Differential Inhibition by Ferulic Acid of Nitrate and Ammonium Uptake in Zea mays L.

The influence of the allelopathic compound ferulic acid (FA) on nitrogen uptake from solutions containing both NO(3) (-) and NH(4) (+) was examined in 8-day-old nitrogen-depleted corn (Zea mays L.) seedlings. Concurrent effects on uptake of Cl(-) and K(+) also were assessed. The presence of 250 micromolar FA inhibited the initial (0-1 hours) rate of NO(3) (-) uptake and also prevented development of the NO(3) (-)-inducible accelerated rate. The pattern of recovery when FA was removed was interpreted as indicating a rapid relief of FA-restricted NO(3) (-) uptake activity, followed by a reinitiation of the induction of that activity. No inhibition of NO(3) (-) reduction was detected. Ammonium uptake was less sensitive than NO(3) (-) uptake to inhibition by FA. An inhibition of Cl(-) uptake occurred as induction of the NO(3) (-) transport system developed in the absence of FA. Alterations of Cl(-) uptake in the presence of FA were, therefore, a result of a beneficial effect, because NO(3) (-) uptake was restricted, and a direct inhibitory effect. The presence of FA increased the initial net K(+) loss from the roots during exposure to the low K, ammonium nitrate uptake solution and delayed the recovery to positive net uptake, but it did not alter the general pattern of the response. The implications of the observations are discussed for growth of plants under natural conditions and cultural practices that foster periodic accumulation of allelopathic substances.