TMV-RNA [tobacco mosaic virus] biosynthesis in the light-green and dark-green sectors of tissues in tobacco leaves

In tobacco mosaic virus-infected plants of tobacco ("alke" strain), in the light- and dark-green sectors of systemically infected leaves, changes were investigated in the activities of specific enzymes which are related to the biosynthesis of viral RNA. The protein content in the dark-green sectors of virus-infected leaves was found to increase to 131 per cent of the values recorded in the control healthy tissues; on the other hand this content in the light-green tissues decreased to 59 per cent. The contents of total chlorophylls a and b in the dark-green sector did not differ from the contents in the control healthy tissues; in the light-green sectors they were considerably lower (total chlorophyll decrease to 23 per cent, chlorophyll a to 27 per cent and chlorophyll b to 14 per cent of the control). The chlorophyll a to b ratio in the dark-green sectors was the same as that in the control tissues 2.57 and 2.60, respectively), the content in the light-green sectors increased to 5.00. In the light-green tissues the content of this virus about 250 times higher than the content of the virus in the dark-green sectors (332 ng per mg of proteins vs. 1.32 ng per mg of proteins). The activity of the key regulating enzyme of the oxidative pentose cycle-glucose-6-phosphate dehydrogenase in the dark-green sectors of virus-infected leaves is not different from the values of the activity in the control healthy tissues while in the light-green sectors it is considerably higher (181 per cent of the control). Similar relationships were observed in ribonucleases; their activity in the dark-green sectors decreased to 81 per cent and in the light-green sectors it increased to 203 per cent of the control. The biosynthesis of viral RNA is restricted by the steady (or reduced) activity of the two key enzymes in the metabolic pathways in the dark-green sectors to such an extent that out of 25 plants recovered by the differentiation of calluses obtained from these tissues, 28 per cent of the plants were healthy and the other plants had largely reduced virus concentrations.