GLUTAMINE-SYNTHETASE OF ROOTS AND LEAVES IN RESPONSE TO NITROGEN APPLICATION AT DIFFERENT GROWTH-STAGES IN FIELD-GROWN RICE

Information on glutamine synthetase (GS) activity of roots and leaves in response to nitrogen (N) application at different growth stages is limited for field-grown rice. Root and leaf GS activity was measured o n field-grown rice plants to compare the effects of fertilizer-N appli cation at midtillering, panicle initiation, and flowering. Leaf GS act ivity was greater than root GS activity, regardless of N application. Root and leaf GS activity generally declined as plant aged, and the de cline was greater in roots than leaves. Leaf and root GS activity were significantly increased by urea-N applied at different growth stages. Root GS activity was maximum three days after N application, while le af GS activity peaked one day after N application. Root GS activity sh owed greater response to N application at midtillering and panicle ini tiation than leaf GS activity, but the opposite was found at flowering . The stimulation of GS activity by N was greatest at midtillering and reduced with plant age.