Abstract: Influence of nitrogen sources on the activity of glutamine synthetase (GS), GS isozymes and GS-mRNA in wheat (Triticum aestivum L. ) seedlings has been studied by DEAE-cellu- lose column chromatography, enzyme activity assay and Northern blot technique, and activity of GS and nitrate reductase (NR) was compared. The results indicated that the activity of GS in roots (GSr) and cytoplasmic GS (GS1) in both intact and excised leaves was higher with NH4+-N as the sole nitrogen source than with NO3--N. However, NO3- promated the activity of chloroplasmic GS (GS2) in leaves of wheat with NO3- -N as the sole nitrogen surce. On the level of transcription, NH+ raised the level of GS mRNA in roots, but NO3- raised the level of GS-mRNA in leaves of wheat seedling.

Key words: Glutamine synthetase, Nitrogen source, Glutamine synthetase-mRNA, Wheat