Studies on the Infection and the Multiplication of Plant Viruses

VI. Analysis of metabolic changes in tobacco tissue infected with cucumber mosaic virus

Abstract

Virus Invaded-cells in the infected tissues can be detected by measuring the DNA content in the nucleus. Making use of this assessment, spread of virus and metabolic changes in CMV inoculated tissue were studied.
Most cells invaded by virus were located in the epidermal tissue during the first 4 hours after inoculation. Four hours after inoculation some of the palisade cells began to be invaded with virus and 8 hours later virus-invaded cells were seen in the spongy parenchyma. Virus reached to the opposite epidermal cells as early as about 12 hours. However, an increase in the number of virus-invaded cells ceased about 36 hours after inoculation and subsequently the speed on the multiplication of virus began to increase.
In CMV inoculated tissue, an increase in respiratory rate occurred immediately after inoculation. This increase in respiration was due to the increase in the number of virus-invaded cell and seemed not to be due to the increase of virus synthesis in the tissue. Namely, even in the prime of virus synthesis, energy required for virus synthesis is not so large as to induce changes of respiration.
The changes of enzymatic activity in virus-invaded cells can be expressed by the equation derived from “Infected cell ratio” and enzymatic activity in the tissue. With the aid of this equation it is possible to detect even a subtle change in host metabolism in the early stages of infection and to estimate net metabolic change in virus-invaded cells. As determined by using this equation, peroxidase activity showed rapid increase immediately after inoculation but 4 hours later it returned to control level and thereafter maintained its level. This finding was in contrast with that obtained by ordinary method.
A marked increase of peroxidase activity was seen at the time when the infection was confined to epidermal tissue but not seen in other infected areas.
Polyphenol oxidase activity, however, decreased markedly during the first 2 hours after inoculation and thereafter increased gradually. It is conceivable that this initial decreased of enzymatic activity is due to the decrease of enzymatic activity in both cells invaded by virus and adjacent cells of it.
Making use the calculation of “Infected cell ratio” as well as the equation derived from “Infected cell ratio” and enzymatic activity in the tissue, the accurate analysis of metabolic changes that take place in host cells invaded with virus was thus possible.