Isopycnic centrifugation of plant viruses in Nycodenz density gradients

Isopycnic centrifugation of plant viruses in density gradients prepared from a new non-ionic medium (Nycodenz) was investigated. Particle density of luteo-, tymo-, nepo-, cocksfoot mild mosaic, tobamo-, hordei-like, potex- and potyviruses in buffered solutions of Nycodenz ranged between 1.23 and 1.28 g/ml and did not strictly reflect their nucleic acid and protein composition. Isopycnic centrifugation of several partially purified viruses yielded preparations which were pure by electron microscopy and, when used as immunogens in rabbit or hen, gave antisera with low titers of antibodies against host plant antigens, as required for enzyme immunoassays. A preparation of purified potato leafroll virus contained a single dominant protein corresponding to the viral coat protein. It is concluded that isopycnic centrifugation in Nycodenz density gradients is particularly useful for the purification and analysis of plant viruses which are unstable in cesium chloride solutions, such as the luteoviruses, and preferable to zonal centrifugation in sucrose density gradients for the purification of rod-shaped multipartite viruses or viruses which aggregate.