Transgenic tobacco plants (Nicotiana tabacum cv. SR1) expressing extracellular pancreatic ribonuclease from Bos taurus and characterized by an increased level of ribonuclease activity in leaf extracts were challenged with tobacco mosaic virus. The transgenic plants exhibited a significantly higher level of protection against the virus infection than the control non-transformed plants. The protection was evidenced by the absence (or significant delay) of the appearance of typical mosaic symptoms and the retarded accumulation of infectious virus and viral antigen. These results demonstrate that modulation of extracellular nuclease expression can be efficiently used in promoting protection against viral diseases.

The protective effect of polysaccharide carrageenan on the damaging effect of endotoxins of gram-negative bacteria was studied in vivo and in vitro. Carrageenan increased mouse resistance to the toxic effect of LPS. The degree of protection depended on polysaccharide concentration and administration time and route. Pretreatment of donor platelets with carrageenan reduced their aggregation activity caused by cooperative effect of LPS and ADP.

The isolates of potato virus X causing disease symptoms of different severity in thorn-apple plants (Datura stramonium L.) can be categorized in terms of the increase in antigen accumulation, as follows: strong, medium and weak. Extracts from leaves of healthy plants and of those infected with separate virus isolate did not differ in set of acidic pathogenesis-related (PR) proteins as shown by discontinuous non-denaturating polyacrylamide gel electrophoresis. Within 2 weeks after inoculation the total content of PR-proteins in leaves of plants infected with weak or medium isolates was higher than in the healthy ones but after 3 weeks these differences became negligible. The plants infected with the strong isolate had higher total content of PR-proteins than healthy plants and plants infected with weak or medium isolates during 3 weeks. It is proposed that the greater the damage to the plant caused by virus infection, the more PR-proteins are accumulated.

The destructive action of Gram-negative bacteria lipopolysaccharides and their complexes with ehitosan, a natural polycation, was compared in vivo and in vitro. Lipopolysaceharides in complex with ehitosan modified the biological properties of endotoxin, among other things, reducing its toxic and aggregation effects.

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