Polyamines and pectins. II. Modulation of pectic-signal transduction.

A previous study had shown that polyamines adsorb selectively on plant cell walls according to the valence of the polyamines (Messiaen et al. Plant Physiol. (1997), 113: 387-395). In this study, the adsorption of polyamines was investigated on isolated carrot cell walls and on pure polygalacturonic acid in the presence of competing mono- and bivalent cations (Na+ and Ca2+). Putrescine was unable to remove all the calcium from cell walls as well as from polygalacturonic acid. Spermidine and spermine adsorbed on all galacturonates and were able to remove calcium completely from either the walls or the pure polygalacturonates. Therefore, Spd3+ and spermine, unlike putrescine, prevented polygalacturonic acid from adopting the calcium induced supramolecular conformation recognized by the 2F4 anti-pectin monoclonal antibody. We show that the signal transduction cascade otherwise initiated in plant cells by calcium-bound -1,4-oligogalacturonides was indeed blocked by both spermidine and spermine, but not by putrescine. The cytosolic free calcium mobilization and cytosolic acidification usually observed after treatment with pectic fragments did not occur and the subsequent phenylalanine ammonia-lyase activation was suppressed. It is hypothesized that the disruption by spermidine and spermine of the calcium-induced supramolecular conformation of pectic fragments was the cause of the inhibition of the pectic signal.