Catalyzes the hydrolysis of phosphoanhydride bonds of nucleoside tri- and di-phosphates. Substrate preference is ATP > ADP. Functions with APY1 to reduce extracellular ATP level which is essential for pollen germination and normal plant development. Plays a role in the regulation of stomatal function by modulating extracellular ATP levels in guard cells. a ribonucleoside 5'-triphosphate + 2 H2O = a ribonucleoside 5'-phosphate + 2 H(+) + 2 phosphate As cell membrane protein, the functional domain could be at the extracellular side. Expressed in roots, root hairs, root cap, leaves, stems, trichomes, phloem throughout the plant, guard cells, filaments of young stamens, stipules, papillae of stigmas, pollen, pollen tubes and the abscission zone of siliques. By hypertonic stress. No visible phenotype under normal growth conditions. Apy1 and apy2 double mutant displays developmental defects including the lack of functional root and shoot meristems, and morphogenetic and patterning abnormalities of the cotyledons. Double mutant exhibits a complete inhibition of pollen germination. Belongs to the GDA1/CD39 NTPase family.