Hydrolyzes 1,4-beta-glycosyl linkages of 1,4-beta-glucans and 1,3-1,4-beta-glucans. Possesses broad substrate specificity for hemicelluloses of type II cell walls. Substrate preference is carboxymethyl-cellulose > 1,3-1,4-beta-glucan > lichenan > arabinoxylan > phospho-swollen cellulose > xylan > glucomannan. May participate in lateral root development. Endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans. Optimum pH is 5.3-5.6 with 1,3-1,4-beta-glucan as substrate (at 35 degrees Celsius). Expressed in roots and flowers. Expressed in lateral root primordia during auxin-induced lateral root development. By auxin in roots (at protein level). Belongs to the glycosyl hydrolase 9 (cellulase E) family.