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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Redox Disproportionation of Glucose as a Major Biosynthetic Energy Source

Previous studies have concluded that very little if any energy is required for the microbial biosynthesis of amino acids and lipids from glucose -- processes that yield almost as much ATP (adenosine triphosphate) as they consume. However, these studies did not establish the strength nor the nature of the energy source driving these biological transformations. To identify and estimate the strength of the energy source behind these processes, we calculated the free energy change due to the redox disproportionation of substrate carbon of (a) 26 redox-balanced fermentation reactions, and (b) the biosynthesis of amino acids, lipids, and nucleotides of E. coli from glucose. A plot of the negative free energy of these reactions per mmole of carbon as a function of the number of disproportionative electron transfers per mmol of carbon showed that the energy yields of these fermentations and biosyntheses were directly proportional to the degree of redox disproportionation of carbon. Since this linear relationship showed that redox disproportionation was the dominant energy source of these reactions, we were able to establish that amino acid and lipid biosynthesis obtained most of their energy from redox disproportionation (greater than 94%). In contrast nucleotide biosynthesis was not driven by redox disproportionation of carbon, and consequently depended completely on ATP for energy. This crucial and previously unrecognized role of sugars as an energy source of biosynthesis suggests that sugars were involved at the earliest stage in the origin of anabolic metabolism.

Weber, Arthur L.↗
NASA NTRS2017

Biosignatures in the Context of Low Energy Flux

Many of the features that are thought of as biosignatures - including the mediation of chemical and physical processes with speed, specificity, and selectivity - result directly or indirectly from life's unique capability to mediate and direct energy flux. As such, it is important to consider the impact that differences in energy flux may have on the quantity and quality of evidence for life. Earth differs from every other body in our solar system in the magnitude of biologically-usable energy flux into a liquid water environment. On a global basis, the capture of light energy into photosynthesis and the flux of chemical energy represented in the products of that photosynthesis (organic material + O2) are about six and four orders of magnitude larger, respectively, than the flux of energy represented in geochemical sources. Our conception of what an inhabited world "looks like" and our intuition about how to search for life are based in this high-energy context. Energy fluxes on worlds beyond Earth may be better approximated by the million-fold smaller flux provided to Earth's biosphere by geochemical sources. As a result, the nature, abundance, and quality of evidence for life that could be expected on an inhabited extraterrestrial world within our solar system may differ profoundly from that found on Earth. Understanding this potential difference in quantitative terms provides important context for the formulation of life detection strategies. The influence of energy flux on biosignatures can be evaluated through reference to the two basic purposes into which life partitions energy flux: (1) Life expends energy to sustain existing biomass in a metabolic steady state (metabolically functional but non-growing). The formal representation of this relationship in the traditional microbiology literature equates biomass directly with energy flux. The direct implication is that worlds having lower energy flux will have correspondingly lower potential to support biomass. Life detection strategies that directly target extant organisms should therefore be prepared to encounter average biomass densities that may be many orders of magnitude smaller than those found in most of Earth's surface environments (2) Life expends energy to synthesize new biomass. An end-member case in which new biomass is created at the energy-limited rate and the corresponding cells are immediately destroyed (so that the energy partitioned to cell maintenance is minimized) establishes an upper bound on the rate at which biological material can enter a bulk global pool. For a specified bulk concentration [i] of any particular biological compound, i, or for biologically produced matter overall, this synthesis rate, R (sub i), defines a characteristic time scale tau (sub i) equals [i] divided by R (sub i). tau (sub i) can be thought of as (a) the minimum time required for biosynthesis to yield a specific bulk concentration (e.g., a detection threshold) of i, and (b) the average residence time of i within a bulk pool when [i] is held in steady state through a balance between biosynthesis and attrition by physical, chemical, or biological consumption. tau (sub i) becomes an important quantity in considering the potential utility of enantiomeric excess (as a product of homochiral biosynthesis) as a biosignature. Spontaneous racemization of amino acids acts to "erase" the signature of homochiral synthesis over time scales that may range from hundreds to hundreds of thousands of years, depending on temperature. For environments in which low energy flux translates to low rates of biosynthesis, including the synthesis of homochiral amino acids, amino acid residence times in pools having detectable concentrations may compare to or significantly exceed the time scale for racemization. This and similar consequences of long residence times should be considered in the formulation of life detection strategies based on detection of biologically-produced species. Fluxes of biologically-useful energy on potentially habitable worlds within our solar system are, at present, not well constrained. Improving such constraint has the potential to inform priorities in the formulation and targeting of search-for-life strategies, based on the implications of energy flux for the abundance and quality of biosignatures overall, and in specific categories.

ENERGY FLUX↗
NASA NTRS2023

Evolutionary Flexibility and Rigidity in the Bacterial Methylerythritol Phosphate (Mep) Pathway

Terpenoids are a diverse class of compounds with wide-ranging uses including as industrial solvents, pharmaceuticals, and fragrances. Efforts to produce terpenoids sustainably by engineering microbes for fermentation are ongoing, but industrial production still largely relies on nonrenewable sources. The methylerythritol phosphate (MEP) pathway generates terpenoid precursor molecules and includes the enzyme Dxs and two iron–sulfur cluster enzymes: IspG and IspH. IspG and IspH are rate limiting-enzymes of the MEP pathway but are challenging for metabolic engineering because they require iron–sulfur cluster biogenesis and an ongoing supply of reducing equivalents to function. Therefore, identifying novel alternatives to IspG and IspH has been an on-going effort to aid in metabolic engineering of terpenoid biosynthesis. We report here an analysis of the evolutionary diversity of terpenoid biosynthesis strategies as a resource for exploration of alternative terpenoid biosynthesis pathways. Using comparative genomics, we surveyed a database of 4,400 diverse bacterial species and found that some may have evolved alternatives to the first enzyme in the pathway, Dxs making it evolutionarily flexible. In contrast, we found that IspG and IspH are evolutionarily rigid because we could not identify any species that appear to have enzymatic routes that circumvent these enzymes. The ever-growing repository of sequenced bacterial genomes has great potential to provide metabolic engineers with alternative metabolic pathway solutions. With the current state of knowledge, we found that enzymes IspG and IspH are evolutionarily indispensable which informs both metabolic engineering efforts and our understanding of the evolution of terpenoid biosynthesis pathways.

Bailey Marshall↗
NASA NTRS1992

The role of pyridoxine as a countermeasure for in-flight loss of lean body mass

Ground based and in flight research has shown that humans, under conditions of microgravity, sustain a loss of lean body tissue (protein) and changes in several biological processes including, reductions in red blood cell mass, and neurotransmitters. The maintenance of muscle mass, the major component of lean body mass, is required to meet the needs of space station EVAs. Central to the biosynthesis of amino acids, the building blocks of protein, is pyridoxine (vitamin B-6). Muscle mass integrity requires the availability of vitamin B-6 for protein metabolism and neurotransmitter synthesis. Furthermore, the formation of red blood cells require pyridoxine as a cofactor in the biosynthesis of hemoglobin, a protein that carries oxygen to tissues. In its active form, pyridoxal-5'-phosphate (PLP), vitamin B-6 serves as a link between amino acid and carbohydrate metabolism through intermediates of glycolysis and the tricarboxylic acid cycle. In addition to its role in energy metabolism, PLP is involved in the biosynthesis of hemoglobin and neurotransmitter which are necessary for neurological functions. Alterations in pyridoxine metabolism may affect countermeasures designed to overcome some of these biochemical changes. The focus of this research is to determine the effects of microgravity on the metabolic utilization of vitamin B-6, integrating nutrition as an integral component of the countermeasure (exercise) to maintain lean body mass and muscle strength. The objectives are: 1) to determine whether microgravity effects the metabolic utilization of pyridoxine and 2) to quantitate changes in B-6 vitamer distribution in tissue and excreta relative to loss of lean body tissue. The rationale for this study encompasses the unique challenge to control biochemical mechanisms effected during space travel and the significance of pyridoxine to maintain and counter muscle integrity for EVA activities. This experiment will begin to elucidate the importance of biochemical interactions between micronutrients and the homeostasis condition of biological processes in the space environment. To address this research topic a simulated microgravity model has been developed. The experiment uses radioisotopically labelled pyridoxine administered as an oral dose to rats which are maintained by tail suspension to simulate a microgravity environment. At the termination of the study, liver, muscle, blood and urine are collected and analyzed by reverse phase high pressure liquid chromatography to determine the quantity and distribution of the B-6 vitamers in tissue and excreta relative to lean body tissue loss. Earlier studies, published by this investigator, have shown that differences in vitamer distribution among samples from experimental versus control subjects indicate changes in metabolic utilization and storage of vitamin B-6.

Gilbert, Joyce A.↗
NASA NTRS1998

Prebiotic Polymer Synthesis and the Origin of Glycolytic Metabolism

Our research resulted in several discoveries which contributed to understanding the origin and operation of life. (1) Most importantly, we discovered a new pathway of prebiotic amino acid synthesis in which formaldehyde and glycolaldehyde (formose reaction substrates) react with ammonia to give alanine and homoserine in the presence of thiol catalysts. The thiol-dependent synthesis of amino acids undoubtedly occurs via amino acid thioester intermediates capable of forming peptides. This 'one-pot' reaction system operates under mild aqueous conditions, and like modern amino acid biosynthesis, uses sugar intermediates which are converted to amino acids by energy-yielding redox disproportionation. Preliminary evidence suggests that this type of process can be "evolved" by a serial transfer methods that lead to enrichment of autocatalytic molecules. (2) We established that prebiotic peptide polymers can be made by condensation of amino acid thioesters (homocysteine thiolactone and S-(N-beta-orotidyl- diaminopropionic acid) ethanethiol), and that prebiotic polydisulfide polymers can be generated by oxidation of dithiols with iron(III) in minerals. (3) In our analysis of metabolism we discovered the primary energy source of biosynthesis -- chemical energy made available by the redox disproportionation of substrate carbon groups. We concluded that the energy and reactivity of sugars make them the optimal substrate for the origin and operation of terrestrial (or extraterrestrial) life. (4) Since it is likely that the use of optimal sugar substrates in biosynthesis sets the average oxidation number of functional biocarbon throughout the Universe near 0.0 (the reduction level of formaldehyde), we proposed that a line(s) in the microwave spectrum of formaldehyde could be rationally selected as a frequency for interstellar communication that symbolizes life. (5) Finally, in preparation for the analysis of Martian meteorite samples, we upgraded our HPLC system to one femtomole sensitivity, and developed a new electrophoretic method of sample preparation for HPLC analysis of the meteoritic amino acids. In a sample of the KT boundary layer from Sussex Wyoming, we found about 300 picomoles per gram of meteoritic alpha-aminoisobutyric acid per gram of KT layer.

Weber, Arthur L.↗
NASA NTRS1999

Interstellar Communication Channel Based on a Biological Universal

Cellular biosynthesis starts with sugar substrates and continues energetically downhill to yield amino acid, rapid, and nucleotide products. To understand the energetics of these processes, we calculated the energy for biosynthesis from sugars of E. cali's amino acids, nucleotides, and lipids. We found that the biosynthesis of amino acids and lipids from sugar substrates proceeds by redox disproportionation. of sugar carbon with a favorable energy of about -11 kcal/mole of carbon. Overall, redox disproportion of sugar carbon accounted for 84% and 96% (ATP only 6% and 1%) of the total biosynthetic energy of amino acids and lipids (the major cellular constituents). Next, we calculated for all 48 possible 3-carbon substrates the energy of maximal disproportionation to carbon dioxide and methane. We found no other carbon substrates than matched sugars in biosynthetic energy, efficiency, and simplicity. From this, we concluded that sugars are the optimal biosynthetic substrate. Since this conclusion is based on universal properties of carbon chemistry, other carbon-based life throughout the Universe would also use optimal sugar substrates. Furthermore, this rather obvious universal role of sugars as the optimal biosubstrate would probably be common knowledge of technological civilizations throughout the Universe. Since the elemental building block of all sugars is formaldehyde, the common knowledge that sugars are the universal optimal biosubstrate could reasonably lead to the selection of a line(s) in the microwave spectrum of formaldehyde as a frequency for interstellar communication.

Weber, Arthur L.↗
NASA NTRS2002

Trends in lignin modification: a comprehensive analysis of the effects of genetic manipulations/mutations on lignification and vascular integrity

A comprehensive assessment of lignin configuration in transgenic and mutant plants is long overdue. This review thus undertook the systematic analysis of trends manifested through genetic and mutational manipulations of the various steps associated with monolignol biosynthesis; this included consideration of the downstream effects on organized lignin assembly in the various cell types, on vascular function/integrity, and on plant growth and development. As previously noted for dirigent protein (homologs), distinct and sophisticated monolignol forming metabolic networks were operative in various cell types, tissues and organs, and form the cell-specific guaiacyl (G) and guaiacyl-syringyl (G-S) enriched lignin biopolymers, respectively. Regardless of cell type undergoing lignification, carbon allocation to the different monolignol pools is apparently determined by a combination of phenylalanine availability and cinnamate-4-hydroxylase/"p-coumarate-3-hydroxylase" (C4H/C3H) activities, as revealed by transcriptional and metabolic profiling. Downregulation of either phenylalanine ammonia lyase or cinnamate-4-hydroxylase thus predictably results in reduced lignin levels and impaired vascular integrity, as well as affecting related (phenylpropanoid-dependent) metabolism. Depletion of C3H activity also results in reduced lignin deposition, albeit with the latter being derived only from hydroxyphenyl (H) units, due to both the guaiacyl (G) and syringyl (S) pathways being blocked. Apparently the cells affected are unable to compensate for reduced G/S levels by increasing the amounts of H-components. The downstream metabolic networks for G-lignin enriched formation in both angiosperms and gymnosperms utilize specific cinnamoyl CoA O-methyltransferase (CCOMT), 4-coumarate:CoA ligase (4CL), cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) isoforms: however, these steps neither affect carbon allocation nor H/G designations, this being determined by C4H/C3H activities. Such enzymes thus fulfill subsidiary processing roles, with all (except CCOMT) apparently being bifunctional for both H and G substrates. Their severe downregulation does, however, predictably result in impaired monolignol biosynthesis, reduced lignin deposition/vascular integrity, (upstream) metabolite build-up and/or shunt pathway metabolism. There was no evidence for an alternative acid/ester O-methyltransferase (AEOMT) being involved in lignin biosynthesis.The G/S lignin pathway networks are operative in specific cell types in angiosperms and employ two additional biosynthetic steps to afford the corresponding S components, i.e. through introduction of an hydroxyl group at C-5 and its subsequent O-methylation. [These enzymes were originally classified as ferulate-5-hydroxylase (F5H) and caffeate O-methyltransferase (COMT), respectively.] As before, neither step has apparently any role in carbon allocation to the pathway; hence their individual downregulation/manipulation, respectively, gives either a G enriched lignin or formation of the well-known S-deficient bm3 "lignin" mutant, with cell walls of impaired vascular integrity. In the latter case, COMT downregulation/mutation apparently results in utilization of the isoelectronic 5-hydroxyconiferyl alcohol species albeit in an unsuccessful attempt to form G-S lignin proper. However, there is apparently no effect on overall G content, thereby indicating that deposition of both G and S moieties in the G/S lignin forming cells are kept spatially, and presumably temporally, fully separate. Downregulation/mutation of further downstream steps in the G/S network [i.e. utilizing 4CL, CCR and CAD isoforms] gives predictable effects in terms of their subsidiary processing roles: while severe downregulation of 4CL gave phenotypes with impaired vascular integrity due to reduced monolignol supply, there was no evidence in support of increased growth and/or enhanced cellulose biosynthesis. CCR and CAD downregulation/mutations also established that a depletion in monolignol supply reduced both lignin contents supply reduced both lignin contents and vascular integrity, with a concomitant shift towards (upstream) metabolite build-up and/or shunting.The extraordinary claims of involvement of surrogate monomers (2-methoxybenzaldehyde, feruloyl tyramine, vanillic acid, etc.) in lignification were fully disproven and put to rest, with the investigators themselves having largely retracted former claims. Furthermore analysis of the well-known bm1 mutation, a presumed CAD disrupted system, apparently revealed that both G and S lignin components were reduced. This seems to imply that there is no monolignol specific dehydrogenase, such as the recently described sinapyl alcohol dehydrogenase (SAD) for sinapyl alcohol formation. Nevertheless, different CAD isoforms of differing homology seem to be operative in different lignifying cell types, thereby giving the G-enriched and G/S-enriched lignin biopolymers, respectively. For the G-lignin forming network, however, the CAD isoform is apparently catalytically less efficient with all three monolignols than that additionally associated with the corresponding G/S lignin forming network(s), which can more efficiently use all three monolignols. However, since CAD does not determine either H, G, or S designation, it again serves in a subsidiary role-albeit using different isoforms for different cell wall developmental and cell wall type responses.The results from this analysis contrasts further with speculations of some early investigators, who had viewed lignin assembly as resulting from non-specific oxidative coupling of monolignols and subsequent random polymerization. At that time, though, the study of the complex biological (biochemical) process of lignin assembly had begun without any of the (bio)chemical tools to either address or answer the questions posed as to how its formation might actually occur. Today, by contrast, there is growing recognition of both sophisticated and differential control of monolignol biosynthetic networks in different cell types, which serve to underscore the fact that complexity of assembly need not be confused any further with random formation. Moreover, this analysis revealed another factor which continues to cloud interpretations of lignin downregulation/mutational analyses, namely the serious technical problems associated with all aspects of lignin characterization, whether for lignin quantification, isolation of lignin-enriched preparations and/or in determining monomeric compositions. For example, in the latter analyses, some 50-90% of the lignin components still cannot be detected using current methodologies, e.g. by thioacidolysis cleavage and nitrobenzene oxidative cleavage. This deficiency in lignin characterization thus represents one of the major hurdles remaining in delineating how lignin assembly (in distinct cell types) and their configuration actually occurs.

Review, Academic↗
NASA NTRS1985

Growth and graviresponsiveness of primary roots of Zea mays seedlings deficient in abscisic acid and gibberellic acid

The objective of this research was to determine if gibberellic acid (GA) and/or abscisic acid (ABA) are necessary for graviresponsiveness by primary roots of Zea mays. To accomplish this objective we measured the growth and graviresponsiveness of primary roots of seedlings in which the synthesis of ABA and GA was inhibited collectively and individually by genetic and chemical means. Roots of seedlings treated with Fluridone (an inhibitor of ABA biosynthesis) and Ancymidol (an inhibitor of GA biosynthesis) were characterized by slower growth rates but not significantly different gravicultures as compared to untreated controls. Gravicurvatures of primary roots of d-5 mutants (having undetectable levels of GA) and vp-9 mutants (having undectable levels of ABA) were not significantly different from those of wild-type seedlings. Roots of seedlings in which the biosynthesis of ABA and GA was collectively inhibited were characterized by gravicurvatures not significantly different for those of controls. These results (1) indicate that drastic reductions in the amount of ABA and GA in Z. mays seedlings do not significantly alter root graviresponsiveness, (2) suggest that neither ABA nor GA is necessary for root gravicurvature, and (3) indicate that root gravicurvature is not necessarily proportional to root elongation.

Zea mays/drug effects/growth & development/metabol↗
NASA NTRS1977

Some questions of space bioengineering

Zero-gravity offers selective effect on growth and metabolic activity unicellular organisms as well as unique opportunities in purification of organic compounds. These make it possible to consider the biosynthesis and recovery of certain metabolites economically feasible in space. Design, construction and operation of systems for the above mentioned purposes requires interdisciplinary actions within the scope of a new discipline: space bioengineering. The problems and perspectives of this discipline particularly in the application of bioreactor-recovery systems in space to manufacture metabolites of high economic and scientific value. Special attention is paid to pivotal factors such as various mass transport phenomena, contamination control, automatic control of optimum environment and synchronization of the operation of the biological (biosynthesis) and the physiochemical (recovery-purification) systems.

Nyiri, L. K.↗
NASA NTRS1985

Control of arachidonic acid release in chick muscle cultures

Cultures from thigh muscles of 12 day old embryonic chicks are utilized to examine arachidonic release, prostaglandin (PG) biosynthesis, and protein synthesis. The preparation of the cultures is described. It is observed that exogenous arachidonic acid is formed into photsphatidylethanolamine and phosphatidylcholine, is released by a calcium ionosphere or phospholiphase simulator, and is the substrate for the biosynthesis of PG; the epidermal growth factor and PGF do not stimulate protein synthesis over the basal levels. The relationship between arachidonate release and melittin is studied. The data reveal that a change in intracellular calcium stimulates phospholiphase activity, arachidonate release, and PG synthesis in chick muscle culture.

Templeton, G. H.↗
NASA NTRS1997

The Role of GH/IGF-I Axis in Muscle Homeostasis During Weightlessness

Exposure to reduced gravity during space travel profoundly alters the loads placed on bone and muscle. Astronauts suffer significant losses of muscle and bone strength during weightlessness. Exercise as a countermeasure is only partially effective in remedying severe muscle atrophy and bone demineralization. Similar wasting of muscles and bones affects people on Earth during prolonged bed rest or immobilization due to injury. In the absence of weight bearing activity, atrophy occurs primarily in the muscles that act in low power, routine movements and in maintaining posture. Hormonal disfunction could contribute in part to the loss of muscle and bone during spaceflight. Reduced levels of human Growth Hormone (hGH) were found in astronauts during space flight, as well as reduced GH secretory activity was observed from the anterior pituitary in 7-day space flight rats. Growth hormone has been shown to be required for maintenance of muscle mass and bone mineralization, in part by mediating the biosynthesis IGF-I, a small polypeptide growth factor. IGF biosynthesis and secretion plays an important role in potentiating muscle cell differentiation and has been shown to drive the expression of myogenin, a myogenic specific basic helix-loop-helix factor. IGF-I has also been shown to have an important role in potentiating muscle regeneration, repair and adult muscle hypertrophy.

Schwartz, Robert J.↗
NASA NTRS1997

Redox Energy and Sulfur Chemistry in Prebiotic Polymer Synthesis and Replication

In the past year we have made significant progress in three research areas: (1) Most importantly, we discovered a new pathway of prebiotic amino acid synthesis in which formaldehyde and glycolaldehyde (substrates of the formose reaction) react with ammonia yielding alanine and homoserine in the presence of thiol catalysts. This thiol-dependent synthesis of amino acids undoubtedly occurs via amino acid thioester intermediates capable of forming peptides. This 'one-pot' reaction system operates under mild aqueous conditions, and like modern amino acid biosynthesis, uses sugar intermediates which are converted to amino acids by energy-yielding redox disproportionation. (2) Finally, in preparation for the analysis of Martian meteorite samples, we upgraded our HPLC system and developed an improved method capable of detecting a I femtomole of amino acid enantiomers. (3) We completed our analysis of the energetics of metabolism that revealed that life depends on biosynthetic processes driven by chemical energy made available by the redox disproportionation of carbon groups of sugars. We established that the favorable energy of redox disproportionation is based on the universal reduction potentials of carbon groups. We concluded that it is hard to imagine any other organic molecule besides sugars (formaldehyde oligomers) having the energy and reactivity needed to drive either modem biosynthesis or the chemical processes behind its origin.

Weber, Arthur L.↗
NASA NTRS1996

The Metabolic World: Sugars as an Energized Carbon Substrate for Prebiotic and Biotic Synthesis

To understand the origin of metabolism and biopolymer synthesis we investigated the energy sources that drive anabolic metabolism. We found that biosynthesis of amino acids and lipids from sugars is driven bz the free energy of redox disproportionation of carbon (see discussion or next page). The indispensable role of sugar disproportionation in the biosynthesis of amino acids and lipids suggests that the origin of life uses the same chemical engine, and was therefore based on nonenzymatic redox disproportionation reactions of sugars that occurred in the presence o ammonia and hydrogen sulfide. The chemistry of this 'metabolic' model of the origin of life is described.

Weber, Arthur L.↗
NASA NTRS2000

Induced phenylpropanoid metabolism during suberization and lignification: a comparative analysis

Induction of the biosynthesis of phenylpropanoids was monitored at the enzyme level through measurement of the temporal change in the activity of two marker enzymes of phenylpropanoid metabolism, phenylalanine ammonia-lyase, (PAL, E.C. 4.1.3.5) and 4-coumaryl-CoA ligase (4-CL, E.C. 6.2.1.12) and two marker enzymes for hydroxycinnamyl alcohol biosynthesis, cinnamoyl-CoA:NADP+ oxidoreductase (CCR, E.C. 1.2.1.44) and cinnamyl alcohol dehydrogenase (CAD, E.C. 1.1.1.195) in both suberizing potato (Solanum tuberosum) tubers and lignifying loblolly pine (Pinus taeda) cell cultures. While measurable activities of PAL, 4-CL and CAD increased upon initiation of suberization in potato tubers, that of CCR did not. By contrast, all four enzymes were induced upon initiation of lignification in pine cell cultures. The lack of CCR induction in potato by wound treatment is consistent with the channelling of hydroxycinnamoyl-CoA derivatives away from monolignol formation and toward other hydroxycinnamoyl derivatives such as those that accumulate during suberization.

Non-NASA Center↗
NASA NTRS1994

Influence of low temperature preincubation on somatic embryogenesis and ethylene emanation from orchardgrass leaves

The objectives of this study were to determine the effects of low temperature (4 degrees C) preincubation on somatic embryogenesis from orchardgrass (Dactylis glomerata L.) leaf cultures and to relate these effects to ethylene emanation during the preincubation and incubation periods. Experiments were also conducted with an ethylene biosynthesis inhibitor aminooxyacetic acid (AOA). Segments from the innermost two leaves were cultured on SH medium with 30 micromoles dicamba at 4 degrees C for 1 to 7 d before transfer to 21 degrees C. Results from a paired design showed that the embryogenic response of leaf segments preincubated at 4 degrees C was equal or superior to nonpreincubated leaves at all time periods. Ethylene emanation was decreased during the low temperature incubation. Transfer of leaf segments from 4 degrees C to 21 degrees C was accompanied by a burst of ethylene which rose to control levels within 30 min. AOA at 20 and 40 micromoles decreased ethylene emanation but did not stimulate the embryogenic response. We conclude that the stimulation of somatic embryogenesis by low temperature is probably due to factors other than suppression of ethylene biosynthesis.

NASA Discipline Number 40-50↗
NASA NTRS1993

Embryonic lung morphogenesis in organ culture: experimental evidence for a proteoglycan function in the extracellular matrix

The lung rudiment, isolated from mid-gestation (11 day) mouse embryos, can undergo morphogenesis in organ culture. Observation of living rudiments, in culture, reveals both growth and ongoing bronchiolar branching activity. To detect proteoglycan (PG) biosynthesis, and deposition in the extracellular matrix, rudiments were metabolically labeled with radioactive sulfate, then fixed, embedded, sectioned and processed for autoradiography. The sulfated glycosaminoglycan (GAG) types, composing the carbohydrate component of the proteoglycans, were evaluated by selective GAG degradative approaches that showed chondroitin sulfate PG principally associated with the interstitial matrix, and heparan sulfate PG principally associated with the basement membrane. Experiments using the proteoglycan biosynthesis disrupter, beta-xyloside, suggest that when chondroitin sulfate PG deposition into the ECM is perturbed, branching morphogenesis is compromised.

NASA Discipline Number 93-10↗
NASA NTRS1990

Effects of ethylene on the kinetics of curvature and auxin redistribution in gravistimulated roots of Zea mays

We tested the involvement of ethylene in maize (Zea mays L.) root gravitropism by measuring the kinetics of curvature and lateral auxin movement in roots treated with ethylene, inhibitors of ethylene synthesis, or inhibitors of ethylene action. In the presence of ethylene the latent period of gravitropic curvature appeared to be increased somewhat. However, ethylene-treated roots continued to curve after control roots had reached their final angle of curvature. Consequently, maximum curvature in the presence of ethylene was much greater in ethylene-treated roots than in controls. Inhibitors of ethylene biosynthesis or action had effects on the kinetics of curvature opposite to that of ethylene, i.e. the latent period appeared to be shortened somewhat while total curvature was reduced relative to that of controls. Label from applied 3H-indole-3-acetic acid was preferentially transported toward the lower side of stimulated roots. In parallel with effects on curvature, ethylene treatment delayed the development of gravity-induced asymmetric auxin movement across the root but extended its duration once initiated. The auxin transport inhibitor, 1-N-naphthylphthalamic acid reduced both gravitropic curvature and the effect of ethylene on curvature. Since neither ethylene nor inhibitors of ethylene biosynthesis or action prevented curvature, we conclude that ethylene does not mediate the primary differential growth response causing curvature. Because ethylene affects curvature and auxin transport in parallel, we suggest that ethylene modifies curvature by affecting gravity-induced lateral transport of auxin, perhaps by interfering with adaptation of the auxin transport system to the gravistimulus.

Non-NASA Center↗
NASA NTRS1995

Root-shoot interaction in the greening of wheat seedlings grown under red light

Wheat seedlings grown with roots exposed to constant red light (300-500 micromoles m-2 s-1) did not accumulate chlorophyll in the leaves. In contrast, seedlings grown with their roots shielded from light accumulated chlorophylls. Chlorophyll biosynthesis could be induced in red-light-grown chlorophyll-deficient yellow plants by either reducing the red-light intensity at the root surface to 100 micromoles m-1 s-1 or supplementing with 6% blue light. The inhibition of chlorophyll biosynthesis was due to impairment of the Mg-chelatase enzyme working at the origin of the Mg-tetrapyrrole pathway. The root-perceived photomorphogenic inhibition of shoot greening demonstrates root-shoot interaction in the greening process.

NASA Center KSC↗