No abstract

SUMMARYThe number of infective centres which were established successfully following the manual inoculation of French bean leaves with tobacco necrosis virus strain D (TNVD) or with TNVD RNA, decreased with increasing temperature between 13 and 30 °C. At 3o °C or above, primary and probably also secondary infections could not be established, though it is likely that a limited amount of virus RNA and nucleoprotein was produced at 3o °C in cells in which infection had been established previously at 23 °C. During the first day after inoculation, 23 °C was optimal for virus accumulation. Between 23 and 3o °C the rate at which lesions increased in diameter decreased with increasing temperature. The inhibitory effect of supraoptimal temperatures on the establishment of infection may be due to degradation of the infective entity by ribonuclease(s).

SUMMARYThe sedimentation coefficients of tobacco necrosis virus strain D (TNV•) in sodium phosphate at pH 5 and pH 7 are io4S and 97S respectively. The change in sedimentation coefficient between pH 5 and 7 is fully reversible and the decrease on transfer to pH 7 is unaffected by the presence of Mg 2+. TNVD is disrupted byBacillus subtilis protease at pH 7"5 but not at pH 5; ribonuclease neither disrupts virions nor destroys the infectivity of TNVD at either pH 7"5 or pH 5. Virions are markedly unstable at alkaline pH but the effectiveness with which different buffers dissociate TNVD varies. Virus is largely resistant to dissociation by I M-NaC1, i M-urea, io M-ethanediol and I% sodium dodecyl sulphate (SDS) at or below pH 6 and is largely susceptible to dissociation by these agents at or above pH 7. Our results suggest that as the pH is lowered some non-covalent bonds important for virion stability may be formed and/or some electronic repellent interactions causing virion instability may be weakened.