Nucleation and early stage crystallization in barium disilicate glass.

Barium disilicate is one of the glass-ceramic systems where internal nucleation and crystallization can occur from quenched glass upon heat treatment without requiring nucleating agents. The structural origin of the nano-clusters formed during low temperature heat treatment is of great interest in gaining a fundamental understanding of nucleation kinetics in silicate glasses. Here, we present experimental investigations on the low temperature heat treatment of barium disilicate (BaO·2SiO2) glass. Several experimental techniques were used to characterize the structural nature of barium disilicate glasses that were heat treated between the glass transition temperature, Tg, and the peak temperature of crystal growth, Tcr. The data show that small amounts of crystallites including BaSi2O5 as well as other higher Ba/Si ratio phases are formed. Moreover, unlike that reported for lower BaO content (BaO<33mol%) barium silicate glass or the analogous Li2O-SiO2 glasses, no clear evidence is observed for liquid/liquid phase separation in barium disilicate glass.

Self-rescue of an EXTENSIN mutant reveals alternative gene expression programs and candidate proteins for new cell wall assembly in Arabidopsis.

Plants encode a poorly understood superfamily of developmentally expressed cell wall hydroxyproline-rich glycoproteins (HRGPs). One, EXTENSIN3 (EXT3) of the 168 putative HRGPs, is critical in the first steps of new wall assembly, demonstrated by broken and misplaced walls in its lethal homozygous mutant. Here we report the findings of phenotypic (not genotypic) revertants of the ext3 mutant and in-depth analysis including microarray and qRT-PCR (polymerase chain reaction). The aim was to identify EXT3 substitute(s), thus gaining a deeper understanding of new wall assembly. The data show differential expression in the ext3 mutant that included 61% (P ≤ 0.05) of the HRGP genes, and ability to self-rescue by reprogramming expression. Independent revertants had reproducible expression networks, largely heritable over the four generations tested, with some genes displaying transgenerational drift towards wild-type expression levels. Genes for nine candidate regulatory proteins as well as eight candidate HRGP building materials and/or facilitators of new wall assembly or maintenance, in the (near) absence of EXT3 expression, were identified. Seven of the HRGP fit the current model of EXT function. In conclusion, the data on phenotype comparisons and on differential expression of the genes-of-focus provide strong evidence that different combinations of HRGPs regulated by alternative gene expression networks, can make functioning cell walls, resulting in (apparently) normal plant growth and development. More broadly, this has implications for interpreting the cause of any mutant phenotype, assigning gene function, and genetically modifying plants for utilitarian purposes.

Enhanced electrocatalytic oxygen reduction through electrostatic assembly of Pt nanoparticles onto porous carbon supports from SnCl2-stabilized suspensions.

Monodisperse Pt nanoparticles with atomic structures that span the cluster to crystal transition have recently been synthesized in electrostatically stabilized, aqueous-based suspensions. In the present study, the anionic charge from the stabilizing SnCl(2) sheath adsorbed on the surface of these particles is used for the first time to assemble Pt directly onto porous carbon supports via electrostatic assembly. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) reveals that these assemblies have substantially higher Pt-C dispersions than obtained from precipitation methods commonly used for commercial electrocatalyst systems. Energy dispersive spectroscopy (EDS) and inductively coupled plasma-mass spectrometry (ICP-MS) are used to determine that loadings of 10-30% by weight Pt (particle packing fractions from 0.05 to 0.25) are obtained through a single electrostatic application of these particles on Vulcan carbon, depending on particle size. The highest average oxygen reduction reaction (ORR) mass activity obtained using this approach is 90.4 A/g(Pt) at 0.9 V vs RHE in 0.1 M perchloric acid is with 1-2 nm particles that exhibit a transitional atomic structure. This activity compares to an average value of 74.0 A/g(Pt) obtained from densely packed electrostatic layer-by-layer (LbL) assemblies of unsupported particles and 36.7 A/g(Pt) commercial Vulcan electrocatalyst from Tanaka Kikinzoku Kogyo (TKK). Enhanced activity is observed with electrostatic assembly of any particle size on Vulcan relative to unsupported or commercial electrocatalyst with comparable durability. Such enhanced activity is attributed to improved reactant accessibility to the catalyst surface due to the increase in particle dispersion. An extinction coefficient of 7.41 m(2)/g at 352 nm is obtained across the entire cluster to crystal transition from 20 atom clusters to 2.9 nm single crystal nanoparticles, indicating that observed variation in ORR activity with particle size may be associated primarily with changes in atomic surface structure as opposed to the metallic character of the nanoparticles as assessed by UV-vis spectroscopy.

Electrochemical and Structural Study of a Chemically Dealloyed PtCu Oxygen Reduction Catalyst.

A carbon-supported, dealloyed platinum-copper (Pt-Cu) oxygen reduction catalyst was prepared using a multi-step synthetic procedure. Material produced at each step was characterized using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), electron energy loss spectroscopy (EELS) mapping, x-ray absorption spectroscopy (XAS), x-ray diffraction (XRD), and cyclic voltammetry (CV), and its oxygen reduction reaction (ORR) activity was measured by a thin-film rotating disk electrode (TF-RDE) technique. The initial synthetic step, a co-reduction of metal salts, produced a range of poorly crystalline Pt, Cu, and Pt-Cu alloy nanoparticles that nevertheless exhibited good ORR activity. Annealing this material alloyed the metals and increased particle size and crystallinity. TEM shows the annealed catalyst to include particles of various sizes, large (>25 nm), medium (12-25 nm), and small (<12 nm). Most of the small and medium-sized particles exhibited a partial or complete coreshell (Cu-rich core and Pt shell) structure with the smaller particles typically having more complete shells. The appearance of Pt shells after annealing indicates that they are formed by a thermal diffusion mechanism. Although the specific activity of the catalyst material was more than doubled by annealing, the concomitant decrease in Pt surface area resulted in a drop in its mass activity. Subsequent dealloying of the catalyst by acid treatment to partially remove the copper increased the Pt surface area by changing the morphology of the large and some medium particles to a "Swiss cheese" type structure having many voids. The smaller particles retained their core-shell structure. The specific activity of the catalyst material was little reduced by dealloying, but its mass activity was more than doubled due to the increase in surface area. The possible origins of these results are discussed in this report.

Characterization of vascular-specific RSs1 and rolC promoters for their utilization in engineering plants to develop resistance against hemipteran insect pests.

Rice sucrose synthase1, RSs1 (isolated from rice) and rolC (isolated from Agrobacterium rhizogenes) promoters were evaluated by binding analyses of their respective cis-elements with host nuclear transcription factors. The expression profile of an insecticidal protein driven by these promoters in transgenic plants was monitored. Motif-search analysis with available phloem-specific promoter sequences revealed the presence of two BoxII elements in RSs1. An octopine synthase element, a stem-specific, a root-specific and a light-responsive element were found in the rolC promoter, whereas the ASL box, GATA and 13 bp motifs were detected in both promoters. Binding analysis of these cis-elements (both in native and mutant forms) with the trans-factors present in the nuclear extracts from rice, tobacco and chickpea, followed by electrophoretic mobility shift assay, documented a highly specific cis-trans interaction. Both promoters were utilized to express Allium sativum leaf agglutinin (ASAL) gene in the three aforementioned plant systems. By immunohistochemistry and immunohistofluorescence, specific patterns of ASAL accumulation were detected in vascular tissues of single copy transgenic plants. Transgenic plants expressing ASAL in a phloem-specific manner demonstrated about 60-65% more insecticidal activity than control plants. The two promoters, which evolved independently from two distinctly unrelated origins, were found to maintain their functionality in a conserved manner. They were able to express the insecticidal protein coding ASAL as transgene both in monocot and dicot hosts. Thus, the two promoters are valuable as prospective phloem-specific promoters for use in plant biotechnological programmes.

Transgenic rice expressing Allium sativum leaf lectin with enhanced resistance against sap-sucking insect pests.

Mannose binding Allium sativum leaf agglutinin (ASAL) has been shown to be antifeedant and insecticidal against sap-sucking insects. In the present investigation, ASAL coding sequence was expressed under the control of CaMV35S promoter in a chimeric gene cassette containing plant selection marker, hpt and gusA reporter gene of pCAMBIA1301 binary vector in an elite indica rice cv. IR64. Many fertile transgenic plants were generated using scutellar calli as initial explants through Agrobacterium-mediated transformation technology. GUS activity was observed in selected calli and in mature plants. Transformation frequency was calculated to be approximately 12.1%+/-0.351 (mean +/- SE). Southern blot analyses revealed the integration of ASAL gene into rice genome with a predominant single copy insertion. Transgene localization was detected on chromosomes of transformed plants using PRINS and C-PRINS techniques. Northern and western blot analyses determined the expression of transgene in transformed lines. ELISA analyses estimated ASAL expression up to 0.72 and 0.67% of total soluble protein in T0 and T1 plants, respectively. Survival and fecundity of brown planthopper and green leafhopper were reduced to 36% (P < 0.01), 32% (P < 0.05) and 40.5, 29.5% (P < 0.001), respectively, when tested on selected plants in comparison to control plants. Specific binding of expressed ASAL to receptor proteins of insect gut was analysed. Analysis of T1 progenies confirmed the inheritance of the transgenes. Thus, ASAL promises to be a potential component in insect resistance rice breeding programme.

The efficacy of a novel insecticidal protein, Allium sativum leaf lectin (ASAL), against homopteran insects monitored in transgenic tobacco.

The homopteran group of polyphagous sucking insect pests causes severe damage to many economically important plants including tobacco. Allium sativum leaf lectin (ASAL), a mannose-binding 25-kDa homodimeric protein, has recently been found to be antagonistic to various sucking insects in the homopteran group through artificial diet bioassay experiments. The present study describes, for the first time, the expression of the ASAL coding sequence under the control of the cauliflower mosaic virus (CaMV) 35S promoter in tobacco by Agrobacterium-mediated transformation technology. Molecular analyses demonstrated the integration of the chimeric ASAL gene in tobacco and its inheritance in the progeny plants. Western blot analysis followed by enzyme-linked immunosorbent assay (ELISA) determined the level of ASAL expression in different lines to be in the range of approximately 0.68%-2% of total soluble plant protein. An in planta bioassay conducted with Myzus persicae, peach potato aphid (a devastating pest of tobacco and many other important plants), revealed that the percentage of insect survival decreased significantly to 16%-20% in T0 plants and T1 progeny, whilst approximately 75% of insects survived on untransformed tobacco plants after 144 h of incubation. Ligand analyses of insect brush border membrane vesicle receptors and expressed ASAL in transgenic tobacco showed that the expressed ASAL binds to the aphid gut receptor in the same manner as native ASAL, pointing to the fact that ASAL maintains the biochemical characteristics even in the transgenic situation. These findings in a model plant open up the possibility of expressing the novel ASAL gene in a wide range of crop plants susceptible to various sap-sucking insects.