Effect of Exogenous Putrescine, Spermidine, and Spermine on K Uptake and H Extrusion through Plasmamembrane in Maize Root Segments.

The action of exogenous polyamines (putrescine, spermidine, and spermine) on ;washing' and fusicoccin-stimulated K(+) uptake and H(+) extrusion through the plasmamembrane in maize (Zea mays L., hybrid line Plenus S 516) root apical segments was studied. The results showed that polyamines inhibit the washing-stimulated K(+) influx and H(+) extrusion without interfering with K(+) uptake and H(+) extrusion stimulated by fusicoccin. Spermidine appeared to be the most effective in inhibiting K(+) uptake and H(+) extrusion while putrescine showed a smaller inhibiting action with respect to the others. The analysis of kinetic constants indicated that the polyamines behave as competitive inhibitors with respect to K(+).