ENZYMATIC DEGRADATION OF CELL-WALLS IN THE XYLEM DEVELOPING ZONE

Lignified cell walls hardly are attacked by cellulolytic enzymes without any pretreatments, because the cellulose is encrusted with lignin. In this study, the xylem developing zones of Betula platyphylla Sukat. var. japonica Hara, Fagus crenata Blume, Cryptomeria japonica D. Don, and Pinus densiflora Sieb. and Zucc. were cut into ultrathin sections and treated with cellulolytic enzymes to learn the effects of lignification on enzymatic susceptibilities of cell-wall polysaccharides. Cell walls of fibers, vessels, and tracheids were lignified first at the cell corner regions of compound middle lamellae (CML) in the S1 layer deposition stage. Then it was extened to entire CML, S1, S2, and S3 layers successively. Cell walls before lignification were degraded completely by the enzyme. CML became resistant against enzymatic attacks in the early stages of S1 layer depositions. S1, S2, and S3 layers became successively resistant following lignification.