INTERCONVERSION OF THE SALICYLIC-ACID SIGNAL AND ITS GLUCOSIDE IN TOBACCO

Salicylic acid (SA) has been proposed to play a role in the induction of pathogenesis-related (PR) proteins and systemic acquired resistance (SAR) in tobacco. Since SA is rapidly converted to salicylic acid bet a-glucoside (SAG) in tobacco, we have attempted to assess the role of SAG in pathogenesis by application of chemically synthesized SAG to to bacco leaves. SAG was as active as SA in induction of PR-1 gene expres sion. This induction was preceded by a transient release of SA, which occurred in the extracellular spaces. The existence of a mechanism tha t releases SA from SAG suggests a possible role for SAG in SAR.