Abiotic stress generates ROS that signal expression of anionic glutamate dehydrogenases to form glutamate for proline synthesis in tobacco and grapevine.
Glutamate dehydrogenase (GDH) may be a stress-responsive enzyme, as GDH exhibits considerable thermal stability, and de novo synthesis of the alpha-GDH subunit is induced by exogenous ammonium and senescence. NaCl treatment induces reactive oxygen species (ROS), intracellular ammonia, expression of tobacco (Nicotiana tabacum cv Xanthi) gdh-NAD;A1 encoding the alpha-subunit of GDH, increase in immunoreactive alpha-polypeptide, assembly of the anionic isoenzymes, and in vitro GDH aminating activity in tissues from hypergeous plant organs. In vivo aminating GDH activity was confirmed by gas chromatorgraphy-mass spectrometry monitoring of (15)N-Glu, (15)N-Gln, and (15)N-Pro in the presence of methionine sulfoximine and amino oxyacetic acid, inhibitors of Gln synthetase and transaminases, respectively. Along with upregulation of alpha-GDH by NaCl, isocitrate dehydrogenase genes, which provide 2-oxoglutarate, are also induced. Treatment with menadione also elicits a severalfold increase in ROS and immunoreactive alpha-polypeptide and GDH activity. This suggests that ROS participate in the signaling pathway for GDH expression and protease activation, which contribute to intracellular hyperammonia. Ammonium ions also mimic the effects of salinity in induction of gdh-NAD;A1 expression. These results, confirmed in tobacco and grape (Vitis vinifera cv Sultanina) tissues, support the hypothesis that the salinity-generated ROS signal induces alpha-GDH subunit expression, and the anionic iso-GDHs assimilate ammonia, acting as antistress enzymes in ammonia detoxification and production of Glu for Pro synthesis.
Skopelitis
Damianos S
DS
Department of Biology, University of Crete, 71409 Heraklion, Greece.
Paranychianakis
Nikolaos V
NV
Paschalidis
Konstantinos A
KA
Pliakonis
Eleni D
ED
Delis
Ioannis D
ID
Yakoumakis
Dimitris I
DI
Kouvarakis
Antonios
A
Papadakis
Anastasia K
AK
Stephanou
Euripides G
EG
Roubelakis-Angelakis
Kalliopi A
KA
D000586:Amination; D000838:Anions; D053938:DNA Fragmentation; D008401:Gas Chromatography-Mass Spectrometry; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005969:Glutamate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D018698:Glutamic Acid / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D011392:Proline / Q000096:biosynthesis*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012965:Sodium Chloride / Q000378:metabolism
D000838:Anions; D017382:Reactive Oxygen Species; D018698:Glutamic Acid; D012965:Sodium Chloride; D011392:Proline; D005969:Glutamate Dehydrogenase