UV photodissociation of methyl bromide and methyl bromide cation studied by velocity map imaging

We employ the velocity map imaging technique to measure kinetic energy and angular distributions of state selected CH3 (v2=0,1,2,3) and Br (2P3/2,2P1/2) photofragments produced by methyl bromide photolysis at 215.9 nm. These results show unambiguously that the Br and Br* forming channels result in different vibrational excitation of the umbrella mode of the methyl fragment. Low energy structured features appear on the images which arise from CH3Br+ photodissociation near 330 nm. The excess energy of the probe laser photon is channeled into CH3+ vibrational excitation, most probably in the nu_4 degenerate bendComment: 11 page

Determination of accurate electron chiral asymmetries in fenchone and camphor in the VUV range: sensitivity to isomerism and enantiomeric purity

Photoelectron circular dichroism (PECD) manifests itself as an intense forward/backward asymmetry in the angular distribution of photoelectrons produced from randomly-oriented enantiomers by photoionization with circularly-polarized light (CPL). As a sensitive probe of both photoionization dynamics and of the chiral molecular potential, PECD attracts much interest especially with the recent performance of related experiments with visible and VUV laser sources. Here we report, by use of quasi-perfect CPL VUV synchrotron radiation and using a double imaging photoelectron/photoion coincidence (i2PEPICO) spectrometer, new and very accurate values of the corresponding asymmetries on showcase chiral isomers: camphor and fenchone. These data have additionally been normalized to the absolute enantiopurity of the sample as measured by a chromatographic technique. They can therefore be used as benchmarking data for new PECD experiments, as well as for theoretical models. In particular we found, especially for the outermost orbital of both molecules, a good agreement with CMS-X PECD modeling over the whole VUV range. We also report a spectacular sensitivity of PECD to isomerism for slow electrons, showing large and opposite asymmetries when comparing R-camphor to R-fenchone (respectively -10% and +16 % around 10 eV). In the course of this study, we could also assess the analytical potential of PECD. Indeed, the accuracy of the data we provide are such that limited departure from perfect enantiopurity in the sample we purchased could be detected and estimated in excellent agreement with the analysis performed in parallel via a chromatographic technique, establishing a new standard of accuracy, in the ±1 % range, for enantiomeric excess measurement via PECD. The i2PEPICO technique allows correlating PECD measurements to specific parent ion masses, which would allow its application to analysis of complex mixtures

Nonadiabatic dynamics in polyatomic systems studied by femtosecond time-resolved photoelectron spectroscopy

We investigate the use of time-resolved photoelectron spectroscopy for studying nonadiabatic polyatomic dissociation dynamics. In particular, we emphasize the importance of the electronic structure of the ionization continuum in interpreting the results and provide an experimental example of these effects in the dissociation dynamics of the NO dimer.Peer reviewed: YesNRC publication: Ye

Bean pod mottle virus: a new powerful tool for functional genomics studies in [i]Pisum sativum[/i].

International audiencePea (Pisum sativum L.) is an important legume worldwide. The importance of pea in arable rotations and nutritional value for both human and animal consumption have fostered sustained production and different studies to improve agronomic traits of interest. Moreover, complete sequencing of the pea genome is currently underway and will lead to the identification of a large number of genes potentially associated with important agronomic traits. Because stable genetic transformation is laborious for pea, virus-induced gene silencing (VIGS) appears as a powerful alternative technology for determining the function of unknown genes. In this work, we present a rapid and efficient viral inoculation method using DNA infectious plasmids of Bean pod mottle virus (BPMV)-derived VIGS vector. Six pea genotypes with important genes controlling biotic and/or abiotic stresses were found susceptible to BPMV carrying a GFP reporter gene and showed fluorescence in both shoots and roots. In a second step, we investigated 37 additional pea genotypes and found that 30 were susceptible to BPMV and only 7 were resistant. The capacity of BPMV to induce silencing of endogenes was investigated in the most susceptible genotype using two visual reporter genes: PsPDS and PsKORRIGAN1 (PsKOR1) encoding PHYTOENE DESATURASE and a 1,4-β-D-glucanase, respectively. The features of the 'one-step' BPMV-derived VIGS vector include (i) the ease of rub-inoculation, without any need for biolistic or agro-inoculation procedures, (ii) simple cost-effective procedure and (iii) noninterference of viral symptoms with silencing. These features make BPMV the most adapted VIGS vector in pea to make low- to high-throughput VIGS studies

The "one-step" Bean pod mottle virus (BPMV)derived vector is a functional genomics tool for efficient overexpression of heterologous protein, virus-induced gene silencing and genetic mapping of BPMV R-gene in common bean (Phaseolus vulgaris L.)

Background: Over the last two years, considerable advances have been made in common bean (Phaseolus vulgaris L.) genomics, especially with the completion of the genome sequence and the availability of RNAseq data. However, as common bean is recalcitrant to stable genetic transformation, much work remains to be done for the development of functional genomics tools adapted to large-scale studies. Results: Here we report the successful implementation of an efficient viral vector system for foreign gene expression, virus-induced gene silencing (VIGS) and genetic mapping of a BPMV resistance gene in common bean, using a "one-step" BPMV vector originally developed in soybean. With the goal of developing this vector for high-throughput VIGS studies in common bean, we optimized the conditions for rub-inoculation of infectious BPMV-derived plasmids in common bean cv. Black Valentine. We then tested the susceptibility to BPMV of six cultivars, and found that only Black Valentine and JaloEEP558 were susceptible to BPMV. We used a BPMV-GFP construct to detect the spatial and temporal infection patterns of BPMV in vegetative and reproductive tissues. VIGS of the PHYTOENE DESATURASE (PvPDS) marker gene was successfully achieved with recombinant BPMV vectors carrying fragments ranging from 132 to 391 bp. Finally, we mapped a gene for resistance to BPMV (R-BPMV) at one end of linkage group 2, in the vicinity of a locus (I locus) previously shown to be involved in virus resistance. Conclusions: The " one-step" BPMV vector system therefore enables rapid and simple functional studies in common bean, and could be suitable for large-scale analyses. In the post-genomic era, these advances are timely for the common bean research communit

Development of molecular markers linked to disease resistance genes in common bean based on whole genome sequence

International audienceCommon bean (Phaseolus vulgaris) is the most important grain legume for direct human consumption in the world, particularly in developing countries where it constitutes the main source of protein. Unfortunately, common bean yield stability is constrained by a number of pests and diseases. As use of resistant genotypes is the most economic and ecologically safe means for controlling plant diseases, efforts have been made to genetically characterize resistance genes (R genes) in common bean. Despite its agronomic importance, genomic resources available in common bean were limited until the recent sequencing of common bean genome (Andean genotype G19833). Besides allowing the annotation of Nucleotide Binding-Leucine Rich Repeat (NB-LRR) encoding gene family, which is the prevalent class of disease R genes in plants, access to the whole genome sequence of common bean can be of great help for intense selection to increase the overall efficiency of crop improvement programs using marker-assisted selection (MAS). This review presents the state of the art of common bean NB-LRR gene clusters, their peculiar location in subtelomeres and correlation with genetically characterized monogenic R genes, as well as how the availability of the whole genome sequence can boost the development of molecular markers for MAS

Comparing Femtosecond Multiphoton Dissociative Ionization of Tetrathiafulvene with Imaging Photoelectron Photoion Coincidence Spectroscopy

In this paper we describe femtosecond photoionization and the imaging photoelectron photoion coincidence spectroscopy of tetrathiafulvene, TTF. Femtosecond photoionization of TTF results in the absorption of up to twelve 808 nm photons leading to ion internal energies up to 12.1 eV as deduced from the photoelectron spectrum. Within this internal energy a variety of dissociation channels are accessible. In order to disentangle the complex ionic dissociation, we utilized the imaging photoelectron photoion coincidence (iPEPICO) technique. Above the dissociation threshold, iPEPICO results show that the molecular ion (<i>m</i>/<i>z</i> = 204) dissociates into seven product ions, six of which compete in a 1.0 eV internal energy window and are formed with the same appearance energy. Ab initio calculations are reported on the possible fragment ion structures of five dissociation channels as well as trajectories showing the loss of C₂H₂ and C₂H₂S from high internal energy TTF cations. A three-channel dissociation model is used to fit the PEPICO data in which two dissociation channels are treated as simple dissociations (one with a reverse barrier), while the rest involve a shared barrier. The two lower energy dissociation channels, <i>m</i>/<i>z</i> = 146 and the channel leading to <i>m</i>/<i>z</i> = 178, 171, 159, 140, and 127, have <i>E</i>₀ values of 2.77 ± 0.10 and 2.38 ± 0.10 eV, respectively, and are characterized by Δ<i>S</i>^‡_600 K values of −9 ± 6 and 1 ± 6 J K^–1 mol^–1, respectively. Competing with them at higher internal energy is the cleavage of the central bond to form the <i>m</i>/<i>z</i> = 102 fragment ion, with an <i>E</i>₀ value of 3.65 ± 0.10 eV and Δ<i>S</i>^‡_600 K = 83 ± 10 J K^–1 mol^–1

Comparing Femtosecond Multiphoton Dissociative Ionization of Tetrathiafulvene with Imaging Photoelectron Photoion Coincidence Spectroscopy

In this paper we describe femtosecond photoionization and the imaging photoelectron photoion coincidence spectroscopy of tetrathiafulvene, TTF. Femtosecond photoionization of TTF results in the absorption of up to twelve 808 nm photons leading to ion internal energies up to 12.1 eV as deduced from the photoelectron spectrum. Within this internal energy a variety of dissociation channels are accessible. In order to disentangle the complex ionic dissociation, we utilized the imaging photoelectron photoion coincidence (iPEPICO) technique. Above the dissociation threshold, iPEPICO results show that the molecular ion (<i>m</i>/<i>z</i> = 204) dissociates into seven product ions, six of which compete in a 1.0 eV internal energy window and are formed with the same appearance energy. Ab initio calculations are reported on the possible fragment ion structures of five dissociation channels as well as trajectories showing the loss of C₂H₂ and C₂H₂S from high internal energy TTF cations. A three-channel dissociation model is used to fit the PEPICO data in which two dissociation channels are treated as simple dissociations (one with a reverse barrier), while the rest involve a shared barrier. The two lower energy dissociation channels, <i>m</i>/<i>z</i> = 146 and the channel leading to <i>m</i>/<i>z</i> = 178, 171, 159, 140, and 127, have <i>E</i>₀ values of 2.77 ± 0.10 and 2.38 ± 0.10 eV, respectively, and are characterized by Δ<i>S</i>^‡_600 K values of −9 ± 6 and 1 ± 6 J K^–1 mol^–1, respectively. Competing with them at higher internal energy is the cleavage of the central bond to form the <i>m</i>/<i>z</i> = 102 fragment ion, with an <i>E</i>₀ value of 3.65 ± 0.10 eV and Δ<i>S</i>^‡_600 K = 83 ± 10 J K^–1 mol^–1