Monolayer self-assembly of a hexabrominated, three-fold symmetric aromatic molecule is studied at the heptanoic acid-graphite interface. Thermodynamical insights are obtained from an adapted ...Born-Haber cycle that is utilized to derive the overall enthalpy change including solvent effects. Comparison with theoretical entropy estimates suggests a minor influence of solvation.
Plants develop an enhanced defensive capacity against a broad spectrum of plant pathogens after colonization of the roots by selected strains of nonpathogenic, fluorescent Pseudomonas spp. In ...Arabidopsis thaliana, this rhizobacteria-induced systemic resistance (ISR) functions independently of salicylic acid but requires responsiveness to the plant hormones jasmonic acid and ethylene. In contrast to pathogen-induced systemic acquired resistance, rhizobacteria-mediated ISR is not associated with changes in the expression of genes encoding pathogenesis-related proteins. To identify ISR-related genes, we surveyed the transcriptional response of over 8,000 Arabidopsis genes during rhizobacteria-mediated ISR. Locally in the roots, ISR-inducing Pseudomonas fluorescens WCS417r bacteria elicited a substantial change in the expression of 97 genes. However, systemically in the leaves, none of the approximately 8,000 genes tested showed a consistent change in expression in response to effective colonization of the roots by WCS417r, indicating that the onset of ISR in the leaves is not associated with detectable changes in gene expression. After challenge inoculation of WCS417r-induced plants with the bacterial leaf pathogen P. syringae pv. tomato DC3000, 81 genes showed an augmented expression pattern in ISR-expressing leaves, suggesting that these genes were primed to respond faster or more strongly upon pathogen attack. The majority of the primed genes was predicted to be regulated by jasmonic acid or ethylene signaling. Priming of pathogen-induced genes allows the plant to react more effectively to the invader encountered, which might explain the broad-spectrum action of rhizobacteria-mediated ISR.
The Air Force Research Laboratory's Demonstration and Science Experiments (DSX) mission investigated wave‐particle interactions and the particle and space environment in Medium Earth Orbit (MEO) from ...June 2019 to May 2021. Its Wave‐Particle Interactions Experiment conducted over 1,300 active high power very low frequency transmissions in the radiation belts providing observations of antenna performance and signal propagation from a controlled source. This included hundreds of transmissions while in magnetic conjunction with other satellites. The Loss Cone Imager and Space Weather Experiment suite observed electron and proton populations over a wide energy range, with several of these instruments providing pitch‐angle resolution. The Space Environmental Effects Experiment investigated effects of the MEO environment on electronics and materials. The Adaptive Controls Experiment demonstrated technology for on‐board identification and control of large structure vibrational modes. We describe the DSX instrument capabilities and on orbit performance, science planning and operations for carrying out an array of active and passive experiments, and some initial results in brief. We also describe plans for further work and data release.
Plain Language Summary
In this paper, we summarize the Air Force Research Laboratory's Demonstration and Science Experiments (DSX) satellite mission which recently concluded after nearly 2 yr in the radiation belts. We describe the DSX science instruments and how we planned and performed experiments during the mission. The mission had a primary goal of conducting high‐power transmissions in near‐Earth space using very low frequency (VLF) radio waves. Such active DSX experiments yielded information about how a high‐voltage antenna interacts with the low‐density charged particles, or plasma, near the spacecraft. DSX experimented with propagating signals along magnetic field lines to other satellites and “bouncing” them back to the spacecraft. DSX also studied interactions between VLF waves and radiation belt electrons, particularly how electrons may be lost from the radiation belts. High‐energy electrons and protons trapped in the Earth's magnetic field make up the radiation belts, and these particles as well as the lower‐energy plasma particles are hazards to spacecraft. The mission had further goals of measuring radiation belt and plasma particles and their effects on spacecraft parts. Collectively, the results of DSX research will improve spacecraft survivability in the harsh space environment.
Key Points
Demonstration and Science Experiments conducted over 1,300 high power very low frequency transmission experiments in the radiation belts, including 315 in coordination with other satellites
The 23‐month mission also collected comprehensive wave, particle, and plasma observations in its inclined medium Earth orbit
Instruments, planning and operations, some initial results, plans for further work, and release of data are described in brief
Feed efficiency is a highly important economic trait in sheep production and has a significant impact on the economic benefits of sheep farming. Microbial fermentation of the rumen has a vital role ...in the host's nutrition; the rumen microbiota might affect host feed efficiency. However, the relationship between the rumen microbiota and feed efficiency in sheep is unclear. In the present study, the microbiota of 195 Hu sheep was investigated and their residual feed intake (RFI), a commonly used measure of feed efficiency, was determined. From birth, all sheep were subjected to the same management practices. At slaughter, samples of liquid rumen contents were collected and subjected to amplicon sequencing for the 16S rDNA gene on the IonS5™XL platform. To identify the bacterial taxa differentially represented at the genus or higher taxonomy levels, we used linear discriminant analysis coupled with effect size and curve fitting. In the sheep rumen, the four most abundant phyla were Firmicutes, Bacteroidetes, Fibrobacteres, and Proteobacteria; and the dominant genera were unidentified Prevotellaceae, Fibrobacter, unidentified Lachnospiraceae, Saccharofermentans, and Succinivibrio. Pathway analysis of the 16S rDNA sequencing data from the rumen microbiota identified that carbohydrate metabolism was enriched. Using α-diversity analysis, we further identified that Observed species, ACE, Good's coverage, and Chao1 are more abundant (P < 0.01) in the low-RFI (L-RFI) group compared to the high-RFI (H-RFI) group. High-RFI sheep had a higher abundance of three bacterial taxa (Prevotellaceae, Negativicutes, and Selenomonadales), and one taxa was overrepresented in the L-RFI sheep (Succinivibrio), respectively. Furthermore, model fitting showed that Veillonellaceae, Sphaerochaeta, Negativibacillus, Saccharofermentans, and members of the Tenericutes, Kiritimatiellaeota, Deltaproteobacteria, and Campylobacterales were correlated with the sheep RFI classification and thus were indicative of a role in animal efficiency. Tax4Fun analysis revealed that metabolic pathways such as “energy metabolism,” “metabolism of cofactors and vitamins,” “poorly characterized,” and “replication recombination and repair proteins” were enriched in the rumen from H-RFI sheep, and “genetic information processing” and “lipopolysaccharide biosynthesis” were overrepresented in L-RFI sheep rumen. In addition, six Kyoto Encyclopedia of Genes and Genomes orthology pathways were identified as different between H-RFI and L-RFI groups. In conclusion, the low RFI phenotype (efficient animals) consistently (or characteristically) exhibited a more abundant and diverse microbiome in sheep.
Effects of clonal integration on land plants have been extensively studied, but little is known about the role in amphibious plants that expand from terrestrial to aquatic conditions. We simulated ...expansion from terrestrial to aquatic habitats in the amphibious stoloniferous alien invasive alligator weed (Alternanthera philoxeroides) by growing basal ramets of clonal fragments in soils connected (allowing integration) or disconnected (preventing integration) to the apical ramets of the same fragments submerged in water to a depth of 0, 5, 10 or 15 cm. Clonal integration significantly increased growth and clonal reproduction of the apical ramets, but decreased both of these characteristics in basal ramets. Consequently, integration did not affect the performance of whole clonal fragments. We propose that alligator weed possesses a double-edged mechanism during population expansion: apical ramets in aquatic habitats can increase growth through connected basal parts in terrestrial habitats; however, once stolon connections with apical ramets are lost by external disturbance, the basal ramets in terrestrial habitats increase stolon and ramet production for rapid spreading. This may contribute greatly to the invasiveness of alligator weed and also make it very adaptable to habitats with heavy disturbance and/or highly heterogeneous resource supply.
The solvation-dependent excited state dynamics of two push-pull fluorophores with donor-π-acceptor (D-π-A) structures were investigated using steady-state and ultrafast transient absorption (TA) ...spectroscopy, backed by theoretical calculations. Identical D and A groups were present in both dyes, which differed only in the structure of their central π-conjugated linkers. Dye
1
features a
p
-phenylenediethynyl linker, while dye
2
contains a 2,5-diethynylthiophene linker. From the steady-state spectra, no appreciable shifts in absorption bands were observed, whereas large red-shifts in emission were seen with increasing solvent polarity, which indicated that the excited states were more polar than the ground state. Theoretical calculations support charge transfer from the triphenylamine (TPA) donor to the pentafluorosulfanyl (SF
5
) acceptor
via
π-conjugated linkers to form an intramolecular charge transfer (ICT) state. TA spectra revealed that a solvation-stabilized conformationally relaxed intramolecular charge transfer (ICT′) state was formed in polar solvents, but only an ICT state was observed in nonpolar solvent. The SE band was quenched within 1 ps in high-polarity solvent, which corresponds to the low fluorescence quantum yield. It can be concluded that the dye with the
p
-phenylenediethynyl π-linker (
i.e.
, dye
1
) exhibits a larger degree of ICT than the thiophene analogue (
i.e.
, dye
2
). These findings demonstrate how solvation can fine-tune the photophysical properties of push-pull dyes, and this study highlights the importance of π-conjugated linkers in the excited state ICT process.
The solvation-dependent excited state dynamics of two push-pull fluorophores with donor-π-acceptor (D-π-A) structures were investigated using steady-state and ultrafast transient absorption (TA) spectroscopy, backed by theoretical calculations.
Hydrogel scaffolding of stem cells is a promising strategy to overcome initial cell loss and manipulate cell function post‐transplantation. Matrix degradation is a requirement for downstream cell ...differentiation and functional tissue integration, which determines therapeutic outcome. Therefore, monitoring of hydrogel degradation is essential for scaffolded cell replacement therapies. It is shown here that chemical exchange saturation transfer magnetic resonance imaging (CEST MRI) can be used as a label‐free imaging platform for monitoring the degradation of crosslinked hydrogels containing gelatin (Gel) and hyaluronic acid (HA), of which the stiffness can be fine‐tuned by varying the ratio of the Gel:HA. By labeling Gel and HA with two different near‐infrared (NIR) dyes having distinct emission frequencies, it is shown here that the HA signal remains stable for 42 days, while the Gel signal gradually decreases to <25% of its initial value at this time point. Both imaging modalities are in excellent agreement for both the time course and relative value of CEST MRI and NIR signals (R2 = 0.94). These findings support the further use of CEST MRI for monitoring biodegradation and optimizing of gelatin‐containing hydrogels in a label‐free manner.
Chemical exchange saturation transfer (CEST) magnetic resonance imaging can be used to monitor composite hydrogel degradation in vivo in a non‐invasive and label‐free manner. Using two different near‐infrared dyes for labeling gelatin and hyaluronic acid, it is shown that the gelatin component is the major source of not only CEST contrast but also biodegradation.
Cold tolerance adaption is a crucial determinant for the establishment and expansion of invasive alien plants into new cold environments; however, its evolutionary mechanism is poorly understood. ...Crofton weed (Ageratina adenophora), a highly invasive alien plant, is continuously spreading across subtropical areas in China, north‐eastward from the first colonized south‐western tropical regions, through cold tolerance evolution. Close relations between the cold tolerance levels of 34 populations, represented by 147 accessions, and the latitude, extreme lowest temperature, coldest month average temperature, and invasion period have provided direct insight into its cold tolerance divergence. A comparative study of the CBF pathway, associated with the cold tolerance enhancement of cold‐susceptible CBF1‐transgenic plant, among four geographically distinct crofton weed populations revealed that the CBF pathway plays a key role in the observed cold tolerance divergence. Four epialleles of the cold response regulator ICE1 ranged from 66 to 50 methylated cytosines, representing a 4.4% to 3.3% methylation rate and significantly corresponding to the lowest to highest cold tolerance levels among these different populations. The significant negative relation between the transcription levels of the primary CBF pathway members, except for CBF2, and the methylation levels among the four populations firstly demonstrates that the demethylation‐upregulated transcription level of CBF pathway is responsible for this evolution. These facts, combined with the cold tolerance variation and methylation found among three native and two other introduced populations, indicate that the ICE1‐demethylated upregulation of cold tolerance may be the underlying evolutionary mechanism allowing crofton weed to expand northward in China.
The interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted enormous interests due to its rich physical phenomena, such as metallic nature, magnetism and superconductivity. In this work, we ...report our experimental investigations on the influence of the LAO stoichiometry to the metallic interface. Taking advantage of the oxide molecular beam epitaxy (MBE) technique, a series of high quality LAO films with different nominal La/Al ratios and LAO thicknesses were grown on the TiO2-terminated STO substrates, where systematic variations of the LAO lattice constant and transport property were observed. In particular, the sheet density can be largely reduced by nearly an order of magnitude with merely about 20% increase in the nominal La/Al ratio. Our finding provides an effective method on tuning the electron density of the two-dimensional electron liquid (2DEL) at the LAO/STO interface.
The efficiency of RNA interference (RNAi) varies substantially among different insect species. Rapid degradation of double‐stranded RNA (dsRNA) by dsRNA‐degrading nucleases (dsRNases) has been ...implicated to cause low RNAi efficiency in several insect species. In this study, we identified four dsRNase genes (OfdsRNase1, OfdsRNase2, OfdsRNase3 and OfdsRNase4) from the Asian corn borer (Ostrinia furnacalis) transcriptome database. Bioinformatic analyses showed that each deduced protein sequence contained endonuclease NS domains and signal peptides. Gene expression analysis revealed that OfdsRNase2 was exclusively expressed in the midgut of larvae. RNAi efficiency was investigated in 2‐d‐old fifth‐instar larvae (high expression of dsRNase2) and 2‐d‐old pupae (low expression of dsRNase2) by feeding or injecting dsRNA targeting a marker gene that encodes the lethal giant larvae protein (OfLgl). Our results showed that OfLgl only partially silenced the expression of OfLgl in pupae, but not in larvae, suggesting that OfdsRNase2 could contribute to lower RNAi efficiency in larval stages. This hypothesis was supported by our RNAi‐of‐RNAi experiment using a tissue culture technique where the silencing efficiency against the reporter gene, OfHex1, was significantly improved after knockdown of OfdsRNase2. When double luciferase assays were performed to evaluate the role of the four dsRNases in vitro, only OfdsRNase2 expressed in S2 cells significantly affected RNAi efficiency by degrading dsRNA. Taken together, our results suggested that the degradation of dsRNA by OfdsRNase2 in the midgut contributed to low RNAi efficiency in O. furnacalis larvae.
Four dsRNA‐degrading nuclease (dsRNase) genes, including OfdsRNase1, OfdsRNase2, OfdsRNase3 and OfdsRNase4, were identified in Ostrinia furnacalis. The stage‐specific RNAi, RNAi of RNAi in tissue culture, and dual‐luciferase assays revealed that OfdsRNase2 contributes significantly to low RNAi efficiency in O. furnacalis.
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