PURIFICATION AND ELECTRON MICROSCOPY OF POTATO LEAFROLL VIRUS

A procedure for purification of potato leafroll virus (PLRV) from its plant host was improved. An extract from diseased Physalis floridana plants was emulsified with an n-butanol-chloroform mixture. The virus in the aqueous phase was concentrated by centrifugation, the pellet was resuspended in 0.01 M phosphate buffer and subjected to emulsification with fluorocarbon (Daifron S-3). The virus, concentrated by additional centrifugation from the aqueous phase, was fractionated in a sucrose density-gradient column. When the final preparation was suspended in 0.01 M phosphate buffer at pH 6.0 and negatively stained by 2% PTA at pH 5.5, the resulting suspension contained uniform particles 25 mμ in diameter (side by side) and with more or less hexagonal profiles. High infectivity was associated with the zone containing these particles. Preparations obtained from healthy plants and virus-free aphids by the same purification procedure did not contain these particles. Examination of ultrathin sections of the infected P. floridana and Datura stramonium plants by electron microscopy indicated that the virus occurred in some of the phloem cells. When PLRV particles were measured in crystalline array in ultrathin sections the size obtained (23 mμ diameters) agreed approximately with that of the purified virus particles. © 1969.