Visual representation by atomic force microscopy (AFM) of tomato spotted wilt virus ribonucleoproteins

Atomic force microscopy (AFM) allows the observation of biological material without fixation procedures. Here we present AFM images of ribonucleoprote ins (nucleocapsids) derived from a plant infecting RNA virus (tomato spotte d wilt virus, TSWV), which have been recorded in contact mode. The nucleoca psids, prepared from systemically infected leaves of tobacco, were spreaded on a glass surface and dried in air, and appeared as regularly formed ring s, resembling the proposed pseudocircular and panhandle structure of encaps idated genomic RNA. Average values between 1300 and 2200 nm of nucleocapsid lengths could be related to dimensions estimated by electron microscopy, t hereby validating a filamentous configuration of the TSWV ribonucleoprotein s. However, to our knowledge regular, ring-like forms of ribonucleoproteins have not been obtained by electron microscopy, which rather showed an amor phous structure of the virus particles. Hence, the AFM approach provides a starting point for further detailed studies on TSWV ribonucleoprotein compl exes.