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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Life: past, present and future

Molecular methods of taxonomy and phylogeny have changed the way in which life on earth is viewed; they have allowed us to transition from a eukaryote-centric (five-kingdoms) view of the planet to one that is peculiarly prokarote-centric, containing three kingdoms, two of which are prokaryotic unicells. These prokaryotes are distinguished from their eukaryotic counterparts by their toughness, tenacity and metabolic diversity. Realization of these features has, in many ways, changed the way we feel about life on earth, about the nature of life past and about the possibility of finding life elsewhere. In essence, the limits of life on this planet have expanded to such a degree that our thoughts of both past and future life have been altered. The abilities of prokaryotes to withstand many extreme conditions has led to the term extremophiles, used to describe the organisms that thrive under conditions thought just a few years ago, to be inconsistent with life. Perhaps the most extensive adaptation to extreme conditions, however, is represented by the ability of many bacteria to survive nutrient conditions not compatible with eukaryotic life. Prokaryotes have evolved to use nearly every redox couple that is in abundance on earth, filling the metabolic niches left behind by the oxygen-using, carbon-eating eukaryotes. This metabolic plasticity leads to a common feature in physically stratified environments of layered microbial communities, chemical indicators of the metabolic diversity of the prokaryotes. Such 'metabolic extremophily' forms a backdrop by which we can view the energy flow of life on this planet, think about what the evolutionary past of the planet might have been, and plan ways to look for life elsewhere, using the knowledge of energy flow on earth.

NASA Discipline Developmental Biology↗
NASA NTRS2000

Through form to function: root hair development and nutrient uptake

Root hairs project from the surface of the root to aid nutrient and water uptake and to anchor the plant in the soil. Their formation involves the precise control of cell fate and localized cell growth. We are now beginning to unravel the complexities of the molecular interactions that underlie this developmental regulation. In addition, after years of speculation, nutrient transport by root hairs has been demonstrated clearly at the physiological and molecular level, with evidence for root hairs being intense sites of H(+)-ATPase activity and involved in the uptake of Ca(2+), K(+), NH(4)(+), NO(3)(-), Mn(2+), Zn(2+), Cl(-) and H(2)PO(4)(-).

Review, Tutorial↗
NASA NTRS1999

Growing crops for space explorers on the moon, Mars, or in space

An option in the long-duration exploration of space, whether on the Moon or Mars or in a spacecraft on its way to Mars or the asteroids, is to utilize a bioregenerative life-support system in addition to the physicochemical systems that will always be necessary. Green plants can use the energy of light to remove carbon dioxide from the atmosphere and add oxygen to it while at the same time synthesizing food for the space travelers. The water that crop plants transpire can be condensed in pure form, contributing to the water purification system. An added bonus is that green plants provide a familiar environment for humans far from their home planet. The down side is that such a bioregenerative life-support system--called a controlled environment life-support system (CELSS) in this paper--must be highly complex and relatively massive to maintain a proper composition of the atmosphere while also providing food. Thus, launch costs will be high. Except for resupply and removal of nonrecycleable substances, such a system is nearly closed with respect to matter but open with respect to energy. Although a CELSS facility is small compared to the Earth's biosphere, it must be large enough to feed humans and provide a suitable atmosphere for them. A functioning CELSS can only be created with the help of today's advanced technology, especially computerized controls. Needed are energy for light, possibly from a nuclear power plant, and equipment to provide a suitable environment for plant growth, including a way to supply plants with the necessary mineral nutrients. All this constitutes the biomass production unit. There must also be food preparation facilities and a means to recycle or dispose of waste materials and there must be control equipment to keep the facility running. Humans are part of the system as well as plants and possibly animals. Human brain power will often be needed to keep the system functional in spite of the best computer-driven controls. The particulars of a CELSS facility depend strongly on where it is to be located. The presence of gravity on the Moon and Mars simplifies the design for a facility on those bodies, but a spacecraft in microgravity is a much more challenging environment. One problem is that plants, which are very sensitive to gravity, might not grow and produce food in the virtual absence of gravity. However, the experience with growing super-dwarf wheat in the Russian space station Mir, while not entirely successful because of the sterile wheat heads, was highly encouraging. The plants grew well for 123 days, producing more biomass than had been produced in space before. This was due to the high photon flux available to the plants and the careful control of substrate moisture. The sterile heads were probably due to the failure to remove the gaseous plant hormone, ethylene, from the Mir atmosphere. Since ethylene can easily be removed, it should be possible to grow wheat and other crops in microgravity with the production of viable seeds. On the ground Biosphere-2 taught us several lessons about the design and construction of a CELSS facility, but Bios-3 came much closer to achieving the goals of such a facility. Although stability was never completely reached, Bios-3 was much more stable than Biosphere-2 apparently because every effort was made to keep the system simple and to use the best technology available to maintain control. Wastes were not recycled in Bios-3 except for urine, and inedible plant materials were incinerated to restore CO2 to the atmosphere. Since much meat (about 20% of calories) was imported, closure in the Bios-3 experiments was well below 100%. But then, a practical CELSS on the Moon might also depend on regular resupply from Earth. Several important lessons have been learned from the CELSS research described in this review.

Review↗
NASA NTRS1999

Nutrition and muscle loss in humans during spaceflight

The protein loss in humans during spaceflight is partly due to a normal adaptive response to a decreased work load on the muscles involved in weight bearing. The process is mediated by changes in prostaglandin release, secondary to the decrease in tension on the affected muscles. On missions, where there is a high level of physical demands on the astronauts, there tends to be an energy deficit, which adds to the muscle protein loss and depletes the body fat reserves. While the adaptive response is a normal part of homeostasis, the additional protein loss from an energy deficit can, in the long run, have a negative effect on health and capability of humans to live and work in space and afterward return to Earth.

NASA Program Biomedical Research and Countermeasur↗
NASA NTRS1999

Is skeletal muscle ready for long-term spaceflight and return to gravity?

It is now clear that prevention of muscle debilitation during spaceflight will require a broader approach than simple exercise aimed at strengthening of the muscle fibers. The levels of several hormones and receptors are altered by unloading and must be returned to homeostasis. Pharmacotherapy and gene transfer strategies to raise the relative level of structural proteins may minimize the problems faced by astronauts in readapting to Earth-gravity. Up to now, we have only minimally exploited microgravity for advancing our understanding of muscle biology. A research laboratory in the space station with a centrifuge facility (gravity control) is essential for conducting basic research in this field. Microgravity has proven an excellent tool for noninvasively perturbing the synthesis of muscle proteins in the search for molecular signals and gene regulatory factors influencing differentiation, growth, maintenance and atrophy of muscle. Understanding the relation between blood flow and interstitial edema and between workload and subsequent structural failure are but two important problems that require serious attention. The roles of hormones and growth factors in regulating gene expression and their microgravity-induced altered production are other urgent issues to pursue. These types of studies will yield information that advances basic knowledge of muscle biology and offers insights into countermeasure design. This knowledge is likely to assist rehabilitation of diseased or injured muscles in humans on Earth, especially individuals in the more vulnerable aging population and persons participating in strenuous sports. Will the skeletal muscle system be prepared for the increased exposure to microgravity and the return to gravity loading without injury when space station is operational? The answer depends in large part on continued access to space and funding of ground-based models and flight experiments. The previous two decades of spaceflight research have described the effects of microgravity on multiple systems. The next generation of experiments promises to be even more exciting as we are challenged to define the cellular and molecular mechanisms of microgravity-induced changes.

manned↗
NASA NTRS1999

Molecular evolution inferred from small subunit rRNA sequences: what does it tell us about phylogenetic relationships and taxonomy of the parabasalids?

The Parabasala are a primitive group of protists divided into two classes: the trichomonads and the hypermastigids. Until recently, phylogeny and taxonomy of parabasalids were mainly based on the comparative analysis of morphological characters primarily linked to the development of their cytoskeleton. Recent use of molecular markers, such as small subunit (SSU) rRNA has led to now insights into the systematics of the Parabasala and other groups of prolists. An updated phylogeny based on SSU rRNA is provided and compared to that inferred from ultrastructural data. The SSU rRNA phylogeny contradicts the dogma equating simple characters with pumitive characters. Hypermastigids, possessing a hyperdeveloped cytoskeleton, exhibit the most basal emergence in the parabasalid lineage. Other observations emerge from the SSU rRNA analysis, such as the secondary loss of some cytoskeleton structures in all representatives of the Monocercomonadidae, the existence of secondarily free living taxa (reversibility of parasitism) and the evidence against the co-evolution of the endobiotic parabasalids and their animal hosts. According to phylogenies based on SSU rRNA, all the trichomonad families are not monophyletic groups, putting into question the validity of current taxonomic assignments. The precise branching order of some taxa remains unclear, but this issue can possibly be addressed by the molecular analysis of additional parabasalids. The goal of such additional analyses would be to propose, in a near future, a revision of the taxonomy of this group of protists that takes into account both molecular and morphological data.

NASA Discipline Exobiology↗
NASA NTRS1999

Radiation: microbial evolution, ecology, and relevance to mars missions

Ultraviolet (UV) radiation has been an important environmental parameter during the evolution of life on Earth, both in its role as a mutagen and as a selective agent. This was probably especially true during the time from 3.8 to 2.5 billion years ago, when atmospheric ozone levels were less than 1% of present levels. Early Mars may not have had an "ozone shield" either, and it never developed a significant one. Even though Mars is farther away from the Sun than the Earth, a substantial surficial UV flux is present on Mars today. But organisms respond to dose rate, and on Mars, like on Earth, organisms would be exposed to diurnal variations in UV flux. Here we present data on the effect of diurnal patterns of UV flux on microbial ecosystems in nature, with an emphasis on photosynthesis and DNA synthesis effects. These results indicate that diurnal patterns of metabolism occur in nature with a dip in photosynthesis and DNA synthesis in the afternoon, in part regulated by UV flux. Thus, diurnal patterns must be studied in order to understand the effect of UV radiation in nature. The results of this work are significant to the success of human missions to Mars for several reasons. For example, human missions must include photosynthetic organisms for food production and likely oxygen production. An evolutionary approach suggests which organisms might be best suited for high UV fluxes. The diurnal aspect of these studies is critical. Terraforming is a potential goal of Mars exploration, and it will require studies of the effect of Martian UV fluxes, including their diurnal changes, on terrestrial organisms. Such studies may suggest that diurnal changes in UV only require mitigation at some times of day or year.

Review, Tutorial↗
NASA NTRS1999

Biomarkers of exposure, sensitivity and disease

PURPOSE: This review is to evaluate the use of biomarkers as an indication of past exposure to radiation or other environmental insults, individual sensitivity and risk for the development of late occurring disease. OVERVIEW: Biomarkers can be subdivided depending on their applications. Markers of exposure and dose can be used to reconstruct and predict past accidental or occupational exposures when limited or no physical measurements were available. Markers of risk or susceptibility can help identify sensitivity individuals that are at increased risk for development of spontaneous disease and may help predict the increased risk in sensitive individuals associated with environmental or therapeutic radiation exposures. Markers of disease represent the initial cellular or molecular changes that occur during disease development. Each of these types of biomarkers serves a unique purpose. OUTLINE: This paper concentrates on biomarkers of dose and exposure and provides a brief review of biomarkers of sensitivity and disease. The review of biomarkers of dose and exposure will demonstrate the usefulness of biomarkers in evaluation of physical factors associated with radiation exposure, such as LET, doserate and dose distribution. It will also evaluate the use of biomarkers to establish relationships that exist between exposure parameters such as energy deposition, environmental concentration of radioactive materials, alpha traversals and dose. In addition, the importance of biological factors on the magnitude of the biomarker response will be reviewed. Some of the factors evaluated will be the influence of species, tissue, cell types and genetic background. The review will demonstrate that markers of sensitivity and disease often have little usefulness in dose-reconstruction and, by the same token, many markers of dose or exposure may not be applicable for prediction of sensitivity or risk.

Non-NASA Center↗
NASA NTRS1999

Progress toward an explicit mechanistic model for the light-driven pump, bacteriorhodopsin

Recent crystallographic information about the structure of bacteriorhodopsin and some of its photointermediates, together with a large amount of spectroscopic and mutational data, suggest a mechanistic model for how this protein couples light energy to the translocation of protons across the membrane. Now nearing completion, this detailed molecular model will describe the nature of the steric and electrostatic conflicts at the photoisomerized retinal, as well as the means by which it induces proton transfers in the two half-channels leading to the two membrane surfaces, thereby causing unidirectional, uphill transport.

Review, Tutorial↗
NASA NTRS1999

If walls could talk

The plant cell wall is very complex, both in structure and function. The wall components and the mechanical properties of the wall have been implicated in conveying information that is important for morphogenesis. Proteoglycans, fragments of polysaccharides and the structural integrity of the wall may relay signals that influence cellular differentiation and growth control. Furthering our knowledge of cell wall structure and function is likely to have a profound impact on our understanding of how plant cells communicate with the extracellular environment.

Review↗
NASA NTRS1999

Orthologs, paralogs and genome comparisons

During the past decade, ancient gene duplications were recognized as one of the main forces in the generation of diverse gene families and the creation of new functional capabilities. New tools developed to search data banks for homologous sequences, and an increased availability of reliable three-dimensional structural information led to the recognition that proteins with diverse functions can belong to the same superfamily. Analyses of the evolution of these superfamilies promises to provide insights into early evolution but are complicated by several important evolutionary processes. Horizontal transfer of genes can lead to a vertical spread of innovations among organisms, therefore finding a certain property in some descendants of an ancestor does not guarantee that it was present in that ancestor. Complete or partial gene conversion between duplicated genes can yield phylogenetic trees with several, apparently independent gene duplications, suggesting an often surprising parallelism in the evolution of independent lineages. Additionally, the breakup of domains within a protein and the fusion of domains into multifunctional proteins makes the delineation of superfamilies a task that remains difficult to automate.

Non-NASA Center↗
NASA NTRS1999

Fluid shear stress as a regulator of gene expression in vascular cells: possible correlations with diabetic abnormalities

Diabetes mellitus is associated with increased frequency, severity and more rapid progression of cardiovascular diseases. Metabolic perturbations from hyperglycemia result in disturbed endothelium-dependent relaxation, activation of coagulation pathways, depressed fibrinolysis, and other abnormalities in vascular homeostasis. Atherosclerosis is localized mainly at areas of geometric irregularity at which blood vessels branch, curve and change diameter, and where blood is subjected to sudden changes in velocity and/or direction of flow. Shear stress resulting from blood flow is a well known modulator of vascular cell function. This paper presents what is currently known regarding the molecular mechanisms responsible for signal transduction and gene regulation in vascular cells exposed to shear stress. Considering the importance of the hemodynamic environment of vascular cells might be vital to increasing our understanding of diabetes.

Review, Tutorial↗
NASA NTRS1999

Survival of life on asteroids, comets and other small bodies

The ability of living organisms to survive on the smaller bodies in our solar system is examined. The three most significant sterilizing effects include ionizing radiation, prolonged extreme vacuum, and relentless thermal inactivation. Each could be effectively lethal, and even more so in combination, if organisms at some time resided in the surfaces of airless small bodies located near or in the inner solar system. Deep within volatile-rich bodies, certain environments theoretically might provide protection of dormant organisms against these sterilizing factors. Sterility of surface materials to tens or hundreds of centimeters of depth appears inevitable, and to greater depths for bodies which have resided for long periods sunward of about 2 A.U.

NASA Discipline Exobiology↗
NASA NTRS1999

Tracking with the mind's eye

The two components of voluntary tracking eye-movements in primates, pursuit and saccades, are generally viewed as relatively independent oculomotor subsystems that move the eyes in different ways using independent visual information. Although saccades have long been known to be guided by visual processes related to perception and cognition, only recently have psychophysical and physiological studies provided compelling evidence that pursuit is also guided by such higher-order visual processes, rather than by the raw retinal stimulus. Pursuit and saccades also do not appear to be entirely independent anatomical systems, but involve overlapping neural mechanisms that might be important for coordinating these two types of eye movement during the tracking of a selected visual object. Given that the recovery of objects from real-world images is inherently ambiguous, guiding both pursuit and saccades with perception could represent an explicit strategy for ensuring that these two motor actions are driven by a single visual interpretation.

NASA Discipline Neuroscience↗
NASA NTRS1999

Root gravitropism: a complex response to a simple stimulus?

Roots avoid depleting their immediate environment of essential nutrients by continuous growth. Root growth is directed by environmental cues, including gravity. Gravity sensing occurs mainly in the columella cells of the root cap. Upon reorientation within the gravity field, the root-cap amyloplasts sediment, generating a physiological signal that promotes the development of a curvature at the root elongation zones. Recent molecular genetic studies in Arabidopsis have allowed the identification of genes that play important roles in root gravitropism. Among them, the ARG1 gene encodes a DnaJ-like protein involved in gravity signal transduction, whereas the AUX1 and AGR1 genes encode proteins involved in polar auxin transport. These studies have important implications for understanding the intra- and inter-cellular signaling processes that underlie root gravitropism.

Review, Tutorial↗
NASA NTRS1999

Protein machines and self assembly in muscle organization

The remarkable order of striated muscle is the result of a complex series of protein interactions at different levels of organization. Within muscle, the thick filament and its major protein myosin are classical examples of functioning protein machines. Our understanding of the structure and assembly of thick filaments and their organization into the regular arrays of the A-band has recently been enhanced by the application of biochemical, genetic, and structural approaches. Detailed studies of the thick filament backbone have shown that the myosins are organized into a tubular structure. Additional protein machines and specific myosin rod sequences have been identified that play significant roles in thick filament structure, assembly, and organization. These include intrinsic filament components, cross-linking molecules of the M-band and constituents of the membrane-cytoskeleton system. Muscle organization is directed by the multistep actions of protein machines that take advantage of well-established self-assembly relationships. Copyright 1999 John Wiley & Sons, Inc.

NASA Discipline Musculoskeletal↗