451 research outputs found
Physiological characterization of Mg deficiency in Arabidopsis thaliana
Although the symptoms of magnesium deficiency are well documented in plants, the primary physiological effects of low Mg availability remain largely unknown. This paper describes the physiological responses of Mg starvation in Arabidopsis thaliana. Growth characteristics, Mg and sugar concentration, and photochemical performance were measured at regular intervals during the induction of Mg deficiency. These data show that Mg deficiency increased the sugar concentration and altered sucrose export from young source leaves before any noticeable effect on photosynthetic activity was seen. The decline in photosynthetic activity might be elicited by increased leaf sugar concentrations. Transcript levels of Cab2 (encoding a chlorophyll a/b protein) were lower in Mg-deficient plants before any obvious decrease in the chlorophyll concentration. These transcriptional data suggest that the reduction of chlorophyll is a response to sugar levels, rather than a lack of Mg atoms for chelating chlorophyl
The Shrinking City as a Testing Ground for Urban Degrowth Practices
To inform and operationalize an urban degrowth agenda, more systematic and larger-scale experimentation with degrowth practices is needed. The aim of this study was to explore the suitability of shrinking cities as testing grounds for urban degrowth practices. To answer this question, we analyzed two cases, both urban greening initiatives, located in the shrinking urban region of Parkstad Limburg, in the Netherlands. The cases show that in a shrinking city, with a large surplus of urban land and long-term vacancy and demolishing of buildings, there is literally abundant "room" to experiment with alternative ways and types of urban land use. There is also interest on the side of the local government in alternatives to the conventional approaches to urban planning and development. As both cases can be interpreted as "experiments with urban degrowth practices," it can be concluded that shrinking cities offer ample opportunities for urban degrowth experiments. The lessons learned from the two studied cases are not very positive concerning the wider feasibility of the tested degrowth practices, but as experiments, the cases can be considered successful. This is because they provided a better understanding of the conditions required for the implementation and upscaling of these practices, also in growing cities. To inform and operationalize an urban degrowth agenda, we, therefore, recommend more research on cases in shrinking cities that can be interpreted and analyzed as experiments with urban degrowth practices
Physiological characterisation of magnesium deficiency in sugar beet: acclimation to low magnesium differentially affects photosystemsI and II
Magnesium deficiency in plants is a widespread problem, affecting productivity and quality in agriculture, yet at a physiological level it has been poorly studied in crop plants. Here, a physiological characterization of Mg deficiency in Beta vulgaris L., an important crop model, is presented. The impact of Mg deficiency on plant growth, mineral profile and photosynthetic activity was studied. The aerial biomass of plants decreased after 24days of hydroponic culture in Mg-free nutrient solution, whereas the root biomass was unaffected. Analysis of mineral profiles revealed that Mg decreased more rapidly in roots than in shoots and that shoot Mg content could fall to 3mgg−1 DW without chlorosis development and with no effect on photosynthetic parameters. Sucrose accumulated in most recently expanded leaves before any loss in photosynthetic activity. During the development of Mg deficiency, the two photosystems showed sharply contrasting responses. Data were consistent with a down-regulation of PSII through a loss of antenna, and of PSI primarily through a loss of reaction centres. In each case, the net result was a decrease in the overall rate of linear electron transport, preventing an excess of reductant being produced during conditions under which sucrose export away from mature leaf was restricte
Shadow banking in the euro area: risks and vulnerabilities in the investment fund sector
This paper first highlights the structural features of shadow banking in the euro area, focussing on investment funds. It then discusses the potential systemic risks that the recent expansion of the investment fund sector presents. While investment funds provide important intermediation services to the real sector, including market and liquidity risk-sharing and the bridging of information gaps, their rapid expansion may present systemic risks that need to be detected, monitored and managed. In particular, the risk of fund outflows and the possible negative impacts on the wider financial system have risen due to the rapid expansion of the investment fund sector, its growing involvement in capital markets, its use of synthetic leverage, and the inherent and growing maturity and liquidity mismatch arising from the demandable nature of fund share investments. While available data suggest that vulnerabilities within the investment fund sector are growing and links to the wider financial system and real economy have strengthened, data limitations prevent drawing a definitive conclusion on the sectors' contribution to systemic risk
A comparative study of ethylene emanation upon nitrogen deficiency in natural accessions of Arabidopsis thaliana
An original approach to develop sustainable agriculture with less nitrogen fertilizer inputs is to tackle the cross-talk between nitrogen nutrition and plant growth regulators. In particular the gaseous hormone, ethylene, is a prime target for that purpose. The variation of ethylene production in natural accessions of the model species Arabidopsis thaliana was explored in response to the nitrate supply. Ethylene was measured with a laser-based photoacoustic detector. First, experimental conditions were established with Columbia-0 (Col-0) accession, which was grown in vitro on horizontal plates across a range of five nitrate concentrations (0.5, 1, 2.5, 5, or 10 mM). The concentrations of 1 and 10 mM nitrate were retained for further characterization. Along with a decrease of total dry biomass and higher biomass allocation to the roots, the ethylene production was 50% more important at 1 mM than at 10 mM nitrate. The total transcript levels of 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID SYNTHASES (ACS) in roots and those of ACC OXIDASES (ACO) in shoots increased by 100% between the same treatments. This was mainly due to higher transcript levels of ACS6 and of ACO2 and ACO4 respectively. The assumption was that during nitrogen deficiency, the greater biomass allocation in favor of the roots was controlled by ethylene being released in the shoots after conversion of ACC originating from the roots. Second, biomass and ethylene productions were measured in 20 additional accessions. Across all accessions, the total dry biomass and ethylene production were correlated negatively at 1 mM but positively at 10 mM nitrate. Furthermore, polymorphism was surveyed in ACC and ethylene biosynthesis genes and gene products among accessions. Very few substitutions modifying the amino acids properties in conserved motifs of the enzymes were found in the accessions. Natural variation of ethylene production could be further explored to improve Nitrogen Use Efficiency (NUE), in particular by manipulating features like the biomass production and the timing of senescence upon nitrogen limitation
Magnesium deficiency in sugar beets alters sugar partitioning and phloem loading in young mature leaves
Magnesium deficiency has been reported to affect plant growth and biomass partitioning between root and shoot. The present work aims to identify how Mg deficiency alters carbon partitioning in sugar beet (Beta vulgaris L.) plants. Fresh biomass, Mg and sugar contents were followed in diverse organs over 20days under Mg-sufficient and Mg-deficient conditions. At the end of the treatment, the aerial biomass, but not the root biomass, of Mg-deficient plants was lower compared to control plants. A clear inverse relationship between Mg and sugar contents in leaves was found. Mg deficiency promoted a marked increase in sucrose and starch accumulation in the uppermost expanded leaves, which also had the lowest content of Mg among all the leaves of the rosette. The oldest leaves maintained a higher Mg content. [14C]Sucrose labelling showed that sucrose export from the uppermost expanded leaves was inhibited. In contrast, sucrose export from the oldest leaves, which are close to, and export mainly to, the roots, was not restricted. In response to Mg deficiency, the BvSUT1 gene encoding a companion cell sucrose/H+ symporter was induced in the uppermost expanded leaves, but without further enhancement of sucrose loading into the phloem. The observed increase in BvSUT1 gene expression supports the idea that sucrose loading into the phloem is defective, resulting in its accumulation in the lea
Equations for solar tracking
Direct Sun light absorption by trace gases can be used to quantify them and
investigate atmospheric chemistry. In such experiments, the main optical
apparatus is often a grating or a Fourier transform spectrometer. A solar
tracker based on motorized rotating mirrors is also needed to direct the light
along the spectrometer axis, correcting for the apparent rotation of the Sun.
Calculating the Sun azimuth and altitude for a given time and location can be
achieved with high accuracy but different sources of angular offsets appear in
practice when positioning the mirrors. A feedback on the motors, using a light
position sensor closed to the spectrometer is almost always needed. This paper
aims to gather the main geometrical formulas necessary for the use of a widely
used kind of solar tracker, based on two 45{\deg} mirrors in altazimuthal
set-up with a light sensor on the spectrometer, and to illustrate them with a
tracker developed for atmospheric research by our group.Comment: 14 pages, 7 figures. Second version of the paper as published in
Sensors. Main correction: a rotation matrix converted to a reflection matrix.
Main addition: a discussion on how the control theory applies to this kind of
tracking syte
Toxic Effects of Cd and Zn on the Photosynthetic Apparatus of the Arabidopsis halleri and Arabidopsis arenosa Pseudo-Metallophytes
Hyperaccumulation and hypertolerance of Trace Metal Elements (TME) like Cd and Zn are highly variable in pseudo-metallophytes species. In this study we compared the impact of high Cd or Zn concentration on the photosynthetic apparatus of the Arabidopsis arenosa and Arabidopsis halleri pseudo-metallophytes growing on the same contaminated site in Piekary Slaskie in southern Poland. Plants were grown in hydroponic culture for 6 weeks, and then treated with 1.0 mM Cd or 5.0 mM Zn for 5 days. Chlorophyll a fluorescence and pigment content were measured after 0, 1, 2, 3, 4, and 5 days in plants grown in control and exposed to Cd or Zn treatments. Moreover, the effect of TME excess on the level of oxidative stress and gas-exchange parameters were investigated. In both plant species, exposure to high Cd or Zn induced a decrease in chlorophyll and an increase in anthocyanin contents in leaves compared to the control condition. After 5 days Cd treatment, energy absorbance, trapped energy flux and the percentage of active reaction centers decreased in both species. However, the dissipated energy flux in the leaves of A. arenosa was smaller than in A. halleri. Zn treatment had more toxic effect than Cd on electron transport in A. halleri compared with A. arenosa. A. arenosa plants treated with Zn excess did not react as strongly as in the Cd treatment and a decrease only in electron transport flux and percentage of active reaction centers compared with control was observed. The two species showed contrasting Cd and Zn accumulation. Cd concentration was almost 3-fold higher in A. arenosa leaves than in A. halleri. On the opposite, A. halleri leaves contained 3-fold higher Zn concentration than A. arenosa. In short, our results showed that the two Arabidopsis metallicolous populations are resistant to high Cd or Zn concentration, however, the photosynthetic apparatus responded differently to the toxic effects.Narodowe Centrum Nauk
Procalcitonin-Guided Antibiotic Therapy after Stroke
Background: Pneumonia is among the most common acute complications after
stroke and is associated with poor long-term outcome. Biomarkers may help
identifying stroke patients at high risk for developing stroke-associated
pneumonia (SAP) and to guide early treatment. Aims: This trial investigated
whether procalcitonin (PCT) ultrasensitive (PCTus)-guided antibiotic treatment
of SAP can improve functional outcome after stroke. Methods: In this
international, multicenter, randomized, controlled clinical trial with blinded
assessment of outcomes, patients with severe ischemic stroke in the middle
cerebral artery territory were randomly assigned within 40 h after symptom
onset to PCTus-based antibiotic therapy guidance in addition to stroke unit
care or standard stroke unit care alone. The primary endpoint was functional
outcome at 3 months, defined according to the modified Rankin Scale (mRS) and
dichotomized as acceptable (≤4) or unacceptable (≥5). Secondary endpoints
included usage of antibiotics, infection rates, days of fever, and mortality.
The trial was registered with http://ClinicalTrials.gov (Identifier
NCT01264549). Results: In the intention-to-treat-analysis based on 227
patients (112 in PCT and 115 in control group), 197 patients completed the
3-month follow-up. Adherence to PCT guidance was 65%. PCT-guided therapy did
not improve functional outcome as measured by mRS (odds ratio 0.79; 95%
confidence interval 0.45–1.35, p = 0.47). Pneumonia rate and mortality were
similar in both groups. Days with fever tended to be lower (p = 0.055),
whereas total number of days treated with antibiotics were higher (p = 0.004)
in PCT compared to control group. A post hoc analysis including all PCT values
in the intention-to-treat population demonstrated a significant increase on
the first day of infection in patients with pneumonia and sepsis compared to
patients with urinary tract infections or without infections (p < 0.0001).
Conclusion: PCTus-guided antibiotic therapy did not improve functional outcome
at 3 months after severe ischemic stroke. PCT is a promising biomarker for
early detection of pneumonia and sepsis in acute stroke patients
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