Pathogen-derived methods for improving resistance of transgenic plums (Prunus domestica L.) for Plum pox virus infection

Plum pox virus (PPV), the causal agent of Sharka disease, is considered to be one of the most serious pathogens of stone fruits including apricots, plums and peaches. This disease is of particular concern in central and southern Europe, the Mediterranean areas and North America. The transformation of plum with viral genes, such as coat protein, can provide virus resistant varieties or gene resources for breeding new resistant varieties. In the current study we report the evaluation of two technologies for producing plants resistance to PPV, one based on co-suppression and another on RNA-silencing. Two gene constructs were evaluated; the binary vector pCamPPVcp that contained the selective hpt gene and ppv-cp gene in sense-orientation (driven by double 35S promoter) and vector pCamPPVRNAi that contained self-complementary fragments of gene ppvcp (698bp) driven by double 35S promoter and the hpt and gus genes.The fragments of the ppv-cp gene in pCamPPVRNAi were separated by a pdk-intron to produce a “hairpin” RNA structure in antisense-sense orientation. Seven independent transgenic lines with the sense-oriented ppv-cp gene and five transgenic lines with inverted repeats of the ppv-cp gene fragment were produced. The accumulation of coat protein in five pCamPPVcp lines was confirmed by Western blotting. Transgenic shoots were rooted and acclimatized to the greenhouse. After grafting with PPV infected buds PPV-CP was detected by Western blotting in all control and pCamPPVcp transformed plants whereas no PPV coat protein were observed in samples from plants transformed with the pCamPPVRNAi “hairpin” construct. These preliminary results confirmed the efficiency of the RNAi strategy for producing virus resistant plants in general and PPV resistant stone fruits in particular.Keywords: RNA interference, PPV, transformation, coat protein, Prunus domestic

Thermodynamics of Two - Band Superconductors: The Case of MgB2_{2}

Thermodynamic properties of the multiband superconductor MgB$_{2}$ have often been described using a simple sum of the standard BCS expressions corresponding to $\sigma$- and $\pi$-bands. Although, it is \textit{a priori} not clear if this approach is working always adequately, in particular in cases of strong interband scattering. Here we compare the often used approach of a sum of two independent bands using BCS-like $\alpha$-model expressions for the specific heat, entropy and free energy to the solution of the full Eliashberg equations. The superconducting energy gaps, the free energy, the entropy and the heat capacity for varying interband scattering rates are calculated within the framework of two-band Eliashberg theory. We obtain good agreement between the phenomenological two-band $\alpha$-model with the Eliashberg results, which delivers for the first time the theoretical verification to use the $\alpha$-model as a useful tool for a reliable analysis of heat capacity data. For the thermodynamic potential and the entropy we demonstrate that only the sum over the contributions of the two bands has physical meaning.Comment: 27 pages, 10 figures, 1 table, submitted to Phys. Rev.

Infrared and optical properties of pure and cobalt-doped LuNi_2B_2C

We present optical conductivity data for Lu(Ni$_{1-x}$Co$_x$)$_2$B$_2$C over a wide range of frequencies and temperatures for x=0 and x=0.09. Both materials show evidence of being good Drude metals with the infrared data in reasonable agreement with dc resistivity measurements at low frequencies. An absorption threshold is seen at approximately 700 cm-1. In the cobalt-doped material we see a superconducting gap in the conductivity spectrum with an absorption onset at 24 +/- 2 cm-1 = 3.9$ +/- 0.4 k_BT_c suggestive of weak to moderately strong coupling. The pure material is in the clean limit and no gap can be seen. We discuss the data in terms of the electron-phonon interaction and find that it can be fit below 600 cm-1 with a plasma frequency of 3.3 eV and an electron-phonon coupling constant lambda_{tr}=0.33 using an alpha^{2}F(omega) spectrum fit to the resistivity.Comment: 10 pages with 10 embedded figures, submitted to PR

The oxygen isotope effect in the ab-plane reflectance of underdoped YBa_2Cu_3O_{7-delta}

We have measured the effect of oxygen isotope substitution on the ab-plane reflectance of underdoped YBCO. The frequency shift of the transverse optic phonons due to the substitution of O-16 by O-18 yields an isotope effect of the expected magnitude for copper-oxygen stretching modes with alpha=0.5 +- 0.1. The reflectance shoulder at 400 - 500 cm^-1 shows a much smaller exponent of alpha=0.1 +- 0.1 in the normal state and alpha=0.23+- 0.1 in the superconducting state. These observations suggest that the shoulder is of electronic origin and not due to a phonon mode as has been suggested recently.Comment: 4 pages 2 figure