Required for both, loosening of the micropylar endosperm, and rupture of the seed coat in germinating seeds. May participate in the hydrolysis of the mannans in the cell wall of germinating seeds. Random hydrolysis of (1->4)-beta-D-mannosidic linkages in mannans, galactomannans and glucomannans. Expressed in stems, flowers, siliques and seeds (PubMed:16897088). Expressed in root vasculature, leaf hydathodes, anther filaments, stigma, sepal vasculature, at the base and apical parts of siliques, and replum. Expressed in the micropylar endosperm and radicle tip in early germinating seeds (PubMed:23461773). By gibberellin in germinating seeds. Belongs to the glycosyl hydrolase 5 (cellulase A) family.