Changes in photoelectron transport of chloroplasts isolated from dark stressed leaves of maize seedlings.

Transfer of light-grown maize seedlings to dark causes a loss in the the contents of chlorophyll, protein and RNA of leaves, and a decline in DCPIP photoreduction by isolated chloroplasts. The loss in DCPIP-Hill reaction is attributed to the dark stress-induced damage of O2 evolving system of thylakoid membranes.     

Circadian variation of diazepam acute toxicity in mice

Summary The LD₅₀ of i.p. injected diazepam was determined every 4 h over a 24-h period in albino mice adapted to a 12-h dark/12-h light programmed illumination cycle. Results show that diazepam is more toxic during the light phase of the cycle than during the dark phase and demonstrate circadian variation in the toxicity of the compound in mice.     

Influence of oxygen concentration on development ofDrosophila melanogaster

Summary 1st, 2nd, and early 3rd instarDrosophila larvae are extremely sensitive to 100% O₂ or 75% O₂/25% N₂ (at atmospheric pressure) whereas eggs, late 3rd instar larvae, and pupae are relatively insensitive under our exposure conditions. Eclosing flies exposed to an O₂ enriched environment consistently possessed 2 eye abnormalities: dark eye color and altered eye shape.Supported by NSF-URP grant SP1782684 and a Summer Faculty Fellowship to Harry Nickla.     

Die Einlagerung von radioaktivem Schwefel in die Flügel von Acrididen nach Applikation von35S-Natriumsulfat-und35S-l-Cystinlösungen

Summary Psophus stridulus L. andOedipoda coerulescens L. were fed or injected with solutions of Na ₂ ³⁵ SO₄ and³⁵S-l-cystine. The radioactive radiation pattern of the wings was found to depend on the time of application. Differences in radiation intensity were found to correspond to the red, blue and dark areas.     

Feeding induced by blockade of histamine H1-receptor in rat brain

Summary Histamine antagonists were infused into the third ventricle of the cerebrum in rats. All the H₁-, but none of the H₂-antagonists tested, induced initial feeding during the early portion of the light phase when histamine level was highest. No periprandial drinking was observed. Ambulation increased during feeding. The effect on feeding was attenuated when brain histamine was normally low during the early portion of the dark phase, or was decreased by -fluoromethylhistidine. Hypothalamic neuronal histamine may suppress food intake through H₁-receptors, and diurnal fluctuations of food intake may mirror neuronal histamine levels.     

Photobiochemistry without light

Summary Efficient excited state formation — much higher than that hitherto expected — may occur in organelles and in intact cells. Excited triplet states can be enzymatically generated in high yields by different routes. An example is the oxidation of isobutanal to acetone and formic acid, catalyzed by horseradish peroxidase. Other enzymatic systems that generate triplet carbonyls are linear aliphatic aldehydes when oxidized by peroxidase/O₂, or the indole-3-acetic acid/peroxidase/O₂-reaction. The latter is widespread in plants.This new field — photobiochemistry without light — has led to a growing awareness of the idea that cells may utilize excited states to trigger photochemical processes even in the dark. Such phenomena are of considerable importance, also for the understanding of weak photon emission from biological systems.     

Ein Durchflusszählrohr mit getrennter Messkammer für Mikroversuche mit biologischem Material in geschlossenen Systemen

Summary A fluid-measuring tube with separate cell measuring and counting chamber, is described with which metabolic transposition of small amounts of biological materials can be examined within an enclosed system. Tests were carried out on the course of the expiration of sucrose through phylloxers weighing 20 mg, and also on the fixation in the dark of CO₂ by 8 green grapes. Tests were also carreied out on the expiration of sucrose and malic acid by yeast in fermentation. The course of metabolism can easily be seen by means of the radioactivity curves.     

Oxidative stress and hypoxia-like injury cause Alzheimer-type molecular abnormalities in central nervous system neurons

Neuronal loss and neuritic/cytoskeletal lesions (synaptic disconnection and proliferation of dystrophic neurites) represent major dementia-associated abnormalities in Alzheimer’s disease (AD). This study examined the role of oxidative stress as a factor contributing to both the cell death and neuritic degeneration cascades in AD. Primary neuron cultures were treated with H₂O₂ (9–90 μM) or desferrioxamine (2–25 μM) for 24 h and then analyzed for viability, mitochondrial mass, mitochondrial function, and pro-apoptosis and sprouting gene expression. H₂O₂ treatment causes free-radical injury and desferrioxamine causes hypoxia-type injury without free radical generation. The H₂O₂-treated cells exhibited sustained viability but neurite retraction, impaired mitochondrial function, increased levels of the pro-apoptosis gene product CD95/Fas, reduced expression of N2J1-immunoreactive neuronal thread protein and synaptophysin, and reduced distribution of mitochondria in neuritic processes. Desferrioxamine treatment resulted in dose-dependent neuronal loss associated with impaired mitochondrial function, proliferation of neurites, and reduced expression of GAP-43, which has a role in path-finding during neurite outgrowth. The results suggest that oxidative stress can cause neurodegeneration associated with enhanced susceptibility to apoptosis due to activation of pro-apoptosis genes, neurite retraction (synaptic disconnection), and impaired transport of mitochondria to cell processes where they are likely required for synaptic function. In contrast, hypoxia-type injury causes neuronal loss with proliferation of neurites (sprouting), impaired mitochondrial function, and reduced expression of molecules required to form and maintain synaptic connections. Since similar abnormalities occur in AD, both oxidative stress and hypoxic injury can contribute to AD neurodegeneration. Received 24 May 2000; received after revision 7 July 2000; accepted 27 July 2000     

Anaerobic microbial conversion of three hydroxycinnamic acids

Summary Caffeic, ferulic and synapic acid are anaerobically degraded by a microbial consortium via the reduction of the double bond of the side chain, the replacement of the nuclear hydroxyl group in position 4 by hydrogen, the demolition of the side chain by the loss of a C₁ unit.     

Intraventricular administration of isoproterenol inhibits both heat production and heat loss mechanisms in rats

Summary At an ambient temperature (T_a) of 8°C, intraventricular administration of isoproterenol inhibited metabolic heat production and led to hypothermia in rats. In contrast, at a T_a of 22°C and of 30°C, isoproterenol decreased cutaneous circulation and led to hyperthermia. The data indicate that isoproterenol inhibits both heat production and heat loss mechanisms in rats.This work was supported by a grant from the National Science Council of the Republic of China. The authors are grateful to Dr C.Y. Chai for pertinent advice.     

A threshold of transmembrane potential is required for mitochondrial dynamic balance mediated by DRP1 and OMA1

As an organellar network, mitochondria dynamically regulate their organization via opposing fusion and fission pathways to maintain bioenergetic homeostasis and contribute to key cellular pathways. This dynamic balance is directly linked to bioenergetic function: loss of transmembrane potential across the inner membrane (Δψ _m) disrupts mitochondrial fission/fusion balance, causing fragmentation of the network. However, the level of Δψ _m required for mitochondrial dynamic balance, as well as the relative contributions of fission and fusion pathways, have remained unclear. To explore this, mitochondrial morphology and Δψ _m were examined via confocal imaging and tetramethyl rhodamine ester (TMRE) flow cytometry, respectively, in cultured 143B osteosarcoma cells. When normalized to the TMRE value of untreated 143B cells as 100%, both genetic (mtDNA-depleted ρ⁰) and pharmacological [carbonyl cyanide m-chlorophenyl hydrazone (CCCP)-treated] cell models below 34% TMRE fluorescence were unable to maintain mitochondrial interconnection, correlating with loss of fusion-active long OPA1 isoforms (L-OPA1). Mechanistically, this threshold is maintained by mechanistic coordination of DRP1-mediated fission and OPA1-mediated fusion: cells lacking either DRP1 or the OMA1 metalloprotease were insensitive to loss of Δψ _m, instead maintaining an obligately fused morphology. Collectively, these findings demonstrate a mitochondrial ‘tipping point’ threshold mediated by the interaction of Δψ _m with both DRP1 and OMA1; moreover, DRP1 appears to be required for effective OPA1 maintenance and processing, consistent with growing evidence for direct interaction of fission and fusion pathways. These results suggest that Δψ _m below threshold coordinately activates both DRP1-mediated fission and OMA1 cleavage of OPA1, collapsing mitochondrial dynamic balance, with major implications for a range of signaling pathways and cellular life/death events.     

Interaction du 2,4-dichlorophénol et de l'eau oxygénée dans la destruction enzymatique de l'acideβ-indolylacétique

Summary DCP increases IAA destruction by bothLens andPhaseolus root breis. H₂O₂ inhibits catabolism byLens extracts but activates it whenPhaseolus is used, mainly when roots are cultivated in the dark and contain inhibitors of IAA destruction. DCP 1·10^–3 M and H₂O₂ 1·10^–4 or 1·10^–3 volume forLens and DCP 1·10^–4 M and H₂O₂ 1·10^–3 volume forPhaseolus nullify auxin catabolism.     

Effects of storage and processing on the nutritive value of certain Nigerian foods

Summary The effects of storage and processing on the nutritive value of two Nigerian foods-raw cowpea (Vigna unguiculata) flour and palm oil, have been investigated. Increased retention of both thiamine and riboflavin as a result of increased water activity (A_w) were recorded for cowpea flour stored for 6 months. A storage temperature of 5°C led to minimal losses of both vitamins in the stored flour. Differences in physico-chemical characteristics were observed between palm oil produced by the traditional method and that produced by a modern commercial method. Increasing A_w led to decreasing loss of unsaturation in the traditionally-produced palm oil during 4-week storage at ambient temperature (25°C).     

Immobilization of chicken liver fructose 1,6-bisphosphatase on CNBr-activated Sepharose

Summary Chicken liver fructose 1,6-bisphosphatase is readily immobilized on CNBr-activated Sepharose. The immobilization alters some enzymatic properties. They include broader pH activity curve, loss of activation by K⁺ or NH ₄ ⁺ , increased resistance to inactivation by trypsin, decreased sensitivity to AMP inhibition, and loss of cooperative interaction among AMP-binding sites. The immobilized enzyme retains about 38% or 19% of the specific activity of the native enzyme when the activity is measured in the absence or presence of K⁺, resepctively.This work was supported by grant RR-8006 from the General Research Branch, Division of Research Resources, NIH (USA).     

Loss of antibody production accompanied by chromosome loss in a cloned hybrid line secreting antibodies to sheep red blood cells

Summary Somatic cell hybrids between Sp2/O-Ag14 mouse myeloma cells and lymphocytes derived from BALB/c mice hyperimmunized with sheep red blood cells (SRBC) were produced. One hybrid producing IgG₁ antibody to SRBC was selected, cloned twice and subsequently transferred to BALB/c mice. After a number of transfers it was found that the antibody titer in ascitec fluid gradually decreased. Cytogenetic analysis revealed gradual chromosome loss in the hybrid clone, which produced progressively less antibody.     

H<Subscript>2</Subscript>S biosynthesis and catabolism: new insights from molecular studies

Hydrogen sulfide (H₂S) has profound biological effects within living organisms and is now increasingly being considered alongside other gaseous signalling molecules, such as nitric oxide (NO) and carbon monoxide (CO). Conventional use of pharmacological and molecular approaches has spawned a rapidly growing research field that has identified H₂S as playing a functional role in cell-signalling and post-translational modifications. Recently, a number of laboratories have reported the use of siRNA methodologies and genetic mouse models to mimic the loss of function of genes involved in the biosynthesis and degradation of H₂S within tissues. Studies utilising these systems are revealing new insights into the biology of H₂S within the cardiovascular system, inflammatory disease, and in cell signalling. In light of this work, the current review will describe recent advances in H₂S research made possible by the use of molecular approaches and genetic mouse models with perturbed capacities to generate or detoxify physiological levels of H₂S gas within tissues.     

Induction of cyst formation by low temperature in the dinoflagellateGonyaulax polyedra Stein: Dependence on circadian phase and requirement of light

Encystment, which at a temperature of 15°C is photoperiodically controlled inGonyaulax polyedra, can also be induced by a decrease of temperature, from 20 to 10 or 8°C in the absence of photoperiodic signals. The cyst-inducing capacity of the decrease in temperature depends on the circadian phase: in constant light, the maximum of sensitivity was found at the beginning of subjective night. In a light/dark cycle, however, cyst formation was reduced during dark phase, indicating that light is required for the process of encystment. A similar light dependence was seen in the effect of the physiologically occurring cyst inducer 5-methoxytryptamine, but not in the encystment response to the protonophores monensin and nigericin.     

Response of the starling circadian system to transitions between light and darkness

Summary The effects of exposure to sudden transitions from dark to light (D/L) and light to dark (L/D) were determined on the free running circadian feding rhythm of European stalings (Sturnus vulgaris). D/L transitions (step-up) produced phase advances throughout the circadian cycle. In contrast L/D transitions (step-down) produced both advances and delays. The L/D transition phase-response curve has a contour and shape similar to the phase-response curves previously obtained in birds with light pulses.     

Testing galaxy formation and dark matter with low surface brightness galaxies

Galaxies are the basic structural element of the universe; galaxy formation theory seeks to explain how these structures came to be. I trace some of the foundational ideas in galaxy formation, with emphasis on the need for non-baryonic cold dark matter. Many elements of early theory did not survive contact with observations of low surface brightness galaxies, leading to the need for auxiliary hypotheses like feedback. The failure points often trace to the surprising predictive successes of an alternative to dark matter, the Modified Newtonian Dynamics (MOND). While dark matter models are flexible in accommodating observations, they do not provide the predictive capacity of MOND. If the universe is made of cold dark matter, why does MOND get any predictions right?     

Pressure acclimation of the eel and liver membrane composition

Homeoviscous adaptation of membrane fluidity is known to exist in fish living at great depths. Is this adaptation also present in fish living near the surface but experimentally acclimated to high pressure? The composition of mitochondria-rich fractions extracted from the livers of eels acclimated for 15 days at 101 ATA was determined. The results show that pressure induced a significant increase (+100%) of total phospholipids (PL) and cholesterol without a change in their ratio. The increase of PL content was accompanied by a decrease in phosphatidylcholine in favour of phosphatidyl ethanolamine which, due to its preference for the H₁₁ form, is able to compensate for the loss in fluidity induced by pressure.