SUMMARY: Purified preparations of the Rothamsted tobacco necrosis virus made by sedimenting the virus from freshly expressed sap lose infectivity slowly at O and rapidly at 18°. Stable infective preparations can be made by ultracentrifugation provided the sap is first frozen or allowed to age; unstable preparations can be stabilized by prolonged centrifugation at 8000 , or by incubation with citrate and azide. Stable virus preparations lose their infectivity when exposed to the material that sediments from leaf sap centrifuged at 4000–8000 This inactivation demands air and is prevented by the presence of azide, but when the sedimented material is kept in air at 0° for some hours a low-molecular weight substance separates from it. and this inactivates the virus whether or not air or azide are present. The material sedimented from the sap of uninfected tobacco leaves, or leaves infected with tobacco mosaic virus, inactivates virus less readily than does material from leaves infected with tobacco necrosis or tobacco ringspot virus. The sediments inactivate tobaceo ringspot but not tobacco mosaic virus. The nature of the inactivating substance made by the sediments is unknown, but aldehydes and derivatives of ascorbic acid have comparable effects. Inactivated virus preparations are still serologically active and resemble active ones in all other properties studied.


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