Simultaneous Uptake of Multiple Amino Acids by Wheat

ABSTRACT

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 inorganic N, 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 K _m values) for glutamine followed by tryptophan, alanine, arginine, glycine, and serine. The V _max values for amino acids uptake by wheat ranged from 2.26 for tryptophan to 16.6 μmol g⁻¹ root FW h⁻¹ in case of serine.

Keywords:

• amino acid uptake
• organic nitrogen
• sterilized system

ACKNOWLEDGMENTS

This work was supported by The Danish Research Agency. We thank Lene Korsholm J⊘rgensen for skilled technical assistance.