Abstract
Leaf ontogeny and virus multiplication in tobacco plants systemically infected with tobacco mosaic virus were investigated using a fluorescent antibody technique to know the origin of mosaic symptoms. Leaf primordium was initiated at the apical meristem where virus antigen was not detected, and contained no virus antigen in the early stages of development. Virus infection was first detected in the phloem after the vascular bundle had differentiated in the leaf primordium and thereafter spread to the lamina. Areas where no virus antigen was found, were produced near the midvein, secondary veins and tertiary veins during leaf development, while abundant virus multiplication occurred in other areas. In the course of mosaic symptom development, dark green areas arose from the areas where no virus antigen was found, and yellow green areas resulted from the areas where the virus multiplied abundantly. In the dark green areas, most cells contained no virus antigen for weeks. after the leaves had fully expanded, although infection was noted in a small number of cell groups. In contrast, no mosaic symptoms appeared in leaves which had fully expanded at the time the plant was inoculated although the virus antigen was found in all parts of the leaf tissues. These results suggested that the occurrence of dark green areas is related to the histogenesis of areas near the leaf veins.
