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Optical studies of dynamical processes in disordered materials

Description: In general terms, our research activities under the present Agency sponsorship continue to focus on processes and interactions which affect the dynamical behavior of excitations/excited states of optically activated amorphous or disordered solids. The framework of our understanding of these processes has been established with work performed over the past two decades. The advent of more refined spectroscopies, most of them laser based, has allowed a re-examination of these properties in a much more detailed and basic way. A deeper understanding of the interactions which lead to relaxation, energy diffusion and nonlinearities in the disordered phases is important to the development of more efficient and better materials to service all of the technologies which employ optically activated materials. In this document, we will present an abbreviated synopsis of the research we have conducted under the auspices of the present grant. We will then outline directions we wish to maintain and will render descriptions of new opportunities which have ensued from our current efforts and which we wish to exploit under renewed sponsorship. 52 refs., 12 figs.
Date: July 1, 1991
Creator: Yen, W.M.
Partner: UNT Libraries Government Documents Department

Savannah River Ecology Laboratory. Annual technical progress report of ecological research

Description: The Savannah River Ecology Laboratory (SREL) is a research unit of the University of Georgia (UGA). The overall mission of the Laboratory is to acquire and communicate knowledge of ecological processes and principles. SREL conducts basic and applied ecological research, as well as education and outreach programs, under a contract with the U.S. Department of Energy (DOE) at the Savannah River Site (SRS) near Aiken, South Carolina. Significant accomplishments were made during the past year in the areas of research, education and service. The Laboratory`s research mission was fulfilled with the publication of two books and 143 journal articles and book chapters by faculty, technical and students, and visiting scientists. An additional three books and about 80 journal articles currently are in press. Faculty, technician and students presented 193 lectures, scientific presentations, and posters to colleges and universities, including minority institutions. Dr. J Vaun McArthur organized and conducted the Third Annual SREL Symposium on the Environment: New Concepts in Strewn Ecology: An Integrative Approach. Dr. Michael Newman conducted a 5-day course titled Quantitative Methods in Ecotoxicology, and Dr. Brian Teppen of The Advanced Analytical Center for Environmental Sciences (AACES) taught a 3-day short course titled Introduction to Molecular Modeling of Environmental Systems. Dr. I. Lehr Brisbin co-hosted a meeting of the Crocodile Special Interest Group. Dr. Rebecca Sharitz attended four symposia in Japan during May and June 1996 and conducted meetings of the Executive Committee and Board of the International Association for Ecology (ENTECOL).
Date: July 31, 1996
Creator: Smith, M.H.
Partner: UNT Libraries Government Documents Department

Theoretical models of the impact of climate change on natural populations, communities and ecosystems. Final report, 1989--1992

Description: Land use change is a relatively understudied aspect of global change. In many cases, the impact of land use on plant and animal species may be far greater than the impact of climate change per se. As an integral part of our long-term studies of the response of animal populations to global change, we have focused on land use change as a dominant driving force. Climate change, no doubt, will also play a role in determining the future abundance and distribution of many species, but, for many species, the signal from climate change per se may be difficult to detect if we do not first understand the impact of land use change. This formed the dominant theme of the research by the PI (Pulliam). Both land use change and year to year climate change can directly affect other populations and two examples of this formed the focus of the remaining research, models of invertebrates in Carolina Bays and a model of a commercial estuarine population of blue crabs.
Date: December 31, 1992
Creator: Wiegert, R.
Partner: UNT Libraries Government Documents Department

Nitrogen control of chloroplast differentiation. Final report

Description: This project was directed toward understanding at the physiological, biochemical and molecular levels of how photosynthetic organisms adapt to long-term nitrogen-deficiency conditions is quite incomplete even though limitation of this nutrient is the most commonly restricts plant growth and development. For our work on this problem, the unicellular green alga, Chlamydomonas reinhardtii, was grown in continuous cultures in which steady-state levels of nitrogen can be precisely controlled. N-limited cells exhibit the classical symptoms of deficiency of this nutrient, chlorosis and slow growth rates, and respond to nitrogen provision by rapid greening and chloroplast differentiation. We have addressed three aspects of this problem: (1) the regulation of pigment synthesis; (2) control of expression of nuclear genes encoding photosynthetic proteins; (3) changes in metabolic and electron transport pathways that enable sustained CO{sub 2} fixation even though they cannot be readily converted into amino and nucleic acids. For the last, principle components are: (a) enhanced mitochondrial respiratory activity intimately associated with photosynthates, and (b) the occurrence in thylakoids of a supplemental electron transport pathway that facilitates reduction of the plastoquinone pool. Together, these distinguishing features of N-limited cells are likely to enable cell survival, especially under conditions of high irradiance stress.
Date: May 1, 1998
Creator: Schmidt, G.W.
Partner: UNT Libraries Government Documents Department

Environmental stress-mediated changes in transcriptional and translational regulation of protein synthesis in crop plants. Final report

Description: The research described in this final report focused on the influence of stress agents on protein synthesis in crop plants (primarily soybean). Investigations into the `heat shock` (HS) stress mediated changes in transcriptional and translocational regulation of protein synthesis coupled with studies on anaerobic water deficit and other stress mediated alterations in protein synthesis in plants provided the basis of the research. Understanding of the HS gene expression and function(s) of the HSPs may clarify regulatory mechanisms operative in development. Since the reproductive systems of plants if often very temperature sensitive, it may be that the system could be manipulated to provide greater thermotolerance.
Date: December 31, 1996
Partner: UNT Libraries Government Documents Department

Microbiology and physiology of anaerobic fermentation of cellulose. Annual report for 1990, 1992, 1993 and final report

Description: This report focuses on the bioconversion of cellulose to methane by various anaerobes. The structure and enzymatic activity of cellulosome and polycellulosome was studied in Clostridium thermocellum. The extracellular enzymes involved in the degradation of plant material and the physiology of fermentation was investigated in anaerobic fungi. Enzymes dealing with CO, CO{sub 2}, H{sub 2}, CH{sub 3}OH, as well as electron transport and energy generation coupled to the acetyl-CoA autotrophic pathway was studied in acetogenic clostridia.
Date: August 31, 1993
Creator: Ljungdahl, L.G.; Wiegel, J.; Peck, H.D. Jr. & Mortenson, L.E.
Partner: UNT Libraries Government Documents Department

Hemicellulases from anaerobic thermophiles. Progress report

Description: The longterm goal of this research effort is to obtain an anaerobic thermophilic bacterium that efficiently converts various hemicellulose-containing biomass to ethanol over a broad pH range. The strategy is to modify the outfit and regulation of the rate-limiting xylanases, glycosidases and xylan esterases in the ethanologenic, anaerobic thermophile Thermoanaerobacter ethanolicus, which grows between pH 4.5 and 9.5. Although it utilizes xylans, the xylanase, acetyl(xylan) esterase and O-methylglucuronidase activities in T. ethanolicus are barely measurable and regarded as the rate limiting steps in its xylan utilization. Thus, and also due to the presently limited knowledge of hemicellulases in anaerobic thermophiles, we characterize the hemicellulolytic enzymes from this and other anaerobic thermophiles as enzyme donors. Beside the active xylosidase/arabinosidase from T. ethanolicus, exhibiting the two different activities, we characterized 2 xylosidases, two acetyl(xylan) esterases, and an O-methylglucuronidase from Thermoanaerobacterium spec. We will continue with the characterization of xylanases from novel isolated slightly acidophilic, neutrophilic and slightly alkalophilic thermophiles. We have cloned, subcloned and partially sequenced the 165,000 Da (2 x 85,000) xylosidase/arabinosidase from T. ethanolicus and started with the cloning of the esterases from Thermoanaerobacterium spec. Consequently, we will develop a shuttle vector and continue to apply electroporation of autoplasts as a method for cloning into T. ethanolicus.
Date: May 1, 1994
Creator: Wiegel, J.
Partner: UNT Libraries Government Documents Department

Microbiology and physiology of anaerobic fermentation of cellulose. Progress report (4/30/91--4/30/92) and outline of work for the period 9/1/92--9/1/93

Description: The authors are continuing their efforts to partly dissociate the cellulolytic enzyme complex of C. thermocellum. This complex named cellulosome (also existing as polycellulosome) consists of perhaps as many as 26 different subunits. It is extremely resistant to dissociation and denaturation. Treatments with urea and SDS have little effect unless the latter treatment is at high temperature. Significantly, some of the subunits after SDS dissociation have CMCase (endoglucanase) activity but no activity toward crystalline cellulose. The only reported success of hydrolysis of crystalline cellulose by cellulosomal subunits is by Wu et al. who isolated two protein fractions labeled SL and SS which when combined exhibit a low (about 1% of the original cellulosome) activity toward crystalline cellulose. The long standing goal is still to determine the activities of the individual subunits, to characterize them, to find out how they are associated in the cellulosome, and to establish the minimum number of subunits needed for efficient hydrolysis of crystalline cellulose. This report also presents the results of experiments on cellulose hydrolysis in aerobic fungi, as well as other anaerobic bacteria.
Date: December 31, 1992
Creator: Ljungdahl, L.G.
Partner: UNT Libraries Government Documents Department

The hemicellulases from the ethanologenic thermophile: Themoanaerobacter ethanolius

Description: Previously, we had only obtained extremely low xylanase activity in cultures of {ital Thermoanaerobacter ethanolicus} strain JW200, despite demonstrated xylan hydrolysis. We were not able to increase the enzyme activity or concentrate it in solution. Therefore, we decided to isolate new strains of thermophilic anaerobes with higher xylanase activity as a future source for cloning xylanases into {ital T. ethanolicus}. We now have organisms exhibiting 100-fold higher xylanase activity than JW200, but still cannot isolate or concentrate the enzyme activity except at very low yields. We have concentrated and partially purified a xylanase from strain N.D. using preparative matrix-free isoelectric focusing. We have also purified to homogeneity and partially characterized a xylosidase from {ital T. ethanolicus}. We have detected and measured arabinosidase and acetyl esterase activity in {ital T.ethanolicus}, {ital Clostridium thermohydrosulfuricum} and strain N.D. 7 refs., 2 tabs. (MHB)
Date: May 1, 1991
Creator: Wiegel, J.
Partner: UNT Libraries Government Documents Department

Nitrogen control of chloroplast development and differentiation

Description: The growth and development of plants and photosynthetic microorganisms is commonly limited by the availability of nitrogen. Our work concerns understanding the mechanisms by which plants and algae that are subjected to nitrogen deprivation alter the composition of photosynthetic membranes and enzymes involved in photosynthetic carbon metabolism. Toward these ends, we study biosynthetic and gene expression processes in the unicellular green alga Chlamydomonas reinhardtii which is grown in an ammonium-limited continuous culture system. We have found that the expression of nuclear genes, including those encoding for light-harvesting proteins, are severely repressed in nitrogen-limited cells whereas, in general, chloroplast protein synthesis is attenuated primarily at the level of mRNA translation. Conversely, nitrogen deprivation appears to lead to enhanced synthesis of enzymes that are involved in starch and storage lipid deposition. In addition, as a possible means by which photosynthetic electron transport activities and ATP synthesis is sustained during chronic periods of nitrogen deprivation, thylakoid membranes become enriched with components for chlororespiration. Characterization of the chlororespiratory electron transport constituents, including cytochrome complexes and NAD(P)H dehydrogenase is a major current effort. Also, we are striving to isolate the genes encoding chlororespiration proteins toward determining how they and others that are strongly responsive to nutrient availability are regulated.
Date: December 1, 1991
Creator: Schmidt, G.W.
Partner: UNT Libraries Government Documents Department

Molecular biology of Lea genes of higher plants

Description: This report contains our progress to date in determining the function of the D-7 Lea proteins in cotton embryos. We have completely sequenced the D-7 gene and established {ital E. coli} transformants which synthesize reasonable amounts of the D-7 protein. Two-dimensional electrophoresis was required to assay fractions for D-7 protein during purification to homogeneity, since D-7 has no known enzymatic activity, contains no Trp, and little Phe or Tyr, and {ital E. coli} has several proteins of similar molecular weight to D-7. Purified D-7 was used to generate monospecific antibodies which are being used for determination of the cellular distribution of D-7, and also for exact quantitation of D-7 in late-stage cotton embryos. Computerized modelling of D-7 has shown similarities to proteins with a coiled-coil structure, but fitting D-7 to this structure resulted in a violation of the handedness rule. If the pitch of the helix is changed from 3.6 to 3.667, however, a three dimensional structure (not a coiled coil) is generated which has overall energetics of formation nearly as favorable as the traditional {alpha} helix. The driving force for the change in pitch is proposed to result from favorable energetics of dimerization. Preliminary evidence indicates that D-7 does indeed dimerize in solution. Future experiments will determine the exact 3D structure of D-7 and the related protein D-29, as well as test the hypothesis that D-7 and D-29 are involved in mitigating dehydration of embryos and plants through sequestering phosphate or other ions in sufficient quantity to prevent ion precipitation or crystallization. 13 refs., 3 figs. (MHB)
Date: July 1, 1991
Partner: UNT Libraries Government Documents Department