Mixed Linkage (1→3),(1→4)‐β‐d‐Glucans of Grasses

Abstract

The mixed‐linkage (1→3),(1→4)‐β‐d‐glucans are unique to the Poales, the taxonomic order that includes the cereal grasses. (1→3), (1→4)‐β‐Glucans are the principal molecules associated with cellulose microfibrils during cell growth, and they are enzymatically hydrolyzed to a large extent once growth has ceased. They appear again during the developmental of the endosperm cell wall and maternal tissues surrounding them. The roles of (1→3),(1→4)‐β‐glucans in cell wall architecture and in cell growth are beginning to be understood. From biochemical experiments with active synthases in isolated Golgi membranes, the biochemical features and topology of synthesis are found to more closely parallel those of cellulose than those of all other noncellulosic β‐linked polysaccharides. The genes that encode part of the (1→3),(1→4)‐β‐glucan synthases are likely to be among those of the CESA/CSL gene superfamily, but a distinct glycosyl transferase also appears to be integral in the synthetic machinery. Several genes involved in the hydrolysis of (1→3),(1→4)‐β‐glucan have been cloned and sequenced, and the pattern of expression is starting to unveil their function in mobilization of β‐glucan reserve material and in cell growth.