Carrot mottle, a persistent aphid-borne virus transmissible by inoculation of sap, lost infectivity when sap was diluted 10, heated for 10 min. at 70°, or stored at room temperature for 9 to 24 hr. Leaf extracts made using phenol contained infective RNA. Infectivity was abolished from leaf extracts by treatment with di-ethyl ether, chloroform or other organic solvents. Partially purified preparations, made by clarification with bentonite, followed by chromatography on calcium phosphate (brushite) columns and sucrose density gradient centrifugation, contained approximately spherical particles about 50 nm. in diameter. After equilibrium sedimentation in caesium chloride gradients, infectivity was found in fractions of density 1.14 to 1.17 g./ml., with a maximum at 1.154 g./ml. Ultrathin sections of infected leaves revealed approximately spherical particles about 50 mµ in diameter in the cell vacuoles associated with the tonoplast. Some particles seemed in process of budding from the membrane. The particles seem unique among known plant viruses but resemble those of some viruses of vertebrates; they probably contain lipid. The cryptogram for carrot mottle is therefore /*:*/*:.


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