Characteristics of amino acid uptake in barley

Plants have the ability to take up organic nitrogen (N) but this has not been thoroughly studied in agricultural plants. A critical question is whether agricultural plants can acquire amino acids in a soil ecosystem. The aim of this study was to characterize amino acid uptake capacity in barley (Hordeum vulgare L.) from a mixture of amino acids at concentrations relevant to field conditions. Amino acids in soil solution under barley were collected in microlysimeters. The recorded amino acid composition, 0-8.2 mu M of L-Serine, L-Glutamic acid, Glycine, L-Arginine and L-Alanine, was then used as a template for uptake studies in hydroponically grown barley plants. Amino acid uptake during 2 h was studied at initial concentrations of 2-25 mu M amino acids and recorded as amino acid disappearance from the incubation solution, analysed with HPLC. The uptake was verified in control experiments using several other techniques. Uptake of all five amino acids occurred at 2 mu M and below. The concentration dependency of the uptake rate could be described by Michaelis-Menten kinetics. The affinity constant (K (m)) was in the range 19.6-33.2 mu M. These K-m values are comparable to reported values for soil micro-organisms.