The storage cell walls in the endosperm of Asparagus officinalis L. seeds during development and following germination

Abstract

The thickened cell walls of endosperm cells of asparagus (Asparagus officinalis) seeds are composed of glucomannans. During development, the extensive thickening of the cell wall is specific to the lateral region of the endosperm and not to the micropylar region. The micropylar endosperm may thus be predisposed to facilitate germination. Following germination there is a progressive mobilization of the reserves in the cells of the lateral endosperm in a wave-like manner away from the haustorial cotyledon, accompanied by the loss of cytoplasm and the crushing of the lateral endosperm cells. Although the internal reserves are mobilized from the micropylar endosperm cells, the cells themselves remain intact throughout the period of lateral endosperm mobilization and may form a living barrier to prevent the loss of soluble hydrolysis products of the lateral endosperm to the surrounding environment. The location and timing of endo-β-mannanase production and the increase in activity of β-mannoside mannohydrolase in seeds of germinated asparagus were followed. Endo-β-mannanase activity increases greatly in the endosperm until the mid-point of mobilization, and is about 45 times higher than in the embryo on a per seed part basis. Unlike endo-β-mannanase, which is extractable in low-salt buffer, β-mannoside mannohydrolase requires high salt (0.5 M NaCl) for extraction. This enzyme continually increases in activity in both the endosperm and embryo following germination, with the majority of the activity being concentrated in the embryo when considered on a per seed part basis.