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, Pla nt Physiol. 113: 387-395). In this study, the adsorption of polyamines onto isolated carrot cell walls and onto pure polygalacturonic acid was investi gated in the presence of competing mono- and divalent cations (Na+ and Ca2). Putrescine (Put(2+)) was unable to remove all the calcium (Ca2+) from ce ll walls or from polygalacturonic acid. Spermidine (Spd(3+)) and spermine ( Spm(4+)) adsorbed on all galacturonates and were able to remove Ca2+ comple tely from both the walls and the pure polygalacturonates. Therefore, Spd(3) and Spm(4+), unlike Put(2+), prevented polygalacturonic acid from adoptin g the Ca2+-induced supramolecular conformation recognized by the 2F4 anti-p ectin monoclonal antibody. We show that the signal transduction cascade oth erwise initiated in plant cells by Ca2+-bound alpha-1,4-oligogalacturonides was indeed blocked by both Spd3+ and Spm(4+), but not by Put(2+). The mobi lization of cytosolic free Ca2+ and the cytosolic acidification usually obs erved after treatment with pectic fragments did not occur and the subsequen t activation of phenylalanine ammonia-lyase was suppressed. It is hypothesi zed that the disruption by Spd(3+) and Spm(4+) of the Ca2+-induced supramol ecular conformation of pectic fragments was the cause of the inhibition of the pectic signal. We conclude that polyamines can act on plant cell physio logy by modulating the transduction of the pectic signal.