Ammonium uptake capacity and response of cytosolic glutamine synthetase 1;2 to ammonium supply are key factors for the adaptation of ammonium nutrition in Arabidopsis thaliana

Plant requires nitrogen for the growth, and it use nitrate and ammonium from the environment. Plant suffers from the toxicity when excess ammonium is supplied as a sole nitrogen, although it could be a good nitrogen source for plant growth. We hypothesized that the different responses of ecotypes to ammonium nutrient could partly account for the adaptation of Arabidopsis to an ammonium environment. The purpose of this study is to understand the different responses of ecotypes in ammonium environment. The growth of Arabidopsis thaliana ecotypes, Columbia was compared to those of Arabidopsis thaliana ecotypes, Landsberg erecta in ammonium nutrient. The ratio of shoot dry weight to root dry weight was compared to evaluate the adaptation of two ecotypes. The shoot:root ratio of Landsberg was significantly higher than that of Columbia. T-DNA insertion in cytosolic glutamine synthetase 1;2, one of the essential ammonium assimilatory enzymes, led a decrease of shoot:root ratio. We also measured the isotope-labeled ammonium uptake and the expression levels of ammonium transporter genes, and also the expression of ammonium assimilatory genes, glutamine synthetase genes and glutamate synthase genes, in roots after ammonium re-supply using real-time polymerase chain reaction analysis. We found that (1) ammonium uptake of Landsberg erecta was higher than that of Columbia, when ammonium was supplied at higher concentration, and (2) cytosolic glutamine synthetase 1;2 was highly increased by ammonium supply in the root of Landsberg erecta. The present study suggested the importance of these two factors for adaptation of Arabidopsis to an ammonium-rich environment.     

玉米硝酸盐累积及其在适应持续低氮胁迫中的作用

旱地作物吸收氮素的主要形态是硝酸盐,硝酸盐的积累与再利用对植物适应低氮土壤环境具有重要意义。本试验利用两个硝酸盐累积能力不同的玉米自交系478（硝酸盐积累低）和W312（硝酸盐积累高）为研究材料,研究玉米的硝酸盐累积及其在适应持续低氮胁迫中的作用。结果表明,W312的硝酸还原酶活性和NR基因的表达都弱于478,而体内氨基酸含量显著较低。对一个可能与液泡膜硝酸盐转运有关的氯离子通道蛋白基因（ZmCLC）的表达分析发现,478的ZmCLC表达显著强于W312。说明W312硝酸盐积累能力强主要是由于其较弱的氮同化能力,而不是硝酸盐向液泡的运输能力强。在砂培体系并持续缺氮条件下,W312叶绿素含量（SPAD值）显著高于478,表明植株体内较高硝酸盐累积有助于W312适应持续缺氮的土壤环境。     

植物吸收转运硝态氮及其信号调控研究进展

硝态氮是植物吸收利用的主要氮源,其吸收利用是一个高度协调复杂的调控过程。植物为了在各种变化的环境中生存,进化出了适宜不同环境的硝态氮吸收利用机制。植物根系中存在不同类型的硝态氮受体,可以感受外界硝态氮浓度变化,并启用高亲和力或低亲和力硝态氮吸收系统,从而吸收硝态氮;硝态氮进入根系后,大部分被运输到地上部进行同化作用,合成大分子物质,以促进植物生长;如果地上部硝态氮含量过多,植物可把多余的硝态氮运送到液泡内储存,待需要时再从液泡转运至细胞质中利用。植物生长发育过程中,老叶和成熟叶片中的硝态氮可被转运到新生组织中,促进新生组织生长。硝态氮吸收利用过程中大量硝态氮吸收、转运、储存、同化和信号调控基因被有序激活并协调工作,促进植物高效吸收利用硝态氮。本文主要针对NRT1和NRT2硝态氮吸收转运相关基因及其功能,以及参与初级硝态氮反应的相关转录因子和小信号多肽在硝态氮信号传导和组织间的信号交流进行综述,以便深入理解植物吸收利用硝态氮的机理,为高效利用氮素的作物育种和栽培技术的创建提供新的思路。     

不同生态型拟南芥耐铵毒害差异的生理机制

【目的】 利用拟南芥生态型群体研究拟南芥耐铵毒害的生理机制,为挖掘耐铵基因提供生理基础及理论指导。 【方法】 共收集了95份生态型拟南芥材料,采用水培实验方法,将拟南芥幼苗移栽后在正常培养液(2 mmol/L NO₃–-N处理)中培养8天,然后转移至含有1 mmol/L (NH₄)₂SO₄的营养液(2 mmol/L NH₄+-N处理)中培养8天,收获后,测定植株全氮量、地上部游离铵含量,以及谷氨酰胺合成酶 (GS) 活性;培养3天后取样,采用RT-PCR技术分析根部主要的铵态氮转运蛋白基因AMT1;1和AMT1;2的表达水平;拟南芥幼苗移栽后在正常培养液中培养8天,转移至丰度为5%的1 mmol/L (15NH₄)₂SO₄中培养,分别处理3 h、6 h和24 h取样,用于同位素分析。 【结果】 2 mmol/L铵态氮处理下拟南芥群体地上部的生长被显著抑制,并且大量游离铵离子累积于地上部,铵态氮下拟南芥群体体内铵含量是对照硝态氮下的1.5倍以上,其中Si-0生态型在铵态氮下铵含量为19.17 μmol/g, FW,是对照的20倍。在硝态氮培养条件下,内源铵的含量与拟南芥地上部生长呈显著负相关,铵态氮培养条件下,地上部生长与铵含量同样呈较高的负相关性,因此内源铵含量少的生态型拟南芥在铵态氮下亦耐铵,所以本研究以拟南芥群体组织内铵含量为主因子,筛选出耐铵拟南芥生态型Or-1、Ta-0,HSM和铵敏感拟南芥生态型Rak-2、Lpv-18、Hi-0,结果表明铵敏感生态型在硝态氮下铵含量是耐铵生态型的1.7倍至10倍。耐铵拟南芥生态型铵转运蛋白基因AMT1;1和AMT1;2的表达水平较铵敏感拟南芥高,植株全氮和地上部15N标记试验结果表明,耐铵拟南芥铵态氮吸收速率高于敏感型。并且耐铵拟南芥生态型在两种氮形态下其谷氨酰胺合成酶 (GS) 活性均显著高于铵敏感生态型,在硝态氮培养条件下GS活性是铵敏感生态型的1.1～1.8倍,在铵态氮培养条件下是1.2～1.6倍,说明耐铵拟南芥生态型的铵同化能力强于敏感型。 【结论】 耐铵生态型拟南芥是通过更高的谷氨酰胺合成酶 (GS) 活性将大量的游离铵同化以减少植株体内游离铵含量,从而减轻植株铵毒害;而不是通过减少铵态氮的吸收。      

Identification of genomic regions regulating ammonium-dependent inhibition of primary root length in Arabidopsis thaliana

Plant roots grow into the soil for efficient acquisition of various nutrients, such as inorganic nitrogen, ammonium, and nitrate. A previous study has revealed the genetic diversity of foliar functions of Arabidopsis thaliana ecotypes in an environment containing ammonium; however, the function of roots remains unclear. This work focuses on the root system architecture (RSA) of Arabidopsis ecotypes to investigate the genetic factors regulating ammonium-dependent RSA changes. Arabidopsis ecotypes were grown on vertical agar medium containing ammonium as a major nitrogen source, and root growth and RSA were determined. Arabidopsis ecotypes showed differential sensitivity to ammonium. The shoot dry weight of some ecotypes decreased, whereas that of other ecotypes increased in ammonium medium. The RSA changes also varied among the different ecotypes in response to ammonium. The total root length, measured as the sum of primary root and lateral root length, of some ecotypes was reduced, whereas that of other ecotypes showed no significant difference in ammonium medium. Compared with lateral roots, the primary roots showed a sharp response to ammonium supply. Notably, the RSA showed a partial correlation with shoot dry weight in ammonium medium. Because Col-4 and Ler-0 showed opposite RSA responses to ammonium supply, these two ecotypes were selected for further genetic analysis. Quantitative trait locus (QTL) analysis of recombinant inbred lines of Col and Ler showed the involvement of several genetic factors in ammonium-dependent RSA changes. Moreover, QTL analysis revealed that the primary structure of nitrogen-related enzymes do not account for changes in RSA in response to ammonium supply.     

增硝营养对不同基因型水稻苗期硝酸还原酶活性及其表达量的影响

利用控制条件下的溶液培养方法,研究了增硝营养(NH4+∶NO3-比例为100∶0和50∶50)对两种不同的基因型水稻南光和云粳苗期生长和硝酸还原酶(NR)活性及基因表达量的影响。结果表明,不同基因型水稻在增NO3-营养下生物量、氮素含量、氮积累量的增幅南光大于云粳。NO3-的存在增强了水稻硝酸还原酶的活力和NR基因OsNia1、OsNia2的表达。不同基因在水稻幼苗中,两个品种OsNia2的相对表达量均高于OsNia1。就品种而言,无论叶片还是根系,增硝后南光OsNia2mRNA表达量都高于云粳;南光叶片OsNia1mRNA表达量也较云粳叶片高。增硝营养提高了水稻NR基因的表达,增加了NR活性,促进了水稻NO3-的同化利用,从而增加了氮素在植株地上部的积累同化。南光和云粳相比,前者对NO3-的响应更为强烈。     

Response of Lowland and Aerobic Rice to Ammonium and Nitrate Supply During Early Growth Stages

Decreasing fresh water availability has intensified the search for alternative rice cultivation systems with reduced water input, but most evidence suggests negative effects on growth of lowland (LL) rice cultivars. Yield in such production systems may be improved by selection of adapted aerobic ‘Han Dao’ (HD) rice cultivars. Lowland and HD rice were compared under sole nitrate or ammonium supply as well as under mixed supply of both nitrogen (N) forms during the seedling and tillering stage; pronounced differences were found in response to the supplied N form. Shoot dry mass (DM) of HD was significantly lower than that of LL under sole and predominant ammonium supply, whereas LL showed the opposite trend, with significantly lower shoot DM under sole-nitrate supply. Nitrogen concentration of LL rice under sole-nitrate supply was significantly lower compared with other treatments at tillering stage. Han Dao rice had a significantly higher potassium (K) concentration than LL rice under sole-nitrate supply, while the opposite result was observed under sole-ammonium supply. At seedling stage, the portion of N that was taken up from nitrate-N varied from 30% to 40% in HD and LL rice in treatments 75N/25A and 50N/50A, while at both growth stages, predominant ammonium supply resulted in a lower portion (20%) of nitrate-derived N in LL than in HD rice. The portion of nitrate-derived N increased at tillering stage (from 40% to 70%). These results further illustrate a synergistic effect of co-provision of nitrate and ammonium on total N fluxes compared with supply of sole nitrate or sole ammonium. It was concluded that the interaction between N form and tiller formation during early growth stages deserves strong attention for the identification of aerobic rice cultivars.     

Nitrogen metabolism is related to improved water‐use efficiency of nodulated alfalfa grown with sewage sludge under drought

Leguminous plants grown in sewage sludge–amended soils can acquire nitrogen by assimilation of nitrate and ammonium from the soil solution or from atmospheric‐dinitrogen (N₂) fixation through association with N₂‐fixing bacteria. We proposed that operation of both metabolic processes could contribute to alleviate the impact of drought in sludge‐treated plants. A greenhouse experiment was conducted to evaluate the involvement of nodule metabolism in the use efficiency of water and N in sludge‐treated plants. Treatments comprised (1) plants inoculated with rhizobia and amended with sewage sludge; (2) plants inoculated with rhizobia without any amendment; and (3) noninoculated plants supplied with ammonium nitrate, each under well‐watered and drought conditions. Under drought, sludge‐treated plants had increased plant growth and higher photosynthetic and water‐use efficiencies than untreated plants. Drought stimulated nitrate reductase and GS/GOGAT activities but did not affect the activities of phosphoenolpyruvate carboxylase and malate dehydrogenase or the leghemoglobin concentration. The results suggest that under drought conditions, both N₂ fixation and nitrate assimilation in nodules of sludge‐treated plants contributed to improve plant N supply and to increase the drought tolerance of alfalfa.     

氮饥饿水稻利用不同形态氮素的差异及其生理机制

通过水培试验，研究了氮饥饿7d后，恢复供应不同形态氮源对水稻氮吸收和积累及氮同化中关键酶活性和光合色素的影响。结果表明，缺氮促进根系生长，增加根冠比。恢复供氮4d显著增加地上部生物量。铵硝混合营养促进了水稻对氮的吸收和转运，叶片和根系中全氮及叶片中铵态氮的含量以硝酸铵处理最高。与单一铵或硝营养相比，铵硝混合营养增强了根系的谷氨酰胺合成酶和叶片中硝酸还原酶的活性，提高了水稻同化和利用氮的能力。另外，与纯硝营养相比，供应铵态氮显著增加了叶片中总叶绿素，尤其是叶绿素a的含量。因此，改善水肥管理、平衡对水稻供氮的铵硝配比将提高水稻氮素的吸收和利用效率。     

Relationship between water and nitrogen uptake in nitrate‐ and ammonium‐supplied Phaseolus vulgaris L. plants

Sole ammonium supply provokes negative effects on dry‐mass formation, leaf growth, and water uptake of ammonium‐sensitive plants. To study the effects of N form on nutrient and water uptake and aquaporin expression, French bean plants were grown in a split‐root system. Five treatments were compared: homogeneous nitrate (NN) and ammonium (AA) supply; spatially separated supply of nitrate and ammonium (NA); and half of the root system supplied with N‐free nutrient solution, the other half with either nitrate (N0) or ammonium (A0). Ten days after onset of treatments, root dry mass (DM) and water‐uptake rate (WUR) were significantly reduced under ammonium compared to nitrate supply. WUR from nitrate‐supplied vessels was 80% higher than that from N‐free nutrient solution, while WUR from N‐free nutrient solution was 130% higher than that from ammonium‐supplied vessels. Potassium uptake was lower under ammonium supply and the ratio of N : K uptake of treatment AA was significantly higher compared to others. High K uptake from N‐free nutrient solution of A0 plants resulted in a ratio of N : K uptake comparable to nitrate‐supplied plants, but shoot growth resembled that to plants under sole ammonium supply. Within 24 h after onset of treatments, expression of aquaporin was lower under ammonium compared to nitrate supply. From these data, it can be concluded that reduced root water transport under ammonium supply is directly related to aquaporin activity.     

有机配体、竞争阳离子和pH对土壤中Zn分解的影响

A series of experiments were conducted to examine the interactive effects of an organic ligand, a competing cation, and pH on the dissolution of zinc （Zn） from three California soils, Maymen sandy loam, Merced clay, and Yolo clay loam. The concentrations of soluble Zn of the three soils were low in a background solution of Ca（NO3）2. Citric acid, a common organic ligand found in the rhizosphere, was effective in mobilizing Zn in these soils; its presence enhanced the concentration of Zn in soil solution by citrate forming a complex with Zn. The ability of Zn to form a complex with citric acid in the soil solution was dependent on the concentration of citric acid, pH, and the concentration of the competing cation Ca^2＋. The pH of the soil solution determined the extent of desorption of Zn in solid phase in the presence of citric acid. The amounts of Zn released from the solid phase were proportional to the concentration of citric acid and inversely proportional to the concentration of Ca（NO3）2 background solution, which supplied the competing cation Ca^2＋ for the formation of a complex with citrate. When the soil suspension was spiked with Zn, the adsorption of Zn by the soils was retarded by citric acid via the formation of the soluble Zn-citrate complex. The dissolution of Zn in the presence of citric acid was pH dependent in both adsorption and desorption processes.     

Influence of N form on growth photosynthesis of Phaseolus vulgaris L. plants

Many plant species are characterized by pronounced sensitivity to sole ammonium supply and exhibit growth depression and particularly reduced leaf growth rates. Stress symptoms under sole ammonium supply may be related to perturbation of photosynthetic processes, e.g., low rates of net CO₂ assimilation, low quantum yield, reduced stomatal conductance, and carboxylation capacity. The results of three experiments with French bean plants supplied with an N concentration of 5 mM illustrate significantly lower dry mass and specific leaf area, reduced leaf expansion, and higher chlorophyll and N content of ammonium‐ compared to nitrate‐supplied plants. Light‐saturated rates of CO₂ assimilation (A_max) per unit leaf area were higher under ammonium compared to nitrate supply while no significant effects of N form on quantum yield and A_max per unit leaf weight and chlorophyll were found. Maximal carboxylation (V_cmax) and electron‐transport (J_Max) rates were significantly higher under ammonium supply only in one of three experiments. V_cmax was linearly related to total leaf N, the slope of the regression was similar with both N forms, the x‐axis intercept was significantly higher for ammonium‐ compared to nitrate‐supplied plants. The ratio V_cmax : J_Max was not affected by N form. It is concluded that ammonium supply had no negative effects on the operation of photosynthetic protein‐enzyme complexes.     

Induction of high affinity nitrate and ammonium uptake systems in wheat

Abstract

The ability of 7 day old wheat seedlings to take up nitrate or ammonium from hydroponic solution was measured. Seedlings were grown under fully aerated hydroponic conditions. The growth solution consisted of either 0.5 mM CaSO₄ alone or in combination with high nitrate (5 mM NO₃ ^‐ ), high ammonium (2 mM NH₄ ⁺) or modified 1/10 Hoaglands solution with nitrate N only (14 mM) or ammonium N only (2 mM). After washing the roots for one hour in CaSO₄, nitrate or ammonium uptake was measured with an ion selective electrode. Plants grown in high nitrate were unable to take up nitrate from a 0.1 mM external solution. Those grown in CaSO₄ were able to take up nitrate at the same external concentration (flux = 10.2 +/‐ 3.0 μmol nitrate/g dry wtlbh). The same result was seen for plants grown in high ammonium vs those grown in CaSO₄ (flux = 21.0 +/‐ 10.0 μmol/g dry wtlbh). Similar results were obtained when modified Hoagland's solution was substituted for the high N solutions. These data indicate that wheat roots possess both high and low affinity nitrate and ammonium uptake systems. The data further indicate that, for a given ion, the high and low affinity systems do not operate simultaneously under high N conditions. The high affinity system is switched off in the range of 1 mM for both ionic forms of N. Developmental studies show that the expression of the high affinity trait is reversible and may be induced (repressed) by conditioning for 24 h in low (high) N media. Plants grown in high N solutions showed efflux of the ion under assay conditions. Neither ion interfered with the induction/repression of the high affinity trait for the other under the conditions used in this study.     

氮素敏感时期水稻分蘖芽的转录分析

  【目的】  氮素影响水稻分蘖芽的发育,从而影响水稻株型和产量。探究水稻分蘖芽在氮素敏感时期的基因表达情况,揭示氮素对水稻分蘖芽调控的可能途径。  【方法】  以水稻品种‘日本晴’为试验材料,萌发后用1/2MS培养基培养一周,之后用2.5 mmol/L的氮素溶液培养,待幼苗长至三叶期,进行0和2.5 mmol/L氮素溶液处理,培养至五叶期。对不同氮素浓度下分蘖芽的生长进行分析,确认水稻材料的氮素敏感时期,并于根茎结合处取样,提取RNA,进行氮素敏感时期水稻分蘖芽的转录组分析,包括差异表达基因的挖掘以及GO功能富集分析、KEGG通路分析、蛋白互作网络分析。  【结果】  缺氮条件下,水稻分蘖芽生长受到抑制,转录分析结果显示,不同供氮条件下842个基因存在显著的表达差异,其中586个基因缺氮时上调,256个基因缺氮时下调。GO功能富集分析发现绝大多数差异表达基因属于胞内 (cell)、胞内成分 (cell part) 和细胞器 (organelle) 的类别。在差异表达基因的KEGG通路分析中,植物激素信号传导途径是最显著富集的通路,氮代谢途径次之,说明植物激素通路和氮代谢通路在水稻分蘖芽的生长过程中具有重要作用。差异表达基因主要涉及生长素、细胞分裂素、脱落酸、水杨酸、茉莉酸等相关激素的合成代谢途径以及参与氮代谢的硝酸还原酶。蛋白互作分析推测硝酸还原酶可能会与植物激素相互作用。  【结论】  通过对氮素敏感时期水稻分蘖芽相关基因的转录分析,发现缺氮条件下,激素信号传导途径和氮代谢途径中相关基因的表达量均受到影响。其中,与硝酸还原酶和植物激素脱落酸合成相关的基因表达量上调,而影响分蘖芽生长的细胞分裂素和生长素基因表达均下调。     

Differences in nitrogen‐assimilating enzyme activity in halophyte species are habitat‐related

The chemical form and content of available nitrogen (N) in salt marsh substrates varies considerably. On the western coast of Ireland, habitats designated as Ombrogenic Atlantic salt marshes were formed on ombrogenic peat substrate. The peat substrate in these systems has three times more ammonium than substrate from adjacent salt marsh habitats on sand and mud substrate. This study examined the extent to which the high concentration of ammonium in peat salt marsh substrate influences the N‐ assimilating enzyme activity of halophytes and the extent to which N metabolism differs between species. Specifically, this work investigated whether plants from peat salt marshes are more likely to assimilate ammonium than plants from non‐peat substrates. Four halophyte plant species—Armeria maritima, Aster tripolium, Plantago maritime, and Triglochin maritime—were sampled from various saltmarsh habitats including three sites on peat substrate and three on non‐peat substrate, comprising sand, mud and sand/mud. The activities of N‐metabolising enzymes—glutamine synthetase (GS), glutamate synthase, glutamate dehydrogenase (GDH), and nitrate reductase (NR)—were quantified in shoot and root parts. Root GS activity in Armeria maritima and shoot GS activity in Triglochin maritima were positively correlated with increasing soil ammonium levels. Root NR activity in Aster tripolium and shoot NR activity in Plantago maritima were significantly higher in plants grown on non‐peat substrates than peat substrates. The shoot : root GS activity ratio in Triglochin maritima on peat substrate was more than double the ratio on non‐peat substrates. It is concluded that all species tested displayed differences in N‐metabolising activities depending on the chemical form and/or concentration of N in the substrate, while three out of the four species were capable of taking advantage of the high levels of ammonium in peat substrates.     

Molecular basis of the nitrogen response in plants

Nitrogen is an essential element for living organisms because it is a crucial constituent of biomolecules. Inadequate supply of usable nitrogen reduces plant growth and crop yield. The primary nitrogen sources for plants are nitrate and ammonium in soils, and plants have multiple layers of sensing and adaptive mechanisms that respond to the availability of these nutrients. The adaptive responses are called ‘nitrogen responses,’ which include morphological and physiological responses enabling plants to efficiently take up nitrogen and adapt to spatiotemporal fluctuations in nitrogen abundance in the field. In this review, we summarize the strategies that plants use to respond to changes in the nitrogen nutrient status in the soil and discuss different effects produced by nitrate and ammonium, emphasizing the important role of nitrate for plant growth. Recent studies revealed the molecular mechanism mediating the primary response to nitrate provision and the molecular mechanisms that coordinate the nitrogen response with responses to another macronutrient, phosphorus. We thus discuss these molecular mechanisms as well.     

不同铵硝比例对水稻铵吸收代谢基因表达的影响

以水稻南光为材料,研究了不同铵硝摩尔比例处理时,水稻NH4^＋吸收代谢基因的表达情况.档结果表明：（1）应用荧光定量PCR方法,可以精确检测水稻氮素吸收代谢基因在不同铵硝处理间的表达量变化;（2）从各基因的表达量上来看,吸收基因中以OsAMT1.1表达量最高,编码GS的基因中以OsGln1.1表达量最高,编码GOGAT的基因中,OsGlu表达量最高;（3）总体来说,不同铵硝处理对NH4^＋吸收代谢基因的表达有显著影响,吸收基因对不同铵硝比例的反应要比代谢基因更敏感;（4）氮吸收基因中OsAMT4.1显著受到NO3的抑制,NH4^＋的诱导.而OsAMT1.1,OsAMT1.2,OsAMT1.3和OsNRT2在铵硝摩尔比例由100：0变为50：50过程中,受到NO3^-的显著抑制,在铵硝摩尔比例由50：50变为0：100过程中OsAMT1.2和OsAMT1.3受到NO3^-的显著诱导,OsAMT1.1和OsNRT2变化不显著;（5）编码GS的基因OsGln1.1表达受NO3诱导,受NH4^＋抑制.OsGln2在铵硝摩尔比例由100：0变为50：50过程中,受到NO3^-增加的诱导,同时,OsGln1.2受到NO3增加的显著抑制作用,铵硝达到50：50以后,NO3^-比例的增加对OsGln1.2和OsGln2的表达没有显著影响;（6）编码GOGAT的基因OsGlt1和OsGlu在不同铵硝摩尔比例中的变化趋势一致：铵硝比例由100：0变为50：50过程中没有显著变化,铵硝比例50：50基础上表达量受到NO3^-比例增加的显著抑制,而OsGlt2的表达受NO3^-的显著抑制,NH;的显著诱导.     

杨梅硝酸还原酶活力研究

用改进的活体法测定了杨梅幼树体内硝酸还原酶(NR)的分布状况。杨梅叶片,枝条、根和根瘤的NR活力分别为404.59,226.40,135.87和45.05 n mol NO_2/30min/gFW。品种、枝梢种类及叶片成熟度不同,其NR活力也不同。介质中氮源的种类和浓度对杨梅叶片的NR活力也有明显影响。对未结瘤的幼苗和离体幼树枝条,硝态氮能提高叶片的NR活力和叶片中的硝态氮含量,两者随硝酸盐浓度的增高而提高;铵态氮抑制叶片的NR活力,浓度愈高,抑制作用愈强。     

供氮水平对芦荟幼苗生长、硝酸盐和次生代谢产物含量的影响

采用温室砂培试验研究了不同氮素水平(5.0、7.5、10.01、5.01、7.5.mmol/L)对二年生库拉索芦荟生长和蒽醌、芦荟甙等次生代谢产物及硝酸盐含量的影响。结果表明,供氮水平由5.0.mmol/L增加到10.0.mmol/L,库拉索芦荟地上部产量和总生物量显著增加,继续提高氮水平芦荟地上部产量和总生物量没有显著增加;芦荟根干重及其根冠比则随着氮水平的增加而下降;叶片和根系的硝酸盐含量则随施氮浓度的提高呈增加趋势。供氮浓度从5.0mmol/L增加到10.0.mmol/L时,叶片的维生素C(Vc)含量显著增加,继续提高供氮水平,叶片Vc含量则明显下降;蒽醌含量则随施氮水平的上升而不断增大,但施氮10.0、15.0、17.5.mmol/L的处理间没有显著性差异。芦荟甙含量变化趋势和Vc含量相似,以施氮10.0.mmol/L为最高,其含量分别是其它处理的1.4、1.2、1.4、1.3倍。由此可见,芦荟在供氮10.0.mmol/L时能够获得较高的产量和蒽醌含量,较低的硝酸盐含量和高的Vc和芦荟甙含量,表明适宜的供氮水平是芦荟高产优质的保证。