Constraining the radio properties of the z = 6.44 QSO VIK J2318-3113

The recent detection of the quasi-stellar object (QSO) VIKING J231818.3−311346 (hereafter VIK J2318−3113) at redshift z = 6.44 in the Rapid ASKAP Continuum Survey (RACS) uncovered its radio-loud nature, making it one of the most distant known to date in this class. By using data from several radio surveys of the Galaxy And Mass Assembly 23h field and from a dedicated follow-up, we were able to constrain the radio spectrum of VIK J2318−3113 in the observed range ∼0.110 GHz. At high frequencies (0.8885.5 GHz in the observed frame) the QSO presents a steep spectrum (αr = 1.24, with Sν ∝ ν−αr), while at lower frequencies (0.40.888 GHz in the observed frame) it is nearly flat. The overall spectrum can be modelled by either a curved function with a rest-frame turnover around 5 GHz, or with a smoothly varying double power law that is flat below a rest-frame break frequency of about 20 GHz and above which it significantly steepens. Based on the model adopted, we estimated that the radio jets of VIK J2318−3113 must be a few hundred years old in the case of a turnover, or less than a few × 104 years in the case of a break in the spectrum. Having multiple observations at two frequencies (888 MHz and 5.5 GHz), we further investigated the radio variability previously reported for this source. We found that the marginally significant flux density variations are consistent with the expectations from refractive interstellar scintillation, even though relativistic effects related to the orientation of the source may still play a non-negligible role. Further radio and X-ray observations are required to conclusively discern the nature of this variation

Effects of salinity and drought on growth, ionic relations, compatible solutes and activation of antioxidant systems in oleander (Nerium oleander L.)

[EN] Nerium oleander is an ornamental species of high aesthetic value, grown in arid and semi- arid regions because of its drought tolerance, which is also considered as relatively resistant to salt; yet the biochemical and molecular mechanisms underlying oleander¿s stress toler- ance remain largely unknown. To investigate these mechanisms, one-year-old oleander seedlings were exposed to 15 and 30 days of treatment with increasing salt concentratio ns, up to 800 mM NaCl, and to complete withholding of irrigation; growth parameters and bio- chemical markers characteristic of conserved stress-response pathways were then deter- mined in stressed and control plants. Strong water deficit and salt stress both caused inhibition of growth, degradation of photosynthetic pigments, a slight (but statistically signifi- cant) increase in the leaf levels of specific osmolytes, and induction of oxidative stress¿as indicated by the accumulation of malondialdehyde (MDA), a reliable oxidative stress marker ¿accompanied by increases in the levels of total phenolic compounds and antioxidant fla- vonoids and in the specific activities of ascorbate peroxidase (APX) and glutathione reduc- tase (GR). High salinity, in addition, induced accumulation of Na + and Cl - in roots and leaves and the activation of superoxide dismutase (SOD) and catalase (CAT) activities. Apart from anatomical adaptations that protect oleander from leaf dehydration at moderate levels of stress, our results indicate that tolerance of this species to salinity and water deficit is based on the constitutive accumulation in leaves of high concentratio ns of soluble carbohydrates and, to a lesser extent, of glycine betaine, and in the activation of the aforementioned antiox- idant systems. Moreover, regarding specifically salt stress, mechanisms efficiently blocking transport of toxic ions from the roots to the aerial parts of the plant appear to contribute to a large extent to tolerance in Nerium oleanderThis work was financed by internal funds of the Polytechnic University of Valencia to Monica Boscaiu and Oscar Vicente. Dinesh Kumar’s stay in Valencia was financed by a NAMASTE fellowship from the European Union, and Mohamad Al Hassan was a recipient of an Erasmus Mundus pre-doctoral scholarship financed by the European Commission (Welcome Consortium).Kumar, D.; Al Hassan, M.; Naranjo Olivero, MA.; Agrawal, V.; Boscaiu, M.; Vicente, O. (2017). Effects of salinity and drought on growth, ionic relations, compatible solutes and activation of antioxidant systems in oleander (Nerium oleander L.). PLoS ONE. 12(9). doi:10.1371/journal.pone.0185017Se018501712

Back to the sea twice: identifying candidate plant genes for molecular evolution to marine life

Background: Seagrasses are a polyphyletic group of monocotyledonous angiosperms that have adapted to a completely submerged lifestyle in marine waters. Here, we exploit two collections of expressed sequence tags (ESTs) of two wide-spread and ecologically important seagrass species, the Mediterranean seagrass Posidonia oceanica (L.) Delile and the eelgrass Zostera marina L., which have independently evolved from aquatic ancestors. This replicated, yet independent evolutionary history facilitates the identification of traits that may have evolved in parallel and are possible instrumental candidates for adaptation to a marine habitat. Results: In our study, we provide the first quantitative perspective on molecular adaptations in two seagrass species. By constructing orthologous gene clusters shared between two seagrasses (Z. marina and P. oceanica) and eight distantly related terrestrial angiosperm species, 51 genes could be identified with detection of positive selection along the seagrass branches of the phylogenetic tree. Characterization of these positively selected genes using KEGG pathways and the Gene Ontology uncovered that these genes are mostly involved in translation, metabolism, and photosynthesis. Conclusions: These results provide first insights into which seagrass genes have diverged from their terrestrial counterparts via an initial aquatic stage characteristic of the order and to the derived fully-marine stage characteristic of seagrasses. We discuss how adaptive changes in these processes may have contributed to the evolution towards an aquatic and marine existence

Ion homeostasis in the Chloroplast

peer reviewedThe chloroplast is an organelle of high demand for macro- and micro-nutrient ions, which are required for the maintenance of the photosynthetic process. To avoid deficiency while preventing excess, homeostasis mechanisms must be tightly regulated. Here, we describe the needs for nutrient ions in the chloroplast and briefly highlight their functions in the chloroplastidial metabolism. We further discuss the impact of nutrient deficiency on chloroplasts and the acclimation mechanisms that evolved to preserve the photosynthetic apparatus. We finally present what is known about import and export mechanisms for these ions. Whenever possible, a comparison between cyanobacteria, algae and plants is provided to add an evolutionary perspective to the description of ion homeostasis mechanisms in photosynthesis