The influence of the allelopathic compound ferulic acid (FA) on nitrogen uptake from solutions containing both N03-and NH4+ was examined in 8-day-old nitrogen-depleted com (Zea mays L.) seedlings. Concurrent effects on uptake of Clr and K+ also were assessed. The presence of 250 micromolar FA inhibited the initial (0-1 hours) rate of NO3-uptake and also prevented development of the NO3--inducible accelerated rate. The pattem of recovery when FA was removed was interpreted as indicating a rapid relief of FA-restricted N03-uptake activity, followed by a reinitiation of the induction of that activity. No inhibitiot of NO3-reduction was detected. Ammonium uptake was less sensitive than N03-uptake to inhibition by FA. An inhibition of Cl-uptake occurred as induction of the N03-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 NO3-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 pattem 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.A deleterious effect of the phenolic compound FA2 on the uptake of phosphorus and potassium has been observed frequently (6,7,13,21 Little is known about the effect of allelopathic compounds on nitrogen uptake. In addition to probable effects of limiting the total nitrogen taken up, the possibility exists for differential effects on NO3-and NH4' uptake. Moreover, the amount and ionic form of nitrogen are significant factors in determining the uptake of other ions such as potassium (23, 28), phosphate (25, 26), chloride (4, 11), and sulfate (2). For example, K+ uptake often is facilitated by NO3-(16) and inhibited by NH4' (27, 28), whereas Cl-influx is inhibited by ambient NO3-and by the sum of NO3-and Cl-in the tissue (4, 1 1). It is possible, therefore, that effects exerted by allelochemicals on nitrogen uptake may alter the uptake of other ions. Accordingly, the objective of this investigation was to ascertain the inhibitory effect ofa typical phenolic compound, FA, on nitrogen uptake and on concurrent uptake of K+ and C1-.
MATERIALS AND METHODS
Plant CultureAll experiments were conducted with intact nitrogen-deprived, 8-d-old maize (Zea mays L., Pioneer Hybrid 3369a) seedlings. At this stage of development, the endosperm is largely depleted of nitrogen reserves. Seeds were germinated in darkness at 30C and 98% RH in paper rolls moistened with 0.1 mm CaSO4. After 78 to 82 h, all roots except the primary root were excised. Primary roots of four seedlings (one culture) were threaded through separate holes in the bottom of polyethylene cups (2.5 cm high and 3.5 cm diameter). The seeds within the cups were packed with c...
