DETERMINING THE RELATIONSHIP BETWEEN SALICYLIC-ACID LEVELS AND SYSTEMIC ACQUIRED-RESISTANCE INDUCTION IN TOBACCO

Salicylic acid (SA) has been proposed as the systemic signal for the i nduction of systemic acquired resistance (SAR). It has been suggested that SA is synthesized at the site of pathogen-induced necrosis and is translocated to induce SAR in uninfected leaves. Grafting studies bet ween wild-type tobacco plants and plants that are unable to accumulate significant amounts of SA have shown that the large increase in SA ac cumulation seen in inoculated leaves is not necessary for SAR inductio n, suggesting that SA is not the primary systemic signal. However, the se studies have not addressed whether decreased levels of SA accumulat ion in inoculated leaves are sufficient to fully induce SAR. In this s tudy, we have determined the relationship between free SA levels in th e inoculated leaf and SAR induction in tobacco, These results support our previous conclusion that SA is not likely to be the systemic signa l.