UPTAKE AND TRANSPORT CHARACTERISTICS OF ORGANIC AND INORGANIC NITROGEN IN RICE SEEDLINGS

The study was conducted in sterile hydroponics using isotopes tracer technique to demonstrate the posibility for rice seedlings (variety: C Liangyou 266) to directly absorb and utilize molecular organic nitrogen, transport and assimilation of organic/inorganic nitrogen. Further the activity of assimilation-related enzymes i.e Glutamic-oxaloacetic transaminase (GOT), Glutamic-pyruvic transaminase (GPT) and Glutamate dehydrogenase (GDH), in rice seedlings were also studied using isotopic tracing technique. In this regard N-15 -ammonium sulfate, 15N -potassium nitrate and 2-C-13 -N-15 -glycine salts were used to analyzes the abundance of C-13/N-15. The results suggest that the 15N excess and the ratio of N-15 excess in shoot to root under glycine nitrogen treatment (Gly-N) were significantly higher than those under ammonium nitrogen or nitrate nitrogen treatment (p<0.05); the C-13 excess/N-15 excess ratios of rice organs and the whole seedling measured at 24h after Gly-N approximated the theoretical value of 1:1, which showed gradual declines 48h and 72h later. The activities of glutamic-oxaloacetic transaminase (GOT), glutamic-pyruvic transaminase (GPT) and glutamate dehydrogenase (GDH), in rice seedlings cultured by organic nitrogen were significantly higher than those by inorganic nitrogen (p<0.05). The findings also showed that rice seedlings are capable for direct absorbing and utilizing molecular glycine nitrogen. The absorption rate of glycine nitrogen was much higher than that of ammonium nitrogen or nitrate nitrogen. The transport capabilities of organic and inorganic nitrogen in rice plants, ranked in descending order are as follows: glycine nitrogen > ammonium nitrogen > nitrate nitrogen.