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Elucidation of Photoinduced Energy and Electron Transfer Mechanisms in Multimodular Artificial Photosynthetic Systems

Description: Multimodular designs of electron donor-acceptor systems are the ultimate strategy in fabricating antenna-reaction center mimics for artificial photosynthetic applications. The studied photosystems clearly demonstrated efficient energy transfer from the antenna system to the primary electron donor, and charge stabilization of the radical ion pair achieved with the utilization of secondary electron donors that permits either electron migration or hole transfer. Moreover, the molecular arrangement of the photoactive components also influences the route of energy and electron transfer as observed from the aluminum(III) porphyrin-based photosystems. Furthermore, modulation of the photophysical and electronic properties of these photoactive units were illustrated from the thio-aryl substitution of subphthalocyanines yielding red-shifted Q bands of the said chromophore; hence, regulating the rate of charge separation and recombination in the subphthalocyanine-fullerene conjugates. These multicomponent photosystems has the potential to absorb the entire UV-visible-NIR spectrum of the light energy allowing maximum light-harvesting capability. Furthermore, it permits charge stabilization of the radical ion pair enabling the utilization of the transferred electron/s to be used by water oxidizing and proton reducing catalysts in full-scale artificial photosynthetic apparatuses.
Date: May 2017
Creator: Lim, Gary Lloyd Nogra
Partner: UNT Libraries

A Combined Genetic, Biochemical, and Biophysical Analysis of the A1 Phylloquinone Binding Site of Photosystem I from Green Algae

Description: This project has resulted in the increase in our understanding of how proteins interact with and influence the properties of bound cofactors. This information is important for several reasons, including providing essential information for the re-engineering of biological molecules, such as proteins, for either improved function or entirely new ones. In particular, we have found that a molecule, such as the phylloquinone used in Photosystem I (PS1), can be made a stronger electron donor by placing it in a hydrophobic environment surrounded by negative charges. In addition, the protein is constrained in its interactions with the phylloqinone, in that it must bind the cofactor tightly, but not in such a way that would stabilize the reduced (negatively-charged) version of the molecule. We have used a combination of molecular genetics, in order to make specific mutations in the region of the phylloquinone, and an advanced form of spectroscopy capable of monitoring the transfer of electrons within PS1 using living cells as the material. This approach turned out to produce a significant savings in time and supplies, as it allowed us to focus quickly on the mutants that produced interesting effects, without having to go through laborious purification of the affected proteins. We followed up selected mutants using other spectroscopic techniques in order to gain more specialized information. In addition to the main project funded by this work, this grant supported several related side-projects that also increased our understanding about related issues.
Date: December 17, 2011
Creator: Redding, Kevin E.
Partner: UNT Libraries Government Documents Department

Use of Controlled Photosynthesis for Maintenance of Gaseous Environment

Description: Abstract: "The problem of maintaining livable oxygen and carbon dioxide pressures in a closed space in which men must live leads to consideration of the possible use of the photosynthesis of green algae. A calculation based on the known respiratory rate of man and the photosynthetic rates of Chlorella indicates that it would be feasible to use algae for this purpose."
Date: September 1954
Creator: Bassham, James Alan
Partner: UNT Libraries Government Documents Department

Signal Transduction Pathways that Regulate CAB Gene Expression

Description: The process of chloroplast differentiation, involves the coordinate regulation of many nuclear and chloroplast genes. The cues for the initiation of this developmental program are both extrinsic (e.g., light) and intrinsic (cell-type and plastid signals). During this project period, we utilized a molecular genetic approach to select for Arabidopsis mutants that did not respond properly to environmental light conditions, as well as mutants that were unable to perceive plastid damage. These latter mutants, called gun mutants, define two retrograde signaling pathways that regulate nuclear gene expression in response to chloroplasts. A major finding was to identify a signal from chloroplasts that regulates nuclear gene transcription. This signal is the build-up of Mg-Protoporphyrin IX, a key intermediate of the chlorophyll biosynthetic pathway. The signaling pathways downstream of this signal are currently being studied. Completion of this project has provided an increased understanding of the input signals and retrograde signaling pathways that control nuclear gene expression in response to the functional state of chloroplasts. These studies should ultimately influence our abilities to manipulate plant growth and development, and will aid in the understanding of the developmental control of photosynthesis.
Date: January 16, 2006
Creator: Chory, Joanne
Partner: UNT Libraries Government Documents Department

Signal Transduction Pathways that Regulate CAB Gene Expression

Description: The process of chloroplast differentiation, involves the coordinate regulation of many nuclear and chloroplast genes. The cues for the initiation of this developmental program are both extrinsic (e.g., light) and intrinsic (cell-type and plastid signals). During this project period, we utilized a molecular genetic approach to select for Arabidopsis mutants that did not respond properly to environmental light conditions, as well as mutants that were unable to perceive plastid damage. These latter mutants, called gun mutants, define two retrograde signaling pathways that regulate nuclear gene expression in response to chloroplasts. A major finding was to identify a signal from chloroplasts that regulates nuclear gene transcription. This signal is the build-up of Mg-Protoporphyrin IX, a key intermediate of the chlorophyll biosynthetic pathway. The signaling pathways downstream of this signal are currently being studied. Completion of this project has provided an increased understanding of the input signals and retrograde signaling pathways that control nuclear gene expression in response to the functional state of chloroplasts. These studies should ultimately influence our abilities to manipulate plant growth and development, and will aid in the understanding of the developmental control of photosynthesis.
Date: December 31, 2004
Creator: Chory, Joanne
Partner: UNT Libraries Government Documents Department

Maltose Biochemistry and Transport in Plant Leaves

Description: Transitory starch builds up in photosynthesizing leaves during the day and is then degraded each night. It has recently been shown through mutant analysis and genetically engineered plants that transitory starch is required for maximal rates of photosynthesis, especially in high carbon dioxide atmospheres. Understanding the pathway by which carbon is exported from chloroplasts at night is limited. Previous work has shown that starch conversion to sucrose at night involves maltose export from chloroplasts. This pathway for carbon export from chloroplasts normally does not occur during the day. The regulation of maltose formation, the transporters that allow export of maltose from the chloroplast, and the cytosolic reactions by which maltose is converted to sucrose remain obscure. Genomic and biochemical approaches are proposed here to address maltose metabolism and transport. The research will cover three areas (1) how are hydrolytic and phosphorylytic starch degradation regulated, (2) how is maltose exported from chloroplasts, and (3) how is maltose converted to sucrose in the cytosol? It is expected that this research will lead to new insights about photosynthesis at high carbon dioxide levels, how carbon is partitioned in plants, and how partitioning can be altered to adapt plants to human needs.
Date: April 25, 2008
Creator: Weber, Andreas P.M.
Partner: UNT Libraries Government Documents Department

Final Report

Description: This report describes basic science studies of conversion of starch to sucrose in plant leaves. The importance of maltose is described. The studies proved that hydrolysis of the starch is more important than phosphorolysis.
Date: February 7, 2005
Creator: Sharkey, Thomas D.
Partner: UNT Libraries Government Documents Department

Excitation energy transfer in natural photosynthetic complexes and chlorophyll trefoils: hole-burning and single complex/trefoil spectroscopic studies

Description: In this project we studied both natural photosynthetic antenna complexes and various artificial systems (e.g. chlorophyll (Chl) trefoils) using high resolution hole-burning (HB) spectroscopy and excitonic calculations. Results obtained provided more insight into the electronic (excitonic) structure, inhomogeneity, electron-phonon coupling strength, vibrational frequencies, and excitation energy (or electron) transfer (EET) processes in several antennas and reaction centers. For example, our recent work provided important constraints and parameters for more advanced excitonic calculations of CP43, CP47, and PSII core complexes. Improved theoretical description of HB spectra for various model systems offers new insight into the excitonic structure and composition of low-energy absorption traps in very several antenna protein complexes and reaction centers. We anticipate that better understanding of HB spectra obtained for various photosynthetic complexes and their simultaneous fits with other optical spectra (i.e. absorption, emission, and circular dichroism spectra) provides more insight into the underlying electronic structures of these important biological systems. Our recent progress provides a necessary framework for probing the electronic structure of these systems via Hole Burning Spectroscopy. For example, we have shown that the theoretical description of non-resonant holes is more restrictive (in terms of possible site energies) than those of absorption and emission spectra. We have demonstrated that simultaneous description of linear optical spectra along with HB spectra provides more realistic site energies. We have also developed new algorithms to describe both nonresonant and resonant hole-burn spectra using more advanced Redfield theory. Simultaneous description of various optical spectra for complex biological system, e.g. artificial antenna systems, FMO protein complexes, water soluble protein complexes, and various mutants of reaction centers continues; this work is supported by the new DOE BES grant.
Date: September 12, 2012
Creator: Jankowiak, Ryszard
Partner: UNT Libraries Government Documents Department

PS2007 Satellite Meeting on Photosynthetic Antennas, 19-22 July 2007, Drymen, Scotland

Description: A Satellite Workshop of the 14th International Congress on Photosynthesis on the topic of photosynthetic light-harvesting systems was held on 18-21 July 2007, at the Buchanan Arms Hotel in Drymen, Scotland, near Glasgow. This meeting continued the tradition of satellite light-harvesting conferences occurring prior to the last five international photosynthesis congresses in Japan, France, Hungary, Australia and Canada, dating from 1992. With an attendance of 124 participants, this Workshop represents an intimate gathering of scientists interested in a thorough coverage of the light-harvesting aspects of photosynthesis. A significant amount of time was set aside for discussion and poster sessions. The organizers were: Richard J. Cogdell, UK (Chairperson), Alastair T. Gardiner, UK, Conrad W. Mullineaux, UK, Robert A. Niederman, USA, Robert E. Blankenship, USA, Harry Frank, USA, Bruno Robert, France. Sessions were focused on new concepts relating to the function, regulation, assembly, photoprotection and evolution of a wide variety of antenna systems. Cutting-edge scientific methods used to study these systems that were covered included time-resolved and single-molecule spectroscopy, structure determination by X-ray diffraction, NMR and electron and atomic force microscopy, molecular genetics, protein chemistry, model systems and theory. A central theme was how emerging high-resolution structural information on antenna proteins continues to provide an enhanced understanding of areas ranging from the kinetics of energy transfer processes to the assembly of the photosynthetic apparatus.
Date: June 4, 2009
Creator: Blankenship, Robert E.
Partner: UNT Libraries Government Documents Department

Maltose Biochemistry and Transport in Plant Leaves

Description: Final Technical Report for DOE grant DE-FG02-04ER15565 Maltose Biochemistry and Transport in Plant Leaves PI Thomas D. Sharkey University of Wisconsin-Madison Starch is a desirable plant product for both food and biofuel. Leaf starch is ideal for use in biofuels because it does not compete with grain starch, which is used for food. Starch is accumulated in plant leaves during the day and broken down at night. If we can manipulate leaf starch breakdown it may be possible to design a plant that provides both grain starch for food and leaf starch for biofuel. The pathway of leaf starch breakdown was not known when this work started. Preliminary evidence had shown that maltose was the primary product of leaf starch breakdown (Weise, Weber & Sharkey, 2004) and that it was metabolized by a disproportionating enzyme called amylomaltase but given the initials DPE2 (Lu & Sharkey, 2004). In this work we showed that only one form of maltose was metabolically active (Weise et al., 2005a) and that maltose was located in two different places when the amylomaltase was knocked out but only inside the chloroplast when the maltose transporter was knocked out (Lu et al., 2006a). This allowed us to estimate the energetics of maltose export and to show that maltose export is more efficient than glucose export (Weise et al., 2005b). We examined how daylength affected starch breakdown rate and found that starch breakdown rate could respond to changes in daylength within one day (Lu, Gehan & Sharkey, 2005). We also were able to show a second starch breakdown pathway by chloroplastic starch phosphorylase (Weise et al., 2006). Work to this point was summarized in a review (Lu & Sharkey, 2006). We were able to show that the amylomaltase in plants could substitute for the amylomaltase in bacteria (Lu et …
Date: January 28, 2010
Creator: Sharkey, Thomas D.
Partner: UNT Libraries Government Documents Department

œNADPH: Protochlorophyllide Oxidoreductase-Structure, Catalytic Function, and Role in Prolamellar Body Formation and Morphogenesis

Description: The biosynthesis of chlorophyll is a critical biochemical step in the development of photosynthetic vascular plants and green algae. From photosynthetic bacteria (cyanobacteria) to algae, non-vascular plants, gymnosperms and vascular plants, mechanisms have evolved for protochlorophyllide reduction a key step in chlorophyll synthesis. Protochlorophyllide reduction is carried out by both a light-dependent (POR) and light-independent (LIPOR) mechanisms. NADPH: protochlorophyllide oxidoreductase (EC 1.3.1.33, abbreviated POR) catalyzes the light-dependent reduction of protochlorophyllide (PChlide) to chlorophyllide (Chlide). In contrast, a light-independent protochlorophyllide reductase (LIPOR) involves three plastid gene products (chlL, chlN, and chlB) and several nuclear factors. Our work focused on characterization of both the POR and LIPOR catalyzed processes.
Date: February 1, 2013
Creator: Timko, Michael P.
Partner: UNT Libraries Government Documents Department

Photosynthesis

Description: Encyclopedia article entry in the Encyclopedia of Time: Science, Philosophy, Theology, and Culture by H. James Birx. This encyclopedia article discusses photosynthesis.
Date: 2009
Creator: O'Toole, Erin
Partner: UNT Libraries

PS2004 Light-harvesting Systems Workshop

Description: This special issue of the international scientific research journal Photosynthesis Research consists of 25 original peer-reviewed contributions from participants in the PS 2004 Lisht-Harvesting Systems Workshop. This workshop was held from 26-29, 2004 at Hotel Le Chantecler, Sainte-Adele, Quebec, Canada. The workshop was a satellite meeting of the XIII International Congress on Photosynthesis held August 29-September 3, 2004 in Montreal, Canada. The workshope dealt with all types of photosynthetic antenna systems and types of organisms, including anoxygenic photosynthetic bacteria, cyanobacteria, algae and higher plants, as well as in vitro studies of isolated pigments. This collection of papers is a good representation of the highly interdisciplinary nature of modern research on photosynthetic antenna complexes, utilizing techniques of advanced spectroscopy, biochemistry, molecular biology, synthetic chemistry and structural determination to understand these diverse and elegant molecular complexes.
Date: November 1, 2005
Creator: Blankenship, Robert E.
Partner: UNT Libraries Government Documents Department

Plant Formate Dehydrogenase

Description: The research in this study identified formate dehydrogenase, an enzyme that plays a metabolic role on the periphery of one-carbon metabolism, has an unusual localization in Arabidopsis thaliana and that the enzyme has an unusual kinetic plasticity. These properties make it possible that this enzyme could be engineered to attempt to engineer plants with an improved photosynthetic efficiency. We have produced transgenic Arabidopsis and tobacco plants with increased expression of the formate dehydrogenase enzyme to initiate further studies.
Date: January 10, 2005
Creator: Markwell, John
Partner: UNT Libraries Government Documents Department

Photoinduced Electron Transfer in Ordered Macromolecular Assemblies. Final report for May 1, 1988 - June 30, 2002

Description: The final report describes studies over a 13 year period having to do with photoinduced electron transfer for active chromophores and redox agents, including assembly of the components in water soluble polymers or polypeptides. The findings include observation of long range charge separation and electron transport using laser phototransient spectroscopy. The systems targeted in these studies include peptide assemblies for which helical conformations and aggregation are documented. Oligomeric peptides modified with non-native redox active groups were also selected for investigation. Highly charged polymers or peptides were investigated as host agents that resemble proteins. The overall goal of these investigations focused on the design and characterization of systems capable of artificial photosynthesis.
Date: February 11, 2005
Creator: Jones, G.
Partner: UNT Libraries Government Documents Department

17th International Conference on Arabidopsis Research

Description: The 17th International Conference on Arabidopsis Research was held at the University of Madison, Wisconsin from June 27- July 2, 2006. ICAR-2006 included approximately 625 scientists from across the world. The scientific program was of excellent quality featuring 73 talks, including 30 from invited speakers. There were also 6 community-organized workshops (facilitated by conference staff) featuring additional talks on topics including ‘Submitting data to long-term repositories,’ ‘TAIR introductory workshop,’ ‘Web services and demonstration,’ ‘Public engagement: broadening the impact of your research,’ ‘Systems biology approaches to analysis of metabolic and regulatory networks of Arabidopsis,’ and ‘Mechanotransduction in Arabidopsis.’ Approximately 440 posters were presented in general topic areas including, among others, Development, Modeling/Other Systems, Energy, Environment, and Genetic/Epigenetic mechanisms. Graduate students, postdoctoral researchers, junior faculty, and underrepresented minorities made up a significant portion of the oral presentations thereby promoting the training of young scientists and facilitating important career development opportunities for speakers. Several poster sessions provided an opportunity for younger participants to freely meet with more established scientists. The North American Arabidopsis Steering Committee (NAASC) continued its outreach effort and again sponsored two special luncheons to encourage personal and professional development of young scientists and also underrepresented minorities. The ‘Emerging Scientists Luncheon’ featured 10 graduate students selected on the basis of scientific excellence of their submitted research abstracts. The ‘Minority Funding Luncheon,’ featured 8 awardees selected by the NAASC through a widely-publicized application process. This luncheon was established specifically to provide an opportunity for underrepresented minorities, and/or scientists from Minority-Serving Institutions/Historically Black Colleges and Universities to network with NAASC members and representatives from federal funding agencies in an informal and intimate setting. This luncheon included introductions of each award recipient and discussion of outreach efforts and informal research and career discussions. Outreach Activities: The conference is the largest annual international Arabidopsis venue …
Date: July 1, 2006
Creator: Bender, Judith
Partner: UNT Libraries Government Documents Department

The Effects of Selected Algicides and Some Coordination Complexes upon the Apparent Photosynthesis of Chlorella Pyrenoidosa

Description: Many experiments have been performed with the Warburg apparatus, or variations of this manometric technique, since Warburg's experiments (52, 53) where the effects of cyanides upon dark reactions and of urethanes upon light reactions of photosynthesis were demonstrated. The same basic techniques were utilized in this research in attempting to determine the effects of some coordination complexes upon the apparent photosynthetic rate of Chlorella pyrenoidosa. A second goal of the present paper was to investigate the potential of the Warburg apparatus as a tool for screening algicidal compounds.
Date: June 1965
Creator: Phelps, Robert G.
Partner: UNT Libraries
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