Direct detection of the asteroidal YORP effect

The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect is believed to alter the spin states of small bodies in the solar system. However, evidence for the effect has so far been indirect. We report precise optical photometric observations of a small near-Earth asteroid, (54509) 2000 PH5, acquired over 4 years. We found that the asteroid has been continuously increasing its rotation rate omega over this period by domega/dt = 2.0 (+/-0.2) x 10(-4) degrees per day squared. We simulated the asteroid's close Earth approaches from 2001 to 2005, showing that gravitational torques cannot explain the observed spin rate increase. Dynamical simulations suggest that 2000 PH5 may reach a rotation period of approximately 20 seconds toward the end of its expected lifetime.     

Priming negatively affects feeding behaviour and aphid biomass of Rhopalosiphum padi on barley

Plants have developed numerous strategies for responding to abiotic and biotic stresses. In particular, the microbiota surrounding plants may have a positive effect on plant stress responses. One is the reaction to rhizobacteria, which can lead to induced systemic resistance. Gram-negative soil bacteria that produce N-acyl homoserine lactones (AHL), for example, Ensifer meliloti, induce a primed state in plants that is part of the inducible resistance phenomenon. Observing Rhopalosiphum padi feeding behaviour on a priming sensitive barley genotype, treated with the AHL-producing E. meliloti strain expR?+?ch, using electrical penetration graph technique showed decreased ingestion of food. Aphids appear to overcome this effect within the eight-hour observation period, possibly explaining the absence of differences of reproduction. Reproduction was observed for a period of 14 days on primed and control-treated plants. Long-term observations over a period of 40 days after aphid infestation showed a lower aphid biomass in contrast to a control group, interpreted as delayed population growth, and an increase in the biomass of barley plants. Priming-related genotypic effects of the defence response to aphids were observed, with no beneficial effects on the plant genotype when its sensitivity to priming was low. Previously, an AHL-priming sensitive barley genotype showed enhanced resistance against fungi when primed with the expR?+?ch strain of E. meliloti. The present study reports the same effect against R. padi. These findings suggest that sensitivity to AHL-priming may represent a new approach for plant breeding, targeting multiple pests in parallel by induced plant resistance.

     

Impact of nitrogen amount and timing on the potential of acrylamide formation in winter wheat (Triticum aestivum L.)

Acrylamide (AA), a potential human carcinogen, is formed in strongly heated carbohydrate-rich food as a part of the Maillard reaction. The amino acid asparagine (Asn) and reducing sugars are considered to be the main precursors for AA formation. In a 2-year field trial the impact of nitrogen (N) amount and timing on the content of AA precursors and the potential of AA formation in different winter wheat cultivars (cv.) were studied in association with respective grain yields and parameters of baking quality. Depending on year, cultivar and nitrogen treatment Asn contents ranged between 4 and 18 mg 100 g⁻¹ flour dry-matter (DM). Nitrogen treatments affecting crude protein contents in flours above 13% caused a considerable increase in free Asn. Nitrogen amounts of 220 kg N ha⁻¹ increased the contents of free Asn by between 130% and 270% depending on year and cultivar compared to the untreated controls. A close linear correlation between the content of free Asn and the potential of AA formation (2004: R² = 0.89, 2005: R² = 0.83) could be observed, whereas no correlation could be found between reducing sugars and the potential of AA formation, pointing to the importance of free Asn as the limiting and thus determining factor for the AA formation potential in wheat flours. To reach high crude protein contents and good sedimentation values demanded for breadstuffs, nitrogen amounts of at least 180 kg N ha⁻¹ were necessary. Nitrogen fertilization measures resulting in high crude protein contents above 13% enhanced the potential of AA formation by increasing the content of free Asn in flours. As long as demands from traders and producers for flour with high crude protein contents are not revised, lowering Asn contents and thus the potential for AA formation by application of N amounts below 180 kg N ha⁻¹ and abandoning the late application of N do not appear to be successful ways to reduce the risk of AA formation in breadstuffs.     

A rational chemical synthesis of C60

Isolable quantities of C60, the smallest stable fullerene, have been synthesized in 12 steps from commercially available starting materials by rational chemical methods. A molecular polycyclic aromatic precursor bearing chlorine substituents at key positions forms C60 when subjected to flash vacuum pyrolysis at 1100 degrees C. No other fullerenes are formed as by-products. The methods we have developed for the target-specific synthesis of fullerenes, applied here to a synthesis of C60, should make possible the directed laboratory preparation of other fullerenes as well, including those not accessible by graphite vaporization.     

Contributions of anthropogenic and natural forcing to recent tropopause height changes

Observations indicate that the height of the tropopause-the boundary between the stratosphere and troposphere-has increased by several hundred meters since 1979. Comparable increases are evident in climate model experiments. The latter show that human-induced changes in ozone and well-mixed greenhouse gases account for approximately 80% of the simulated rise in tropopause height over 1979-1999. Their primary contributions are through cooling of the stratosphere (caused by ozone) and warming of the troposphere (caused by well-mixed greenhouse gases). A model-predicted fingerprint of tropopause height changes is statistically detectable in two different observational ("reanalysis") data sets. This positive detection result allows us to attribute overall tropopause height changes to a combination of anthropogenic and natural external forcings, with the anthropogenic component predominating.     

Adaptive recognition by nucleic acid aptamers

Nucleic acid molecules play crucial roles in diverse biological processes including the storage, transport, processing, and expression of the genetic information. Nucleic acid aptamers are selected in vitro from libraries containing random sequences of up to a few hundred nucleotides. Selection is based on the ability to bind ligand molecules with high affinity and specificity. Three-dimensional structures have been determined at high resolution for a number of aptamers in complex with their cognate ligands. Structures of aptamer complexes reveal the key molecular interactions conferring specificity to the aptamer-ligand association, including the precise stacking of flat moieties, specific hydrogen bonding, and molecular shape complementarity. These basic principles of discriminatory molecular interactions in aptamer complexes parallel recognition events central to many cellular processes involving nucleic acids.     

Species-specific recognition of single-stranded RNA via toll-like receptor 7 and 8

Double-stranded ribonucleic acid (dsRNA) serves as a danger signal associated with viral infection and leads to stimulation of innate immune cells. In contrast, the immunostimulatory potential of single-stranded RNA (ssRNA) is poorly understood and innate immune receptors for ssRNA are unknown. We report that guanosine (G)- and uridine (U)-rich ssRNA oligonucleotides derived from human immunodeficiency virus-1 (HIV-1) stimulate dendritic cells (DC) and macrophages to secrete interferon-alpha and proinflammatory, as well as regulatory, cytokines. By using Toll-like receptor (TLR)-deficient mice and genetic complementation, we show that murine TLR7 and human TLR8 mediate species-specific recognition of GU-rich ssRNA. These data suggest that ssRNA represents a physiological ligand for TLR7 and TLR8.     

Inhibition of 11β-hydroxysteroid dehydrogenase type 1 by plant extracts used as traditional antidiabetic medicines

Elevated glucocorticoids are a key risk factor for metabolic diseases, and the glucocorticoid-activating enzyme 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) represents a promising therapeutic target. We measured the potential of six traditional antidiabetic medicinal plants extracts to inhibit 11β-HSD1 activity and glucocorticoid receptor (GR) activation in transfected HEK-293 cells. Leave extracts of Eriobotrya japonica preferentially inhibited 11β-HSD1 over 11β-HSD2. Extracts of roasted but not native coffee beans preferentially inhibited 11β-HSD1 over 11β-HSD2, emphasizing the importance of sample preparation. Thus, natural compounds inhibiting 11β-HSD1 may contribute to the antidiabetic effect of the investigated plant extracts.     

Plant water stress and K starvation reduce absorption of foliar applied K by olive leaves

Three-month-old mist-rooted ‘Picual’ olive cuttings were transplanted into 2-l plastics pots containing perlite as substrate and fertigated with a complete nutrient solution containing 0.05, 0.1 or 2.5 mM KCl depending on the experiment. In the first experiment, plants were sprayed with RbCl (Rb⁺ is a K⁺ analog) at a rate of 4% at 63 days after transplanting (DAT). Foliar Rb⁺ uptake through leaves increased with K⁺ concentration in the nutrient solution, indicating that foliar Rb⁺ uptake was lower when plants were K⁺ deficient than when they were adequate. On the contrary, it was observed that translocation of Rb⁺ from leaves to other organs of the plant was higher under K⁺ deficiency conditions. In the second and third experiments, when differences appeared on shoot length due to K⁺ nutritional status (0.05 or 2.5 mM KCl) at 63 DAT, a group of plants were subjected to water stress during 7 weeks. On the other hand, another group of plants (control plants) did not receive any water stress treatment during the experiments. After this period of 7 weeks, all plants were sprayed with RbCl at 4%. Leaf K⁺ concentration diminished in water-stressed plants independently of plants nutritional status. Foliar Rb⁺ uptake through leaves was restricted by water stress either in plants with low K⁺ (0.05 mM KCl) or plants with high K⁺ (2.5 mM KCl). Translocation of Rb⁺ from leaves was greater under water stress conditions in both K⁺ nutritional statuses. In conclusion, the results obtained could explain the irregular response in olive trees to foliar K⁺ sprays, particularly, when they grow in rainfed orchards.