Biolistic transfection of plants by infectious cDNA clones of Plum pox virus

Plant biolistic transfection by two Plum pox virus (PPV) infectious cDNA clones (strains PPV-M and PPV-D) using the gene gun apparatus PDS 1000-He was optimized. Nicotiana benthamiana plants were germinated on Petri dishes with MS growth medium. At the age of four weeks the plants were subjected to biolistic transfection and three days later were transplanted into common soil substrate. The plant survival after transplantation was about 70 %, the transfection efficiency was over 80 % (compared to 6 – 10 % efficiency reached by mechanical plant inoculation). The plants showed typical PPV symptoms two weeks post transfection. The virus presence was confirmed by immunoblotting, RTPCR, as well as by successful transmission by sap to healthy plants. The co-transfection of N. benthamiana plants by PPV-M and PPV-D led to mixed infections with PPV-D strongly prevalent. We assumed the properties of cDNA constructs responsible for this behaviour.Keywords: gene gun, PPV strains, immunoblottin

Off-equatorial orbits in strong gravitational fields near compact objects

Near a black hole or an ultracompact star, motion of particles is governed by strong gravitational field. Electrically charged particles feel also electromagnetic force arising due to currents inside the star or plasma circling around. We study a possibility that the interplay between gravitational and electromagnetic action may allow for stable, energetically bound off-equatorial motion of charged particles. This would represent well-known generalized Stormer's 'halo' orbits, which have been discussed in connection with the motion of dust grains in planetary magnetospheres. We demonstrate that such orbits exist and can be astrophysically relevant when a compact star or a black hole is endowed with a dipole-type magnetic field. In the case of Kerr-Newman solution, numerical analysis shows that the mutually connected gravitational and electromagnetic fields do not allow existence of stable halo orbits above the outer horizon of black holes. Such orbits are either hidden under the inner black-hole horizon, or they require the presence of a naked singularity.Comment: 16 pages, 7 figures, accepted in Class. Quantum Grav. (2008

Gravitating discs around black holes

Fluid discs and tori around black holes are discussed within different approaches and with the emphasis on the role of disc gravity. First reviewed are the prospects of investigating the gravitational field of a black hole--disc system by analytical solutions of stationary, axially symmetric Einstein's equations. Then, more detailed considerations are focused to middle and outer parts of extended disc-like configurations where relativistic effects are small and the Newtonian description is adequate. Within general relativity, only a static case has been analysed in detail. Results are often very inspiring, however, simplifying assumptions must be imposed: ad hoc profiles of the disc density are commonly assumed and the effects of frame-dragging and completely lacking. Astrophysical discs (e.g. accretion discs in active galactic nuclei) typically extend far beyond the relativistic domain and are fairly diluted. However, self-gravity is still essential for their structure and evolution, as well as for their radiation emission and the impact on the environment around. For example, a nuclear star cluster in a galactic centre may bear various imprints of mutual star--disc interactions, which can be recognised in observational properties, such as the relation between the central mass and stellar velocity dispersion.Comment: Accepted for publication in CQG; high-resolution figures will be available from http://www.iop.org/EJ/journal/CQ

Transcriptomic Analysis of <em>Prunus domestica</em> Undergoing Hypersensitive Response to <em>Plum Pox Virus</em> Infection

Plum pox virus (PPV) infects Prunus trees around the globe, posing serious fruit production problems and causing severe economic losses. One variety of Prunus domestica, named 'Jojo', develops a hypersensitive response to viral infection. Here we compared infected and non-infected samples using next-generation RNA sequencing to characterize the genetic complexity of the viral population in infected samples and to identify genes involved in development of the resistance response. Analysis of viral reads from the infected samples allowed reconstruction of a PPV-D consensus sequence. De novo reconstruction showed a second viral isolate of the PPV-Rec strain. RNA-seq analysis of PPV-infected 'Jojo' trees identified 2,234 and 786 unigenes that were significantly up- or downregulated, respectively (false discovery rate; FDR≤0.01). Expression of genes associated with defense was generally enhanced, while expression of those related to photosynthesis was repressed. Of the total of 3,020 differentially expressed unigenes, 154 were characterized as potential resistance genes, 10 of which were included in the NBS-LRR type. Given their possible role in plant defense, we selected 75 additional unigenes as candidates for further study. The combination of next-generation sequencing and a Prunus variety that develops a hypersensitive response to PPV infection provided an opportunity to study the factors involved in this plant defense mechanism. Transcriptomic analysis presented an overview of the changes that occur during PPV infection as a whole, and identified candidates suitable for further functional characterization