Evidence against specific binding of salicylic acid to plant catalase.

It was demonstrated that salicylic acid (SA) not only binds to catalase from differentiated higher plants and plant cell suspension cultures but also to those of fungi and animals. SA bound specifically to iron-containing enzymes, such as catalase, aconitase, lipoxidase and peroxidase, while not to iron-free plant enzymes. On the grounds of these experiments, the claim is further challenged that SA is a signalling compound and second messenger in plants that activates plant defense-related genes through elevated H2O2 levels by specifically inhibiting catalase activity. SA may just function as a phytoalexin.