Acts in the modification of cell walls via demethylesterification of cell wall pectin. [(1->4)-alpha-D-galacturonosyl methyl ester](n) + n H2O = [(1->4)-alpha-D-galacturonosyl](n) + n H(+) + n methanol Glycan metabolism; pectin degradation; 2-dehydro-3-deoxy-D-gluconate from pectin: step 1/5. Expressed in mature pollen grains in the anthers and on the stigma. Found in pollen tubes within the style. The PMEI region may act as an autoinhibitory domain and prevent untimely PME activity during transport. In the N-terminal section; belongs to the PMEI family. In the C-terminal section; belongs to the pectinesterase family.