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 polyamine (Messiaen et al. 1997, Plant Physiol. 113: 387-395). In this study, the adsorption of polyamines onto isolated carrot cell walls and onto pure polygalacturonic acid was investigated in the presence of competing mono- and divalent cations (Na+ and Ca2+). Putrescine (Put2+) was unable to remove all the calcium (Ca2+) from cell walls or from polygalacturonic acid. Spermidine (Spd3+) and spermine (Spm4+) adsorbed on all galacturonates and were able to remove Ca2+ completely from both the walls and the pure polygalacturonates. Therefore, Spd3+ and Spm4+, unlike Put2+, prevented polygalacturonic acid from adopting the Ca(2+)-induced supramolecular conformation recognized by the 2F4 anti-pectin monoclonal antibody. We show that the signal transduction cascade otherwise initiated in plant cells by Ca(2+)-bound alpha-1,4-oligogalacturonides was indeed blocked by both Spd3+ and Spm4+, but not by Put2+. The mobilization of cytosolic free Ca2+ and the cytosolic acidification usually observed after treatment with pectic fragments did not occur and the subsequent activation of phenylalanine ammonia-lyase was suppressed. It is hypothesized that the disruption by Spd3+ and Spm4+ of the Ca(2+)-induced supramolecular conformation of pectic fragments was the cause of the inhibition of the pectic signal. We conclude that polyamines can act on plant cell physiology by modulating the transduction of the pectic signal.