PATTERNS AND BARRIERS OF CELL-TO-CELL MOVEMENT AND LACK OF SYSTEMIC SPREAD OF TOBACCO ETCH POTYVIRUS (TEV-GUS) IN SOLANUM BREVIDENS

Movement of tobacco etch potyvirus (TEV) was monitored in the resistan t wild potato species Solanum brevidens and susceptible tobacco (Nicot iana tabacum cv. Samsun) using an engineered TEV (TEV-GUS) expressing the beta-glucuronidase reporter gene (GUS). In mechanically inoculated leaves of S. brevidens and tobacco, single infected cells were observ ed on the basis of GUS expression at 2.5 h and 5 b after inoculation, respectively. Lesions up to 4-6 and 20 epidermal cells in diameter wer e observed in tobacco and S. brevidens, respectively, at 7 h after ino culation. At 24 h after inoculation, lesions in S. brevidens fused and could not be distinguished. Most epidermal cells, but few mesophyll c ells, were infected in mechanically inoculated leaves of S. brevidens at 3 days after inoculation. In tobacco, cell-to-cell movement occurre d concurrently from the initially infected epidermal cells to the neig hbouring epidermal and mesophyll cells. TEV-GUS neither was transporte d systemically from mechanically inoculated leaves of S. brevidens nor established infection in graft-inoculated S. brevidens. These data in dicated that resistance to TEV-GUS in S. brevidens is associated with restricted cell-to-cell movement in mesophyll tissue and lack of syste mic spread. It is also suggested that the cell-to-cell movement of TEV -GUS between epidermal cells, between mesophyll cells, and possibly be tween epidermal and mesophyll cells have different requirements in S. brevidens.