Allelochemical effects on net nitrate uptake and plasma membrane H+-ATPase activity in maize seedlings

Seven-day-old maize seedlings grown in a nitrogen-free hydroponic culture were exposed for 48 h to 0, 100 and 300 mu M trans-cinnamic, p-coumaric, ferulic, caffeic acids, umbelliferone and 200 mu M KNO3. Net nitrate uptake was affected by trans-cinnamic, ferulic and p-coumaric acids in a concentration-dependent manner, and trans-cinnamic acid appeared to be the strongest inhibitor. Conversely, at low concentrations, caffeic acid stimulated net nitrate uptake while umbelliferone did not influence it. After 24 h of treatment, plasma membrane H+-ATPase activity significantly decreased in a concentration-dependent manner in response to trans-cinnamic, ferulic and p-coumaric acids, while umbelliferone and caffeic acid had no effect on H+-ATPase activity.