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 a- polypeptide, assembly of the anionic isoenzymes, and in vitroGDHaminating activity in tissues from hypergeous plant organs. In vivo aminatingGDHactivity was confirmed by gas chromatorgraphy-mass spectrometry monitoring of N-15- Glu, N-15- Gln, and N-15- 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 ROSand immunoreactive alpha- polypeptide andGDHactivity. This suggests thatROSparticipate in the signaling pathway forGDH 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 ROSsignal induces alpha- GDH subunit expression, and the anionic isoGDHs assimilate ammonia, acting as antistress enzymes in ammonia detoxification and production of Glu for Pro synthesis.