植物应答缺铁胁迫的分子生理机制及其调控

铁是植物生长发育中所必需的微量营养元素。虽然土壤中铁的丰度很高,但其生物有效性非常低,特别是在碱性石灰性土壤上,高pH和高重碳酸盐含量严重降低了土壤中铁的有效性。因此如何有效地提高植物对铁的利用效率及增强植物对缺铁胁迫的响应已成为目前该领域的研究热点。本文重点阐述了植物两种不同的铁吸收机制,以及对缺铁胁迫的应答反应;对目前所发现的植物中调控缺铁胁迫的相关基因进行了全面的综述,包括新发现的吞噬机理中所涉及的NRAMP基因;同时也介绍了感应铁缺乏的众多相关信号,包括植物激素、气体信号分子及microRNAs等;此外,还提出利用铁吸收相关基因的转导、控制铁吸收相关因子以及各种农艺措施的实施来提高植物铁的生物有效性从而有效缓解缺铁胁迫。最后对未来有关植物吞噬机制、铁缺乏感应信号及改善植物铁营养新途径等研究方向作了初步展望。     

机理Ⅰ植物铁吸收与运输的分子机制

铁虽然在地壳中的含量很高,但生物有效性非常低,植物如何适应缺铁胁迫一直是植物营养与植物逆境生理领域研究的热点问题。近两年来,人们对于植物,尤其是机理Ⅰ植物适应铁胁迫的机制又有了新的认识,铁还原酶基因的表达部位除根系外,在地上部、花等器官也能够检测到;IRT1基因是机理Ⅰ植物主要的Fe(Ⅱ)运输基因;烟碱酰胺在铁的长距离运输中起到重要作用。本文从还原、吸收、长距离运输及对这些过程的调控等方面综述了近年来有关机理Ⅰ植物适应铁胁迫的研究进展,并对将来的研究方向进行了初步展望。     

缺铁条件下酵母中铁转运转录水平的研究进展

铁作为生物体内重要元素,在很多细胞功能以及生化过程中具有重要作用。尽管多数土壤中铁含量较为丰富,但在碱性或中性土壤中可以吸收利用的可溶性铁量却无法满足植物需要。在这种情况下所导致的缺铁胁迫不利于植物生长发育。本文从铁吸收系统的激活、胞内铁源的启动和铁相关代谢活动的调控三个方面阐述了酵母细胞中铁转运转录水平上的研究现状,最后展望了其发展前景。     

机理I植物铁吸收与运输的分子机制

铁虽然在地壳中的含量很高，但生物有效性非常低，植物如何适应缺铁胁迫一直是植物营养与植物逆境生理领域研究的热点问题。近两年来，人们对于植物，尤其是机理I植物适应铁胁迫的机制又有了新的认识：铁还原酶基因的表达部位除根系外，在地上部、花等器官也能够检测到；IRT1基因是机理I植物主要的Fe (Ⅱ) 运输基因；烟碱酰胺在铁的长距离运输中起到重要作用。本文从还原、吸收、长距离运输及对这些过程的调控等方面综述了近年来有关机理I植物适应铁胁迫的研究进展，并对将来的研究方向进行了初步展望。     

策略Ⅰ植物铁吸收稳态调控研究进展

铁是植物生长发育所必需的微量元素。作为辅酶因子和电子传递链组分，铁参与了光合作用、呼吸作用等多种重要的生理代谢过程。铁在地壳中的含量虽然丰富，但在中性和碱性土壤中大多以Fe³⁺的形式存在，溶解度极低，限制了土壤中铁的生物有效性，导致植物生长发育易受缺铁影响，致使植物缺铁失绿已成为全世界普遍关注的问题。但在低pH和长期淹水条件下，植物会吸收累积过量的铁，产生活性氧，导致植物伤害甚至死亡。因此精确调控铁的吸收转运，保持体内铁稳态是植物生长发育的基础。本文就策略I植物铁稳态调控方面的最新研究进展做一阶段性总结，并对存在的问题和未来的发展动态提出了作者的观点。     

植物吸收和转运铁的分子生理机制研究进展

铁是植物正常生命活动过程中的必需微量元素之一。由于土壤中铁的有效性很低,导致植物极易缺铁,不仅影响作物的产量和品质,而且影响人类微量元素健康,因此如何通过生物强化达到人类铁营养状况改善的目的是目前该研究领域关注的热点。本文就近5年来植物铁吸收、体内转运、子粒中积累等重要生物过程的分子生理机制的研究进展进行了详细阐述,其中对水稻兼备机理I和机理II铁吸收机制有了新的认识,而且发现YSL蛋白家族在植物铁吸收、转运和子粒积累过程中的重要性。同时,讨论了利用上述机制的研究结果通过基因工程和农学措施改善植物铁营养和提高作物子粒铁富集的技术途径。     

外界铁浓度调控缺磷植物铁吸收相关基因的表达量

磷和铁都是植物必需营养元素,缺磷和缺铁都会严重影响植物生长发育导致作物产量和品质下降。前期研究表明缺磷会导致植物铁吸收基因的表达量下降,但这种下降与外界铁浓度是否相关还不清楚。本文检测了缺磷和正常磷条件下不同铁浓度对植物铁吸收基因的表达变化。结果显示,缺磷导致植物主根生长受到显著抑制,但该抑制现象和铁浓度显著相关,在铁浓度下降到一定范围后该抑制作用消失。qPCR结果显示,缺磷显著诱导缺磷响应基因IPS、SPX3、PHT1;4表达量增加,且这种表达量增加仅受缺磷诱导,和铁浓度无关。缺磷也显著诱导铁吸收相关基因FRO2、IRT1和CYP82C4的表达量下降,但这种下降具有明显铁浓度依赖性。随着铁浓度升高,缺磷诱导的铁吸收基因的表达量下降幅度随之增大,这可能是由于缺磷导致培养基中铁的有效性增加所致。本研究结果为土壤磷、铁肥料管理提供了新的视角。     

矿质养分和激素对根毛生长发育的影响及作用机制

【目的】植物矿质养分和水分的吸收利用赖于根系,根系中根毛的生长发育不仅扩大了根系吸收表面积,促进了矿质养分和水分的吸收还有助于植物根的固定以及与土壤微生物的互作。本文从矿质养分角度(氮、 磷、 钾、 钙、 铁)和激素角度(生长素、 乙烯、 茉莉酸、 独脚金内酯、 油菜素内酯)探讨影响根毛生长发育的因子及作用机理。【主要进展】氮对根毛生长发育的影响与茉莉酸和乙烯有关, 磷与生长素、 乙烯、 独脚金内酯互作调控根毛生长发育;生长素和乙烯以交互作用调控根毛生长发育,茉莉酸、 独角金内酯和油菜素甾醇对根毛生长发育的作用是部分依赖生长素或乙烯途径;植物体内生长素和乙烯等激素的平衡对根毛的生长发育起着重要作用。【建议和展望】基于以上分析,从蛋白激酶及其相关调控基因及转录因子等方面可深入探析矿质养分、 植物激素等对根毛和丛枝菌根生长发育的影响。     

微生物在植物铁营养中的潜在作用

根据近十多年来相关研究成果讨论了土壤微生物在植物根系吸收铁中可能的作用机理。这种机理可能包括缺铁植物根系分泌小分子有机化合物,如酚类和黄素类等化合物,这些化合物作为抑菌剂和(或)作为微生物生长的碳源物质来影响根际(Rhizosphere)微生物的群落结构,并在植物根际诱导形成特异性微生物种群,此类特异性微生物转而通过分泌高铁载体(Siderophore),增加土壤中铁的生物有效性,从而提高了根系对铁的吸收。此外,与植物根系共生的一些微生物也会改善植物的铁营养,这种作用可能包括:根瘤菌(Rhizobium)的结瘤作用,增强植物耐缺铁的生理响应;根系感染的菌根真菌通过增加植物根系的养分吸收面积和分泌对铁具有螯合作用的物质来改善植物的铁营养。本文在讨论这种可能的微生物作用机制的基础上,指出今后的研究方向和有待解决的问题。     

果树缺铁黄化研究进展

果树缺铁黄化是一个世界性的难题，各国对此进行了广泛深入的研究。本文根据国内外有关铁素营养方面研究的最新成果，对果树生长的主要障碍因子，植物对缺铁胁迫的反应和可能机理以及矫治措施等进行了综述。     

Iron deficiency‐induced zinc uptake by bread wheat

The present study aimed to test the contribution of the iron (Fe) deficiency‐induced uptake system to zinc (Zn) and copper (Cu) uptake by using bread wheat (Triticum aestivum cv. Bezostaja). For this purpose, two different uptake experiments, long‐term and short‐term, were set up in a nutrient solution culture under controlled growth chamber conditions. For the long‐term experiment, wheat cv. plants were grown with different concentrations of Fe or Zn. Results show that there was an uptake system induced under Fe‐limiting conditions which also contributed to Zn and Cu uptake. However, the Zn deficiency‐induced uptake mechanism affected neither Fe nor Cu uptake by wheat. Short‐term uptake experiments indicate that Fe deficiency‐induced Zn²⁺ uptake was more enhanced than the absorption of Zn‐phytosiderophore (PS) complexes. In addition, the Fe‐deficient plants absorbed more Zn in comparison to those plants supplied with sufficient Fe. Similar tendencies in Zn uptake under Fe deficiency in both short‐ and long‐term experiments suggest that there may be a specific Fe uptake system induced under Fe‐limiting conditions for non‐chelated metals in bread wheat. Moreover, this system also contributes to the transport of inorganic forms of some other metals, such as Zn and Cu. Although evidence is still needed involving the use of molecular biological techniques, it is hypothesized that IRT‐like proteins are responsible for this uptake system. Moreover, the release of Fe deficiency‐induced phytosiderophores and uptake of Fe(III)‐phytosiderophore complexes may not be the only mechanisms involved in the adaptation of wheat to Fe‐limiting conditions.     

Iron deficiency causes zinc excess in Zea mays

Iron deficiency stress causes a severe reduction in plant growth. Although Fe deficiency causes an imbalance in divalent heavy metal nutrients, the mechanisms underlying the growth reduction caused by this imbalance remain unclear. We investigated Zn uptake and accumulation in maize under Fe-deficient conditions. Under Fe-deficient conditions, Zn uptake was 15-fold higher and Zn accumulation was 16-fold higher than that under normal nutrient conditions. The Zn content of maize leaves under Fe-deficient conditions was >0.4 mg g⁻¹ dry weight, which was higher than the content of plants grown in a nutrient solution containing 50 µM ZnCl₂. Plant growth under conditions of both Fe and Zn deficiency was significantly higher than that under only Fe-deficient conditions. Moreover, Fe deficiency increased the thiol content of the plant. These results indicate that Fe deficiency causes excess uptake and accumulation of Zn, and that the stress resulting from the Zn overload accelerates growth reduction in maize.     

Fe uptake from meso and D,L-racemic Fe(o,o-EDDHA) isomers by strategy I and II plants

One of the most efficient fertilizers to correct Fe deficiency in calcareous soils and waters with high bicarbonate content is based on ferric ethylenediamine-N,N'-bis(o-hydroxyphenylacetic) acid [Fe(o,o-EDDHA)]. Fe(o,o-EDDHA) forms two groups of geometric isomers known as meso and D,L-racemic. To determine the Fe uptake from meso and D,L-racemic Fe(o,o-EDDHA), four iron-efficient plants, two plants representative of strategy I (tomato and pepper) and two plants representative of strategy II (wheat and oats), were grown in hydroponic culture. Results indicated that strategy II plants took up iron from both Fe(o,o-EDDHA) isomers equally. However, strategy I plants took mainly the iron associated with the meso form (the lowest stability isomer).     

Mechanisms for the Movement of Fe,Mn,Cu and Zn to Plant Roots in Loessal Soil and Lou Soil

The pot experiments were conducted in the artificial climate laboratories to determine the relative importance of mass flow and diffusion in supplying ,Fe,Mn,Cu,and Zn to wheat,soybean and maize plants growing in loessal soil and lou soil.It was found that the calculated relative contribution of mass flow of iron,manganese,copper and zinc to plant uptake varied from 5% to more than 100%,depending on the crop species and soil types as well as plant growth stage,soil moisture,atmosphere humidity,etc.The results also showed that the major transportation mechanisms of these micronutrients in soil-root system varied with the crop and its growth,climate and soil,singnificantly,In general,mass flow was more important for Cu and Zn and diffusion was more significant for Fe and Mn at the seedling stage.     

黄土和塿土中Fe, Mn, Cu和Zn向植物根部移动的机理

The pot experiments were conducted in the artificial climate laboratories to determine the relative importance of mass flow and diffusion in supplying Fe, Mn, Cu and Zn to wheat, soybean and maize plants growing in loessal soil and lou soil. It was found that the calculated relative contribution of mass flow of iron, manganese, copper and zinc to plant uptake varied from 5% to more than 100%, depending on the crop species and soil types as well as plant growth stage, soil moisture, atmosphere humidity, etc. The results also showed that the major transportation mechanisms of these micronutrients in soil-root system varied with the crop and its growth, climate and soil, significantly. In general, mass flow was more important for Cu and Zn and diffusion was more significant for Fe and Mn at the seedling stage.     

铁和ATP酶抑制剂对鸭跖草(Commelina communis)铜吸收的影响

缺铁条件下研究了鸭跖草 (Commelinacommunis)对不同浓度铜及不同形态铜的吸收和P 型ATP酶抑制剂对铜吸收的影响。结果表明 ,鸭跖草铜累积量随着营养液中铁浓度的下降而显著上升 ,缺铁在不同铜浓度下都显著促进鸭跖草对铜的吸收 ,说明鸭跖草铜吸收与铁元素关系密切。在缺铁条件下 ,EDTA Cu、NTA Cu、草酸 Cu、柠檬酸 Cu处理鸭跖草的铜吸收量均低于单Cu处理 ,但缺铁处理植株对不同形态铜的吸收量均高于完全培养液生长的植株。缺铁处理下鸭跖草会产生根际酸化效应。P 型ATP酶抑制剂钒酸钠对铜吸收有抑制作用 ,缺铁对铜吸收的促进作用可能与P 型ATP酶活性无关     

不同梨砧木对缺铁胁迫的生理响应差异研究

【目的】 旨在通过探究缺铁胁迫下不同梨砧木幼苗体内铁分配规律及有机酸种类和含量的差异,为培育铁高效利用梨砧木提供理论依据。 【方法】 以三种不同梨砧木,杜梨Ⅰ (湖北杜梨HB-Pyrus betulaefolia)、杜梨Ⅱ (郑州杜梨ZZ-Pyrus betulaefolia) 、山梨 (黑龙江山梨HS-Pyrus ussuriensis) 幼苗为试材,进行水培试验。以Hogland营养液为基础,在其他养分含量不变的情况下,设两个Fe水平1和40 μmol/L,分别代表缺铁胁迫和正常供铁。在砧木幼苗培养21天后,测定了幼苗活性铁和全铁元素含量、根系构型及各部位不同种类有机酸的含量。 【结果】 缺铁胁迫下,杜梨Ⅰ茎叶中活性铁/全铁比例是杜梨Ⅱ的2.80倍和2.94倍, 是山梨的3.29倍和2.05倍,其叶中的活性铁和全铁积累量分别达到15.71 mg/plant和78.82 mg/plant。缺铁胁迫下,杜梨Ⅱ和山梨的倒一叶叶绿素含量下降幅度显著高于杜梨Ⅰ。三种梨砧木幼苗体内柠檬酸含量最高,其次是苹果酸,这两种酸占有机酸总量的74.8%以上。与正常供铁相比,缺铁胁迫下山梨根和叶中苹果酸含量提高了4.70和1.69倍,分别达到0.96 mg/g和4.80 mg/g,显著高于杜梨Ⅰ和杜梨Ⅱ,而杜梨根和叶中的柠檬酸含量较高,尤其是杜梨Ⅰ品种,达到4.02 mg/g和11.98 mg/g。 【结论】 三种梨砧木对铁的吸收和运输存在较大差异。杜梨Ⅰ根系吸收能力较强,根和叶中活性铁含量及积累量均较高,因而耐缺铁。缺铁胁迫下,两种杜梨根系中主要合成柠檬酸而山梨主要合成苹果酸,可能是山梨对缺铁敏感的机制之一。      

Reduction of ferric iron by tumorous crown gall tissue is associated with cells modified by agro‐bacterium tumefaciens

Iron (Fe) uptake and use in plants is genetically controlled and physiological mechanisms such as Fe reduction are induced during Fe‐deficiency stress to make it available. Transfer of DNA into the cell genome by Agrobacterium tumefaciens alters physiological processes and causes undifferentiated growth. Tumor cells in sunflower (Helianthus annus L. cv. Mammoth Russian) show enhanced Fe reduction compared to normal stem tissue in a manner similar to root cells in plants that are genetically switched on or off to manage Fe acquisition. This study addresses whether alterations caused by the DNA transfer from A. tumefaciens result in Fe reduction or whether A. tumefaciens inoculum alone reduces Fe. Reduction of Fe was quantified from A. tumefaciens inoculum and from uninoculated or inoculated sunflower stem tissues daily over a 14‐day period. Neither A. tumefaciens inoculum nor uninoculated stem tissue alone activated massive Fe reduction. High rates of Fe reduction were associated with the proliferation of cells modified by A. tumefaciens. The mechanisms that transformed normal tissue to uncontrolled tumor growth appeared to be linked to active Fe reduction. These modified cells may provide a key to locating and understanding the genetic control of the Fe reduction process in plant cells. Our results suggest a critical role for Fe in development of tumorous tissues and raises the question of whether other tumor cells induce similar mechanisms for Fe acquisition.