植物体对硝态氮的吸收转运机制研究进展

硝态氮是高等植物重要的氮素营养,直接影响植物的生长。植物根系吸收硝态氮并向地上部转运的机制一直是研究者十分关注的问题。近几年的深入研究使得新的现象与结论被揭示,推动了我们对植物体吸收转运硝态氮生理与分子机制的认识。本文综述了近年来国内外关于植物硝态氮吸收转运的生理及分子机制的相关研究结果。通过整理归类植物硝酸盐吸收相关的生理学数据,介绍了影响植物吸收硝态氮的各种因素。基于膜转运体在植物硝态氮吸收转运过程中发挥的重要作用,本文还重点介绍参与该过程的四大基因家族的成员及功能,即硝酸盐转运体1(NRT1)、硝酸盐转运体2(NRT2)、氯离子通道(CLC)和s型阴离子通道(SLAC),以期为后续研究者提供一个较为全面的理论依据。     

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。     

植物吸收铵态氮的分子生物学基础

植物对铵离子的吸收和铵离子在细胞间的转运是铵转运蛋白介导的需能主动运输过程。植物铵转运蛋白位于细胞膜上,含有101～1个跨膜域,分子量约为48.kD。研究表明,植物体内的铵转运蛋白由小基因家族成员编码,在表达特性上不同成员具有时空特异性。植物体内铵转运蛋白在功能、生化特性和转录调节水平上存在差异。在不同氮素水平下,铵转运蛋白基因通过转录和翻译调控,对于保持植株的适宜氮素供应以及氮胁迫条件下维持植物细胞中氮素的内稳态具有重要作用。     

作物硝态氮转运利用与氮素利用效率的关系

【目的】 铵态氮（NH₄+）和硝态氮（NO₃-）是作物氮素吸收利用的主要形态,旱作作物NO₃-的累积与利用是氮素营养研究的主要组成部分,关系到理解作物NO₃-的转运和利用关系及作物体内NO₃-含量和氮素利用效率（nitrogen utilization efficiency,NUE）高低的问题。主要进展 作物吸收的NO₃-分为被作物直接利用、分泌到根外、储存在液泡和向地上部分运输四种途径。其中NO₃-短途分配（液泡NO₃-分配）和长途转运（地上、地下部NO₃-的转运）共同调控着NO₃-的利用效率,进而影响作物的NUE。液泡NO₃-不能被作物直接利用,只有分配到液泡外细胞质中的NO₃-才能被作物迅速代谢和利用;同时有更大比例的NO₃-分配到地上部分,使得作物可以充分利用太阳光能进行NO₃-代谢和能量转换,从而提高了作物的NUE。此外,液泡对NO₃-起到分隔作用,储存在液泡中的NO₃-并不能对NO₃-转运相关基因（如NR、NO₃-长途转运基因NRT1.5和NRT1.8）起到诱导效果;只有分配在液泡外原生质体中的NO₃-才能对NO₃-诱导基因产生强烈的诱导。因此,作物细胞原生质体中液泡内、外NO₃-的分配不仅影响了NO₃-的同化利用,而且直接影响了NO₃-的长途转运。展望 本文对植物原生质体中液泡内、外NO₃-的短途分配和地上、地下部间NO₃-的长途转运机制进行了总结,为进一步深入研究作物地上、地下部NO₃-长途转运和液泡NO₃-短途分配的关系,以及更好地揭示作物NUE对NO₃-转运和利用的响应机理提供参考。     

菠菜叶片硝态氮还原对叶柄硝态氮含量的影响

选用3个菠菜品种,设置N.0.1和0.3.g/kg2个施氮水平进行盆栽试验。在不同时期采样测定叶片内、外源硝酸还原酶活性、硝态氮代谢/贮存库大小,以及加入外源硝态氮培养后叶片硝酸还原酶活性的变化,探讨菠菜叶片的硝态氮还原与叶柄硝态氮含量的关系。结果表明,叶片内源硝酸还原酶活性、内源/外源硝酸还原酶活性比值、叶片的硝态氮代谢库大小及代谢/贮存库比值与叶柄硝态氮含量呈相反趋势。加入外源硝态氮培养后叶片硝酸还原酶活性的增加程度与叶柄硝态氮含量相一致。叶片内源硝酸还原酶活性高低及其发挥程度,叶片硝态氮代谢库大小及硝态氮在代谢、贮存库中的分配是造成品种间叶柄硝态氮含量高低差异的重要原因。     

华北平原水浇玉米-小麦轮作农田硝态氮的淋失

Soil water deep drainage and nitrate (NO3^-) leaching losses below the root zone were investigated in a 1 ha wheatmaize rotation field under traditional agricultural management that local farmers generally follow in the North China Plain, using the soil water balance method and NO3-N concentration in suction samples. Water drainage, and NO3-N distribution and leaching losses exhibited pronounced spatial and temporal variability. Soil water deep drainage and NO3- N leaching loss mostly occurred during the summer maize growing season (rainy season), which coincided with irrigations and significant rainfall. On average, soil water deep drainage was 39 and 90 mm in the 1998/1999 and 1999/2000 cropping years, correspondingly, accounting for 10% and 19% of the total irrigation plus rainfall, respectively. The NO3-N leaching loss from soil and fertilizer N below the root zone ranged from 6 to 17 (averaging 12) and 30 to 84 (averaging 61) kg N ha^-1 in 1998/1999 and 1999/2000, correspondingly, equivalent to 1.4%-4.1% and 7.3%-20.3% of N fertilizer applied,respectively. The results indicated that water and fertilizer inputs could be greatly reduced, thus improving water and nutrient use efficiency in this region.     

硝态氮供应下植物侧根生长发育的响应机制

旱地土壤上硝态氮是作物吸收和利用的主要无机氮形态。硝态氮不仅是植物营养的主要氮源,而且还可以作为信号物质调节植物根系生长发育。为适应土壤中硝态氮非均衡供应,植物侧根发育往往呈现出可塑性反应。本文综述了植物侧根生长发育对硝态氮供应的响应机制。在拟南芥、玉米、大麦等植物上研究表明,硝态氮对植物侧根发育具有双向调节途径,即:1)局部供应硝态氮,硝态氮自身作为信号物质通过信号传导通路发生作用,对侧根具有伸长的刺激效应,硝态氮转运蛋白AtNRT1.1作用于转录因子ANR1的上游,ANR1的转录调节侧根发育;2)植物组织中高浓度的硝态氮对侧根分裂组织活动具有抑制效应,植物激素如生长素和脱落酸可能参与其中的信号传导过程。近些年来研究发现小RNA也参与调控硝态氮供应下植物侧根发育。     

植物液泡硝态氮累积的营养和生理学意义

液泡是一个多功能而又复杂的细胞器。成熟植物茎叶的液泡占细胞体积的90%左右。细胞中的NO3--N有58%~99%存在于液泡中。因此,液泡被称为NO3--N的贮存库。研究植物细胞液泡的NO3--N累积引起了人们的重视,但是由于液泡中NO3--N测定技术的困难,这方面的研究目前并不很多。本文结合国内外相关研究结果,从以下几方面分析了NO3--N在液泡的累积:①植物液泡中NO3--N的累积数量;②NO3--N在细胞质与液泡间的转运;③液泡累积NO3--N的营养学意义;④液泡NO3--N累积的生理作用;⑤有关液泡中NO3--N累积研究的展望。     

Carbon costs of nitrate reduction in broad bean (Vicia faba L.) and pea (Pisum sativum L.) plants

The present study aimed at the assessment of carbon (C) costs for nitrate reduction by measuring the additional CO₂ amounts released from roots of nitrate‐fed plants in comparison with urea‐fed plants. Only roots were suitable for these determinations, because nitrate reduction in illuminated shoots is fed nearly exclusively by reducing equivalents coming directly from photosynthetic processes. Therefore, in a first experiment, the sites of nitrate reduction were determined in nodule‐free broad bean (Vicia faba L.) and pea (Pisum sativum L.) plants grown in pots filled with quartz sand and supplied with KNO₃. The extent of nitrate reduction in the various plant organs was determined by measuring in vitro nitrate reductase activity and in situ ¹⁵NO reduction. Only between 9% and 16% of nitrate were reduced in roots of German pea cultivars, whilst 52% to 65% were reduced in broad bean roots. Therefore, C costs of the process could be determined only in broad bean, using an additional pot experiment. The C costs amounted to about 4.76 mol C (mol N)^–1 or 4 mg C (mg N)^–1, similar to those measured earlier for N₂ fixation. The high proportion of nitrate reduction in shoots of pea plants implies that only very little C is required for this nitrate fraction. This can explain the better root growth of nitrate‐nourished pea plants in comparison with N₂‐fixing organisms, which need C compounds for N₂ reduction in roots. Moreover, a different availability of photosynthates in roots of plant genotypes could explain physiologically the occurrence of “shoot and root reducers” in nature.     

高等植物GS/GOGAT循环研究进展

高等植物体内 95%以上的NH4+通过GS/GOGAT(谷氨酰胺合成酶 /谷氨酸合成酶 )循环同化。GS、GOGAT在植物叶片、根瘤以及根中均有分布 ,但在不同器官中GS/GOGAT循环的作用不尽相同。在绿色组织中 ,GS/GOGAT循环的主要作用是同化光呼吸产生的NH4+以及硝酸盐在叶中还原产生的NH4+,在根瘤中则主要同化根瘤菌固N产生的NH4+,而在根中则是同化吸收到体内的NH4+以及硝酸盐被吸收后在根中还原产生的NH4+。迄今有关植物GS/GOGAT循环的研究还不太深入 ,但是随着基因工程技术、免疫组织化学技术以及现代植物生理学技术的发展 ,GS/GOGAT循环研究展示广阔前景。对该循环及其调控机制的进一步了解 ,可为合理利用氮肥、提高植物N的利用率提供理论依据。本文综述了近年来对GS/GOGAT循环的研究进展情况     

Effect of nitrate and humic substances of different molecular size on kinetic parameters of nitrate uptake in wheat seedlings

The kinetic parameters of nitrate uptake (I_max, Km and C_min) were evaluated in young seedlings of Triticum durum L., cv. Appulo, exposed to nitrate and/or to soil‐extracted humic acids (HAs) of different molecular weight. The uptake was enhanced after induction at low levels of nitrate (50 μM KNO₃), while it was inhibited after induction at higher concentrations (2000 μM). The kinetic parameters of uptake were selectively influenced by pre‐treatment with HAs: total (TE) and, at a greater extent, low (LMS, < 3500 Da) molecular size humic fraction increased either the nitrate uptake rate (I_max) and the efficiency of the whole transport system (low Km and C_min), while an opposite result was evidenced in high molecular size (HMS, > 3500 Da)‐treated plants. An additive effect was shown when nitrate and humic substances were provided simultaneously: the uptake rate was enhanced in TE‐ and LMS‐treated plants, but was strongly delayed in HMS‐treated plants. Removal of nitrate and/or humic fractions de‐induced the system and NO₃^— uptake rate decreased. Exposure to HAs was not able to induce nitrate reductase activity in root and leaf tissues. Inhibitors of protein synthesis p‐fluorophenylalanine and cycloheximide reversed the positive effect of LMS fraction on nitrate uptake. This would support the hypothesis of a promoting effect of HAs on the molecular expression of proteins of the nitrate transport system.     

Nitrogen transport in plants,with an emphasis on the regulation of fluxes to match plant demand

Physiological methods, especially the use of isotopes of N, have allowed for the detailed characterizations of the several putative transport systems for nitrate and ammonium in roots of higher plants. In the last decade, the cloning of genes that appear to encode both high- and low-affinity transporters represent major advances, as well as substantiating the inferences based on earlier physiological methods. Nevertheless, the unexpected plethora of genes that have been identified now presents even greater challenges, to resolve their individual functions and to attempt to place these functions in a whole plant/environmental context.     

Use of the nitrate electrode for determination of nitrates in soils

Abstract

A procedure for the rapid and accurate determination of water‐extractable soil nitrates is described. Use of this procedure resulted in quantitative recovery of nitrates added to soil. Reproducibility of results was high, with nitrate‐nitrogen in 40 soil samples determined on successive days differing by a maximum of 4 ppm with 33 determinations differing by 2 ppm or less. Comparison with a phenoldisulfonic acid method on 513 soil samples had a maximum difference of 7 ppm with a majority of determinations having a difference of 4 ppm or less.     

植物细胞质雄性不育分子生物学研究进展

阐述了植物细胞质雄性不育相关的线粒体嵌合基因结构、起源、作用机理及其离体表达 ,花粉发育特异基因表达 ,导致植物细胞质雄性不育因素 ,植物细胞质雄性不育恢复育性等方面分子生物学研究进展 ,简介了现代基因工程构建细胞质雄性不育系的策略     

Effect of nitrate leaching in oxisol columns on 15N abundance and nitrate breakthrough curves

Abstract

Nitrate (20 mg N0₃‐ N l^?1) was leached through 180 cm columns of oxisol subsoil until the leachate attained the initial nitrate concentration. Leaching was continued with water until no nitrate was detectable in the leachate.

The Δ¹⁵N for the first aliquot of leachate containing nitrate was 2.2 units lower than that of the added solution indicating that ¹⁵Nwas preferentially adsorbed to ¹⁴N. The breakthrough curve for nitrate indicated that nitrate adsorption decreased after six pore volumes. The implications for modelling nitrate leaching are discussed.     

Rapid field determination of nitrate in natural waters

Abstract

Brucine, an organic reagent used for nitrate determinations, proved stable for at least one year when dissolved in methanol. This makes possible a consistently accurate and rapid method for field determinations of nitrate in clear solutions with a minimum of equipment. The method is also useful in the laboratory for determining nitrate in water or soil extracts. It is quicker and simpler than other colorimetric methods and more sensitive to low concentrations than the nitrate electrode.