The ion-binding and -exchange properties of putrescine, spermidine, an
d spermine on purified walls of carrot (Daucus carota L.) cell suspens
ions were investigated by producing ion-exchange isotherms and compari
ng them with the behavior of Na+, Mg2+, and Ca2+. The cation exchange
capacity of the carrot cell walls was 0.8 equivalent kg(-1) dry matter
, and the ionic selectivity sequence of the walls for polyamines follo
wed the sequence spermine(4+) > spermidine(3+) approximate to Ca2+ > p
utrescine(2+). The polyamines were subjected to only electroselectivit
y and probably did not induce any favorable supramolecular conformatio
n of pectin like the one induced by Ca2+. Triangular ion exchanges wer
e also performed with three diamines: ethanediamine, butanediamine, an
d octanediamine. The shorter the diamine, the higher the total adsorpt
ion and selectivity of the exchange. The lower selectivity of the cell
wall for putrescine was partly attributed to its inability to access
and displace Ca2+ from higher affinity sites within dimerized pectic s
equences. The polyamine adsorption and exchange on pectic sequences co
uld result in pectic signal modulation in pathogenesis and in differen
tiation.