1.11.28
CHARACTERIZATION OF UNUSUAL VIRUS PARTICLES INFECTING SENNA BIFLORA, A LEGUME SPECIES NATIVE TO LOWLAND TROPICAL AREAS

E MARYS1, O CARBALLO1 and ML IZAGUIRRE1

1Instituto Venezolano de Investigaciones Cientificas, Laboratorio de Biotecnologia y Virologia Vegetal, Centro de Microbiologia y Biologia Celular, Caracas, Venezuela

Background and objectives
The present investigation was undertaken to analyse the biological and physicochemical properties of virus particles found infecting the native legume Senna biflora under natural conditions. Infected plants were dwarfed, with bright yellow to pale green mosaic in the leaves. Partial purification of the agent causing these symptoms revealed peculiar thread-like virus particles, similar in size to those of members of the genus Closterovirus.

Results and conclusions
Long, flexuous, closterovirus-like particles were isolated from field-infected S. biflora plants. Particles were 1650-2000 nm long, and banded at a density equivalent to 1.35 g/ml in cesium chloride equilibrium gradients. Two major protein species with sizes of 35 and 31 kDa were resolved from dissociated virions, which encapsidated a single-stranded RNA molecule ca 7.2 kb. Crude extracts from infected leaves, as well as purified virions, failed to infected a wide range of plant species belonging to the following families: Asteraceae, Balsaminaceae, Brassicaceae, Caryophyllaceae, Cucurbitaceae, Chenopodiaceae, Graminae, Labiatae, Moraceae, Nyctaginaceae, Rosaceae and Solanaceae, when inoculated by mechanical means. Ultrastructural examination of thin sections of virus-infected leaves showed cytoplasmic alterations similar to those induced by members of the closterovirus group [1]. Numerous small membrane-bound vesicles were found in phloem parenchyma cells, containing fine, densely stained fibrillar material. Three virus-specific dsRNA species of 9.4, 8.5 and 4.7 kbp were detected in extracts of infected S. biflora plants. This appears to be the first report of closterovirus-like particles infecting a native legume, and its properties distinguish it from all previously reported plant closterovirus. Therefore, serological and molecular characterization of the isolated virus are under way, in order to better understand its taxonomic position.

References
1. Coffin RS, Coutts RHA, 1993. Journal of General Virology 74, 1475-1483.