Serine/threonine-protein phosphatase that possesses phosphatase activity toward para-nitrophenyl phosphate (pNPP) in vitro. H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds 2 manganese ions per subunit. Phosphatase activity is strongly reduced by the protein phosphatase inhibitor 2 (I-2). Strongly up-regulated within developing flowers, especially in the tapetum, the developing and mature pollen and in the ovaries. Belongs to the PPP phosphatase family. PP-1 subfamily.