Benzothiadiazole, an inducer of plant defenses, inhibits catalase and ascorbate peroxidase

Benzothiadiazole (BTH) is a recently described synthetic inducer of plant defenses. Molecular and genetic studies have suggested that it acts as a functional analogue of the endogenous defense signalling molecule salicylic acid (SA). Here we demonstrate that BTH inhibits catalase and ascorbate peroxidase, two potential targets through which SA has been proposed to act. BTH was found to be a considerably better inhibitor of catalase than SA. This is consistent with its greater potency for inducing the expression of defense-related genes, such as the acidic PR-1, PR-2 and PR-3 genes. In addition, induction of PR-1 gene expression by either BTH or SA was suppressed by antioxidants. These results suggest that changes in H₂O₂ levels or the cellular redox status may be involved in the BTH/SA-mediated activation of certain defense responses.