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

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Abstract
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+.