OAT ENDOSPERM CELL-WALLS .2. HOT-WATER SOLUBILIZATION AND ENZYMATIC DIGESTION OF THE WALL

Isolated cell walls from two cultivars of oats, one with a high conten t of beta-glucan (Marion) and one with a low beta-glucan content (OA51 6-2), were fractionated in an attempt to understand the structure of t he endosperm cell wall. Isolated walls were sequentially extracted wit h hot water (65 degrees C), digested with lichenase ([1-->3][1-->4]-be ta-D-glucan 4-glucanohydrolase, EC 3.2.1.73), and then digested with e ndoxylanase. The final residue after consecutive hot-water extraction and digestion by the two enzymes was acid hydrolyzed for analysis of t he monosaccharide composition by high-performance liquid chromatograph y (HPLC). The whole wall composition, as well as the composition of th e fractions generated during hot-water extraction and enzymatic dissoc iation, was similar for the two cultivars of oats. The fractionation c haracteristics of the walls were consistent with a layered model: a re latively thin outer layer, adjacent to the middle lamella, consisting of an insoluble polysaccharide skeleton (cellulose and glucomannan) pl us matrix polysaccharides (beta-glucan and arabinoxylan), and a large inner layer of soluble polysaccharides (beta-glucan and arabinoxylan). These layers correspond to the residue after hot-water extraction and the hot-water extract, respectively.