Absence of transglycosylation with oligogalacturonides in plant cells

Incubation of non-radioactive pectic polysaccharides with α-(1→4)-Oligo-d-[6-¹⁴C]galacturonides (degree of polymerization two-12) in the presence of various enzyme preparations at pH 4-8 did not yield any detectable ¹⁴C- transglycosylation products. Polysaccharides tested were polygalacturonate, citrus pectin, rhamnogalacturonan-II, soluble polysaccharides from the culture filtrates of rose (Rosa sp.) cell suspensions, partially degraded pectic polysaccharides extracted by autoclaving the walls of cultured rose cells and citrus pectin after treatment with pectin methylesterase. Potential enzyme sources tested were culture filtrates and ionically bound wall proteins from rose and sycamore (Acer pseudoplatanus) cell suspension cultures, and extracts of several ripening fruits. In addition, in experiments designed to detect transglycosylation catalysed by an inextractable or labile apoplastic enzyme, ³H from exogenous [reducing terminus-1-³H]pentagalacturonide was not incorporated into either wall-bound or soluble extracellular polymers by living cell suspension cultures. Thus, no evidence could be obtained for transglycosylation with oligogalacturonides as either donor or acceptor substrates under experimental regimes similar to those previously used to demonstrate transglycosylation with xyloglucan oligosaccharides.