Search

The aim of tliis stiady was to investigate the effects of diferent N forms on activity and expression of N metabolizing enzymes in tomato seedlings root，and to elucidate the difference of different N forms on NO3- and NH4+ uptake and utilization. In the present study，whole- and split-root experiments were together conducted to study the effects of different nitrogen (N) forms on activity and expression of nitrate reductase (NR) and glutamine synthetase (GS) in root of tomato (Lycopersicon esculentum Mill. ) seedlings. Results showed that in whole-root system，root dry weight in 50 % NO3- plus 50 e NH4+ supply was decreased by 50. 00 e and 28. 57 e，respectively，compared to sole NO3- supply and 75 e NO3- plus 25 e NH4+ supply. In split-root system，dry weight of root supply with sole NO3- and NH4+ in the NR treatment was found to be increased by 76. 76 e and 33. 28 e，respectively，compared to the corresponding values in the NR treatment. In whole-root system，with the increase of NH4+ /NO3- ratio in nutrient solution，the NRactivity decreased notably，but the GS activity increased with the NH4+ /NO3- ratio reaching a maximumat 75/25 and decreased at 50/50. In split-root system，localized supply of sole NH4+ significantly decreased the NRactivity and significantly increased the GS activity in the root which was exposed to the sole NH4+，compared with sole NO3- supply. Otherwise，the expression of NR gene (LeNR，accession number : X14060) was depressed witli the increase of NH4+ in nutrient solution in a homogeneous supply. In a split-root system， however， in comparison to N I N treatment，the expression of LeNR was significantly depressed in the root which was supplied by sole NH4+ but was no significant diference in the opposite root which was supplied with sole NO3-. Spatially separately supplied by sole NO3 and the mixture of 75 e NO3 plus 25 e NH4+ were no significant difference in the expression of LeNR in bothi half roots. Both in a homogeneous and a localized supply, there was no significant dlference in the expression of GS gene (LeGS, accession number: U15059) in root of tomato seedlings no matter what N form was supplied. It was concluded that NH$ in nutrient solution decreased the NRactivity and the expression of NRgene in tomato seedling root, and increased the GS activity, but had no significant effect on the expression of LeGS. [ABSTRACT FROM AUTHOR]