Salicylic acid can induce resistance to plant virus movement

Salicylic acid (SA) treatment has recently been reported to inhibit replication of tobacco mosaic virus (TMV) in inoculated tissue. Furthermore, resistance is induced via a novel defensive signal transduction pathway sensitive to inhibition by salicylhydroxamic acid (SHAM; S. Chivasa, A.M. Murphy, M. Naylor, and J.P. Carr, Plant Cell 9: 547-557, 1997). The goals of this study were to determine if replication of viruses other than TMV could be inhibited by SA and, if so, whether the resistance to other viruses could also be prevented by SHAM. Potato virus X (PVX) RNA accumulation in inoculated tobacco leaf tissue was reduced by SA treatment and resistance was dependent on the SHAM-sensitive signaling pathway. However, although symptoms of cucumber mosaic virus (CMV) infection were delayed in SA-treated tobacco plants, this was not due to inhibition of replication but rather to inhibition of systemic movement of the virus. ¹⁴CO₂-feeding experiments indicated that SA-induced interference with long-distance virus movement is not a by-product of disrupted photosynthate translocation. Significantly, SA-induced resistance to CMV was abolished by SHAM. Thus, the SHAM-sensitive signaling pathway activates both resistance mechanisms: inhibition of long-distance CMV movement and inhibition of TMV and PVX replication.