title: Acquisition and assimilation of nitrogen as peptide-bound and D-enantiomers of amino acids by wheat.
abstract: 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.
authors.affiliation: Environment Centre Wales, Bangor University, Bangor, Gwynedd, United Kingdom. p.w.hill@bangor.ac.uk
authors.forename: Paul W
authors.initials: PW
authors.lastname: Hill
authors.forename: Richard S
authors.initials: RS
authors.lastname: Quilliam
authors.forename: Thomas H
authors.initials: TH
authors.lastname: DeLuca
authors.forename: John
authors.initials: J
authors.lastname: Farrar
authors.forename: Mark
authors.initials: M
authors.lastname: Farrell
authors.forename: Paula
authors.initials: P
authors.lastname: Roberts
authors.forename: Kevin K
authors.initials: KK
authors.lastname: Newsham
authors.forename: David W
authors.initials: DW
authors.lastname: Hopkins
authors.forename: Richard D
authors.initials: RD
authors.lastname: Bardgett
authors.forename: David L
authors.initials: DL
authors.lastname: Jones
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D009584:Nitrogen / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D012987:Soil / Q000737:chemistry; D012996:Solutions; D013237:Stereoisomerism; D014908:Triticum / Q000378:metabolism*; D006113:United Kingdom
chemical_list: D000596:Amino Acids; D010455:Peptides; D012987:Soil; D012996:Solutions; D009584:Nitrogen