Some Effects of Salicylate on Plant Viruses

Abstract

DURING an investigation into the effects of various anions on the precipitation of the paracrystalline solid phase of tobacco mosaic virus nucleoprotein (Marmor tabaci, var. vulgare, Holmes) from its solution in water, the salicylate ion was found to behave differently from other anions. For each salt there was found a critical concentration at and above which the virus was precipitated from solution in the form of spontaneously birefringent microtactoids or fibres. The white precipitate of virus nucleoprotein is still fully infective and may be redispersed to give a clear solution by mechanical agitation or dilution as described previously1. However, the precipitate produced by solutions of potassium salicylate at concentrations above 0.46M. is very different in character from that obtained with other salts. It consists of an insoluble, amorphous, white, granular solid deposit of denatured protein. Mechanical agitation or dilution does not cause re-solution. At the same time the virus loses its infectivity irreversibly. The accompanying graph illustrates the rate of inactivation of a 0.2 per cent solution of the pure virus by 1.0M. potassium salicylate at pH. 7 and 30° C. The straight line nature of curve Bindicates that the rate of inactivation is logarithmic. The rate of inactivation is greater the greater the concentration of salicylate and is markedly influenced by the temperature. With solutions of salicylate of the order of half molar there is only a partial inactivation, and a steady state appears to be set up after a few hours. At a concentration of 1.0M. there is no loss of infectivity, of stream double refraction or solubility after a contact of forty-eight hours. Denaturation, loss of stream double refraction and of infectivity all run parallel.