The cell walls of higher plants are dynamic structures whichundergo changes in composition and structure in relation to cellage, tissue type, and environmental stimuli. Individual compo-nents of the cell wall respond to physical damage (wounding),hormones, pathogen infection, and treatment with fungal elici-tors (for review, see Showalter and Varner [11]). Moreover,endogenous cell wall oligosaccharins have been identified whichwhen released affect the synthesis of defense related plant en-zymes as well as serve to initiate a variety of developmentalprograms (3, 14). Thus, an understanding of cell wall compo-nents and their interactions is a prerequisite toward elucidatingthe roles cell wall chemistry and architecture play in plant growthand development.sequenceswhichmayinteractuniquelywiththewallmatrixtobe spaced between a common backbone of Ser(Hyp)l spacersequences.In any guessing game about how the extensins function weneed to keep in mind that recently several plant genes have beenisolatedwhichmay code for structural cell wall proteinsunrelatedto the HRGPs. cDNA and genomic clones encoding proline/hydroxyproline-rich proteins have been isolated from bothwounded carrot rootsand from soybean cell cultures treated withauxin (7, 11). In the case of carrot, these cDNAs have beenshown to code for a protein which accumulates in the cell wallafter wounding (13). The cDNAs from both carrot and soybean