Multiple Forms of 1,4- β -Glucanase in Ripening Tomato Fruits Include a Xyloglucanase Activatable by Xyloglucan Oligosaccharides

Abstract

Extracts of ripening tomato (Lycopersicon esculentum L. var. Sunny) were tested for their capacity to hydrolyse carboxymethylcellulose (CMC) and seed xyloglucan (XG) at different pH values in the presence or absence of seed XG oligosaccharide subunits (7 to 9 sugar residues). CMC-ase activities were most active at pH 5 and 7 in locule extracts, whereas XG-ase activity was most active in the presence of XG oligosaccharides at pH 6 in pericarp extracts. The cation exchange FPLC column, Mono S, separated three zones of CMC-ase activity in pericarp extracts. One zone was most active at pH 5, and two at pH 7. The three CMC-ases had some XG-ase activity in the presence of oligosaccharide but, in addition, there were two regions of the eluate with XG-ase but no CMC-ase activity. The presence of XG-ase activity, separate from CMC-ases, was also observed after hydrophobic interaction chromatography, and in protein precipitated by lowering the salt content of extracts. During ripening, the CMC-ases and the oligosaccharide-activated XG-ases in pericarp extracts increased in total and specific activities, while endogenous XG-ase activity, that is in the absence of XG oligosaccharides, remained unchanged or declined. It is concluded that multiple, 1,4-β-glucanase activities develop in ripening tomato fruit, including, in pericarp tissue, a specific XG-ase which is latent and activated by XG oligosaccharides.