Dye-coupling in Tobacco Mesophyll Cells Surrounding Growing Tobacco Mosaic Tobamovirus-induced Local Lesions

Some factors related to cessation of the movement of tobacco mosaic tobamovirus "TMV# in the late phase of a defence response were examined[ Mesophyll cells surrounding the local lesions induced by TMV in N[ tabacum cv[ Xanthi!nc were micro!injected with ~u! orescent dye 1\ 2 and 6 days post!inoculation[ At 6 days post!inoculation\ twelve out of 19 injections into cells adjacent to the lesion\ showed the expected dye!coupling "out~ow of ~uorescent dye from injected cell to adjacent ones via plasmodesmata# whereas 06 19 out of 19 injec! tions were successful in other cases[ Callose inhibitor "tunicamycin#\ dark treatment and incubation of plants with ascorbic acid\ which play a role in blocking plas! modesmata or induction of defence responses\ did not seem to have an e}ect on lesion growth[ These data imply that defects in the plasmodesmal function\ although not total\ may account for the formation of late local defence reaction together with other factors that restrict viral spread in the continuous cell!to!cell mode in mesophyll tissu