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The effect of Potato virus Y NTN (PVY) infection upon photosynthesis was analysed in transgenic Pssu-ipt tobacco overproducing endogenous cytokinins in comparison with control, nontransgenic Nicotiana tabacum plants. The course of the infection from the early to the late stage was monitored by measuring of photosynthetic gas exchange and fast chlorophyll (Chl) a fluorescence induction kinetics. Leaf photosynthesis was also analysed using Chl fluorescence imaging (Chl-FI). From the different fluorescence parameters obtained using Chl-FI, the nonphotochemical quenching (NPQ) proved to be the most useful parameter to assess the effect of PVY infection. On the other hand, Chl-FI was found to be inapplicable for any presymptomatic detection of PVY infection in tobacco. The lower accumulation of the virus was found in transgenic plants and corresponded also with the presence of visible symptoms of PVY infection. The net photosynthetic rate (P N ), transpiration rate (E), and stomatal conductance (g s ) significantly decreased with the progress of the infection in both control plant types and transgenic rooted plants, while transgenic grafts were much less affected. The analysis of the Chl fluorescence transient revealed higher number of silent dissipative reaction centres, higher nonphotochemical dissipation, and significantly lower performance index, PI (abs) , in the healthy transgenic grafts. Chl-FI also confirmed significantly higher NPQ in transgenic grafts.

Transient expression of foreign genes based on plant viral vectors is a suitable system for the production of relevant immunogens that can be used for the development of a new generation of vaccines against a variety of infectious diseases. In the present study the epitope derived from HPV-16 L2 minor capsid protein (amino acids 108-120) was expressed from Potato virus X (PVX)-based vector pGR106 as N- or C-terminal fusion with the PVX coat protein (PVX CP) in transgenic Nicotiana benthamiana plants. The fusion protein L2 108-120-PVX CP was successfully expressed in plants at a level of 170 mg/kg of fresh leaf tissue. The C-terminal fusion protein PVX CP- L2 108-120 was expressed using mutated vector sequence to avoid homologous recombination at a level of 8 mg/kg of fresh leaf tissue. Immunogenicity of L2 108-120-PVX CP virus-like particles was tested after immunization of mice by subcutaneous injection or tattoo administration. In animal sera the antibodies against the PVX CP and the L2 108-120 epitope were found after both methods of vaccine delivery.

The gene encoding the triple gene block protein 1 (TGBp1) of Potato mop-top virus (PMTV) was cloned into expression vector pQE32 tagging the protein with 6xHis on the N-terminus. When the gene was enshortened on its 3¢-end by two different restriction digestions, efficient and high yield bacterial expression was achieved in both cases, as shown by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot. One of these two constructs was used for raising rabbit polyclonal antibodies. The obtained sera and antibodies were tested for the detection of PMTV in laboratory host Nicotiana benthamiana and natural host Solanum tuberosum by enzyme-linked immunosorbent assay (ELISA) as well as by Western blots. The obtained antisera are more suitable for Western blot analysis of infected plants than for ELISA.

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