Identification of EDTA-Soluble Polysaccharides from Pea Epicotyl Cell Walls and Their Interaction with Xyloglucan

Nascent pectin and glucuronoxylan were prepared from membrane-bound enzymes obtained from pea epicotyls. They had previously been shown to exhibit a proteinand pH-dependent pattern of binding to cell wall ghosts and to xyloglucan extracted from cell walls prepared from pea epicotyls; maximum binding required a pH of 3-4, and the presence of cell wall proteins, namely assemblins. To determine whether wall polysaccharides deposited in cell walls behave in the same manner as nascent polymers, radioactively labeled EDTA-soluble polymers were prepared from newly-deposited pea epicotyl cell walls. Different enzyme treatments followed by column chromatography, in addition to complete acid hydrolysis followed by paper and thin layer chromatography, indicated the presence of pectin, together with smaller amounts of glucuronoxylan, in this EDTA-soluble extract. These radioactively labeled polysaccharides were found to bind to cell wall ghosts and to xyloglucan extracted from the second and third internodes of pea epicotyls cell walls in a pH-dependent manner, similar to the binding pattern obtained with nascent polymers. Maximum binding occurred at pH 3-4, and also required the presence of protein.