Subcellular concentrations of sugar alcohols and sugars in relation to phloem translocation in Plantago major, Plantago maritima, Prunus persica, and Apium graveolens

Sugar and sugar alcohol concentrations were analyzed in subcellular compartments of mesophyll cells, in the apoplast, and in the phloem sap of leaves of Plantago major (common plantain), Plantago maritima (sea plantain), Prunus persica (peach) and Apium graveolens (celery). In addition to sucrose, common plantain, sea plantain, and peach also translocated substantial amounts of sorbitol, whereas celery translocated mannitol as well. Sucrose was always present in vacuole and cytosol of mesophyll cells, whereas sorbitol and mannitol were found in vacuole, stroma, and cytosol in all cases except for sea plantain. The concentration of sorbitol, mannitol and sucrose in phloem sap was 2- to 40-fold higher than that in the cytosol of mesophyll cells. Apoplastic carbohydrate concentrations in all species tested were in the low millimolar range versus high millimolar concentrations in symplastic compartments. Therefore, the concentration ratios between the apoplast and the phloem were very strong, ranging between 20- to 100-fold for sorbitol and mannitol, and between 200- and 2000-fold for sucrose. The woody species, peach, showed the smallest concentration ratios between the cytosol of mesophyll cells and the phloem as well as between the apoplast and the phloem, suggesting a mixture of apoplastic and symplastic phloem loading, in contrast to the herbal plant species (common plantain, sea plantain, celery) which likely exhibit an active loading mode for sorbitol and mannitol as well as sucrose from the apoplast into the phloem

Rad51 Polymerization Reveals a New Chromatin Remodeling Mechanism

Rad51 protein is a well known protagonist of homologous recombination in eukaryotic cells. Rad51 polymerization on single-stranded DNA and its role in presynaptic filament formation have been extensively documented. Rad51 polymerizes also on double-stranded DNA but the significance of this filament formation remains unclear. We explored the behavior of Saccharomyces cerevisiae Rad51 on dsDNA and the influence of nucleosomes on Rad51 polymerization mechanism to investigate its putative role in chromatin accessibility to recombination machinery. We combined biochemical approaches, transmission electron microscopy (TEM) and atomic force microscopy (AFM) for analysis of the effects of the Rad51 filament on chromatinized templates. Quantitative analyses clearly demonstrated the occurrence of chromatin remodeling during nucleoprotein filament formation. During Rad51 polymerization, recombinase proteins moved all the nucleosomal arrays in front of the progressing filament. This polymerization process had a powerful remodeling effect, as Rad51 destabilized the nucleosomes along considerable stretches of DNA. Similar behavior was observed with RecA. Thus, recombinase polymerization is a powerful mechanism of chromatin remodeling. These remarkable features open up new possibilities for understanding DNA recombination and reveal new types of ATP-dependent chromatin dynamics

Interlaboratory Comparison Reveals State of the Art in Microplastic Detection and Quantification Methods

\ua9 2025 The Authors. Published by American Chemical Society. In this study, we investigate the current accuracy of widely used microplastic (MP) detection methods through an interlaboratory comparison (ILC) involving ISO-approved techniques. The ILC was organized under the prestandardization platform of VAMAS (Versailles Project on Advanced Materials and Standards) and gathered a large number (84) of analytical laboratories across the globe. The aim of this ILC was (i) to test and to compare two thermo-analytical and three spectroscopical methods with respect to their suitability to identify and quantify microplastics in a water-soluble matrix and (ii) to test the suitability of the microplastic test materials to be used in ILCs. Two reference materials (RMs), polyethylene terephthalate (PET) and polyethylene (PE) as powders with rough size ranges between 10 and 200 μm, were used to press tablets for the ILC. The following parameters had to be assessed: polymer identity, mass fraction, particle number concentration, and particle size distribution. The reproducibility, SR, in thermo-analytical experiments ranged from 62%-117% (for PE) and 45.9%-62% (for PET). In spectroscopical experiments, the SR varied between 121% and 129% (for PE) and 64% and 70% (for PET). Tablet dissolution turned out to be a very challenging step and should be optimized. Based on the knowledge gained, development of guidance for improved tablet filtration is in progress. Further, in this study, we discuss the main sources of uncertainties that need to be considered and minimized for preparation of standardized protocols for future measurements with higher accuracy

The Rate of Decomposition of Nitrogen Pentoxide at Very Low Pressures

In a previous article [1] the results have been reported of some experiments on the rate of decomposition of gaseous nitrogen pentoxide at moderately low pressures in the range 0.2 to 2 mm. of mercury. The special features of the experimental method employed, included the use of a very large reaction vessel constructed from a 45-liter flask, thus minimizing the effect of the walls, and the use of a specially sensitive "click" gauge to follow the reaction by direct pressure measurements, thus avoiding the dangers involved in following the reaction by periodically freezing out the oxides of nitrogen and measuring the evolved oxygen, as has sometimes been done. The results obtained at these moderately low pressures showed no falling-off in the specific unimolecular rate of decomposition below that obtained at high pressures. In the present article we desire to report the results of some further experiments on the rate of decomposition of nitrogen pentoxide at total initial pressures down to 0.0055 mm

THE RATE OF DECOMPOSITION OF NITROGEN PENTOXIDE AT MODERATELY LOW PRESSURE

Introduction. - At moderately high pressures, the decomposition of gaseous nitrogen pentoxide was shown by the original work of Daniels and Johnston [1] to be homogeneous and of the first order and this has been completely confirmed by the work of subsequent investigators [2]. At low pressures, however, there has been a striking lack of agreement as to the rate of decomposition of this substance. Hirst and Rideal [3], Hibben [4], and Loomis and Smith [5] have all tried to follow the rate of the decomposition at low pressures by freezing out the nitrogen oxides during the course of the reaction and measuring the pressure of the oxygen which had been formed. Working at initial pressures in the range 0.035-1.450 mm. of mercury Hirst and Rideal report that the specific rate of decomposition becomes greater at low pressures, the increase in rate being appreciable at 0.25 mm. and several fold at their lowest pressures. Hibben, on the other hand, working in the pressure range 0.03 to 0.18 mm. finds throughout the same specific rate of decomposition as at high pressures. Loomis and Smith, however, conclude that the method used in all three sets of experiments is unreliable, since, in the first place, they find that appreciable amounts of oxygen can be occluded and carried down with the condensed oxides of nitrogen, and in the second place, find that nitrogen pentoxide is appreciably adsorbed on the surface of pyrex glass. More recently Sprenger [6] has attempted to follow the rate of decomposition by pressure measurements made with a quartz fibre gauge. Working in the range 0.01 to 0.05 mm. pressure, he comes to the extraordinary conclusion that the nitrogen pentoxide decomposes at approximately its high-pressure rate when it is first introduced into the reaction flask, and later, with a considerable fraction of the original nitrogen pentoxide still remaining, it ceases to decompose at all. Finally, Rice, Urey and Washburne [7] report that preliminary measure ments made by Miss E. Wilson show that the specific rate of decomposition of nitrogen pentoxide falls below the high-pressure rate even at pressures of several millimeters. Since the low-pressure rate of homogeneous gas reactions is of great theoretical interest, especially in connection with the theory of activation by collision as developed by Rice and Ramsperger [8] and by Kassel [9], further work on the low-pressure rate of decomposition of nitrogen pentoxide seems desirable in view of the almost complete lack of agreement in the results described above