Capturing the Surface Texture and Shape of Pollen: A Comparison of Microscopy Techniques

Research on the comparative morphology of pollen grains depends crucially on the application of appropriate microscopy techniques. Information on the performance of microscopy techniques can be used to inform that choice. We compared the ability of several microscopy techniques to provide information on the shape and surface texture of three pollen types with differing morphologies. These techniques are: widefield, apotome, confocal and two-photon microscopy (reflected light techniques), and brightfield and differential interference contrast microscopy (DIC) (transmitted light techniques). We also provide a first view of pollen using super-resolution microscopy. The three pollen types used to contrast the performance of each technique are: Croton hirtus (Euphorbiaceae), Mabea occidentalis (Euphorbiaceae) and Agropyron repens (Poaceae). No single microscopy technique provided an adequate picture of both the shape and surface texture of any of the three pollen types investigated here. The wavelength of incident light, photon-collection ability of the optical technique, signal-to-noise ratio, and the thickness and light absorption characteristics of the exine profoundly affect the recovery of morphological information by a given optical microscopy technique. Reflected light techniques, particularly confocal and two-photon microscopy, best capture pollen shape but provide limited information on very fine surface texture. In contrast, transmitted light techniques, particularly differential interference contrast microscopy, can resolve very fine surface texture but provide limited information on shape. Texture comprising sculptural elements that are spaced near the diffraction limit of light (∼250 nm; NDL) presents an acute challenge to optical microscopy. Super-resolution structured illumination microscopy provides data on the NDL texture of A. repens that is more comparable to textural data from scanning electron microscopy than any other optical microscopy technique investigated here. Maximizing the recovery of morphological information from pollen grains should lead to more robust classifications, and an increase in the taxonomic precision with which ancient vegetation can be reconstructed

Indicators of river system hydromorphological character and dynamics: understanding current conditions and guiding sustainable river management

The work leading to this paper received funding from the EU’s FP7 programme under Grant Agreement No. 282656 (REFORM). The Indicators were developed within the context of REFORM deliverable D2.1, therefore all partners involved in this deliverable contributed to some extent to their discussion and development

Allosteric pyruvate kinase-based "logic gate" synergistically senses energy and sugar levels in <i>Mycobacterium tuberculosis</i>

Pyruvate kinase (PYK) is an essential glycolytic enzyme that controls glycolytic flux and is critical for ATP production in all organisms, with tight regulation by multiple metabolites. Yet the allosteric mechanisms governing PYK activity in bacterial pathogens are poorly understood. Here we report biochemical, structural and metabolomic evidence that Mycobacterium tuberculosis (Mtb) PYK uses AMP and glucose-6-phosphate (G6P) as synergistic allosteric activators that function as a molecular "OR logic gate" to tightly regulate energy and glucose metabolism. G6P was found to bind to a previously unknown site adjacent to the canonical site for AMP. Kinetic data and structural network analysis further show that AMP and G6P work synergistically as allosteric activators. Importantly, metabolome profiling in the Mtb surrogate, Mycobacterium bovis BCG, reveals significant changes in AMP and G6P levels during nutrient deprivation, which provides insights into how a PYK OR gate would function during the stress of Mtb infection

Determination of radium-226 in aqueous solutions by alpha-spectrometry

International audienceThe new European legislation imposes a lower threshold for radioactivity in drinking water.. This requires the development of more sensitive and reliable analytical methods. This work presents an improved a-spectrometric technique to determine the radium-226 activity in aqueous solution relying on the radium adsorption onto a thin manganese oxide layer followed by a-measurement. The preparation of the MnO2 deposit has been optimized as well as the radium adsorption conditions. Detection threshold and limit of 5 and 10 mBq .L-1, respectively, with a 10% (95% confidence) uncertainty are currently reached. This paper reports on the overall technique and on its application to assess the radium-226 activity in 28 French mineral waters. In addition, the gross alpha- and beta -activities have been evaluated using proportional counting while the uranium concentrations were derived from ICPMS

Study of the ion exchange selectivity of layered titanosilicate Na-3(Na,H)Ti2O2[Si2O6](2) center dot 2H(2)O, AM-4, for strontium

International audienceThis paper describes for the first time the sorption behaviour of a titanosilicate, AM-4, that exhibits an extremely high affinity for strontium in neutral and alkaline media. The ion exchange selectivity of this layered titanosilicate is explained in relation to the crystalline structure. The simple approach which consists in studying carefully the distribution of formal charges of oxygens in the anionic framework and calculating a normalized bond length in order to measure the ion stability in its site has enabled us to account for the AM-4 performances for the strontium remediation in competition with alkali and alkaline earth metal ions, The Sr uptake amounts as a function of the pH were determined, they can be correlated to the formal charges of Si-O-nbo. The effect of sodium, potassium, calcium and magnesium on the Sr2+ ions sorption was also studied in binary solutions Sr2+/Na+, Sr2+/K+, Sr2+/Ca2+, Sr2+/Mg2+. The determination of the equilibrium constant Sr2+/2Na(+) and of the ion competitive effects with adsorption data have shown that Ca2+ is the most efficient to reduce the uptake of Sr2+. The preliminary Kd values provide an indication that this exchanger may act as a sorber for groundwater and nuclear remediation applications

Study of the ion exchange selectivity of layered titanosilicate Na-3(Na,H)Ti2O2[Si2O6](2) center dot 2H(2)O, AM-4, for strontium

International audienceThis paper describes for the first time the sorption behaviour of a titanosilicate, AM-4, that exhibits an extremely high affinity for strontium in neutral and alkaline media. The ion exchange selectivity of this layered titanosilicate is explained in relation to the crystalline structure. The simple approach which consists in studying carefully the distribution of formal charges of oxygens in the anionic framework and calculating a normalized bond length in order to measure the ion stability in its site has enabled us to account for the AM-4 performances for the strontium remediation in competition with alkali and alkaline earth metal ions, The Sr uptake amounts as a function of the pH were determined, they can be correlated to the formal charges of Si-O-nbo. The effect of sodium, potassium, calcium and magnesium on the Sr2+ ions sorption was also studied in binary solutions Sr2+/Na+, Sr2+/K+, Sr2+/Ca2+, Sr2+/Mg2+. The determination of the equilibrium constant Sr2+/2Na(+) and of the ion competitive effects with adsorption data have shown that Ca2+ is the most efficient to reduce the uptake of Sr2+. The preliminary Kd values provide an indication that this exchanger may act as a sorber for groundwater and nuclear remediation applications