Chicory yellow mottle virus (CYMV), an isometric plant virus containing RNA, is degraded when infected tissues or purified virus suspensions are frozen and thawed. Virus preparations obtained from frozen tissues contain substantial proportions of empty capsids (top component) which increase in relation to the length of time for which plant material is kept frozen before processing. Virus suspensions frozen after purification behave similarly in that, after exposure to - 25 °C, they are almost totally dissociated into RNA and protein shells. Most of the dissociation takes place within the first 10 min of freezing at - 25 °C. Lower temperatures (- 78 °C and - 196 °C) are less effective in inducing virus dissociation.

The extent of dissociation varies with the chemical composition of the suspending medium. Na-acetate and NaCl confer complete protection from freezing injury, whereas no protection is given by water and (K-Na)phosphate buffer plus NaCl. (K-Na)phosphate alone, (Na-Na)phosphate and KCl afford only partial protection.

It is possible that several factors, i.e. increased molarity and lowering of pH of solutions at the eutectic point and removal of water associated with protein macromolecules have a bearing in explaining the influence of the various chemicals.


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