Salicylic acid: transport and long-distance immune signaling.

•SA is preferentially transported from pathogen-infected to uninfected parts via the apoplast.•The transport of SA into apoplastic space is likely facilitated by the proton gradient generated upon deprotonation of SA.•The apoplastic SA transport is regulated by the transpirational pull and partitioning of SA between the symplast and cuticle.•Distal transport of SA is essential for systemic acquired resistance.