Exhibits pyrophosphatase activity with stronger affinity for pyrophosphate (PPi), moderate affinity for ATP and ADP, and weak affinity for tripolyphosphate (PPPi) (PubMed:25185123, PubMed:28733390). No activity observed toward uridine substrate (PubMed:28733390). Negative regulator of the salicylic acid (SA)-mediated amplification of defense responses against both virulent and avirulent pathogens, including oomycetes (e.g. H.arabidopsidis) and bacteria (e.g. P.syringae). Represses systemic acquired resistance (SAR) (PubMed:25185123). diphosphate + H2O = H(+) + 2 phosphate Optimum pH is 8-9. Predominantly expressed in the shoot apices of inflorescences. Repressed by the oomycete pathogen H.arabidopsidis. Negatively regulated by salicylic acid (SA), benzothiadiazole (BTH) and pathogen-associated molecular patterns (PAMP, e.g. flg22). Enhanced hypersensitive response, elevated pathogen resistance against both virulent and avirulent pathogens (e.g. isolates Emwa1 and Emco5 of the oomycete pathogen H.arabidopsidis, the bacterial pathogen P.syringae DC3000 (AvrRps4)). Elevated accumulation of salicylic acid (SA) and conjugates (e.g. salicylic acid glucoside (SAG)) upon infection. Stronger systemic acquired resistance (SAR). These increased defense responses are PAD4-, ICS1- and NPR1-dependent.