Long-Distance Movement of Tobacco Mosaic Virus within the Tobacco Plant

Abstract

Tobacco mosaic virus was inoculated on the midrib of the secondary developed leaf of a 10 leaf-stage tobacco plant (Nicotiana tabacum L. CV. Xanthi), and the movement of the virus was traced by tissue culture method. Midribs and internodes of the inoculated plant were cut into many pieces at different stages of infection. These pieces were cultured on the modified Murashige and Skoog's medium at 25C for 14 days, and developed the calluses. Each of them was homogenized in 0.01M phosphate buffer, pH 8.0 and the infectivities of the homogenates were assayed on N. glutinosa.The results showed that the infectivity was detected first in the callus developed from the stem below the inoculated leaf 6 hours after inoculation and from the upper stem after 10 hours. After 15 hours the virus infectivity was detected from the 7th leaf and the top leaves, after 24 hours from the 5th and 6th leaves and after 60 hours from the 4th leaf. Thus far, the virus was detected in calluses developed from all parts of the plant after 120 hours, except for the root which was not used in this experiment.On a tobacco plant having about 20 leaves, midrib of the 6th leaf was inoculated with tobacco mosaic virus and after 6 hours the upper part from the 4th leaf was cultured in water for 30 hours. The midribs of each leaf were then cultured and the calluses developed were tested. The virus infectivity were detected only in the callus developed from 11th or 16th leaf, but not in the stem below the inoculated leaf.These results suggest that the virus translocates in vascular bundles depending on the phyllotaxy of tobacco plant (2/5) in the early stage of systemic infection.