Oligogalacturonides are able to induce flowers to form on tobacco explants

Summary Oligogalacturonides (α‐1,4‐D‐galactosyluronic acid oligomers) are fragments of the homogalacturonan component of the primary cell walls of higher plants. Treatment of cell walls with endopolygalacturonase (EPG) releases the polysaccharides rhamnogalacturonan‐1 (RG‐I) and rhamnogalacturonan‐II (RG‐II), and variously sized oligogalacturonide fragments of homogalacturonan. The EPG‐released sycamore cell wall components are able to regulate several morphogenetic processes of tobacco thin‐cell layer (TCL) explants. We followed one of these morphogenesis‐regulating activities, namely, the induction of flower formation on TCLs, to purify the biologically active component from EPG‐released material. Saponification of the methyl and acetyl esters of the EPG‐released material did not reduce the flower‐inducing activity. However, EPG treatment of the deesterified EPG‐released material destroyed the flower‐inducing activity, establishing that the active substance contained several, consecutive α‐1,4‐linked galactosyluronic acid residues that are required for the flower‐inducing activity. The flower‐inducing activity was purified and shown to be α‐1,4‐linked Oligogalacturonides with a degree of polymerization (DP) of 12‐14, which exhibited half‐maximum activity at approximately 0.4 μM. Smaller oligogalacturonides, RG‐I and RG‐II, did not, even at higher concentrations, induce flowers to form. The ability of oligogalacturonides to stimulate the formation of flowers on tobacco explants provides further evidence of the pleiotropic nature of this oligosaccharin.