POLYAMINES AND PECTINS .1. ION-EXCHANGE AND SELECTIVITY

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.