Acts in the modification of cell walls via demethylesterification of cell wall pectin. Involved in the pollen tube growth and determination of pollen tube morphology. [(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. Interacts with PMEI2, and in vitro with PMEI1. Expressed in mature pollen grains in the anthers and on the stigma. Found in pollen tubes within the style. Located at the tip and in the shank of the pollen tube. After germination, the pollen tube is sunted, curved and has an irregular morphology. No effect on the morphology of ungerminated pollen grains, on the efficiency of pollen germination, fertilization or seed production. The pectin methylesterase activity is inhibited by PMEI2. Belongs to the pectinesterase family.