Dephosphorylates and represses plasma membrane H(+)-ATPases (PM H(+)-ATPases, e.g. AHA1 and AHA2), thus influencing negatively plant growth and fitness (PubMed:24858935). Promotes the apical hook maintenance of etiolated seedlings (PubMed:24858935). H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds 2 magnesium or manganese ions per subunit. Interacts with SAUR19 (PubMed:24858935). Interacts with AHA2 at the plasma membrane (PubMed:24858935). Reduced apical hook maintenance in etiolated seedlings (PubMed:24858935). The pp2c-d1 pp2c-d2 double mutant displays a long hypocotyl phenotype and strongly reduced apical hook maintenance in etiolated seedlings (PubMed:24858935). Belongs to the PP2C family.