铵硝营养对番茄幼苗根系中NR、GS活性及表达的影响

Effects of Different Nitrogen Forms on Activity and Expression of NR and GS in Root of Tomato Seedlings

为探讨不同形态氮(N)素对番茄幼苗根系中N素代谢相关酶活性及其基因表达差异,揭示不同形态N素影响番茄幼苗吸收和同化NO_3^-、NH_4^+差异的机理,本文采用全根和分根两种培养方式,研究了番茄幼苗在不同形态N素处理下,硝酸还原酶(NR)、谷氨酰胺合成酶(GS)活性以及NR基因(Le NR)、GS基因(Le GS)表达差异。结果表明,在全根培养下,当营养液中NO_3^-/NH_4^+为50/50处理下根系干重分别是NO_3^-/NH_4^+为100/0和75/25的50.00%和28.5 7%;在分根培养下,在N|A处理下,供单一NO_3^-和单一NH_4^+营养根系干重分别是N|N处理下的176.76%和133.28%。在全根培养下,随着营养液中NH_4^+比例的增加,根系中NR活性显著降低,GS活性呈先增加后降低的趋势,Le NR的表达量逐渐降低。在分根培养下,与N|N处理相比,局部根系供单一NH_4^+营养显著降低了自身根系中NR活性和Le NR表达量,显著提高了GS活性,但对另一侧(供NO_3^-)根系中Le NR的表达量没有影响。局部根系供NO_3^-、NH_4^+混合营养对自身根系中Le NR的表达量没有显著影响,但显著抑制了另一侧(供NO_3^-)根系中Le NR的表达量。在不同培养方式和不同形态N素处理下,Le GS表达量均没有显著性差异。由此可得,介质中NH_4^+营养降低了根系中NR活性和Le NR的表达量,提高了根系中GS活性但对Le GS表达量无显著影响。

The aim of this study was to investigate the effects of different 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 % NH4^＋supply was decreased by 50. 00 % and 28. 57 %,respectively,compared to sole NO3^-supply and 75 % NO3^-plus 25 % NH4^＋supply. In split-root system,dry weight of root supply with sole NO3^-and NH4^＋in the N ｜ A treatment was found to be increased by 76. 76 % and 33. 28 %,respectively,compared to the corresponding values in the N ｜ N treatment. In whole-root system,with the increase of NH4^＋/ NO3^-ratio in nutrient solution,the NR activity decreased notably,but the GS activity increased with the NH4^＋/ NO3^-ratio reaching a maximum at 75 /25 and decreased at 50 /50. In split-root system,localized supply of sole NH4^＋significantly decreased the NR activity 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（ LeN R,accession number： X14060） was depressed with the increase ofNH4^＋in nutrient solution in a homogeneous supply. In a splitroot system,however,in comparison to N ｜ N treatment,the expression of LeN R was significantly depressed in the root which was supplied by sole NH4^＋but was no significant difference in the opposite root which was supplied with sole NO3^-. Spatially separately supplied by sole NO--3and the mixture of 75 % NO3 plus 25% NH4^＋were no significant difference in the expression of LeN R in both half roots. Both in a homogeneous and a local-ized supply,there was no significant difference in the expression of GS gene（ LeG S,accession number： U15059） in root of tomato seedlings no matter what N form was supplied. It was concluded that NH4^＋in nutrient solution decreased the NR activity and the expression of NR gene in tomato seedling root,and increased the GS activity,but had no significant effect on the expression of LeG S.