The transient nature of the oligogalaturonide-induced ion fluxes of tobacco cells is not correlated with fragmentation of the oligogalacturonides

The metabolism by suspension-cultured tobacco cells of oligogalacturonides was investigated. Dodecagalacturonic acid-[H-3]galactitol induces a rapid a nd transient atkalinization of the incubation medium resulting in part from enhanced K+ efflux from tobacco cells. However, a threefold higher concent ration of dodecagalacturonic acid-[H-3]galactitol is required to induce a r esponse with the same amplitude and kinetics as that induced by the unreduc ed tridecagalacturonic acid. Approximately 20% of the dodecagalacturonic ac id-[H-3]galactitol added to suspension-cultured tobacco ionically binds to the cell walls within 1 min; maximum binding (approximately 30% of the olig ogalacturonide) occurs in approximately 25 min. The unbound dodecagalacturo nic acid-[H-3]galactitol is rapidly (half-life, 30 min) fragmented to small er, biologically inactive fragments by a polygalacturonase present in the g rowth medium. In contrast, the wall-bound dodecagalacturonic acid-[H-3]gala ctitol is not degraded for at least 150 min. However, the kinetics, amplitu de and duration of oligogalacturonide-induced ion fluxes are not correlated with the rate at which oligogalacturonides are converted to biologically i nactive fragments. We propose that the transient nature of the oligogalactu ronide-induced responses is likely to result from a temporary desensitizati on of the plant cells to the bioactive oligogalacturonides.