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Microbiology Society logo - Volume 15, Issue 1, 1956

Volume 15, Issue 1

Volume 15, Issue 1, 1956

  • Articles

      • The Infectivity of Extracts made from Leaves at Intervals after Inoculation with Viruses

        https://doi.org/10.1099/00221287-15-1-210

        SUMMARY: When leaves are macerated at intervals after being inoculated with plant viruses, the infectivity of the extracts obtained decreases with increasing time until newly produced virus becomes detectable. Infectivity does not start to increase until approximately twice the time apparently needed for virus to multiply in the epidermis and spread from there to the mesophyll. Epidermal cells infected by inoculation seem to produce too few virus particles to be detected by infectivity tests or else the first-formed particles are unstable

        No evidence was obtained, with Rothamsted tobacco necrosis virus (RTNV) in leaves of tobacco and French bean, that the initial decrease in infectivity occurs because of changes in virus particles that succeed in infecting and causing lesions. If such changes occur they are obscured by the inactivation of particles that do not multiply and cause lesions. Washing inoculated leaves removes 95 % of the inoculated virus, but only slightly decreases the numbers of infections, and adding ‘Celite’ to the inoculum greatly increases the numbers of lesions without increasing the amount of virus retained by washed leaves. Neither washing nor adding ‘Celite’ to the inoculum affects the rate at which the infectivity of successive extracts from inoculated leaves decreases. Infectivity continues to decrease after virus appears to have multiplied in and spread from the epidermis.

        Cells of that are infected by tobacco mosaic virus spreading from inoculated epidermal cells die only a few hours after the infectivity of leaf extracts starts to increase: few cells seem to become infected from virus produced in these secondarily infected cells and, at 20°, infectivity reaches a maximum in 2 days. Mesophyll cells of French bean leaves at 22° seem to synthesize new RTNV particles within 5 hr. of becoming infected from the epidermis and to continue synthesizing for another 30 hr., when they probably contain about 10virus particles/cell. Although the cells then die, the virus spreads to further cells and the infectivity of leaf extracts increases for at least five days.

    • The Statistical Distribution of Phenotypically Modifiable Particles and Host-ranǵe Mutants in Populations of Vi-phage II

      https://doi.org/10.1099/00221287-15-1-225

      SUMMARY: The distribution of adapted particles of Vi-phage II has been examined. Fluctuation tests in which phage A was grown for a single cycle in type A of showed that phage E1 particles conformed to a Poisson distribution in a series of small samples and cannot, therefore, be spontaneous mutants of phage A. Particles of phage D1, on the other hand, showed a clonal distribution in a similar series of samples and are thus spontaneous host-range mutants of phage A. Phage E1 reverted to phage A during a single cycle of growth in type A organisms, which confirms that phage E1 is a phenotypic modification of phage A. In contrast, phage D1 was unaltered by a single cycle of propagation in type A organisms and its mutant nature is thus verified. Phage 29 has also been shown to be a host-range mutant of Vi-phage II. The adsorption of phage A to type E1 is lethal to the bacteria, of which only a small proportion support phage growth. The general applicability of these findings to the numerous adaptations of Vi-phage II is discussed.

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