Properties and structure of lettuce necrotic yellows virus

Abstract

Lettuce necrotic yellows virus (LNYV) loses infectivity less rapidly in partially purified preparations than in leaf sap. Infectivity is greatly decreased or abolished by treatment with chloroform, diethyl ether, or water-saturated phenol. Isolates of LNYV from widely separated parts of Australia are antigenically similar. Partially purified preparations from lettuce contain one major component with a sedimentation coefficient of 943 ± 16 S, a buoyant density in sucrose solution of about 1.20 g/ml, and bacilliform or bullet-shaped particles 66 mμ wide and most commonly about 227 mμ long. When treated with uranyl acetate or uranyl formate, the particles appear to have an outer coat loosely enclosing a tubular inner body showing cross-banding at intervals of 4.5 mμ. In sucrose density-gradients, infectivity is associated with the zone containing these particles. Two other types of particle are also seen only in preparations from LNYV-infected lettuce or Nicotiana glutinosa L., one probably the empty outer coat and the other almost spherical, probably a distorted form of the bacilliform particle. Preparations of a virulent isolate of LNYV cultured in N. glutinosa contain, in addition to the 943 S component, a second which sediments about 1.4 times faster but has the same buoyant density, is infective, and is antigenically similar to the 943 S component. Electron microscopy suggests that it consists of particles aggregated in pairs or threes.