Long before its chemical identity was known, the phytohormone auxin was postulated to regulate plant growth. In the late 1800s, Sachs hypothesized that plant growth regulators, present in small ...amounts, move differentially throughout the plant to regulate growth. Concurrently, Charles Darwin and Francis Darwin were discovering that light and gravity were perceived by the tips of shoots and roots and that the stimulus was transmitted to other tissues, which underwent a growth response. These ideas were improved upon by Boysen-Jensen and Paal and were later developed into the Cholodny-Went hypothesis that tropisms were caused by the asymmetric distribution of a growth-promoting substance. These observations led to many efforts to identify this elusive growth-promoting substance, which we now know as auxin. In this review of auxin field advances over the past century, we start with a seminal paper by Kenneth Thimann and Charles Schneider titled "The relative activities of different auxins" from the American Journal of Botany, in which they compare the growth altering properties of several auxinic compounds. From this point, we explore the modern molecular understanding of auxin—including its biosynthesis, transport, and perception. Finally, we end this review with a discussion of outstanding questions and future directions in the auxin field. Over the past 100 yr, much of our progress in understanding auxin biology has relied on the steady and collective advance of the field of auxin researchers; we expect that the next 100 yr of auxin research will likewise make many exciting advances.
Seven contrasting feedstocks were subjected to slow pyrolysis at low (300 or 350°C) and high temperature (550 or 600°C), and both biochars and the corresponding feedstocks tested for short-term ...ecotoxicity using basal soil respiration and collembolan reproduction tests. After a 28-d incubation, soil basal respiration was not inhibited but stimulated by additions of feedstocks and biochars. However, variation in soil respiration was dependent on both feedstock and pyrolysis temperature. In the last case, respiration decreased with pyrolysis temperature (r=-0.78; p<0.0001, n=21) and increased with a higher volatile matter content (r=0.51; p<0.017), these two variables being correlated (r=-0.86, p<0.0001). Collembolan reproduction was generally unaffected by any of the additions, but when inhibited, it was mostly influenced by feedstock, and generally without any influence of charring itself and pyrolysis temperature. Strong inhibition was only observed in uncharred food waste and resulting biochars. Inhibition effects were probably linked to high soluble Na and NH4 concentrations when both feedstocks and biochars were considered, but mostly to soluble Na when only biochars were taken into account. The general lack of toxicity of the set of slow pyrolysis biochars in this study at typical field application rates (≤20 Mg ha(-1)) suggests a low short-term toxicity risk. At higher application rates (20-540 Mg ha(-1)), some biochars affected collembolan reproduction to some extent, but only strongly in the food waste biochars. Such negative impacts were not anticipated by the criteria set in currently available biochar quality standards, pointing out the need to consider ecotoxicological criteria either explicitly or implicitly in biochar characterization schemes or in management recommendations.
Context.
Contemporary research suggests that the reionisation of the intergalactic medium (IGM) in the early Universe was predominantly realised by star-forming (proto-)galaxies (SFGs). Due to ...observational constraints, our knowledge on the origins of sufficient amounts of ionising Lyman continuum (LyC) photons and the mechanisms facilitating their transport into the IGM remains sparse. Recent efforts have thus focussed on the study of local analogues to these high-redshift objects.
Aims.
We aim to acquire a set of very low-redshift SFGs that exhibit signs of a hard radiation field being present. A subsequent analysis of their emission line properties is intended to shed light on how the conditions prevalent in these objects compare to those predicted to be present in early SFGs that are thought to be LyC emitters (LCEs).
Methods.
We used archival spectroscopic SDSS DR12 data to select a sample of low-redshift He
II
4686 emitters and restricted it to a set of SFGs with an emission line diagnostic sensitive to the presence of an active galactic nucleus, which serves as our only selection criterion. We performed a population spectral synthesis with
FADO
to reconstruct these galaxies’ star-formation histories (SFHs). Utilising the spectroscopic information at hand, we constrained the predominant ionisation mechanisms in these galaxies and inferred information on interstellar medium (ISM) conditions relevant for the escape of LyC radiation.
Results.
Our final sample consists of eighteen ionised, metal-poor galaxies (IMPs). These low-mass (6.2 ≤ log(
M
⋆
/
M
⊙
) ≤ 8.8), low-metallicity (7.54 ≤ log(O/H) + 12 ≤ 8.13) dwarf galaxies appear to be predominantly ionised by stellar sources. We find large O
III
5007/O
II
3727 ratios and S
II
6717,6731/H
α
deficiencies, which provide strong indications for these galaxies to be LCEs. At least 40% of these objects are candidates for featuring cosmologically significant LyC escape fractions ≳10%. The IMPs’ SFHs exhibit strong similarities and almost all galaxies appear to contain an old (> 1 Gyr) stellar component, while also harbouring a young, two-stage (∼10 Myr and < 1 Myr) starburst, which we speculate might be related to LyC escape.
Conclusions.
The properties of the compact emission line galaxies presented here align well with those observed in many local LCEs. In fact, our sample may prove as an extension to the rather small catalogue of local LCEs, as the extreme ISM conditions we find are assumed to facilitate LyC leakage. Notably, all of our eighteen candidates are significantly closer (
z
< 0.1) than most established LCEs. If the inferred LyC photon loss is genuine, this demonstrates that selecting SFGs from He
II
4686 is a powerful selection criterion in the search for LCEs.
An overview is given of variations in placentation with particular focus on yolk sac, paraplacenta, and other structures important to histotrophic nutrition. The placenta proper varies in general ...shape, internal structure, and the number of tissues in the interhemal barrier. Yolk sac membranes persist to term in insectivores, colugos, rodents, and lagomorphs. In the latter two orders, they are of known importance for maternal–fetal transfer of antibodies, vitamins, lipids, and proteins. The detached yolk sac of bats is also active throughout gestation. A vascular paraplacenta, or smooth chorioallantois, has known functions in ruminants and carnivores and is found in several other orders of mammal where its function has yet to be explored. In human gestation, the chorion (avascular chorioallantois) is important for hormone synthesis. The true chorion of squirrels and hedgehogs is avascular but may nevertheless allow transfer from mother to fetus through the exocelom. Hemophagous areas with columnar trophoblast are paraplacental structures in carnivores and elephants but occur also within the placenta as in hyenas and moles. In shrews, it is the yolk sac that ingests and processes red cells. Areolas and chorionic vesicles are other structures important for absorption of uterine secretions and ingestion of cellular debris. In conclusion, we find that paraplacental structures, while showing less variation than the placenta proper, contribute not just to the integrity of overall placentation, but in various ways to maternal–fetal interrelationships.
Changes in gene expression are important for responses to abiotic stress. Transcriptome profiling of heat- or cold-stressed maize genotypes identifies many changes in transcript abundance. We used ...comparisons of expression responses in multiple genotypes to identify alleles with variable responses to heat or cold stress and to distinguish examples of cis- or trans-regulatory variation for stress-responsive expression changes. We used motifs enriched near the transcription start sites (TSSs) for thermal stress-responsive genes to develop predictive models of gene expression responses. Prediction accuracies can be improved by focusing only on motifs within unmethylated regions near the TSS and vary for genes with different dynamic responses to stress. Models trained on expression responses in a single genotype and promoter sequences provided lower performance when applied to other genotypes but this could be improved by using models trained on data from all three genotypes tested. The analysis of genes with cis-regulatory variation provides evidence for structural variants that result in presence/absence of transcription factor binding sites in creating variable responses. This study provides insights into cis-regulatory motifs for heat- and cold-responsive gene expression and defines a framework for developing models to predict expression responses across multiple genotypes.
Temperature- and coverage-dependent studies of the Au(1 1 1)-supported spin crossover Fe(II) complex (SCO) of the type Fe(H2B(pz)2)2(bipy) with a suite of surface-sensitive spectroscopy and ...microscopy tools show that the substrate inhibits thermally induced transitions of the molecular spin state, so that both high-spin and low-spin states are preserved far beyond the spin transition temperature of free molecules. Scanning tunneling microscopy confirms that Fe(H2B(pz)2)2(bipy) grows as ordered, molecular bilayer islands at sub-monolayer coverage and as disordered film at higher coverage. The temperature dependence of the electronic structure suggest that the SCO films exhibit a mixture of spin states at room temperature, but upon cooling below the spin crossover transition the film spin state is best described as a mix of high-spin and low-spin state molecules of a ratio that is constant. This locking of the spin state is most likely the result of a substrate-induced conformational change of the interfacial molecules, but it is estimated that also the intra-atomic electron-electron Coulomb correlation energy, or Hubbard correlation energy U, could be an additional contributing factor.
ABSTRACT
This paper presents, in a tutorial form, some analytical inversion techniques for the Goupillaud‐layered earth model. Finding the reflection coefficients from the reflection seismogram is ...the inverse problem for the model. For this reason we present a thorough description of the inverse problem for the Goupillaud model, two solutions to solve the inverse scattering problem using linear discrete equations and the solution obtained using the classic dynamic deconvolution method. The inversion is achieved using Robinson's polynomials Pk(z), Qk(z), Ak(z) and their reverse polynomials, as well as some properties of the model (the Lorentz transformation and the Einstein subtraction formula). The method of dynamic deconvolution, which makes the inversion of the model very simple computationally, is based on the physical structure of the reflection seismogram. We present the classic dynamic deconvolution algorithm for the non‐free‐surface Goupillaud model to show that the dynamic deconvolution method can provide efficient discrete procedures for the inversion. For this reason, though the inverse dynamic deconvolution procedures are old algorithms, they could be useful today for solving inverse scattering problems arising in exploration geophysics and various fields.
Abstract Endotheliochorial placentas occur in orders from all four major clades of eutherian mammal. Species with this type of placenta include one of the smallest (pygmy shrew) and largest (African ...elephant) land mammals. The endotheliochorial placenta as a definitive form has an interhemal area consisting of maternal endothelium, interstitial lamina, trophoblast, individual or conjoint basal laminas, and fetal endothelium. We commonly think of such placentas as having hypertrophied maternal endothelium with abundant rough endoplasmic reticulum (rER), and as having hemophagous regions. Considering them as a whole, the trophoblast may be syncytial or cellular, fenestrated or nonfenestrated, and there may or may not be hemophagous regions. Variations also appear in the extent of hypertrophy of the maternal endothelium and in the abundance of rER in these cells. This combination of traits and a few other features produces many morphological variants. In addition to endotheliochorial as a definitive condition, a transitory endotheliochorial condition may appear in the course of forming a hemochorial placenta. In some emballonurid bats the early endotheliochorial placenta has two layers of trophoblast, but the definitive placenta lacks an outer syncytial trophoblast layer. In mollosid bats a well developed endotheliochorial placenta is present for a short time even after a definitive hemochorial placenta has developed in a different region. It is concluded that the endotheliochorial placenta is more widespread and diversified than originally thought, with the variant with cellular trophoblast in particular appearing in several species studied recently.
Recent trends in the emerging field of surface-supported magnetic nanostructures are reviewed. Current strategies for nanostructure synthesis are summarized, followed by a predominantly theoretical ...description of magnetic phenomena in surface magnetic structures and a review of experimental research in this field. Emphasis is on Fe- or Co-based nanostructures in various low-dimensional geometries, which are studied as model systems to explore the effects of dimensionality, atomic coordination, chemical bonds, alloying and, most importantly, interactions with the supporting substrate on the magnetism. This review also includes a discussion of closely related systems, such as 3d element impurities integrated into organic networks, surface-supported Fe-based molecular magnets, Kondo systems or 4d element nanostructures that exhibit emergent magnetism, thereby bridging the traditional areas of surface science, molecular physics and nanomagnetism.
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