Degradation of chlorophylls during senescence is a highly regulated process which requires the concerted action of several enzymes. Traditionally, it has been stated that the dismantling process of ...the chlorophyll molecule begins with a dephytilation step, followed by Mg
2+ removal and other breakdown reactions. Recently, new evidence suggests the possibility of a rearrangement in the first two steps of this process, occurring Mg
2+ removal prior to the loss of the phytol side chain. With the purpose of approximating to the real sequential order of these reactions and to assess if dephytilation occurs on intact (catalyzed by chlorophyllase) or Mg-free (catalyzed by pheophytinase) chlorophyll, expression of both genes was analyzed in broccoli tissue during senescence. Samples of broccoli florets treated with plant hormones, such as cytokinin and ethylene were utilized, as to assess the effect of such compounds on the expression of these genes. Results showed that chlorophyllase expression did not correlate to typical expression patterns for genes related to senescence, since a decrease in expression during senescence was found for one of the two chlorophyllase genes analyzed, and the hormonal-treatment effects on gene expression did not match those observed on chlorophyll content for both chlorophyllase genes. Pheophytinase expression patterns, on the other hand, displayed an increase in the first 3 days of induced senescence, followed by lower expression values towards the end of the experiment. Samples subjected to postharvest treatments mostly showed an inhibition of pheophytinase expression, especially in samples in which degradation of chlorophylls had been delayed. These results suggest that pheophytinase expression correlates to the visual manifestation of postharvest treatments, supporting the possibility that this enzyme is responsible for the dephytilation step in chlorophyll breakdown.
Neutrino production in starburst galaxies Carulli, Agustín M; Reynoso, Matías M
Monthly notices of the Royal Astronomical Society,
03/2024, Volume:
529, Issue:
4
Journal Article
Peer reviewed
Open access
ABSTRACT
Understanding the origin of the diffuse flux of high-energy astrophysical neutrinos detected by IceCube has become a challenging issue within present High Energy Astrophysics. In this work, ...we present a model to explore the potential neutrino emission of starburst galaxies (SBG) by considering three different neutrino production zones that can be associated to a typical single SBG. The first zone is the starburst nucleus, where due to the high rate of supernova explosions, a significant amount of protons can be accelerated to high energies and undergo pp interactions with cold protons of the interstellar medium. The second zone we consider is the corresponding to the starburst wind, which is formed by the hot gas that emerges from the nucleus and interacts with the intergalactic medium generating shocks. Protons accelerated there can undergo pp interactions with the ambient matter. The third neutrino production zone we consider, is an external one, where we account for the possibility that protons escaping from the whole system interact with the cosmic microwave background. Finally, adding the neutrino contributions of the three zones, we calculate the diffuse neutrino flux and the diffuse photon flux by integration on the redshift range appropriate for SBG. We find that the model behaves well applied to nearby galaxies such as M82 and NGC 253. The contributions made to the diffuse neutrino flux are able to explain part of the data provided by IceCube if typical parameters are considered.
In this work, we study the propagation of high energy neutrinos produced in extragalactic sources including the effect of a possible interaction with ultralight axion-like particles (UALP) with a ...mass
m
a
∼
10
-
22
eV
as the constituents of dark matter (DM) under the assumption that their coupling to neutrinos is dominant. We compute the cross section and describe the propagation of a diffuse neutrino flux using transport equations for each mass eigenstate. This allows us to obtain the neutrino fluxes of the different flavors to be observed at the Earth with neutrino telescopes under different assumptions for the flavor composition emitted at the sources and for a normal ordering (NO) or an inverted ordering (IO) of the neutrino masses. If the coupling of neutrinos with UALPs is the same for all flavors (
g
ν
a
), we find that interactions change the flavor composition of neutrinos arriving on Earth for
g
ν
a
≳
0.5
GeV
-
1
, causing the electron(muon) flavor to dominate in the NO(IO) case for neutrino energies above
∼
10
5
GeV
. Although current data on the flavor ratios suggest that interactions with UALP DM do not take place within the range of coupling studied (particularly in the NO case) more data is needed to improve the precision of the experimentally measured flavor composition.
Both metal-catalyzed and organocatalytic transfer hydrogenation reactions are widely employed for the reduction of C&z.dbd;O and C&z.dbd;N bonds. However, selective transfer hydrogenation reactions ...of C&z.dbd;C bonds remain challenging. Therefore, the chemoselective transfer hydrogenation of olefins under mild conditions and in the absence of metal catalysts, using readily available and inexpensive reducing agents (
i.e.
primary and secondary alcohols), will mark a significant advancement towards the development of green transfer hydrogenation strategies. Described herein is an unconventional catalyst-free transfer hydrogenation reaction of activated alkenes using isopropanol as an eco-friendly reductant and solvent. The reaction gives convenient synthetic access to a wide range of substituted malonic acid half oxyesters (SMAHOs) in moderate to good yields. Mechanistic investigations point towards an unprecedented hydrogen bond-assisted transfer hydrogenation process.
Described herein is an unconventional catalyst-free transfer hydrogenation reaction of activated alkenes using isopropanol as an eco-friendly reductant and solvent.
Basic knowledge on the biology and ecology of a species is fundamental for the realistic assessment of its conservation status and for planning effective conservation strategies. The latest ...assessment of the 21 extant armadillo species (Xenarthra, Dasypodidae) by the International Union for Conservation of Nature (IUCN) for its Red List of Threatened Species shows that considerable gaps exist in our knowledge of these Neotropical mammals.
Our goal was to analyse the existing literature on armadillos to define thematic and regional research priorities that will eventually benefit their conservation.
We categorized 3117 publications on extant armadillos published between 1660 and 2011 according to their research topic, species studied, country and publication language.
The number of publications per research topic and the number per species were very variable. The nine best‐studied species are classed as Least Concern by the IUCN, while three of the four least‐studied species are classed as Data Deficient. At least one field study was done in each range country, but over 80% of field research took place in the USA, Brazil, Argentina and Bolivia. Most research was done in the USA on leprosy in Dasypus novemcinctus. Most ecological research has been focused on four species, and data on the ecology of Data Deficient and Vulnerable taxa are virtually absent.
Field research on armadillos should be intensified to broaden conservation‐relevant knowledge. Additional studies in the Guianas, Peru, Ecuador, Colombia, Venezuela and Paraguay are urgently needed to assess the conservation status of armadillos in these regions. Future research should focus on ecology, conservation, population genetics, reproduction and threats. Species priorities should include country endemics, such as Dasypus pilosus (Peru), Tolypeutes tricinctus (Brazil) and Dasypus yepesi and Chlamyphorus truncatus (Argentina), as well as other Data Deficient and Vulnerable species, especially Cabassous centralis and Calyptophractus retusus.
This paper reports the presence of the common dolphinfish, Coryphaena hippurus, in Argentinian waters for the first time, with a specimen collected by experienced sport fishermen near Mar del Plata ...(38°S). This finding also represents the first record of a species from the Coryphaenidae family in Argentinian waters. The collection of these specimens coincided with sightings of other rarely-seen pelagic and oceanic fish species during the same period, providing further evidence supporting the influx of subtropical fish species from warmer Brazilian waters. These observations highlight the need for continued monitoring of fish populations and their distribution and the ecological dynamics within the region.
This paper examines the implications of the association patterns in our understanding of the mental lexicon. By applying the principles of graph theory to word association data, we intend to explore ...which measures tap better into lexical knowledge. To that end, we had different groups of English as Foreign language learners complete a lexical fluency task. Based on these empirical data, a study was undertaken on the corresponding lexical availability graph (LAG). It is observed that the aggregation (mentioned through human coding) of all lexical tokens on a given topic allows the emergence of some lexical-semantic patterns. The most important one is the existence of some key terms, featuring both high centrality in the sense of network theory and high availability in the LAG, which define a hub of related terms. These communities of words, each one organized around an anchor term, or most central word, are nicely apprehended by a well-known network metric called
modularity
. Interestingly enough, each module seems to describe a conceptual class, showing that the collective lexicon, at least as approximated by LA Graphs, is organised and traversed by semantic mechanisms or associations via hyponymy or hiperonymy, for instance. Another empirical observation is that these conceptual hubs can be appended, resulting in high diameters compared to same-sized random graphs; even so it seems that the
small-world
hypothesis holds in LA Graphs, as in other social and natural networks.
Oxide-confined vertical cavity surface emitting lasers (VCSELs) with anti-waveguiding AlAs-rich core presently attract a lot of attention. Anti-waveguiding cavity enables the maximum possible optical ...confinement of the VCSEL mode ("λ/2 design"), increases its oscillator strength and reduces dramatically the optical power accumulated in the VCSEL mesa regions outside the aperture. VCSEL designs are suggested that favor single transverse mode operation. Modeling including current-induced and absorption-induced overheating shows that the preference for the transverse fundamental mode persists up to 10 mA current at 5 µm aperture diameter. Error-free data transmission is realized up to 160 Gb/s in digital-multitone (DMT) format using single-mode anti-waveguiding VCSELs. The approach to single-mode anti-waveguiding VCSELs is extended over a broad spectral range realizing error-free high-speed data transmission at both 850 nm and 910 nm.
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