Model of AtPNP-A action at the cellular level. The model proposes that AtPNP-A can dock to receptor-like molecules that directly act as particulate guanylyl cyclases (pGCs) or indirectly activate soluble GCs (sGCs). GCs catalyse the reaction from GTP to cGMP. The latter acts as second messenger affecting cytosolic Ca2+ levels, modulating ion channels, activating phosphorylation through kinases and influences the transcriptome. Phosphodiesterases (PDEs) in turn metabolise cGMP to GMP (adapted from ).