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

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The metabolism by suspension-cultured tobacco cells of oligogalacturonides was investigated. Dodecagalacturonic acid-[3H]galactitol induces a rapid and transient alkalinization of the incubation medium resulting in part from enhanced K+ efflux from tobacco cells. However, a threefold higher concentration of dodecagalacturonic acid-[3H]galactitol is required to induce a response with the same amplitude and kinetics as that induced by the unreduced tridecagalacturonic acid. Approximately 20% of the dodecagalacturonic acid-[3H]galactitol added to suspension-cultured tobacco ionically binds to the cell walls within 1 min; maximum binding (approximately 30% of the oligogalacturonide) occurs in approximately 25 min. The unbound dodecagalacturonic acid-[3H]galactitol is rapidly (half-life, 30 min) fragmented to smaller, biologically inactive fragments by a polygalacturonase present in the growth medium. In contrast, the wall-bound dodecagalacturonic acid-[3H]galactitol is not degraded for at least 150 min. However, the kinetics, amplitude and duration of oligogalacturonide-induced ion fluxes are not correlated with the rate at which oligogalacturonides are converted to biologically inactive fragments. We propose that the transient nature of the oligogalacturonide-induced responses is likely to result from a temporary desensitization of the plant cells to the bioactive oligogalacturonides.

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