F. Monti

Overexpression of PhEXPA1 increases cell size, modifies cell wall polymer composition and affects the timing of axillary meristem development in Petunia hybrida.

• Expansins are cell wall proteins required for cell enlargement and cell wall loosening during many developmental processes. The involvement of the Petunia hybrida expansin A1 (PhEXPA1) gene in cell expansion, the control of organ size and cell wall polysaccharide composition was investigated by overexpressing PhEXPA1 in petunia plants. • PhEXPA1 promoter activity was evaluated using a promoter-GUS assay and the proteins subcellular localization was established by expressing a PhEXPA1-GFP fusion protein. PhEXPA1 was overexpressed in transgenic plants using the cauliflower mosaic virus (CaMV) 35S promoter. Fourier transform infrared (FTIR) and chemical analysis were used for the quantitative analysis of cell wall polymers. • The GUS and GFP assays demonstrated that PhEXPA1 is present in the cell walls of expanding tissues. The constitutive overexpression of PhEXPA1 significantly affected expansin activity and organ size, leading to changes in the architecture of petunia plants by initiating premature axillary meristem outgrowth. Moreover, a significant change in cell wall polymer composition in the petal limbs of transgenic plants was observed. • These results support a role for expansins in the determination of organ shape, in lateral branching, and in the variation of cell wall polymer composition, probably reflecting a complex role in cell wall metabolism.

On the cumulant analysis of EXAFS in crystalline solids

The analysis of temperature-dependent EXAFS spectra based on the cumulant expansion is critically reviewed, seeking for accurate relations between EXAFS parameters and physical properties of crystals. The treatment is based on the distinction between the real and effective distribution of distances, and is divided into three logical steps. (a) The connection between lattice dynamics and cumulants C(n)* of the real distribution is studied and the extent of the usual approximations are numerically evaluated. Atomic vibrations perpendicular to the bond direction make the EXAFS thermal expansion larger than the crystallographic one; the difference is connected to a shift of the effective pair potential rather than to its asymmetry. Peculiar information on lattice dynamics of crystals can be obtained from accurate EXAFS measurements and their cumulant analysis. (b) The differences between cumulants of the real and effective distribution (C(n)* and C(n), respectively) are calculated for various physically realistic distributions. The largest discrepancy concerns the first cumulant: C(1)* measures the thermal expansion of the interatomic bond, while C(1) is a better estimate of the crystallographic thermal expansion. (c) The convergence properties of the cumulant series are discussed and some phenomenological procedures are suggested to monitor and possibly work out the connected failures of the cumulant method. Benefits and risks of the use of an effective pair potential are at last debated.

Selenite biotransformation and detoxification by Stenotrophomonas maltophilia SeITE02: Novel clues on the route to bacterial biogenesis of selenium nanoparticles

A putative biosynthetic mechanism for selenium nanoparticles (SeNPs) and efficient reduction of selenite (SeO32-) in the bacterial strain Stenotrophomonas maltophilia SeITE02 are addressed here on the basis of information gained by a combined approach relying on a set of physiological, chemical/biochemical, microscopy, and proteomic analyses. S. maltophilia SeITE02 is demonstrated to efficiently transform selenite into elemental selenium (Se°) by reducing 100% of 0.5mM of this toxic oxyanion to Se° nanoparticles within 48h growth, in liquid medium. Since the selenite reducing activity was detected in the cytoplasmic protein fraction, while biogenic SeNPs showed mainly extracellular localization, a releasing mechanism of SeNPs from the intracellular environment is hypothesized. SeNPs appeared spherical in shape and with size ranging from 160nm to 250nm, depending on the age of the cultures. Proteomic analysis carried out on the cytoplasmic fraction identified an alcohol dehydrogenase homolog, conceivably correlated with the biogenesis of SeNPs. Finally, by Fourier Transformed Infrared Spectrometry, protein and lipid residues were detected on the surface of biogenic SeNPs. Eventually, this strain might be efficaciously exploited for the remediation of selenite-contaminated environmental matrices due to its high SeO32- reducing efficiency. Biogenic SeNPs may also be considered for technological applications in different fields.

EXAFS studies of the local structure of Er3+ ions in silica xerogels co-doped with aluminium

Abstract The local environment around Er 3+ ions in wet and densified (at 900°C) silica xerogels (pure and co-doped with aluminium) has been studied at the Er L 3 -edge by X-ray absorption spectroscopy using the fluorescence detection technique. The radial distribution functions (RDF), reconstructed from X-ray absorption fine structure (EXAFS), show several changes in the local co-ordination of erbium ions upon densification: shortening of the Er–O and Er–Si/Al distances, decrease of the co-ordination numbers and broadening of the Er–O RDF. The effect of Al co-doping is clearly discerned by EXAFS in both the first and second co-ordination shells for densified gels and mainly in the second shell for wet gels. For increasing Al content, the interatomic distances between erbium ions and the second co-ordination shell ions become longer and have narrower distribution. A preferential bonding of Er to Al ions is clearly detected, with increasing ordering at higher Al content. EXAFS does not show evidence of a clustering for Er 3+ ions after densification: the short range Er–Er co-ordination is absent or not detectable in the present experiments.

EXAFS studies of the local thermal expansion in borate glasses

Temperature-dependent EXAFS measurements have recently been made on the silver borate glass [Ag 2 O.4B 2 O 3 ], and the superionic Agl-doped glass [AgI] 0.75 [3Ag 2 O.1B 2 O 3 ] 0.25 . The Ag-O co-ordination has been studied in the first sample, the I -Ag in the second one. In both cases a significant reduction of the first shell inter-atomic distance has been observed as temperature increases from 15 to 300 K. Here a detailed analysis of the EXAFS results for the AgI-doped glass is presented. The distributions of first shell I-Ag distances reconstructed from EXAFS for the glass and c-AgI, and their leading statistical parameters, are compared and critically discussed. The local negative expansion in the glass is partially attributed to the relaxation of the a-AgI network within the host binary matrix.

Pectins, Hemicelluloses and Celluloses Show Specific Dynamics in the Internal and External Surfaces of Grape Berry Skin During Ripening

Grapevine berry skin is a complex structure that contributes to the final size and shape of the fruit and affects its quality traits. The organization of cell wall polysaccharides in situ and their modification during ripening are largely uncharacterized. The polymer structure of Corvina berry skin, its evolution during ripening and related modifying genes were determined by combing mid-infrared micro-spectroscopy and multivariate statistical analysis with transcript profiling and immunohistochemistry. Spectra were acquired in situ using a surface-sensitive technique on internal and external sides of the skin without previous sample pre-treatment, allowing comparison of the related cell wall polymer dynamics. The external surface featured cuticle-related bands; the internal surface showed more adsorbed water. Application of surface-specific normalization revealed the major molecular changes related to hemicelluloses and pectins in the internal surface and to cellulose and pectins in the external surface and that they occur between mid-ripening and full ripening in both sides of the skin. Transcript profiling of cell wall-modifying genes indicated a general suppression of cell wall metabolism during ripening. Genes related to pectin metabolism-a β-galactosidase, a pectin(methyl)esterase and a pectate lyase-and a xyloglucan endotransglucosylase/hydrolase, involved in hemicellulose modification, showed enhanced expression. In agreement with Fourier transform infrared spectroscopy, patterns due to pectin methyl esterification provided new insights into the relationship between pectin modifications and the associated transcript profile during skin ripening. This study proposes an original description of polymer dynamics in grape berries during ripening, highlighting differences between the internal and external sides of the skin.

Vibrational and structural investigations on adipose tissues

Two types of adipose tissue are found in mammals, including humans: the white adipose tissue (WAT) and the brown adipose tissue (BAT). The WAT has a major role in lipid storage and body thermal insulation, while the BAT is a thermogenic tissue that produces heat by oxidizing fatty acids. Both structural characterization and spectroscopic discrimination of these different adipose tissues are matters of current interest, also in view of possible medical and bio-technological applications. In this work, vibrational and structural investigations on rat BAT and WAT have been carried out by means of infrared and Raman micro-spectroscopy. By comparing their vibrational spectra some characteristic peaks have been identified as useful markers to discriminate between the two tissues. Moreover, a quantitative evaluation of the relative degree of unsaturation of the triglyceride component in WAT and BAT has been derived. These results corroborate the vibrational spectroscopy as a reliable and minimally invasive tool in biological and medical research.

Building the Basic Concepts of Quantum Mechanics with Math and Computer Science Students

A teaching module of eight hours was carried out with four computer science Ph.D. students and five math students enrolled at the University of Verona (Italy) in order to calibrate an Inquiry-Based proposal on Quantum Mechanics for non-physics majors and to develop educational supporting tools. The path is situated in the context of linear polarization of photons, employing a formal approach based on the description of the quantum state as an abstract vector, both representing a needed background for students interested in Quantum Computing and Quantum Cryptography. A special focus is given to the superposition principle and its interpretation in a particle-like description, as well as to the different and new meaning of measurement. Single photon entanglement and the superposition of spatially separated states are also addressed. The proposal includes exploration through real experiments with macroscopic light beams, using Polaroid filters and birefringent crystals, and through ideal experiments on single photons, using a specifically developed Java applet. Seven worksheets were developed to support student concept building. Preliminary data analysis elicits two important conceptual hurdles: recognizing the active role of Polaroid filters with respect to the polarization of the photon; recognizing that a single particle can exist in a superposition of spatially separated states.

Characterization of Static Disorder by Cumulant Analysis of EXAFS: an Investigation on a Two-Gaussian Distribution

The EXAFS of a two-Gaussian distribution is simulated. It is shown that the cumulant analysis of an EXAFS signal in the case of static disorder allows the reconstruction of the corresponding asymmetric interatomic distance distribution by the splice method. In addition, the relationships between the parameters of two Gaussians and the leading cumulants of their superposition are derived. The possibility of determining the parameters of the two Gaussians by analytical means is investigated.

EXAFS study of the α-AgI phase stabilized at room temperature in a glass matrix

Abstract The local structure around iodine in a new superionic glassy composite containing AgI in the α-phase stabilized at room temperature has been studied by EXAFS. A temperature dependent study (10–300 K) has been performed at the iodine K-edge in order to follow the modification of the local structure when changing temperature and ionic conductivity. The paper presents the experimental data and their analysis based on the cumulant method. The results for the new glassy composite, containing α-AgI, are compared with analogous results obtained for crystalline AgI in the β- and α-phases and AgI superionic glasses.