Recent research has proven that higher plants can utilize amino acids as nitrogen (N) and carbon (C) sources. Most studies have focused on single amino acids with or without inorganicN, but a range of amino acids may be expected under conditions where the main N input derives from turnover of organic N sources. This study investigated the uptake of multiple amino acids by plant roots and further the active versus passive uptake was determined. Under minimum microbial activity conditions, seedlings of wheat (Triticum aestivum L. cv. ‘Baldus’) were exposed to a series of different concentrations of seven mixed amino acids solutions. Samples of the depleted solutions were periodically collected over a period of ten hours to measure the concentration of amino acids. For all tested amino acids passive uptake was a minor contribution compared to the total uptake. The uptake rates of the amino acids were well described by single Michaelis- Menten kinetic equations with R2 ranging from 0.87 to 0.96. All of the tested amino acids showed a similar uptake pattern.Wheat plants had the highest affinity (lowest Km values) for glutamine followed by tryptophan, alanine, arginine, glycine, and serine. The Vmax values for amino acids uptake by wheat ranged from 2.26 for tryptophan to 16.6 ìmol g.1 root FW h.1 in case of serine.
This study reports, for the first time the simultaneous uptake of multiple amino acids in important agricultural crops. The simultaneous uptake of the six mixed amino acids was dependent on the outer concentration and not on the amino acid type . The uptake kinetics for the six amino acids showed similar trends, a results that agrees with the conclusion of Fischer et al. (1998) that plants contain multiple sets of amino acid transport proteins and that there are also a large number of general amino acid transporters, which can transport many different amino acids. The finding of multiple amino acids uptake also agrees with the expectations of Okumoto et al. (2002) that multiple transporters with differing kinetic characteristics are responsible for import of amino acids into seeds since this action could allow the growing seed to adapt to varying N-supply and alteration in amino acids available.
Ref: A. El-Naggar, A. de Neergaard, A. El-Araby & H. Hogh-Jensen (2009): Simultaneous Uptake of Multiple Amino Acids by Wheat, Journal of Plant Nutrition, 32:5, 725-740