Nitrogen recycling during phenylpropanoid metabolism in sweet potato tubers

J Plant Physiol. 1998 Oct;153(3-4):316-23. doi: 10.1016/s0176-1617(98)80157-0.


In the first step of the phenylpropanoid metabolic pathway, L-phenylalanine (L-Phe) is deaminated to form E-cinnamate, in a conversion catalyzed by phenylalanine ammonia-lyase (PAL; EC The metabolic fate of the ammonium ion (NH4+) produced in this reaction was investigated in sweet potato (Ipomoea batatas) tuber discs. [15N]-Labeled substrates including L-Phe, in the presence or absence of specific enzyme inhibitors, were administered to sweet potato discs in light under aseptic conditions. 15N-Nuclear magnetic resonance spectroscopic analyses revealed that the 15NH4+ liberated during the PAL reaction is first incorporated into the amide nitrogen of L-glutamine (L-Gln) and then into L-glutamate (L-Glu). These results extend our previous observations in pine and potato that PAL-generated NH4+ is assimilated by the glutamine synthetase (GS; EC synthase (GOGAT; EC pathway, with the NH4+ so formed ultimately being recycled back to L-Phe via L-Glu as aminoreceptor and donor.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Ammonium Chloride / chemistry
  • Darkness
  • Enzyme Inhibitors
  • Gas Chromatography-Mass Spectrometry
  • Glutamic Acid / chemistry
  • Glutamine / chemistry
  • Indans / chemistry
  • Light
  • Magnetic Resonance Spectroscopy
  • Nitrogen / chemistry
  • Nitrogen / metabolism*
  • Nitrogen Isotopes
  • Phenylalanine / metabolism*
  • Phenylalanine Ammonia-Lyase / antagonists & inhibitors
  • Phenylalanine Ammonia-Lyase / chemistry
  • Phenylalanine Ammonia-Lyase / metabolism*
  • Plant Stems / metabolism*
  • Quaternary Ammonium Compounds / metabolism
  • Solanaceae / metabolism
  • Time Factors
  • Tyrosine / metabolism


  • Enzyme Inhibitors
  • Indans
  • Nitrogen Isotopes
  • Quaternary Ammonium Compounds
  • Ammonium Chloride
  • Glutamine
  • Glutamic Acid
  • Tyrosine
  • Phenylalanine
  • Phenylalanine Ammonia-Lyase
  • Nitrogen