Plant's Systemic Immune Response

Illustration shows the process of a plant's systemic immune response. When a plant is infected by a pathogen, a plant hormone called salicylic acid (SA) activates defenses locally. Some of this SA is converted by an enzyme known as SAMT into an aspirin-like compound, called methyl salicylate (MeSA), which travels to uninfected parts of the plant and thereby activates a plant-wide immune response. But some SA at the infection site binds to an enzyme called salicylic acid binding protein 2 (SABP2). This binding prevents the enzyme from converting SA at the infection site into biologically inactive MeSA.