Purification, serological relationships and some characteristics of plum line-pattern virus

Plum line-pattern virus (PLV) was purified by homogenizing inoculated leaves of Nicotiana megalosiphon in 0·02 M phosphate buffer, pH 8·0 (1·5 ml/g leaf), containing 0·02 M 2-mercaptoethanol. The homogenate was centrifuged at low speed and the supernatant liquid was clarified by adjusting the pH to 4·8 with 0·1 M citric acid. The green coagulum was removed by centri-fugation and the extract adjusted to pH 6·5. After concentrating the virus by high-speed centrifugation, remaining host protein was precipitated with the gamma-globulin fraction of antiserum to N. megalosiphon protein. Purification was completed with two cycles of high- and low-speed centrifugation. Purified PLV had an A₂₆₀/A₂₈₀ ratio of c. 1·7 and formed two zones when centrifuged in density gradients at pH 6·0–7·0. The virus was about 30 mμ in diameter in negatively stained preparations. The particles were easily disrupted. PLV was closely serologically related to cultures of plum line-pattern virus from other areas, but no relationship was found to apple mosaic, Prunus necrotic ringspot or prune dwarf viruses, or to a plum line-pattern virus from Denmark.