The chemical identity of intervessel pit membranes in Acer challenges hydrogel control of xylem hydraulic conductivity.

Ion-mediated enhancement of the hydraulic conductivity of xylem tissue (i.e., the ionic effect) has been reported for various angiosperm species. One explanation of the ionic effect is that it is caused by the swelling and shrinking of intervessel pit membranes due to the presence of pectins and/or other cell wall matrix polymers such as heteroxylans or arabinogalactan-proteins (AGPs) that may contain acidic sugars. Here, we examined the ionic effect for six Acer species and their pit membrane chemistry using immunocytochemistry, including antibodies against glycoproteins. Moreover, anatomical features related to the bordered pit morphology and vessel dimensions were investigated using light and electron microscopy. The ionic effect varied from 18% (± 9) to 32% (± 13). Epitopes of homogalacturonan (LM18) and xylan (LM11) were not detected in intervessel pit membranes. Negative results were also obtained for glycoproteins (extensin: LM1, JIM20; AGP glycan: LM2), although AGP (JIM13) related epitopes were detected in parenchyma cells. The mean vessel length was significantly correlated with the magnitude of the ionic effect, unlike other pit or vessel related characteristics.Our results suggest that intervessel pit membranes of Acer are unlikely to contain pectic or other acidic polysaccharides. Therefore, alternative explanations should be tested to clarify the ionic effect

Alginate/silica hybrid materials for immobilization of green microalgae \u3ci\u3eChlorella vulgaris\u3c/i\u3e for cellbased sensor arrays

Thin layers and patterned dot arrays of sodium alginate containing living microalgal cells were deposited onto glass carriers which were subsequently gelled using amino-functionalized silica sol to obtain reinforced alginate hydrogels. The resulting alginate/silica hybrid materials showed improved stability in salt-containing solutions compared to alginate gels gelled by traditional methods using Ca2+-ions. Cell arrays were patterned by printing nanolitre-scale drops of sodium alginate/cell suspension using a noncontact micro-dosage system which allows the printing of solutions of high viscosity. Cultures of the green microalga Chlorella vulgaris were immobilized within the newly developed alginate/silica hydrogels in order to demonstrate the potential of the hybrid matrix for the design of cell-based detection systems. The herbicide atrazine as well as copper ions have been used as model toxicants. Short-term toxicity tests (exposure time: 1 h) have been carried out using atrazine and changes in chlorophyll a (Chl a) fluorescence were measured by imaging pulse amplitude modulated-fluorometry (Imaging-PAM). C. vulgaris cells immobilized within alginate/silica hydrogels demonstrated a highly reproducible response pattern and compared well to freely suspended cells. Activity and response sensitivity of immobilized cells to atrazine was largely maintained for up to 8 weeks, especially when stored under cool conditions in the dark. Furthermore, immobilized cells could be repeatingly used for short-term toxicity tests as atrazine produces a reversible inhibition of photosynthesis

Alginate/silica hybrid materials for immobilization of green microalgae \u3ci\u3eChlorella vulgaris\u3c/i\u3e for cellbased sensor arrays

Thin layers and patterned dot arrays of sodium alginate containing living microalgal cells were deposited onto glass carriers which were subsequently gelled using amino-functionalized silica sol to obtain reinforced alginate hydrogels. The resulting alginate/silica hybrid materials showed improved stability in salt-containing solutions compared to alginate gels gelled by traditional methods using Ca2+-ions. Cell arrays were patterned by printing nanolitre-scale drops of sodium alginate/cell suspension using a noncontact micro-dosage system which allows the printing of solutions of high viscosity. Cultures of the green microalga Chlorella vulgaris were immobilized within the newly developed alginate/silica hydrogels in order to demonstrate the potential of the hybrid matrix for the design of cell-based detection systems. The herbicide atrazine as well as copper ions have been used as model toxicants. Short-term toxicity tests (exposure time: 1 h) have been carried out using atrazine and changes in chlorophyll a (Chl a) fluorescence were measured by imaging pulse amplitude modulated-fluorometry (Imaging-PAM). C. vulgaris cells immobilized within alginate/silica hydrogels demonstrated a highly reproducible response pattern and compared well to freely suspended cells. Activity and response sensitivity of immobilized cells to atrazine was largely maintained for up to 8 weeks, especially when stored under cool conditions in the dark. Furthermore, immobilized cells could be repeatingly used for short-term toxicity tests as atrazine produces a reversible inhibition of photosynthesis

Observation of enhanced X-ray emission from the CTTS AA Tau during a transit of an accretion funnel

AA Tau was observed for about 5h per XMM orbit (2 days) over 8 successive orbits, which covers two optical eclipse periods (8.2 days). The XMM optical/UV monitor simultaneously provided UV photometry with a ~15 min sampling rate. Some V-band photometry was also obtained from the ground during this period in order to determine the dates of the eclipses. Two X-ray and UV measurements were secured close to the center of the eclipse. The UV flux is the highest just before the eclipse starts and the lowest towards the end of it. We model the UV flux variations with a weekly modulation (inner disk eclipse), plus a daily modulation, which suggests a non-steady accretion. No eclipses are detected in X-rays. For one measurement, the X-ray count rate was nearly 50 times stronger than the minimum observed level, and the plasma temperature reached 60 MK, i.e., a factor of 2-3 higher than in the other observations. This X-ray event, observed close to the center of the optical eclipse, is interpreted as an X-ray flare. We identify the variable column density with the low-density accretion funnel flows blanketing the magnetosphere. The lack of X-ray eclipses indicates that X-ray emitting regions are located at high latitudes. Furthermore, the occurrence of a strong X-ray flare near the center of the optical eclipse suggests that the magnetically active areas are closely associated with the base of the high-density accretion funnel flow. We speculate that the impact of this free falling accretion flow onto the strong magnetic field of the stellar corona may boost the X-ray emission (abridged).Comment: 17 pages and 9 Figures. Accepted by A&

Simultaneous X-ray spectroscopy of YY Gem with Chandra and XMM-Newton

We report on a detailed study of the X-ray spectrum of the nearby eclipsing spectroscopic binary YY Gem. Observations were obtained simultaneously with both large X-ray observatories, XMM-Newton and Chandra. We compare the high-resolution spectra acquired with the Reflection Grating Spectrometer onboard XMM-Newton and with the Low Energy Transmission Grating Spectrometer onboard Chandra, and evidence in direct comparison the good performance of both instruments in terms of wavelength and flux calibration. The strongest lines in the X-ray spectrum of YY Gem are from oxygen. Oxygen line ratios indicate the presence of a low-temperature component (1-4 MK) with density n_e < 2 10^{10} cm^-3. The X-ray lightcurve reveals two flares and a dip corresponding to the secondary eclipse. An increase of the density during phases of high activity is suggested from time-resolved spectroscopy. Time-resolved global fitting of the European Photon Imaging Camera CCD spectrum traces the evolution of temperature and emission measure during the flares. These medium-resolution spectra show that temperatures > 10^7 K are relevant in the corona of YY Gem although not as dominant as the lower temperatures represented by the strongest lines in the high-resolution spectrum. Magnetic loops with length on the order of 10^9 cm, i.e., about 5 % of the radius of each star, are inferred from a comparison with a one-dimensional hydrodynamic model. This suggests that the flares did not erupt in the (presumably more extended) inter-binary magnetosphere but are related to one of the components of the binary.Comment: 15 pages, accepted for publication in A&

Exposure pathways matter: Aquatic phototrophic communities respond differently to agricultural run-off exposed via sediment or water

1. Small shallow ponds are widespread but understudied water bodies in agricultural landscapes. Agricultural run-off (ARO) transports pesticides and nutrients into adjacent aquatic ecosystems where they occur dissolved in the water column or are bound to sediments. Consequently, aquatic communities are affected by ARO via different exposure pathways. We hypothesize that sediment-bound ARO mainly affects submerged rooted macrophytes, while phytoplankton and periphyton are more prone to ARO in water. These primary producers compete for resources resulting in a regime shift between alternative stable states of macrophyte or phytoplankton dominance. We hypothesize that warming increases nutrient release from sediments and thereby facilitates the occurrence of phytoplankton dominance. 2. Using a full-factorial microcosm design, we exposed aquatic primary producers to either sediment or water application of a mixture of common pesticides (terbuthylazine, pirimicarb, tebuconazole and copper) and nitrate at two concentrations and two temperatures (22°C and 26°C) for 4 weeks. Initial and final concentrations of pesticides and nitrate, final biomass of macrophytes, periphyton and phytoplankton, pesticide accumulation in macrophytes and changes in carbon, nitrogen and phosphorus content and selected exoenzyme activities in the sediment were measured. 3. We found lower final macrophyte biomass for both ARO treatments compared to controls, indicating a prevalence of negative effects by herbicides and competition for light with other phototrophs. In contrast, phytoplankton and periphyton biomass increased, but only when exposed to ARO via the water column, indicating a prevalence of positive effects by nutrient supply. Microbial carbon and nutrient cycling in sediments was not affected by ARO. Higher temperature mitigated ARO-related effects on macrophytes under sediment exposure. 4. Synthesis and application. ARO poses a strong risk of submerged macrophyte loss and establishment of turbid conditions with phytoplankton dominance in aquatic ecosystems. In conclusion, exposure pathways as well as indirect and interacting effects of multiple stressors need to be considered when designing appropriate mitigation measures. Under climate change, we suggest to prioritize local measures as buffer strips a reduced use of pesticides and fertilizers, and sediment removal as appropriate measures to protect these vulnerable but widespread aquatic systems, which are highly relevant for biodiversity in agricultural landscapes

Living in a Dangerous World: The Shaping of Behavioral Profile by Early Environment and 5-HTT Genotype

Anxiety and anxiety disorders are influenced by both, environmental and genetic factors. One genetic factor under scrutiny for anxiety disorders is the genetically encoded variation of the serotonin transporter (5-HTT). The aim of this study was to elucidate the effects of a threatening environment during early phases of life on anxiety-like (ANX) and exploratory behavior (EXP) in adult mice, varying in serotonin transporter (5-HTT) genotype. For this purpose, pregnant and lactating 5-HTT +/− dams were repeatedly exposed to olfactory cues of unfamiliar adult males by introducing small amounts of soiled bedding to their home cage. These stimuli signal the danger of infanticide and simulate a threatening environment. Control females were treated with neutral bedding. The offspring (5-HTT +/+, +/−, −/−) were examined for their ANX and EXP. The main results were: (1) a main effect of genotype existed, with 5-HTT −/− showing higher levels of ANX and lower levels of EXP than 5-HTT +/− and wildtypes. (2) When mothers had lived in a threatening environment, their offspring showed increased ANX and reduced EXP compared to controls. (3) These effects were most pronounced in 5-HTT −/− mice. By applying a new ecologically relevant paradigm we conclude: If 5-HTT +/− mothers live in a threatening environment during pregnancy and lactation, their offspring behavioral profile will, in principle, be shaped in an adaptive way preparing the young for an adverse environment. This process is, however, modulated by 5-HTT genotype, bearing the risk that individuals with impaired serotonergic neurotransmission (5-HTT −/−) will develop an exaggerated, potentially pathological level of anxiety from gene × environment interactions

Aspects of Relativistic Sum Rules

The status of our understanding of relativistic sum rules is reviewed. The recent development of new theoretical methods for the evaluation of these sum rules offers hope for further advances in this challenging field. These new techniques are described, along with a discussion of the source of difficulties inherent in such relativistic calculations. A connection is pointed out between certain sum rules for atomic interactions with charged particles and those for interactions with photons.Comment: 32 pages, accepted for publication in Advances in Quantum Chemistr