INFLUENCE OF EXOGENOUS SPERMIDINE ON POTASSIUM-BALANCE IN MAIZE SEEDLINGS

Two-day-old maize seedlings were incubated in the presence or absence of 1 mM spermidine in the external medium. After 2 h, an increase of p otassium (K+) efflux from roots was observed in treated seedlings up t o a maximum after a 4 h treatment, decreasing to control values in the following hours. Simultaneously, an inhibition of K+ uptake occurred in roots from treated seedlings up to minimum values after 7-9 h treat ment. Successively, roots from treated seedlings progressively recover ed their K+ uptake capacity up to values about 50% higher than control seedlings. No variations in K+ content were observed after 24 h betwe en control and spermidine-treated seedlings taken as a whole, while th e K+ content of roots and shoots showed different values when individu ally analysed. Our results suggest that for spermidine-treated plants, the K+ content is mantained constant after 24 h by an equilibrium of the influx/efflux systems while a different K+ content in shoots and r oots is related to a different growth rate induced by the presence of spermidine in the external medium.