabolic responses to light stress have been extensively studied in local leaves, and to a lesser degree in systemic leaves, very little is known about the metabolic responses that occur in the different tissues that connect the local to the systemic leaves. These could be important in defining the specificity of the systemic response as well as in supporting the propagation of different systemic signals, such as the reactive oxygen species (ROS) wave. Here we report that local application of light stress to one rosette leaf resulted in a metabolic response that encompassed local, systemic and transport tissues (tissues that connect the local and systemic tissues), demonstrating a high degree of physical and metabolic continuity between different tissues throughout the plant. We further show that the response of many of the systemically altered metabolites could be associated with the function of the ROS wave, and that the level of eight different metabolites is altered in a similar way in all tissues tested (local, systemic, and transport tissues). These compounds could define a core metabolic signature for light stress that propagates from the local to the systemic leaves. Taken together, our findings suggest that metabolic changes occurring in cells that connect the local and systemic tissues could play an important role in mediating rapid systemic signaling and systemic acquired acclimation to light stress.

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Brown, Jordan C. "Photoreceptor regulation of plant responses to light and carbon dioxide." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/21595/.

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The scarcity of fresh water resources has highlighted concerns about the high percentage used for agricultural purposes. The strain on freshwater could be alleviated by improving crop water use as this is the largest consuming factor. Stomata are microscopic pores on the leaf epidermis which plants use to regulate their gas exchange. Importantly, stomata are required to balance CO2 uptake with water loss, with, 1-10 mmol CO2 taken up per mole of water lost. This is achieved through a combination of altering the aperture of the stomatal pores and regulating the number of stomata that develop on the leaf surface. These changes occur in response to environmental cues and hormone signals (Casson and Hetherington, 2010). An overall genetic pathway of light-controlled stomatal development has advanced the understanding of the regulatory light signaling mechanism. However, it remains unknown how light signaling interacts with other environmental signals, such as that of CO2, to impact intrinsic developmental pathways. In this thesis I describe experiments that investigate, in vivo, the impact of photoreceptor signaling on CO2 signal response within the context of stomatal development and function. The final results chapter of this thesis discusses that phyB mutants have altered stomatal response to combined changes in light and CO2 concentrations. I was able to observe increased water use efficiency of phyB via control of stomatal number, size and aperture. Furthermore I was able to observe that phyB is important to sensing elevated CO2 in terms of stomatal aperture response. These results indicate a key role of phyB in light and CO2 signal integration to control stomatal development and response.

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Maai, Eri. "Factors inducing the chloroplast movement in C₄ plants underhigh light-stress conditions and effects of the response on photosynthesis." Doctoral thesis, Kyoto University, 2020. http://hdl.handle.net/2433/253468.

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京都大学
0048
新制・論文博士
博士(農学)
乙第13360号
論農博第2891号
新制||農||1080(附属図書館)
学位論文||R2||N5299(農学部図書室)
(主査)教授中﨑鉄也, 教授白岩立彦, 教授土井元章
学位規則第4条第2項該当
Doctor of Agricultural Science
Kyoto University
DGAM

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Li, Xiaochun. "Development and Light Response of Leaves of Metasequoia and Close Relatives." Fogler Library, University of Maine, 2004. http://www.library.umaine.edu/theses/pdf/LiX2004.pdf.

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Rasool, Brwa Mohammad Ali. "The influence of light and leaf antioxidant status on plant responses to aphids." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/15443/.

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Cross-tolerance to environmental stresses results from the synergistic co-activation of defence pathways that cross biotic-abiotic stress boundaries. However, the signalling mechanisms that underpin such responses remain poorly characterised. The effects of an abiotic stress (high light; HL) on the responses of Arabidopsis thaliana and tobacco (Nicotiana tabacum) plants to a biotic stress (infestation by the green peach aphid, Myzus persicae) were therefore analysed. Particular focus was placed on the role of cellular redox state as a regulator of cross-tolerance phenomena and the identification of signalling pathways that underpin aphid resistance. Aphid fecundity was measured in a range of A. thaliana mutants that have defects in non-enzymatic antioxidants (ascorbate and glutathione), enzymatic antioxidants (catalase) or downstream kinase/phosphatase signalling cascades, and in transgenic tobacco lines that have either increased or decreased levels of ascorbate oxidase. A pre-treatment with HL increased the resistance of transgenic tobacco plants with low ascorbate oxidase to aphid infestation. In contrast, the A. thaliana ascorbate oxidase knockout mutants did not show the HL-dependent decrease in aphid infestation. Aphid fecundity was decreased on A. thaliana mutants that have altered antioxidant (ascorbate, glutathione, catalase) status, or that lack the gamma (γ) subunit of protein phosphatase (PP2A). A pre-treatment with HL increased the resistance of A. thaliana plants to aphid infestation in all of the genotypes, except for the cat2 mutants that lack the photorespiratory form of leaf catalase and glutathione defective mutants. Taken together these findings demonstrate that redox processes and oxidative signalling are important modulators of aphid resistance and the light-aphid interaction. Moreover, the analysis of aphid fecundity on these A. thaliana mutants, which also have different levels of leaf camalexin, suggests that the levels of this secondary metabolite alone do not influence aphid infestation. A transcriptome and metabolome profiling analysis of the responses of the different tobacco lines highlights the central role of cell wall modifications/signalling as key components in plant responses to aphid infestation.

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Goodman, Jill Lynn. "Photosynthetic Responses of Eelgrass (Zostera marina L) to Light and Sediment Sulfide in a Shallow Barrier Island Lagoon." W&M ScholarWorks, 1992. https://scholarworks.wm.edu/etd/1539617651.

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Niechayev, Nicholas Alexander. "The Environmental Productivity and Photosynthetic Light Response of Agave americana:A Potential Semi-Arid Biofuel Feedstock." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1468518584.

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Arshad, Naheed. "The response of a baffled plate to plane waves, with light and heavy fluid loading." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394279.

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Barnes, Charles. "Morphological Responses of Wheat (Triticum Aestivum L.) to Changes in Phytochrome Photoequilibria, Blue Light and Photoperiod." DigitalCommons@USU, 1990. https://digitalcommons.usu.edu/etd/4353.

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Wheat (triticum aestivum, L.) plants were exposed to three different levels of phytochrome photoequilibria (φ), two different photoperiods, end-of-day far-red radiation, two different levels of blue (400-500 nm) light, three levels of photosynthetic photon flux (PPF), and two types of high intensity discharge lamp types. Tillering was reduced by lowered φ, by reduced amounts on blue light and by end-of-day far-red. Main culm development was increased by lowered φ, by increased PPF, and was reduced by shortened photoperiod and by reduced blue light. Leaf length was increased by increased PPF, lowered φ, and reduced blue light but was not affected by photoperiod, end-of-day far-red or lamp type. Dry-mass accumulation increased under increasing PPF but was unaffected by other treatment in these experiments.

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Hoppe-Speer, Sabine Clara Lisa. "The response of the red mangrove rhizophora mucronata lam, to changes in salinity, inundation and light : predictions for future climate change." Thesis, Nelson Mandela Metropolitan University, 2009. http://hdl.handle.net/10948/1249.

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Mangrove forests are subjected to many environmental factors which influence species distribution, zonation patterns as well as succession. Important driving factors in these forests are salinity, water level fluctuations and available light. This study investigated the response of red mangrove (Rhizophora mucronata Lam.) seedlings to these factors in controlled laboratory experiments. Increase in salinity and prolonged inundation within estuaries are predicted impacts resulting from sea level rise due to climate change. The study investigated the effect of five salinity treatments (0, 8, 18, 35 and 45 ppt) with a semi-diurnal tidal cycle on seedling growth. In a separate experiment the effect of different inundation treatments: no inundation, 3, 6, 9 hour tidal cycles and continuous inundation (24 h) were investigated. Both morphological and physiological responses of R. mucronata seedlings were measured. There was a decrease in growth (plant height, biomass and leaf production) with increasing salinity. Seedlings in the seawater, hypersaline and no inundation treatments showed symptoms of stress, having increased leaf necrosis ("burn marks"). The highest growth occurred in the low salinity (8 ppt) treatment, but the highest photosynthetic performance and stomatal conductance occurred in the freshwater treatment (0 ppt). The typical response of stem elongation with increasing inundation was observed in the 24 hr inundation treatment. In the light and salinity combination study there were ten different treatments of five different light treatments (unshaded, 20 percent, 50 percent, 80 percent and 90 percent shade) combined with two salinity concentrations (18 and 35 ppt). In this study the seedling growth: plant height, biomass, leaf surface area and leaf production were higher in the moderate salinity (18 ppt) treatments compared to the seawater (35 ppt) treatments. Biomass in the 35 ppt experiment decreased with increasing shade as well as in the unshaded treatments. Photosynthetic performance and stomatal conductance were lower for the unshaded treatment in both 18 and 35 ppt salinity compared to all other treatments with the same salinity. This suggests that R. mucronata more shade than sun tolerant, but overall it can be concluded that the species has a broad tolerance range. The results may be relevant in mangrove rehabilitation and predicting responses to climate change. This is important as mangrove ecosystems may adapt to changing sea levels and in order to restore areas it will be necessary to choose the mangrove species which will grow best. The results may also help to increase the protection of existing mangrove habitats.

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Gan, Yuhong. "The involvement of nature : a study of the response and interaction between architecture and its surroundings in rural dwelling spaces." Virtual Press, 1994. http://liblink.bsu.edu/uhtbin/catkey/902491.

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The involvement of nature happens at the edge of architecture, influencing the space of man from the outside and the inside. This design is intended to open man's space to his surroundings, and for establishing a new relationship between man and nature.Peter Noever writes in Architecture in Transition: "In order to become an autonomous subject, man distances himself from nature. This process of distance helps men to learn increasingly to control himself and nature. However, this origin of subjectivity becomes hybrid and turns against man himself: he falls prey to his natural need to dominate, and the dominator of nature becomes the prey of nature."The idea of dominating nature is strongly reflected in the American rural dwellings. Like an "icon of individualism," "operating objectively in their relationship to the landscape,"2 the houses appear isolated from the surroundings. Man might control himself by building this isolated relationship with his surroundings, but it does not have to be like this. Because man not only needs to control himself but also needs to live healthily. The energy of the natural world is an essential part of a healthy human life. Especially in the living environment, natural elements-(defined as "a creative and controlling force in the universe")--are indispensable. For a healthy life, in balance with nature, man should be receptive to his surroundings.The Involvement of Nature is a study of dwelling space, using the language of architecture to improve and cultivate a harmonious relationship between man and nature. This project will focus on the connection between the dwelling space and its natural surroundings. It will create a contextual connection by the interactions between human perceptions of space inside the dwelling and the natural or cultural landscapes which is the outdoor environmental phenomena and features; the sun, the wind and the changing landscape.
Department of Architecture

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Mateo, Alfonso. "Roles of LESIONS SIMULATING DISEASE1 and Salicylic Acid in Acclimation of Plants to Environmental Cues : Redox Homeostasis and physiological processes underlying plants responses to biotic and abiotic challenges." Doctoral thesis, Stockholm University, Department of Botany, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-698.

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In the natural environment plants are confronted to a multitude of biotic and abiotic stress factors that must be perceived, transduced, integrated and signaled in order to achieve a successful acclimation that will secure survival and reproduction. Plants have to deal with excess excitation energy (EEE) when the amount of absorbed light energy is exceeding that needed for photosynthetic CO2 assimilation. EEE results in ROS formation and can be enhanced in low light intensities by changes in other environmental factors.

The lesions simulating disease resistance (lsd1) mutant of Arabidopsis spontaneously initiates spreading lesions paralleled by ROS production in long day photoperiod and after application of salicylic acid (SA) and SA-analogues that trigger systemic acquired resistance (SAR). Moreover, the mutant fails to limit the boundaries of hypersensitive cell death (HR) after avirulent pathogen infection giving rise to the runaway cell death (rcd) phenotype. This ROS-dependent phenotype pointed towards a putative involvement of the ROS produced during photosynthesis in the initiation and spreading of the lesions.

We report here that the rcd has a ROS-concentration dependent phenotype and that the light-triggered rcd is depending on the redox-state of the PQ pool in the chloroplast. Moreover, the lower stomatal conductance and catalase activity in the mutant suggested LSD1 was required for optimal gas exchange and ROS scavenging during EEE. Through this regulation, LSD1 can influence the effectiveness of photorespiration in dissipating EEE. Moreover, low and high SA levels are strictly correlated to lower and higher foliar H2O2 content, respectively. This implies an essential role of SA in regulating the redox homeostasis of the cell and suggests that SA could trigger rcd in lsd1 by inducing H2O2 production.

LSD1 has been postulated to be a negative regulator of cell death acting as a ROS rheostat. Above a certain threshold, the pro-death pathway would operate leading to PCD. Our data suggest that LSD1 may be subjected to a turnover, enhanced in an oxidizing milieu and slowed down in a reducing environment that could reflect this ROS rheostat property. Finally, the two protein disulphide isomerase boxes (CGHC) present in the protein and the down regulation of the NADPH thioredoxin reductase (NTR) in the mutant connect the rcd to a putative impairment in the reduction of the cytosolic thioredoxin system. We propose that LSD1 suppresses the cell death processes through its control of the oxidation-reduction state of the TRX pool. An integrated model considers the role of LSD1 in both light acclimatory processes and in restricting pathogen-induced cell death.

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Wilson, Ashley A. "SENSORY STRESSORS IMPACT SPECIES RESPONSES ACROSS LOCAL AND CONTINENTAL SCALES." DigitalCommons@CalPoly, 2020. https://digitalcommons.calpoly.edu/theses/2224.

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Pervasive growth in industrialization and advances in technology now exposes much of the world to anthropogenic night light and noise (ANLN), which pose a global environmental challenge in terrestrial environments. An estimated one-tenth of the planet’s land area experiences artificial light at night — and that rises to 23% if skyglow is included. Moreover, anthropogenic noise is associated with urban development and transportation networks, as the ecological impact of roads alone is estimated to affect one-fifth of the total land cover of the United States and is increasing in space and intensity. Existing research involving impacts of light or noise has primarily focused on a single sensory stressor and single species; yet, little information is known about how different sources of sensory stressors impact the relationships within tightly-knit and complex systems, such as within plant-pollinator communities. Furthermore, ANLN often co-occur, yet little is known about how co-exposure to these stressors influences wildlife, nor the extent and scale of how these stressors impact ecological processes and patterns. In Chapter 1, we had two aims: to investigate species-specific responses to artificial night light, anthropogenic noise, and the interaction between the two by using spatially-explicit models to model changes in abundance of 140 of the most prevalent overwintering bird species across North America, and to identify functional traits and contexts that explain variation in species-specific responses to ANLN stressors with phylogenetically-informed models. We found species that responded to noise exposure generally decreased in abundance, and the interaction with light resulted in negative synergistic responses that exacerbated the negative influence of noise among many species. Moreover, the interaction revealed negative emergent responses of species that only reacted when both ANLN were presented in combination. The functional trait that was the most indicative of avian response to ANLN was habitat preference. Specifically, species that occupy closed habitat were less tolerant of both sensory stressors compared to those that occupy open habitat. Species-specific responses to ANLN are context-dependent; thus, knowing the information that regulates when, where, how, and why sensory pollutants influence species will help management efforts effectively mitigate these anthropogenic stressors on the natural environment. In Chapter 2, using field-placed light manipulations at sites exposed to a gradient of skyglow, we investigated the influence of direct and indirect light on the yucca-yucca moth mutualism by quantifying chaparral yucca (Hesperoyucca whipplei) fruit set and the obligate moth (Tegeticula maculata maculata) larval density per fruit. Although many diurnal insects are thought to exhibit minimal phototaxis, we show that direct light attracted adult moths and incited higher pollination activity, resulting in an increase in fruit set. However, larval recruitment decreased with elevated light exposure and the effect was strongest for plants exposed to light levels exceeding natural moonlit conditions (> 0.5 lux). Contrarily, increases in ambient skyglow resulted in an increase in both fruit set and larva counts. Our results suggest that plant-pollinator communities may respond in complicated ways to different sources of light, such that novel selection pressures of direct and indirect light have the potential to benefit or disrupt networks within complex diurnal plant-pollinator communities, and ultimately alter the biodiversity reliant on these systems. By analyzing pervasive stressors across a continental-wide scale, we revealed considerable heterogeneity in avian responses to light and noise alone, as well as the interaction between them. Based on overall responses to the interaction between light v and noise, we suggest management efforts should focus on ameliorating excessive noise for overwintering bird species, which should decrease the impact from synergistic responses, as well as the negative impact from noise alone. There is still much to learn about responses to these stressors and smaller-scale studies should take our approach of systematically assessing interaction responses to ANLN. Moreover, our small-scale study revealed both local sources of direct light and skyglow impact the recruitment for both yucca moths and their reciprocal plant hosts. However, it is still unknown if or why other diurnal pollinators experience positive phototaxis, and whether direct lighting influences the physiology, behavior, or multiple factors relating to reproduction and fitness. Correspondingly, it is unknown if the novel selection pressures of direct and indirect light are disrupting complex diurnal plant-pollinator communities. Future research on artificial night light will need to investigate the intricate responses of diurnal pollinators to both direct and indirect light that will identify concrete mechanisms relating to physiological or behavioral susceptibility and inform predictions on how wide-spread communities will shift with this global driver of emerging change.

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Buisson, Daniel Joseph. "Anatomical and morphological responses of papaya, Carica papaya L., to various light conditions." FIU Digital Commons, 1991. http://digitalcommons.fiu.edu/etd/1817.

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Plants that develop under foliar shade encounter both low photosynthetically active radiation (PAR) and low red to far red ratios (R:FR). Both of these factors are important in determining developmental responses to shade. Papaya (Carica papaya L.) seedlings grown under filtered shade (low PAR and low R:FR) were compared with seedlings grown under neutral shade (low PAR with R:FR similar to that of full sunlight), and high light (moderate PAR with R:FR similar to that of full sunlight). The results indicated that papaya exhibits a light seeking strategy as evidenced by morphological and anatomical differences between treatments. Based on past research the results also indicate shade developmental responses in papaya to be phytochrome mediated.

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Huang, Jianjun. "Ecological responses of two forest understory herbs to changes in resources caused by prescribed fire alone on in combination with restoration thinning." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1195062013.

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McKiernan, Marc. "Responses of the photosynthetic appparatus of higher plants to the light environment." Thesis, University of Essex, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375920.

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LAWSON, NICOLAS DELLETT. "LIGHT AND HUMAN RESPONSE." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1053441038.

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Vaughn, Chad Dean. "Light in response to time /." Cincinnati, Ohio : University of Cincinnati, 2008. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1212179576.

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Thesis (Master of Architecture)--University of Cincinnati, 2008.
Committee/Advisors: Michael McInturf (Committee Chair), Elizabeth Riorden (Committee Co-Chair). Title from electronic theses title page (viewed Sep. 2, 2008). Includes abstract. Keywords: Light. Includes bibliographical references.

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VAUGHN, CHAD DEAN. "Light: in response to time." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1212179576.

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Logie, Malcolme Ronald Ruxton. "Photosynthetic gas exchange responses to light, temperature, carbon dioxide and water stress, and changes in photosynthetic pigments to light and water stress in two cultivars of Hordeum vulgare L." Thesis, Rhodes University, 1992. http://hdl.handle.net/10962/d1003779.

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The gas exchange responses of two cultivars of Hordeum vulgare L., to light, temperature, CO₂ and water stress were investigated in the laboratory. The optimum temperature for net CO₂ assimilation was found to be 25°C and 22.5°C for cv. Clipper and cv. Dayan respectively. Net CO₂ assimilation was reduced at 30°C in cv. Dayan. At low light intensity the highest quantum yield efficiency was 0.051 mol.mol⁻¹ at 30°C for cv. Clipper, and 0.066 mol.mol⁻¹ at 20°C for cv. Dayan. At the same temperature, cv. Clipper had a higher water use efficiency than cv. Dayan, but stomatal conductance for cv. Dayan was higher than cv. Clipper. Stomatal limitation to CO₂ was lowest at the optimum temperature for CO₂ assimilation in both cultivars. Stomata limited CO₂ assimilation in cv. Clipper to a larger degree than in cv. Dayan. Relative stomatal limitation for cv. Clipper at 25°C was 0.280 ± 0.010, and for cv. Dayan at 22.5°C was 0.028 ± 0.011. Short-term exposure to elevated CO₂ concentrations increased CO₂ assimilation in both cultivars, but more so for cv. Clipper. Transpiration rate at elevated CO₂ partial pressures were higher in cv. Dayan than in cv. Clipper. At very high CO₂ (860 μmol.m⁻²s⁻¹) partial pressure water use efficiency in cv. Clipper was higher than cv. Dayan, but at low CO₂ partial pressures water use efficiency in cv. Dayan was higher than cv. Clipper. Water stress reduced the relative leaf water content and net CO₂ assimilation in both cultivars. Cultivar Dayan was more tolerant to water stress, and CO₂ assimilation in this cultivar was less affected by water stress. In both cultivars water stress increased the concentration of chlorophyll a, chlorophyll b, and chlorophyll a+b. The chlorophyll a:b ratio remained relatively constant throughout the stress period. No correlation between relative leaf water content and total carotenoid concentration was observed.

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Mapfumo, Emmanuel. "Soil and plant response to compaction." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23028.pdf.

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Borevitz, Justin Oak Chidester. "Natural variation in arabidopsis light response /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2002. http://wwwlib.umi.com/cr/ucsd/fullcit?p3044779.

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Fritzsch, Katrin. "Plant response to changes in disturbance magnitude." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=97325646X.

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Dixon, Laura Evelyn. "Investigation of light inputs into plant circadian clocks." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5266.

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Circadian clocks are biological signalling networks which have a period of ~24 hours under constant environmental conditions. They have been identified in a wide range of organisms, from cyanobacteria to mammals and through the temporal co-ordination of biological processes are believed to increase individual fitness. The mechanisms which generate these self-sustained rhythms, the pathways of entrainment and the target outputs of the clock are all areas of great interest to circadian biologists. The plant circadian clock is believed to comprise of interlocking feedback loops of transcription and translation. The morning MYB-transcription factors CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) bind to the promoter of TIMING OF CAB2 1 (TOC1) and repress its expression, as well as their own. As levels of CCA1 and LHY fall, TOC1 is expressed and activates the expression of its repressors. This is a simplified version of the known clock components and the current model contains this core loop as well as an interlocked morning and evening loop, which also incorporates some post-translational modification (Chapter 1). Understanding the plant circadian network and its entrainment are the topics of this thesis. The study has focused on two plant species, the land plant Arabidopsis thaliana and the picoeukaryotic marine algae Ostreococcus tauri. In both of these species light-mediated entrainment of the clock has been investigated (Chapter 8), as well as the core circadian mechanism. In A. thaliana the role of a circadian associated gene, EARLY FLOWERING 3 has been a particular focus for investigation, through both experimentation and mathematical models (Chapters 4 and 5). In O. tauri the responses to light signals have been tested, as have the circadian responses to pharmacological manipulation (Chapters 6, 7 and 8). The work presented identifies a role for ELF3 in the repression of circadian genes and also links it with the regulation of protein stability. Likewise, in O. tauri the regulation of protein stability is identified to be a key mechanism for sustaining circadian rhythms. As well as investigating the clock in plants, certain photoreceptors have been characterised in S. cerevisiae with the aim of linking them to a synthetic oscillator. Together the work presented in this thesis provides evidence for the circadian community to aid with the understanding of circadian rhythms in plants, and possibly other organisms.

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McLachlan, Deirdre. "Benthic diatom motility in response to light." Thesis, University of Essex, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435583.

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Couldridge, Clare Elizabeth. "Aphid-plant interactions : investigating plant molecular response with implications for aphid pest control." Thesis, University of Birmingham, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487497.

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Faundez, Raul Simon Herrera. "Light regulation of nitrate reductase Sinapis alba." Thesis, University of Reading, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259505.

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Herrington, Edward John. "Light quality effects on in vitro shoot proliferation of Spiraea nipponica." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/28809.

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The work on Spiraea in vitro shoot cultures was done to determine the feasibility of using light quality to modify endogenous phytohormone balances to decrease apical dominance. Such an effect would enable a reduction in the high levels of exogenous cytokinin benzyladenine (BA) applied in culture and thus reduce potential side-effects. The Spiraea in vitro light quality response was characterized by examining the effects of different light wavelengths on growth. A mixture of red/FR induced rates of shoot proliferation with 0.25 mg/1 BA that were as high as rates obtained under white light with 0.5 mg/1 BA. Shoot quality, as determined by the proportion of shoots 1 cm or longer (useful shoots), was highest under red/FR light. The lowest shoot proliferation rate was observed under blue light. When light wavelengths intermediate between blue and red light (green, yellow, and orange) were applied to explants only minor growth modifications occurred. Green light did not inhibit shoot initiation but inhibited shoot elongation at the 0.5 mg/1 BA level. The efficacy of the light source-filter combinations in the first experiment was studied in two further experiments. With the three light sources (tungsten filament, fluorescent, and metal halide) together with a blue filter, results supported the putative blue light inhibitory effect suggested in the first light quality experiment. Under the red filter, the tungsten filament source induced the highest shoot number means at both BA levels used (0.25 and 0.5 mg/1). Two factors may have contributed to the red/FR effect observed in the first experiment; the time under an incubation light regime before transfer to the treatment regime, and the photon fluence rate of each regime. In the subsequent study to examine these factors, shoot initiation was optimized at the lower BA levels of 0.25 and 0.4 mg/1 when cultures under low fluence red/FR were transferred after four weeks to white light of a higher fluence for one more week. Glyphosate, a known promoter of IAA oxidation, was used to investigate the presumed effect of lowered IAA-cytokinin interactions. Two types of responses to glyphosate occurred, each one dependent on the glyphosate concentration. At the lower glyphosate level (0.087 mg/1), cultures under both light regimes with 0.25 mg/1 of BA, showed a strong inhibition of shoot initiation. This inhibitory effect was overcome in cultures with 0.5 mg/1 of BA and an overall stimulatory response occurred as shoot initiation rates were as much as four-fold higher than in the previous experiments. For both BA levels, changes in shoot number were greater under white light than under red/FR. At the higher glyphosate level (0.2 67 mg/1), the shoot initiation rates were greater than glyphosate-free controls for both BA levels under white light although under red/FR the rates were virtually unchanged from controls. The glyphosate effect investigated for Spiraea cultures appears to be influenced by the levels of the cytokinin BA resulting in pleiotropic effects which depend on the specific concentrations of each component.
Land and Food Systems, Faculty of
Graduate

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Del, Bianco Marta. "Context specificity of auxin response in plant development." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610902.

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The shoot apical meristem (SAM) is the source of all above ground organs in the plant. It can be divided into a central zone (CZ) and a surrounding ring region called peripheral zone (PZ). The CZ contains the stem cells, the organizing centre and undifferentiated stem cell daughters. In the peripheral zone, in response to auxin accumulation, cells begin to differentiate to give rise to lateral organs. Application of auxin to other parts of the SAM does not lead to the formation of leaves or flowers and, in fact, the CZ seems to be insensitive to auxin. These differences in responsiveness and output in the meristem zones can be attributed to differences in the auxin signalling network. To allow the identification and sampling of small and inaccessible tissues such as the meristem zones, protocols for the use of fluorescent and histochemical markers to guide Laser Capture Microdissection were developed. These new methods allowed the precise capture of specific plant cell-types in a manner that was compatible with subsequent extraction and amplification of RNA for RNA-Seq analysis. These novel tools together represent a valuable technology platform for future cell-type-specific analysis in other plant developmental contexts. In this work, these sampling techniques have lead to new insight into both meristem . regulation and auxin function in the SAM. Most interestingly, in terms of auxin signalling, it appears that the negative regulators of auxin response, JAAI2 and IAAI8, arc expressed specifically in the PZ and, unexpectedly y, their expression is down-regulated by auxin. Moreover, the gem: ontology analysis of the genes obtained by RNA-seq revealed an enrichment of genes involved in DNA synthesis and response to external stimuli in the PZ. This is consistent with the higher proliferation rate of the PZ cells and might suggest that environmental inputs are perceived in the PZ. which then affects the identity of the entire SAM. These data, together with detailed phenotypic analysis of multiple mutants involved in auxin signalling and meristem function, provide a framework for understanding the complex role of auxin in the regulation of lateral organ formation through the life of a plant.

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ul, Haq M. Anwar. "White rot of onion-plant response and detection." Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367806.

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Ganeteg, Ulrika. "The light-harvesting antenna of higher plant photosystem I." Doctoral thesis, Umeå : Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-209.

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Wentworth, Mark. "Quenching of chlorophyll fluorescence in plant light-harvesting complexes." Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340168.

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Bell, Hester Louise. "Response of Sporobolus virginicus (L.) Kunthto salinity." Thesis, The University of Arizona, 2000. http://hdl.handle.net/10150/291593.

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Optimal growth of euhalophytes requires moderate concentrations of salt and, in dicots, is associated with succulence of leaves and stems and accumulation of Na⁺ in plant tissues. Relative growth rate, water and cation content were studied in Sporobolus virginicus, a C₄ Chlorodoid grass, grown under different concentrations of NaCl. Optimal growth occurred at 100-150 mmol/L NaCl. and was not dependent on nitrogen levels or accompanied by accumulation of Na⁺ in leaves. Na:K ratios were lower in leaves and rhizomes than in roots indicating the possibility of discrimination in Na⁺ and K⁺ transport from roots to leaves. Water content of leaves and shoots was significantly greater in plants grown at optimal levels of salinity than in plants grown at sub or supra optimal salinity. Na⁺ and K⁺ concentrations in leaves contribute approximately 60% of osmolality. These results support the characterization of S. virginicus as a euhalophyte.

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Jackson, Kristina Mary. "Mammalian cell response to long wave UV light." Thesis, Lancaster University, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.536057.

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Norrish, Mark Ian Keith. "The transient component of the pupillary light response." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621582.

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Jia, Wenbo. "A Numerical Study of Catalytic Light-Off Response." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1461256363.

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Smit, Armand. "Apple tree and fruit responses to shade netting." Thesis, Link to the online version, 2007. http://hdl.handle.net/10019/463.

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Pickens, Jeremy Martin Sibley Jeffrey Lynn. "Evaluation of horticulture applications of light expanded clay aggregates." Auburn, Ala, 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SPRING/Horticulture/Thesis/Pickens_Jeremy_57.pdf.

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Deram, Paul. "Light-emitting-diode (LED) lighting for greenhouse tomato production." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=116996.

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The cost of artificial lighting is a major expense in the greenhouse production industry, especially during the winter where supplemental lighting is required to maintain production. Current technology uses broad spectrum high pressure sodium lamps (HPS), which, despite being excellent luminous sources, are not the most efficient light source for plant production. Specific light frequencies have been shown to impact photosynthesis more directly than others (especially in the red and blue ranges); focusing on specific wavelengths, light-emitting diodes (LEDs) could diminish lighting costs due to their high efficiency and lower operating temperatures. LEDs can be selected to target the wavelengths absorbed by plants, enabling the growers to customize the wavelengths of light required to maximize production and limit wavelengths that do not significantly impact plant growth. The primary purpose of this experiment was to test tomato plants (Solanum lycopersicum), in a research greenhouse using a full factorial design with three light intensities (High: 135 µmol m-2 s-1, Medium: 115 µmol m-2 s-1 and Low: 100 µmol m-2 s-1) at three red to blue ratio levels (5:1, 10:1 and 19:1) compared to 100% HPS, and a control (no supplemental lighting). The exact wavelengths chosen were 449 nm for the blue and 661 nm for the red. Secondary treatments were also tested using 100% red light supplied from the top, 100% red light supplied from the bottom, a 50%:50% LED:HPS and a replicate of the 10:1 ratio with High light intensity. The experiment was replicated over two different seasons (Summer-Fall 2011 and Winter-Spring 2011-2012). During the experiment, the highest biomass production (excluding fruit) occurred with the 19:1 ratio (red to blue), with increasing intensity resulting in more growth, whereas a higher fruit production was obtained using the 5:1 ratio. The highest marketable fruit production (fruit over 90 g, Savoura internal standard) was the 50%:50% LED:HPS, followed by 5:1 High and 19:1 High. From this research, LEDs have been shown to be superior in fruit production over HPS alone, and LEDs can improve tomato fruit production with HPS and have the ability to become the dominant supplemental greenhouse lighting system.
Le coût de l'éclairage artificiel est une dépense importante dans le secteur de la production en serre, surtout en hiver lorsqu'un éclairage supplémentaire est nécessaire pour maintenir le niveau de production. La technologie actuelle utilise des lampes à haute pression de sodium (HPS), qui en dépit d'être d'excellentes sources lumineuses, ne sont pas les sources lumineuses les plus efficaces pour la production végétale. Certaines fréquences spécifiques de lumière ont montré avoir un impact plus direct sur la photosynthèse que d'autres (en particulier dans les gammes de rouge et de bleu); en mettant l'accent sur certaines longueurs d'onde, les diodes électroluminescentes (LED) pourraient diminuer les coûts d'éclairage, en raison du rendement élevé et des températures plus basses de ce type de lampe. Les LED peuvent cibler les principales fréquences de lumière mieux absorbées par les plantes, ce qui permettrait aux producteurs de créer une lumière aux longueurs d'onde adaptées à la production optimale des plantes. Le principal objectif de cette expérience était de tester les lampes sur des plants de tomate (Solanum lycopersicum) dans une serre de recherche en utilisant un plan factoriel complet avec trois intensités lumineuses (Haute: 135 μmol m-2 s-1, Moyenne: 115 μmol m-2 s-1 et Basse: 100 μmol m-2 s-1) et trois proportions de rouge et bleu (5:1, 10:1 et19: 1), et comparer leur performance à celle de 100% HPS, et d'un contrôle (pas d'éclairage supplémentaire). Les longueurs d'onde choisies sont 449 nm (bleu) et 661 nm (rouge). Certains traitements secondaires ont également été testés, dont 100% rouge (éclairage par le haut ou le bas), un 50%:50% LED:HPS et une reproduction du 10:1 à haute intensité. L'expérience a été menée au cours de deux saisons différentes (été-automne et hiver-printemps). La production végétative la plus importante s'est produite avec le rapport 19:1 (rouge : bleu). La production de fruits était la plus élevé avec le rapport 5:1. La production en fruits commercialisables la plus importante (fruits de 90 g et plus : étalon interne de Savoura) a été pour le 50%:50% LED:HPS, suivi du 5:1 et 19:1 à haute intensité. Les LED se sont montrés supérieures aux HPS quant à la production de tomates.

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Dudley, Tom E. "Plant closure and policy response : an examination of the LDV closure, impact and response." Thesis, Coventry University, 2015. http://curve.coventry.ac.uk/open/items/c2b86698-a866-4246-8004-5600b29290e9/1.

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The de-industrialisation of the UK economy caused by globalised international markets, advancements in technology and production with changing consumer demands have made much of what was ‘traditional’ manufacturing redundant; this has led to industrial restructuring or even collapse, resulting in mass job redundancies. Market and industrial pressures have intensified since the late 1990s, culminating in the symbolic collapse of MG Rover in 2005 in addition to other key producers in the West Midlands, which represented the end of mass automotive production in the region (Donnelly et al. 2012). This came alongside various geographical, political and economic factors, including the restructuring of regional development agencies, prolonged industrial decline and a period of national economic recession, which presented challenges for any recovery. This thesis examines more precisely the closure of the commercial vehicle manufacturer LDV in 2009, once a part of the larger conglomerate British Leyland. The closure further reinforced the decline in UK automotive manufacturing until that point. The research involves the corporate collapse of LDV and the local government reaction to the closure and the following re-employment pathways of the redundant LDV workforce. The research continues the discussion of plant closures and the issues that redundant workers face when engaged in the labour market during economic recession. In particular, the thesis contribution employs a qualitative approach to examine the difficulties faced by the office tier, or ‘white collar’, workers who possess relatively high skills and who regarded as flexible and less vulnerable workers within the labour market. Yet this research exposes that highly skilled specialist workers are themselves also subject to unique issues when adjusting to the labour market. This topic is covered through the concept of worker trajectories: the research illustrates the unique employability issues and job precariousness that highly skilled workers can experience. The research concludes that the ability of highly skilled redundant workers to adapt effectively requires local job recovery strategies to implement short- and long-term policies with an emphasis on better job search and network development for individuals to sustain a resilient economy, and to mitigate the effects of plant closure upon redundant workers and maintain high skills within the region.

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Galvin, Mark Robert. "Maintenance cycle extension in advanced light water reactor plant design." Thesis, Springfield, Va. : Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA393174.

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Parsons, A. "Studies of coleoptile growth and light gradients in plant tissues." Thesis, University of York, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356841.

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Galvin, Mark Robert 1967. "Maintenance cycle extension in advanced light water reactor plant design." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/91336.

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Thesis (Nav.E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2001.
"June 2001."
Includes bibliographical references.
by Mark Robert Galvin.
Nav.E.
S.M.

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Johansson, Åke Henrik. "Investigation into temperature effects on the plant light signalling pathways." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/12231.

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The ability to withstand environmental temperature variation is essential for plant survival. Formative studies in Arabidopsis have revealed that light signalling pathways has a potentially unique role in shielding plant growth and development from seasonal and daily fluctuations in temperature. In this thesis we further investigate the integration of the light signalling networks and temperature signalling on the molecular level in Arabidopsis. First, we identified the transcript of the bHLH transcription factor LONG HYPOCOTYL IN FAR-RED 1 (HFR1) to be highly dependent on the ambient temperature and under strong control of the red light photoreceptor PHYTOCHROME B (phyB). We found that the long hypocotyl phenotype of the hfr1 mutant was exaggerated in warm conditions, specifically in blue light, downstream of cryptochrome 1. We further show that HFR1 acts in the warm by suppressing the function of PHYTOCHROME INTERACTING FACTOR 4 and 5 (PIF4, PIF5). PIF4 appears to act as a master regulator of several temperature responses and is directly regulated by the phytochromes. Thus, we define a molecular network where red light and blue light signals together with temperature merge on the regulation of PIF4. In the second part of this thesis, we investigate the relationship between temperature and the fluence rate of light on the inhibition of hypocotyl elongation in Arabidopsis. We find that the response to increasing fluence rates of light is highly dependent on the ambient temperature and that PIF4 and PIF5 acting downstream of the major red light photoreceptor, phyB, are essential for this response. In addition, we provide evidence that in cool conditions, PIF activity is under strong suppression by the gibberellin and HY5 pathways specifically at high fluence rates of red light. The collected work of this thesis highlights the importance of the PIF proteins as integrators of temperature and light signals and furthermore, demonstrates that the response to temperature is highly dependent on both the quality and quantity of light.

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Burgess, Alexandra Jacquelyn. "The variable light environment within complex 3D canopies." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/38967/.

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With an expanding population and uncertain consequences of climate change, the need to both stabilise and increase crop yields is important. The relationship between biomass production and radiation interception suggests one target for improvement. Under optimal growing conditions, biomass production is determined by the amount of light intercepted and the efficiency with which this is converted into dry matter. The amount of light at a given photosynthetic surface is dependent upon solar movement, weather patterns and the structure of the plant, amongst others. Optimising canopy structure provides a method by which we can improve and optimise both radiation interception and also the distribution of light among canopy layers that contribute to net photosynthesis. This requires knowledge of how canopy structure determines light distribution and therefore photosynthetic capacity of a given crop species. The aim of this thesis was to assess the relationships between canopy architecture, the light environment and photosynthesis. This focused on two core areas: the effect of varietal selection and management practices on canopy structure and the light environment and; the effect of variable light on select photosynthetic processes (photoinhibition and acclimation). An image-based reconstruction method based on stereocameras was employed with a forward ray tracing algorithm in order to model canopy structure and light distributions in high-resolution. Empirical models were then applied using parameterisation from manually measured data to predict the effects of variable light on photosynthesis. The plasticity of plants means that the physical structure of the canopy is dependent upon many different factors. Detailed descriptions of canopy architecture are integral to predicting whole canopy photosynthesis due to the spatial and temporal differences in light profiles between canopies. This inherent complexity of the canopy means that previous methods for calculating light interception are often not suitable. 3-dimensional modelling can provide a quick and easy method to retain this complexity by preserving small variations. This provides a means to more accurately quantify light interception and enable the scaling of cellular level processes up to the whole canopy. Results indicate that a canopy with more upright leaves enables greater light penetration to lower canopy layers, and thus higher photosynthetic productivity. This structural characteristic can also limit radiation-induced damage by preventing exposure to high light, particularly around midday. Whilst these features may lead to higher photosynthetic rates per unit leaf area, per unit ground area, photosynthesis is usually determined by total leaf area of the canopies, and within this study, the erect canopies tended to have lower total leaf areas than the more horizontal canopies. The structural arrangement of plant material often led to low levels of light within the lower canopy layers which were punctuated by infrequent, high light events. However, the slow response of photosynthesis to a change in light levels meant that these sun flecks cannot be used by the plant and thus the optimal strategy should be geared towards light harvesting and efficient photosynthesis under low light conditions. The results of this study contribute to our understanding of photosynthetic processes within the whole canopy and provide a foundation for future work in this area.

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Brunie, Lisa M. "Plant response to fertilization at a cool temperate peatland /." Connect to online version, 2006. http://ada.mtholyoke.edu/setr/websrc/pdfs/www/2006/145.pdf.

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Franklin, Oskar. "Plant and forest dynamics in response to nitrogen availability /." Uppsala : Swedish University of Agricultural Sciences, 2003. http://diss-epsilon.slu.se/archive/00000345/.

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Thesis (doctoral)--Swedish University of Agricultural Sciences, 2003.
Appendix consists of reprints of three papers and a manuscript, three of which are co-authored with others. Includes bibliographical references. Also partially issued electronically via World Wide Web in PDF format; online version lacks appendix.

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Toogood, Sarah Elizabeth. "Response of wet grassland plant communities to water regime." Thesis, University of Brighton, 2005. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413101.

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Atkinson, Nicola Jane. "Plant molecular response to combined drought and nematode stress." Thesis, University of Leeds, 2011. http://etheses.whiterose.ac.uk/2131/.

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Plants are adapted to respond to precise environmental stress conditions, activating specific molecular and physiological changes in order to minimise damage. Response to multiple stresses is therefore different to that to individual stresses. Simultaneous biotic and abiotic stress conditions are of particular interest, as the molecular signalling pathways controlling each interact and antagonise one another. Understanding such processes is crucial for developing broad-spectrum stress-tolerant crops. This study characterised the molecular response of plants to the concurrent stresses of drought (abiotic stress) and infection with plant-parasitic nematodes (biotic stress). Drought stress increased susceptibility to infection with Heterodera schachtii in Arabidopsis thaliana. The whole-genome transcriptome response to these stresses was analysed using microarrays. Each stress induced a particular subset of differentially expressed genes. A novel programme of gene expression was activated specifically in response to a combination of drought and nematode stress, involving 2394 differentially regulated genes. A diverse range of processes was found to be important in the response to multiple stresses, including plant hormone signalling, activation of transcription factors, cell wall modification, production of secondary metabolites, amino acid metabolism and pathogen defence signalling. Ten multiple stress-induced candidate genes were selected and their functions investigated using over-expression lines and loss-of-function mutants. Altered susceptibility to drought stress (TCP9, AZI1, RALFL8) and nematode infection (TCP9, RALFL8, ATMGL, AZI1) was observed in several of these lines. The effect of combined drought and nematode infection on nutritional parameters of tomato fruits was analysed. Drought stress lengthened flowering time and negatively affected carotenoid accumulation. Infection with Meloidogyne incognita reduced yield and ripening time and had a positive effect on the accumulation of phenolic compounds. The stresses in combination increased fruit sugar content. This work comprises the first whole-genome transcriptome study into combined abiotic and biotic stress. The results highlight the importance of studying stress factors in combination.

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Dissertations / Theses on the topic 'Plant response to light'

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