Extracellular vesicles and their convergence with viral pathways

Extracellular vesicles (microvesicles), such as exosomes and shed microvesicles, contain a variety of molecules including proteins, lipids, and nucleic acids. Microvesicles appear mostly to originate from multivesicular bodies or to bud from the plasma membrane. Here, we review the convergence of microvesicle biogenesis and aspects of viral assembly and release pathways. Herpesviruses and retroviruses, amongst others, recruit several elements from the microvesicle biogenesis pathways for functional virus release. In addition, noninfectious pleiotropic virus-like vesicles can be released, containing viral and cellular components. We highlight the heterogeneity of microvesicle function during viral infection, addressing microvesicles that can either block or enhance infection, or cause immune dysregulation through bystander action in the immune system. Finally, endogenous retrovirus and retrotransposon elements deposited in our genomes millions of years ago can be released from cells within microvesicles, suggestive of a viral origin of the microvesicle system or perhaps of an evolutionary conserved system of virus-vesicle codependence. More research is needed to further elucidate the complex function of the various microvesicles produced during viral infection, possibly revealing new therapeutic intervention strategies

Habitat characteristics and the effect of various nutrient solutions on growth and mineral nutrition of Arnica montana L. grown on natural soil

Arnica montana, one of the character species of the replacement plant community Violion caninae on sandy acid humic podzol, is declining in the Netherlands since 1950. Locally, it is even extinct. This process of decline may be attributed to (i) autonomic succession; (ii) increased rate of acidification of the soil and/or (iii) change in competitive relations among Arnica and more productive plant species, such as the successive dominant Deschampsia flexuosa. This paper examines the last two hypothesized factors, supposedly being regulated by atmospheric input of N-input, by (a) describing the habitat characteristics of a seemingly still healthy individual-rich population of Arnica and (b) growing Arnica and Deschampsia in mixed humic podzol soil (mainly A1 horizon) fertilized with variously-composed nutrient solutions in order to assess the nutrient supplying capacity of the podzol soil and species-specific nutritional demands related to their respective growth capabilities. The results suggest that an increased rate of soil acidification yielding extra supply of ionic Al and Mn is presumably of less importance. The implications of growth rate differences among Arnica and Deschampsia as related to their nutritional demands are likely far more important. Arnica grows more slowly than Deschampsia in fertilized humus podzol. The latter species has a much more efficient use of nutrients. Furthermore, both species differ in K-nutrition if NH4+ is the dominant N-source, a situation normally occurring in acid podzolic soils. Deschampsia processes the capability to adapt its metabolic nutrition (avoiding nutritional imbalances) to a wide range of nutrient supplies thereby maintaining a rather constant level of growth. Arnica, on the contrary, lacks this capability. These results are discussed in the framework of competitive relations among co-occurring plant species in the plant community Violion caninae. It is concluded that maintenance of Arnica and likely other character species of that alliance - all characterized by a low growth rate - will only be achieved when the plant community is properly managed by trampling, mowing or light levels of grazing (low stocking rate). Of prime importance is to maintain a low and relatively open vegetation structure at a relatively low level of nutrient supply

Nutrient limitations in wet, drained and rewetted fen meadows : evaluation of methods and results

Restoration of wet grassland communities on peat soils involves management of nutrient supply and hydrology. The concept of nutrient limitation was discussed as well as its interaction with drainage and rewetting of severely drained peat soils. Different methods of assessing nutrient limitation were compared and the type and extent of nutrient limitation were determined for several wet grassland communities. It was concluded that a full-factorial field fertilisation experiment is the most preferable method. Plant tissue analyses and soil chemical analyses were considered less suitable, although they may provide helpful additional information. Fertilisation experiments in the laboratory using sods or using test plants appear to be the proper means to study mechanisms or processes, but have a restricted predictive value for field situations. Generalising the results, it seems that many relativily undisturbed grassland plant communities on peaty soils are characterised by N limitation. Phosphate limitation for vegetation on peat soils is mainly observed in specific circumstances such as extreme calcium richness, high concentrations of Fe or as a result of drainage or long-term hay cropping. The latter two may also cause K limitation. Rewetting is regarded as a prerequisite in restoring wet grassland communities. Further restoration measures to influence nutrient availability depend on aims of the management and the individual site conditions