Abstract
Understanding virus infection in higher plants depends heavily upon knowledge of infection in the individual cells that constitute the whole plant body. Unfortunately, however, experimental materials suitable for studying infection at the cellular level have not been available. Materials such as plants, organs, or tissues are inadequate for this purpose, because the number of cells initially infected by inoculation is extremely small and because the stage of infection in individual cells becomes random as infection spreads. The concept of one-step virus growth was introduced into virology when Ellis & Delbriick (24) devised a procedure to simultaneously inoculate large numbers of Escherichia coli cells with a bacteriophage and to eliminate the chance of secondary infection. With the cells inoculated in this way, it is possible readily to follow one complete replication cycle of a virus. Such one-step growth experiments are one of the methodological foundations of modern bacterial and animal virology. In order to realize one-step growth of plant viruses, two major requirements must be fulfilled in an experimental material: (a) a substantial proportion of cells present must be infected simultaneously and, (b) the material must consist of separated single cells to minimize the possibility of infection being spread. Both of the require ments are not fulfilled by plant cells grown either as callus or in suspension cultures (41). The leaf systems developed by NiIsson-Tillgren et al (59) and by Dawson & Schlegel (21) satisfy the first but not the second requirement, whereas the separated cells from infected leaves (I, 8, 38, 75, 94, 100) meet the second but not the first. Since plant viruses are unable to penetrate rigid plant cell walls, one way to achieve a high frequency of cell infection is to remove the walls, that is, to use cell proto plasts.
Published Version
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