Acquisition and assimilation of nitrogen as peptide-bound and D-enantiomers of amino acids by wheat

• Published in: PloS one Vol. 6; no. 4; p. e19220
• Main Authors: Hill, Paul W, Quilliam, Richard S, DeLuca, Thomas H, Farrar, John, Farrell, Mark, Roberts, Paula, Newsham, Kevin K, Hopkins, David W, Bardgett, Richard D, Jones, David L
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 26-04-2011; Public Library of Science (PLoS)
• Subjects: Alanine; Amino acids; Amino Acids - chemistry; Assimilation; Biological assimilation; Biology; Carbon; D-Alanine; Ecology; Enantiomers; Flowers & plants; Historical account; L-Alanine; Laboratories; Methods; Mineralization; Nitrates; Nitrogen; Nitrogen - metabolism; Nutrition; Peptides; Peptides - metabolism; Plant Roots - metabolism; Productivity; Proteins; Respiration; Soil - chemistry; Soil sciences; Soil solution; Soil testing; Soils; Solutes; Solution chemistry; Solutions; Stereoisomerism; Terrestrial ecosystems; Terrestrial environments; Triticum - metabolism; Triticum aestivum; United Kingdom; Wheat; Zea mays; United Kingdom > UK; Wales
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0019220

Nitrogen is a key regulator of primary productivity in many terrestrial ecosystems. Historically, only inorganic N (NH(4)(+) and NO(3)(-)) and L-amino acids have been considered to be important to the N nutrition of terrestrial plants. However, amino acids are also present in soil as small peptides and in D-enantiomeric form. We compared the uptake and assimilation of N as free amino acid and short homopeptide in both L- and D-enantiomeric forms. Sterile roots of wheat (Triticum aestivum L.) plants were exposed to solutions containing either (14)C-labelled L-alanine, D-alanine, L-trialanine or D-trialanine at a concentration likely to be found in soil solution (10 µM). Over 5 h, plants took up L-alanine, D-alanine and L-trialanine at rates of 0.9±0.3, 0.3±0.06 and 0.3±0.04 µmol g(-1) root DW h(-1), respectively. The rate of N uptake as L-trialanine was the same as that as L-alanine. Plants lost ca.60% of amino acid C taken up in respiration, regardless of the enantiomeric form, but more (ca.80%) of the L-trialanine C than amino acid C was respired. When supplied in solutions of mixed N form, N uptake as D-alanine was ca.5-fold faster than as NO(3)(-), but slower than as L-alanine, L-trialanine and NH(4)(+). Plants showed a limited capacity to take up D-trialanine (0.04±0.03 µmol g(-1) root DW h(-1)), but did not appear to be able to metabolise it. We conclude that wheat is able to utilise L-peptide and D-amino acid N at rates comparable to those of N forms of acknowledged importance, namely L-amino acids and inorganic N. This is true even when solutes are supplied at realistic soil concentrations and when other forms of N are available. We suggest that it may be necessary to reconsider which forms of soil N are important in the terrestrial N cycle.