Plant cell walls

Constituents of the plant cell wall (CW) are among the most abundant biological molecules on earth and the functions of the CW are diverse. The CW provides mechanical strength, maintains cell shape, controls cell expansion, regulates transport, provides protection, functions in signaling processes, and stores food reserves. Pectins function to provide crosslinks and structural support to the CW, whereas proteins can be either structural (extensin) or enzymatic. There are two types of CWs: primary and secondary. Primary are thin, elastic, and permit cell expansion while providing strength. Typical primary plant CWs are composed of cellulose microfibrils (9-25%) and an interpenetrating matrix of hemicelluloses (25-50%), pectins (10-35%), and proteins (10%). Secondary CWs of plants contain cellulose (40-80%), hemicellulose (10-40%), and lignin (5-25%). Lignin biosynthesis starts with the shikimic acid pathway. Plant CW structure and function are fascinating topics with many applications and implications in all aspects of plant growth and development.