A conceptual model proposed for the coupling of phenanthrene transport into root cells and a potassium influx/proton efflux reaction. A is for the high-affinity potassium transport system (HATS), B is for the low-affinity potassium transport system (LATS). In HATS, the symport of H+/K+ activates proton pump mediated by plasma membrane H+-ATPase, then forming a transmembrane electrochemical proton gradient. The electrochemical proton gradient drives the phenanthrene/proton symport system. In LATS, K+ influx via channels stimulates proton pump, and establishes an electrochemical proton gradient acting as a driving force for H+/phenanthrene symport. Pi, inorganic P. PAHs, polycyclic aromatic hydrocarbons.