Ashok Jain

Metabolic engineering of an alternative pathway for ascorbic acid biosynthesis in plants.

Plants and most animals can synthesize their own L-ascorbic acid (vitamin C), but a mutation in the L-gulono-γ-lactone oxidase gene in the primate lineage makes it necessary for humans to acquire this vital compound from their diet. Despite the fact that plants and animals synthesize ascorbic acid via different pathways, transgenic tobacco and lettuce plants expressing a rat cDNA encoding L-gulono-γ-lactone oxidase accumulated up to seven times more ascorbic acid than untransformed plants. These results demonstrate that basal levels of ascorbic acid in plants can be significantly increased by expressing a single gene from the animal pathway.

Manganese-induced oxidative DNA damage in neuronal SH-SY5Y cells: Attenuation of thymine base lesions by glutathione and N-acetylcysteine

Manganese (Mn) is an essential trace element required for normal function and development. However, exposure to this metal at elevated levels may cause manganism, a progressive neurodegenerative disorder with neurological symptoms similar to idiopathic Parkinsons disease (IPD). Elevated body burdens of Mn from exposure to parental nutrition, vapors in mines and smelters and welding fumes have been associated with neurological health concerns. The underlying mechanism of Mn neurotoxicity remains unclear. Accordingly, the present study was designed to investigate the toxic effects of Mn(2+) in human neuroblastoma SH-SY5Y cells. Mn(2+) caused a concentration dependent decrease in SH-SY5Y cellular viability compared to controls. The LD50 value was 12.98 μM Mn(2+) (p<0.001 for control vs. 24h Mn treatment). Both TUNEL and annexin V/propidium iodide (PI) apoptosis assays confirmed the induction of apoptosis in the cells following exposure to Mn(2+) (2 μM, 62 μM or 125 μM). In addition, Mn(2+) induced both the formation and accumulation of DNA single strand breaks (via alkaline comet assay analysis) and oxidatively modified thymine bases (via gas chromatography/mass spectrometry analysis). Pre-incubation of the cells with characteristic antioxidants, either 1mM N-acetylcysteine (NAC) or 1mM glutathione (GSH) reduced the level of DNA strand breaks and the formation of thymine base lesions, suggesting protection against oxidative cellular damage. Our findings indicate that (1) exposure of SH-SY5Y cells to Mn promotes both the formation and accumulation of oxidative DNA damage, (2) SH-SY5Y cells with accumulated DNA damage are more likely to die via an apoptotic pathway and (3) the accumulated levels of DNA damage can be abrogated by the addition of exogenous chemical antioxidants. This is the first known report of Mn(2+)-induction and antioxidant protection of thymine lesions in this SH-SY5Y cell line and contributes new information to the potential use of antioxidants as a therapeutic strategy for protection against Mn(2+)-induced oxidative DNA damage.

Identification of drought-responsive transcripts in peanut (Arachis hypogaea L.)

We have used a reverse transcriptase polymerase chain reaction procedure (differential display) to identify cDNAs corresponding to transcripts affected by water stress in peanuts ( Arachis hypogaea L.). Using this method, we have identified several mRNA transcripts that are up- or down-regulated following water stress. With 21 primer combinations, a total of 1235 differential display products were observed in irrigated samples, compared to 950 differential display products in stressed samples. These products demonstrated qualitative and quantitative differences in the gene expression. The differentially expressed transcripts were collectively named PTRD (Peanut Transcripts Responsive to Drought). We have identified a total of 43 PTRD, which were significantly altered due to water stress. Slot blot analysis of 16 PTRD indicated that 12 were completely suppressed due to prolonged drought, two were down-regulated, and two were up-regulated under drought stress conditions. The 12 completely suppressed transcripts were studied further by RNA dot-blot analysis to compare their expression in drought tolerant and susceptible lines, which underwent three weeks of water stress. PTRD-1, -10, and -16 expressed for longer period in tolerant line compared to the susceptible line and can be used as molecular markers for screening peanut lines for drought tolerance.

Total (Elastic Plus Inelastic) Cross-Sections for Electron Scattering with CF4 and GeH4 Molecules at (10 ÷ 5000) eV

We report first calculations on the total (elastic plus inelastic) cross-sections for electron scattering with CF4 and GeH4 molecules in the energy range of (10 ÷ 5000) eV. For the CF4 case, our total cross-sections are compared with recent measurements. We employ a parameter-free spherical complex optical potential (SCOP) approach in which the static, exchange, polarization and absorption effects are determined from the electronic density of the target by employing multicentre near-Hartree-Fock CF4 and GeH4 wave functions. Our elastic cross-sections for the e-CF4 system are in fair agreement with recent experimental and theoretical results.

Low-energy positron collisions with CH4 and SiH4 molecules by using new positron polarization potentials

The collision of low-energy (below positronium formation threshold) positrons with methane (CH4) and silane (SiH4) molecules is investigated by employing two types of parameter-free model polarization potentials within the density functional description of the target correlation. The first potential is based on the correlation energy, in corr, of one positron in a homogeneous electron gas of the target, while the second one is a modified version of the electron correlation potential in which the exchange interaction is absent. In the asymptotic region, both types of polarization potentials have the correct analytic form (- alpha 0/2r4, where alpha 0 is the polarizability of the target). Results for the total and differential cross sections are compared with recent measurements. The authors found that the first polarization potential mentioned above, is better than the second one.

Theoretical study of low-energy electron-SiH4 collisions using exact-exchange plus parameter-free polarization potential

The authors investigate rotationally elastic, inelastic and summed processes in the e-SiH4 collisions at 0.001-20 eV. In these calculations, the electron exchange interaction is treated exactly in an iterative approach, while the target charge correlation and polarization effects are included using a parameter-free model polarization potential based on the second-order perturbation energy. The coupled integro-differential equations are set up in the one-centre-expansion scheme under the fixed-nuclei approximation. Results on the differential, integral, momentum transfer, viscosity and energy-loss cross sections are presented and compared with other available data (both theoretical and experimental). The value of the scattering length is also reported.

Differential, integral and momentum transfer cross sections for electron scattering with germane (GeH4) molecules at 1–100 eV

Abstract We report the first calculations on the differential, integral and momentum transfer cross sections for electron scattering with germane (GeH 4 ) molecules in the energy range of 1–100 eV, where results are compared with recent measurements of angular distributions. We employ a parameter-free, spherical effective potential approach in which the static, exchange and polarization terms are determined from the target charge density that is in turn evaluated from a multicenter near-Hartree-Fock GeH 4 wavefunction. Our cross sections compare very well with the measured data, particularly above 10 eV where the present scattering treatment is most likely to be valid. There is a shape resonance feature around 5 eV present both in the measured and the theoretical cross sections.

Low energy (0.01-20 eV) electron scattering from acetylene

We report elastic differential, integral and momentum transfer cross sections for the electron-C2H2 system in the energy range of 0.01-20 eV. A parameter-free model potential approach is employed under the fixed-nuclei, single-centre, and close-coupling formalism. The electron exchange interaction is treated via a modified version of the semi-classical exchange model, while the short range correlation and long range polarization effects are included under the correlation-polarization approximation. This local and non-empirical potential, for both the exchange and charge distortion effects, is very successful in describing the 2 Pi g shape-resonance phenomenon around 2 eV. Our final results for both the differential and integral cross section compare very well with recent measurements. A Ramsauer-Townsend minimum is found around 0.2 eV in the total and momentum transfer cross sections.

Electron-Scattering from Polyatomic Molecules Using a Single-Center-Expansion Formulation

Low-energy electron scattering from gaseous molecules of ever increasing complexity has already been studied for more than half a century1–3 both through experimental analysis and with the development of several theoretical treatments. Various types of experiments, in fact, have been performed in order to measure the energy and angular dependence of the magnitude of the cross sections involved in the elastic, inelastic, ionizing and dissociative processes induced by collisions of an electron with a molecule. For nearly the same period of time, reasonably successful theories have been proposed to explain the behaviour of these cross sections.2,3

A treatment of low-energy positron-CO collisions using a new parameter-free positron correlation polarisation (PCOP) potential

The author reports quite accurate calculations on the rotationally elastic, inelastic and summed differential, integral, momentum transfer and energy-loss cross sections for the positron-CO scattering below the positronium formation threshold (7.2 eV). In the body-fixed adiabatic nuclei approximation, a single-centre expansion scheme is used to solve the scattering problem in the close-coupling theory. Fully converged cross sections are obtained via the multipole-extracted adiabatic nuclei (MEAN) method. The polarisation effects are included approximately in a parameter-free way via the positron correlation polarisation (PCOP) potential proposed by the author. The PCOP model is based on the short-range correlation energy, in corr, of one positron in a homogeneous electron gas of the target. In the outside region, the in corr, is joined smoothly with the correct asymptotic form of the polarisation interaction, where they cross each other for the first time. The analytic form of in corr is derived from variational calculations including full positron-electron interactions in the Hamiltonian. The new PCOP results are compared with the authors earlier calculations based on the electron correlation polarisation (ECOP) potential and the R-matrix results of Tennyson and Morgan (1987). The PCOP total cross sections are in very good agreement with the measurements in the whole energy region considered: in particular, at very low energies (below 2 eV), where the ECOP values are in disagreement with experiment. The authors rotationally inelastic cross sections are also in good agreement with the R-matrix calculations.