Effects Of Osmotic Stress On Ammonium Assimilation Enzymes

The effects of NaCl-stress on ammonia assimilation enzymes and the related parameters were determined in the roots of three rice {Oryza sativa L.) cultivars differing in salt tolerance. The results showed that the activities of glutamine synthetase (GS) and NADH-dependent glutamate synthase (NADH-GOGAT), as well as the levels of soluble protein decreased under high concentration salt. The influence extent was in accordance with Zao-hua 2 (salt-sensitive), Jin-zhu 1 (normal cultivar), Jin-dao 779 (salt-resistant), which was consistent with their salt-tolerance. Results from native-PAGE and activity dyeing indicated that GSrb by external nitrogen is more sensitive to the change of the external condition. Under the stress of high salt concentration, NADH-dependent glutamate dehydrogenase (NADH-GDH) activity of Zao-hua 2 and Jin-zhu 1 was induced significantly, but that of Jin-dao 779 did not increased remarkably. The salt stress led to the accumulation of total soluble sugar (TSS) in the root of Jin-zhu 1 and Jin-dao 779 in different degree. The level of TSS in Zao-hua 2 changed with different NaCl concentration, this suggested that the increase of TSS level would decrease the loss of water to keep the relative balance of ions in tissue, and play a role in making the activity of GOGAT and GS enzymes higher. Among the cultivars observed, content of proline increased in different degree, but under high salt concentration, it had a more marked rise in the roots of salt-sensitive cultivars.Under salt stress and iso-osmotic water stress brought by Polyethylene glycol 6000 (PEG-6000), ammonium assimilation enzymes and the relative parameters of the leaves of rice seedlings were detected. Analyzing for ammonium concentration,ammonium-assimilating enzymes, and osmoregulatory solutes showed ammonium assimilation enzymes was affected significantly by two kinds of stress. Under the iso-osmosis condition, compared with water stress, the activity of glutamine synthetase (GS) was remarkably decreased by salt stress which caused a more significant ammonium accumulation in the leaves. The activity of NADH-dependent glutamate dehydrogenase (NADH-GDH) was induced during the ammonium concentration was enhanced under these stress conditions.