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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Genetic separation of phototropism and blue light inhibition of stem elongation

Blue light-induced regulation of cell elongation is a component of the signal response pathway for both phototropic curvature and inhibition of stem elongation in higher plants. To determine if blue light regulates cell elongation in these responses through shared or discrete pathways, phototropism and hypocotyl elongation were investigated in several blue light response mutants in Arabidopsis thaliana. Specifically, the blu mutants that lack blue light-dependent inhibition of hypocotyl elongation were found to exhibit a normal phototropic response. In contrast, a phototropic null mutant (JK218) and a mutant that has a 20- to 30-fold shift in the fluence dependence for first positive phototropism (JK224) showed normal inhibition of hypocotyl elongation in blue light. F1 progeny of crosses between the blu mutants and JK218 showed normal phototropism and inhibition of hypocotyl elongation, and approximately 1 in 16 F2 progeny were double mutants lacking both responses. Thus, blue light-dependent inhibition of hypocotyl elongation and phototropism operate through at least some genetically distinct components.

Non-NASA Center↗
NASA NTRS1994

Calcium influences sensitivity to growth inhibition induced by a cell surface sialoglycopeptide

While studies concerning mitogenic factors have been an important area of research for many years, much less is understood about the mechanisms of action of cell surface growth inhibitors. We have purified an 18 kDa cell surface sialoglycopeptide growth inhibitor (CeReS-18) which can reversibly inhibit the proliferation of diverse cell types. The studies discussed in this article show that three mouse keratinocyte cell lines exhibit sixty-fold greater sensitivity than other fibroblasts and epithelial-like cells to CeReS-18-induced growth inhibition. Growth inhibition induced by CeReS-18 treatment is a reversible process, and the three mouse keratinocyte cell lines exhibited either single or multiple cell cycle arrest points, although a predominantly G0/G1 cell cycle arrest point was exhibited in Swiss 3T3 fibroblasts. The sensitivity of the mouse keratinocyte cell lines to CeReS-18-induced growth inhibition was not affected by the degree of tumorigenic progression in the cell lines and was not due to differences in CeReS-18 binding affinity or number of cell surface receptors per cell. However, the sensitivity of both murine fibroblasts and keratinocytes could be altered by changing the extracellular calcium concentration, such that increased extracellular calcium concentrations resulted in decreased sensitivity to CeReS-18-induced proliferation inhibition. Thus the increased sensitivity of the murine keratinocyte cell lines to CeReS-18 could be ascribed to the low calcium concentration used in their propagation. Studies are currently under way investigating the role of calcium in CeReS-18-induced growth arrest. The CeReS-18 may serve as a very useful tool to study negative growth control and the signal transduction events associated with cell cycling.

NASA Discipline Cell Biology↗
NASA NTRS1982

Quantitation of chlorpromazine-bound calmodulin during chlorpromazine inhibition of gravitropism

The regulatory protein, calmodulin (CaM), controls the activity of a plasma membrane localized ATPase in plants which serves to pump calcium out of cells. Recent data are consistent with the hypothesis that activation of this pump is one of the early steps necessary for gravitropism. Chlorpromazine (CPZ), a CaM antagonist, reversibly inhibits gravitropism in oat coleoptiles at concentrations which permit normal growth rates. C-14-labeled CPZ was used to photo-affinity label endogenous CaM in vivo to learn whether the drug is actually binding to some portion of endogenous CaM when it inhibits gravitropism. Under conditions in which CPZ inhibits gravitropism for over an hour, at least 11% of the CaM in gravitropically stimulated coleoptiles is bound to CPZ. In a given CPZ experiment the degree of inhibition of gravitropism correlates well with the amount of CaM bound to CPZ.

Roux, S. J.↗
NASA NTRS1985

Kinetic separation of phototropism from blue-light inhibition of stem elongation

These experiments tested the hypothesis that phototropic bending arises when a light gradient across the stem differentially inhibits cell elongation because of direct inhibition of cell elongation by light (the Blaauw hypothesis). Continuous irradiation of dark-grown cucumber seedlings (Cucumis sativus L.) with unilateral blue light inhibited hypocotyl elongation within 30 s, but did not induce phototropic curvature until 4.5 h after the start of irradiation. Marking experiments showed that curvature began simultaneously at the top and bottom of the growing region. In situ measurements of the light gradient across the stem with a glass fiber optic indicated that a 5- to 6-fold difference in fluence rate was established on the two sides of the stem. The light gradient established at the start of irradiation was the same as that after 6 h of irradiation. Changes in gravitropic responsiveness during this period were also ruled out. Calculations show that the light gradient should have caused curvature which would be detectable within 30 to 60 min and which would extrapolate to the start of irradiation--if the Blaauw hypothesis were correct. The long lag for phototropism in this case indicates that rapid inhibition of cell elongation by blue light does not cause the asymmetrical growth of phototropism. Rather, phototropism is superimposed upon this separate light growth response.

NASA Discipline Number 40-30↗
NASA NTRS1992

Comparative kinetics and reciprocal inhibition of nitrate and nitrite uptake in roots of uninduced and induced barley (Hordeum vulgare L.) seedlings

Nitrate and NO2- transport by roots of 8-day-old uninduced and induced intact barley (Hordeum vulgare L. var CM 72) seedlings were compared to kinetic patterns, reciprocal inhibition of the transport systems, and the effect of the inhibitor, p-hydroxymercuribenzoate. Net uptake of NO3- and NO2- was measured by following the depletion of the ions from the uptake solutions. The roots of uninduced seedlings possessed a low concentration, saturable, low Km, possibly a constitutive uptake system, and a linear system for both NO3- and NO2-. The low Km system followed Michaelis-Menten kinetics and approached saturation between 40 and 100 micromolar, whereas the linear system was detected between 100 and 500 micromolar. In roots of induced seedlings, rates for both NO3- and NO2- uptake followed Michaelis-Menten kinetics and approached saturation at about 200 micromolar. In induced roots, two kinetically identifiable transport systems were resolved for each anion. At the lower substrate concentrations, less than 10 micromolar, the apparent low Kms of NO3- and NO2- uptake were 7 and 9 micromolar, respectively, and were similar to those of the low Km system in uninduced roots. At substrate concentrations between 10 and 200 micromolar, the apparent high Km values of NO3- uptake ranged from 34 to 36 micromolar and of NO2- uptake ranged from 41 to 49 micromolar. A linear system was also found in induced seedlings at concentrations above 500 micromolar. Double reciprocal plots indicated that NO3- and NO2- inhibited the uptake of each other competitively in both uninduced and induced seedlings; however, Ki values showed that NO3- was a more effective inhibitor than NO2-. Nitrate and NO2- transport by both the low and high Km systems were greatly inhibited by p-hydroxymercuribenzoate, whereas the linear system was only slightly inhibited.

NASA Program CELSS↗
NASA NTRS1989

Timing of growth inhibition following shoot inversion in Pharbitis nil

Shoot inversion in Pharbitis nil results in the enhancement of ethylene production and in the inhibition of elongation in the growth zone of the inverted shoot. The initial increase in ethylene production previously was detected within 2 to 2.75 hours after inversion. In the present study, the initial inhibition of shoot elongation was detected within 1.5 to 4 hours with a weighted mean of 2.4 hours. Ethylene treatment of upright shoots inhibited elongation in 1.5 hours. A cause and effect relationship between shoot inversion-enhanced ethylene production and inhibition of elongation cannot be excluded.

Non-NASA Center↗
NASA NTRS1991

Galactose inhibits auxin-induced growth of Avena coleoptiles by two mechanisms

Galactose inhibits auxin-induced growth of Avena coleoptiles by at least two mechanisms. First, it inhibits auxin-induced H(+)-excretion needed for the initiation of rapid elongation. Galactose cannot be doing so by directly interfering with the ATPase since fusicoccin-induced H(+)-excretion is not affected. Secondly, galactose inhibits long-term auxin-induced growth, even in an acidic (pH 4.5) solution. This may be due to an inhibition of cell wall synthesis. However, galactose does not reduce the capacity of walls to be loosened by H+, given exogenously or excreted in response to fusicoccin.

NASA Discipline Plant Biology↗
NASA NTRS1984

Inhibition of gravitropism in oat coleoptiles by the calcium chelator, ethyleneglycol-bis-(beta-aminoethyl ether)-N,N'-tetraacetic acid

A treatment period as brief as 8 h in 10(-3) M EGTA completely blocks gravitropism in 70-80% of the treated coleoptiles of oats (Avena sativa L. cv. Garry) without inhibiting growth. Only about 10% of the plants perfused in water failed to exhibit gravitropism. Subsequent perfusion of EGTA-treated plants with calcium completely restores gravitropism; post-perfusion with water does not. After perfusion in water for 10 h, gravistimulated oat coleoptile segments show the same asymmetry of 45Ca distribution as reported earlier for non-perfused coleoptiles and sunflower hypocotyls. The degree of this asymmetry is reduced in those coleoptiles partially inhibited by perfusion in EGTA and is essentially absent in those coleoptiles completely inhibited by EGTA. The fact that calcium reverses the inhibitory effects of EGTA on gravitropism indicates that the inhibition was probably due to a reduction in the availability of free calcium required for one or more of the transduction steps of gravitropism.

Egtazic Acid/pharmacology↗
NASA NTRS1994

Inhibition of murine splenic T lymphocyte proliferation by 2-deoxy-D-glucose-induced metabolic stress

Female Swiss-Webster mice were injected with the glucose analogue 2-deoxy-D-glucose (2-DG), which when administered to rodents induces acute periods of metabolic stress. A single or multiple injections of 2-DG invoked a stress response, as evidenced by increases in serum corticosterone levels. The influence of this metabolic stressor on the blastogenic potential of splenic T lymphocytes was then examined. It was found that one, two, or three injections of 2-DG resulted in depressed T cell proliferative responses, with an attenuation of the effect occurring by the fifth injection. The 2-DG-induced inhibition of T cell proliferation was not attributable to 2-DG-induced cytolysis, as in vitro incubation of naive T cells with varying concentrations of 2-DG did not result in a reduction in cell number or viability, and flow cytometric analysis demonstrated that percentages of CD3, CD4, and CD8 splenic T cells were not altered as a result of 2-DG-induced stress. Incubating naive T cells in varying concentrations of 2-DG resulted in a dose-dependent inhibition of T cell blastogenic potential. Following in vivo exposure to 2-DG, T cell proliferation did not return to normal levels until 3 days after the cessation of 2-DG injections. Administering the beta-adrenergic receptor antagonist propranolol did not reverse the inhibited lymphoproliferation in 2-DG-treated mice. The inhibition in T cell proliferation was not observed, however, in mice that had been adrenalectomized or hypophysectomized and injected with 2-DG.(ABSTRACT TRUNCATED AT 250 WORDS).

Non-NASA Center↗
NASA NTRS1988

Inhibited interferon production after space flight

Several studies have been performed in our laboratories indicating that interferon production may be impaired in rodents after space flight. Using an antiorthostatic suspension model that simulates some of the effects of microgravity seen during space flight, we have shown that interferon-alpha/beta production was inhibited. The inhibition was not due solely to the stress of suspension. The inhibited interferon production was transient, as suspended animals returned to normal caging recovered the ability to produce interferon. Antiorthostatic suspension of mice also resulted in a loss of resistance to infection with the diabetogenic strain of encephalomyocarditis virus, which correlated with the drop in interferon production. In rats flown in US Space Shuttle mission SL-3, interferon-gamma production was inhibited severely when spleen cells were challenged with concanavalin-A upon return to earth. In contrast, interleukin-3 production by these cells was normal. These results suggest that immune responses may be altered after antiorthostatic modeling or space flight, and the resistance to viral infections may be especially affected.

Flight Experiment↗
NASA NTRS2014

Controller Inhibition of Automated Conflict Resolutions in a Maximum NextGen Condition

With the continued projection of increases in air traffic density, operations in the National Airspace System are expected to exceed human capabilities in the near future. In order to address the bottleneck of human workload capacity, highly automated safety-critical systems are under development to support air traffic controllers. A human-in-the-loop experiment examined controllers transition through four NextGen automation stages: Current-Day, Minimum, Moderate, and Maximum. Maximum NextGen simulated a fully automated environment where the automation was responsible for detecting and resolving conflicts within simulation parameters in high-density airspace. By allocating these tasks to the automation, the controllers task changed. The human moved to primarily a supervisory position- typically only regaining control over separation assurance tasks during conflict situations deferred by the automation. While tasks were allocated a-priori between the controller and automated agent, controllers maintained authority to inhibit the automation from interacting with particular aircraft. Preliminary work is complete, where significant differences were found in inhibition frequency between simulation participants. However, the contexts in which the controllers inhibited the automation, and their reasons for doing so, remain unclear. This analysis attempts to identity factors contributing to human controllers inhibition of the automation in the Maximum NextGen condition.

adaptable automation↗
NASA NTRS1972

Inhibition of the ablation rate of graphite by gaseous chlorine.

Investigation of the inhibiting effect of gaseous chlorine on the ablation rate of graphite. It is shown that small amounts of chlorine gas, when present in a supersonic high-temperature air environment, can inhibit the ablation rate of graphite and depress its surface temperature below that measured in pure air. The ablation inhibition performance of chlorine is presented in graphs in terms of mass loss rate and surface temperature depression as a function of chlorine concentration.

Maahs, H. G.↗
NASA NTRS1978

The spiral field inhibition of thermal conduction in two-fluid solar wind models

The paper reports on two-field models which include the inhibition of thermal conduction by the spiraling interplanetary field to determine whether any of the major conclusions obtained by Nerney and Barnes (1977) needs to be modified. Comparisons with straight field line models reveal that for most base conditions, the primary effect of the inhibition of thermal conduction is the bottling-up of heat in the electrons as well as the quite different temperature profiles at a large heliocentric radius. The spiral field solutions show that coronal hole boundary conditions do not correspond to states of high-speed streams as observed at 1 AU. The two-fluid models suggest that the spiral field inhibition of thermal conduction in the equatorial plane will generate higher gas pressures in comparison with flows along the solar rotation axis (between 1 and 10 AU). In particular, massive outflows of stellar winds, such as outflow from T Tauri stars, cannot be driven by thermal conduction. The conclusions of Nerney and Barnes remain essentially unchanged.

Nerney, S.↗
NASA NTRS1979

Inhibition of the pituitary-adrenal response to stress during deprivation-induced feeding

Plasma corticosterone and plasma and pituitary ACTH concentrations were determined during feeding and after application of an acute stress at various times after food and water presentation to male rats maintained on a restricted feeding and watering schedule. Both plasma corticosterone and ACTH concentrations fell after the presentation of food and water, and this fall was accompanied by increased levels of ACTH in the pituitary gland. In addition, a rise in plasma levels of ACTH was inhibited in response to an acute stress applied at 0-5 min after presentation of food and water, but ACTH synthesis was not. This inhibition of ACTH and corticosterone secretion in response to stress was transient and dissipated as a relatively linear function of the interval between food presentation and application of the stress. The results suggest that this feeding-induced, corticosteroid-independent inhibition of pituitary-adrenal activity involves active inhibitory mechanisms operating initially on ACTH secretory processes of the pituitary and later on the synthesis of ACTH or on the secretion of hypothalamic corticotropin-releasing factor.

Heybach, J. P.↗
NASA NTRS1984

Inhibition of gravitropism in oat coleoptiles by calcium chelation

Some cellular event necessary for gravitropism is inhibited by EGTA without interferring with the overall growth. Calcium relieves this inhibition and demonstrates both that inhibition is reversible and was probably due to a reduction in the ability to free calcium required for one or more at the transduction steps of gravitropism. At the near neutral pH used, EGTA is charged and would not be expected to readily cross the membrane. One of its primary effects, then, is probably the bringing of free calcium in the apoplastic space exterior to the cell membranes.

Roux, S. J.↗
NASA NTRS1997

Enantiomeric Cross-Inhibition in the Synthesis of Oligonucleotides on a Nonchiral Template

Prebiotic syntheses of chiral monomers always yield racemic mixtures. Living systems, however, utilize L-amino acids and D-nucleotides in their biopolymers. The generation of optical asymmetry by selection and amplification in an autocatalytic process is, therefore, an important element in many theories of the origin of life. Replication of polynucleotides in template-directed syntheses is an obvious candidate for such an amplification step in a pre-'RNA world'. A serious objection to this suggestion is the observation that the efficiency of template-directed syntheses of RNA is limited by enantiomeric cross-inhibition. Peptide Nucleic Acids (PNAs), amide-linked, nonchiral analogues of RNA, have been 'copied' into RNA and constitute an alternative to chiral polynucleotides as an informational replicating system. Here, we use PNA as model for a hypothetical, nonchiral precursor of RNA in experiments re-examining enantiomeric cross-inhibition. We find that enantiomeric cross-inhibition is as serious in the polymerization of nucleotides on a PNA template as it is on a conventional RNA or DNA template.

Schmidt, Jurgen G.↗
NASA NTRS1995

Inhibition of the ATPase from Halobacterium Saccharovorum by Thiol Inhibitors: Evidence for the Presence of More Than One Essential Cysteinyl Residue

The vacuolar-like ATPase from Halobacterium saccha vorum is inhibited by N-ethylmaleimide and p-chloromercudphenylsulfonate. The failure of adenine nucleotides to protect against p-chloromercuriphenyisulfonate inhibition, of p-chloromercuriphenylsulfonate to protect against N-ethylmaleimide inhibition, and the difference in the temperature dependence of inactivation infers that the enzyme contains at least two thiols that are essential for enzyme activity. CNBr cleavage of C-14-N-ethylmaleimide labeled subunit results in two radioactive peptides that locates the N-ethylmaleimide-reactive cysteinyl residue as cysteine-262 in the H. salinarium sequence.

Hochstein, Lawrence I.↗
NASA NTRS2002

Preferential inhibition of the plasma membrane NADH oxidase (NOX) activity by diphenyleneiodonium chloride with NADPH as donor

The cell-surface NADH oxidase (NOX) protein of plant and animal cells will utilize both NADH and NADPH as reduced electron donors for activity. The two activities are distinguished by a differential inhibition by the redox inhibitor diphenyleneiodonium chloride (DPI). Using both plasma membranes and cells, activity with NADPH as donor was markedly inhibited by DPI at submicromolar concentrations, whereas with NADH as donor, DPI was much less effective or had no effect on the activity. The possibility of the inhibition being the result of two different enzymes was eliminated by the use of a recombinant NOX protein. The findings support the concept that NOX proteins serve as terminal oxidases for plasma membrane electron transport involving cytosolic reduced pyridine nucleotides as the natural electron donors and with molecular oxygen as the electron acceptor.

Non-NASA Center↗