(1,4-alpha-D-galacturonosyl)n+m + H2O = (1,4-alpha-D-galacturonosyl)n + (1,4-alpha-D-galacturonosyl)m. Expressed in developing and germinated seeds in the chalazal region immediately adjacent to the site of penetration of the radicle through the testa. Belongs to the glycosyl hydrolase 28 family.