Unstable variants of tobacco necrosis virus

From single lesions caused by two strains of tobacco necrosis virus variants were isolated that were unstable in sap and difficult to maintain by inoculation with sap. Extracts of leaves infected with these variants in water-saturated phenol or in 0.5 M borax pH 9.2, were 10–100 times more infective than sap. The results are consistent with the idea that the unstable variants occur in the plant largely as nucleic acid, which is destroyed by leaf ribonuclease when the leaves are ground in conditions that allow the enzyme to act. Although most of the infectivity of these variants resides in unstable particles, there are in most, if not all populations some stable particles, presumably composed of nucleoprotein, which retain their infectivity in sap and survive purification procedures. About 1 in 20 of the lesions formed by purified preparations of the two strains of tobacco necrosis virus yielded the unstable variant only. During repeated transmission in series the unstable variant did not give rise to stable ones. The satellite virus that multiplies only in leaves simultaneously infected with certain strains of tobacco necrosis virus, multiplied in leaves infected with the unstable variant, but less extensively than with the stable variant.