Glutamine synthetase and glutamate dehydrogenase contribute differentially to proline accumulation in leaves of wheat (Triticum aestivum) seedlings exposed to different salinity.
To investigate the roles of ammonium-assimilating enzymes in proline synthesis under salinity stress, the activities of glutamine synthetase (GS; EC 6.3.1.2) and NADH-dependent glutamate dehydrogenase (NADH-GDH; EC 1.4.1.2) were determined in leaves of wheat (Triticum aestivum) seedlings exposed to salt stress at 150 and 300 mM NaCl for 5d. At the lower salinity, only GS activity increased markedly. At 300 mM NaCl, however, NADH-GDH activity increased while GS activity decreased. A significant accumulation of proline was found only at high-salinity exposure while glutamate, a proline precursor, increased dramatically under both low and high salinity. These data suggests that GS-catalysis might be the main glutamate synthesis pathway under low salinity. At 300 mM NaCl, glutamate seems to be preferentially produced through the process catalyzed by NADH-GDH. The increase of ammonium in salinity-stressed wheat seedlings might have resulted from increased photorespiration, which is responsible for the higher NADH-GDH activity. The activity of Delta(1)-pyrroline-5-carboxylate reductase (P5CR; EC 1.5.1.2) was significantly enhanced at 300 mM NaCl but remained unchanged at 150 mM. Delta(1)-Pyrroline-5-carboxylate synthetase (P5CS) activity did not show a specific response, indicating that P5CR might be the limiting step in proline synthesis from glutamate at high salinity.
Wang
Zhi-Qiang
ZQ
Key Laboratory of MOE for Plant Developmental Biology, College of Life Sciences, Wuhan University, Wuhan 430072, PR China.
Yuan
Yong-Ze
YZ
Ou
Ji-Quan
JQ
Lin
Qing-Hua
QH
Zhang
Chu-Fu
CF
D000596:Amino Acids / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D005969:Glutamate Dehydrogenase / Q000502:physiology*; D018086:Glutamate Dehydrogenase (NADP+) / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000502:physiology*; D007521:Isocitrate Dehydrogenase / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism / Q000502:physiology*; D011392:Proline / Q000096:biosynthesis / Q000378:metabolism*; D011762:Pyrroline Carboxylate Reductases / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D036226:Seedlings / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology*; D014908:Triticum / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D000097502:delta-1-Pyrroline-5-Carboxylate Reductase
D000596:Amino Acids; D002734:Chlorophyll; D005969:Glutamate Dehydrogenase; D018086:Glutamate Dehydrogenase (NADP+); D005974:Glutamate-Ammonia Ligase; D007521:Isocitrate Dehydrogenase; D009584:Nitrogen; D010940:Plant Proteins; D011392:Proline; D011762:Pyrroline Carboxylate Reductases; D000644:Quaternary Ammonium Compounds; D012965:Sodium Chloride; D000097502:delta-1-Pyrroline-5-Carboxylate Reductase; C039355:isocitrate dehydrogenase (NADP+)