Abstract:

The light-emitting-diode（LED）as precision modulation light sources were used in this study with 3 treatments comprised of red（R）light，blue（B）light and combination of red and blue light with proportion of 3︰1（3R1B），white light as the control. The content of main nitrogenous substances including total nitrogen，nitrate nitrogen，ammonium nitrogen，free amino acids and soluble protein，activities and gene expression of key enzymes from nitrogen metabolism including nitrate reductase（NR），nitrite reductase（NiR），glutamine synthetase（GS），glutamate dehydrogenase（GDH），asparagine synthetase（AS）and glutamate synthase（GOGAT）in leaf of tomato seedlings with‘SV0313TG’as experiment material were determined. The results showed that the nitrate nitrogen content and activities of NR and GDH and gene expression levels of 6 key enzymes for nitrogen metabolism under treatment of 3R1B were significantly higher than those of other treatments and the control，and the soluble protein content was also higher under this treatment than that of red and white light. While no significant difference was found between this treatment and blue light. In addition，the content of ammonium nitrogen and free amino acids under blue light was significantly increased compared with those of other treatments and the control，and activities of NR，NiR，GS and GOGAT，as well as relative expression of NR，NiR，GS2，FdGOGAT and LEAS1 were significantly higher than those of the control. Comparing with white light，red light significantly reduced the total nitrogen content，and activities of NiR，GOGAT，GDH and AS and expression of GDH1 were inhibited as well. In conclusion，in comparison with white light，the total nitrogen content and activities of some nitrogen metabolizing enzymes were reduced by red light. However，the content of free amino acids and ammonium nitrogen were enhanced by blue light. Combination of red and blue light could improve transcription levels of nitrogen metabolism-related enzymes and activities of some key enzymes in this pathway，thereby，promoting nitrogen absorption and converting into soluble protein. It is evidently that the combination of red and blue light with appropriate proportion could promote the nitrogen assimilation and the absorption of transformed nitrogen in tomato seedlings，accelerating substances accumulation，and then，stimulating the growth of tomato seedlings.

Key words: tomato, light quality, nitrogen content, nitrogen metabolism, amino acid