水稻吸收转运铁的生物地球化学机制研究进展

铁的生物吸收转移是环境中铁生物地球化学循环的重要过程之一，不仅控制着铁在稻米的累积，且影响水稻累积锌等养分元素及镉等重金属。阐明土壤-水稻体系中铁的吸收转移机制对深入理解稻田铁的环境行为与归趋具有重要的科学意义。主要介绍了水稻中铁吸收转运的功能基因、土壤-水稻系统铁同位素分馏及水稻植株中铁分布的光谱分析方法与手段，重点总结铁在水稻根部吸收及植物体内的转运过程，探讨铁对水稻根部锌和镉吸收的影响机制，可为提高水稻产量及改善稻米品质提供科学依据。     

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。     

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。     

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。     

有机肥与植物种类对铁肥形态转化及其有效性的影响

通过盆栽试验的方法，研究了牛粪和植物种类对石灰性土壤中铁肥形态转化及其有效性的影响。结果表明，牛粪施用改变了土壤中铁（含外源铁）的有效性及其在各形态铁间的分配，从长期的观点来看，牛粪施用能提高土壤铁的有效性，有利于土壤铁有效供给的维持，与花生相比，油菜对土壤铁具有更高的利用和活性能力，种植油菜后，土壤交换态铁被耗竭，而有效铁、氧化锰结合态铁和无定形氧化铁结合态铁的含量明显提高。有机肥的合理施用和铁效率差异性植物间的轮作或间作是增加、维系土壤铁有效性的重要农艺措施。     

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。     

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。     

蛋白质组学分析揭示水稻地上部对缺铁和高铁胁迫的响应

铁在矿质土壤中含量丰富，但在中性和碱性土壤中大多以不易被植物吸收利用的氧化物或氢氧化物形式存在；稻田土壤在淹水条件时氧化还原电位较低，大量铁以易被植物吸收利用的亚铁形式存在。土壤中铁的生物有效性过低或过高均会导致植物的生长发育受阻。本研究对缺铁（0 μmol?L-1）、铁充足（40 μmol?L-1）和高铁（350和500 μmol?L-1）条件生长的水稻地上部进行了非标记蛋白质组学分析。结果显示，与铁充足条件相比，缺铁和两种浓度的高铁胁迫水稻中分别有130、157和118个蛋白质的丰度发生显著变化。基因本体富集分析显示，缺铁和高铁胁迫下的差异蛋白在初级代谢过程、有机氮化合物代谢过程、蛋白质代谢过程和细胞成分组织或生物发生等生物学过程均显著富集；差异蛋白还参与核糖体、光合作用和氧化磷酸化等代谢途径。缺铁胁迫显著影响参与苯丙烷类物质和辅助因子生物合成的蛋白质丰度，而高铁胁迫则引起氨基酸生物合成过程的蛋白质丰度发生显著变化。本研究发掘到一系列可用于水稻铁高效育种工作的候选蛋白，还发现了一些功能未知的差异蛋白可作为后续水稻铁胁迫响应的研究目标，同时为理解植物应对铁胁迫的完整响应网络提供了补充信息。     

氮素供应对玉米子粒铁累积的影响

谷物子粒的铁营养是影响人及动物营养状况的重要因素之一,但对子粒铁营养的生理限制因素了解十分缺乏。氮素供应可能通过影响营养器官中的物质转移从而影响子粒铁的供应。本研究以玉米为材料,在田间两个氮水平(施氮、不施氮)下研究了吐丝至成熟期玉米从土壤中铁的吸收量、不同营养器官中铁的输出量、及其对子粒铁的表观贡献率,探讨了氮素供应对这些过程的影响。结果表明,氮素供应对子粒铁浓度没有显著影响,两个氮水平下,茎(含叶鞘)中铁的净输出量为1.25～1.71.mg/plant、输出率为40.4%～48.2%,对子粒铁的表观贡献率为50.9%～69.8%。中部叶片(穗位叶及其上、下各两片叶)中铁的含量表现为净增加。不施氮时营养器官中铁的净输出量和输出率低于施氮,而吸铁量对子粒铁的表观贡献率却高于施氮。两个氮水平下,吐丝至成熟期子粒铁的源(营养器官输出铁与从土壤中吸收的铁之和)的供应能力均大于子粒铁的累积能力(累积量),说明铁的吸收和转运可能不是决定子粒铁浓度的主要因素,子粒中铁的卸载及代谢可能是限制子粒铁营养的主要生理过程。     

根表铁膜对元素吸收的效应及其影响因素

水生植物根系表面普遍形成铁膜,铁膜的形成是水生植物适应淹水和其他环境胁迫的重要机制之一.大量研究表明铁膜在植物吸收有益营养元素和有害元素中有重要作用.本文总结了植物根表铁膜形成的过程及铁膜的形态、组分、数量等特征,阐述了铁膜对植物吸收元素的效应.水生植物根表的铁膜能够阻止植物对金属元素的吸收,也可充当植物根系表面的养分"库",在植物需要养分时铁膜中的养分可以被活化并被植物吸收利用.此外铁膜的效应还与根表铁膜的数量有关,少量铁膜能够促进植物对养分的吸收,而大量铁膜则阻止植物对养分的吸收.造成铁膜不同效应的因素包括植物、重金属和研究采用的手段和技术等.如植物种类、品种、生育阶段以及营养状况、植物的培养方式、所研究的金属离子种类以及根表铁膜的分析技术等均可影响试验结果.进一步的研究工作需考虑铁膜形成的外部环境,利用原位技术以确定铁膜中元素的分布和化学形态,并将铁膜的效应与土壤植物的整体反应结合起来进行系统的研究.     

Iron toxicity in rice—conditions and management concepts

Iron toxicity is a syndrome of disorder associated with large concentrations of reduced iron (Fe²⁺) in the soil solution. It only occurs in flooded soils and hence affects primarily the production of lowland rice. The appearance of iron toxicity symptoms in rice involves an excessive uptake of Fe²⁺ by the rice roots and its acropetal translocation into the leaves where an elevated production of toxic oxygen radicals can damage cell structural components and impair physiological processes. The typical visual symptom associated with these processes is the “bronzing” of the rice leaves and substantial associated yield losses. The circumstances of iron toxicity are quite well established. Thus, the geochemistry, soil microbial processes, and the physiological effects of Fe²⁺ within the plant or cell are documented in a number of reviews and book chapters. However, despite our current knowledge of the processes and mechanisms involved, iron toxicity remains an important constraint to rice production, and together with Zn deficiency, it is the most commonly observed micronutrient disorder in wetland rice. Reported yield losses in farmers' fields usually range between 15% and 30%, but can also reach the level of complete crop failure. A range of agronomic management interventions have been advocated to reduce the Fe²⁺ concentration in the soil or to foster the rice plants' ability to cope with excess iron in either soil or the plant. In addition, the available rice germplasm contains numerous accessions and cultivars which are reportedly tolerant to excess Fe²⁺. However, none of those options is universally applicable or efficient under the diverse environmental conditions where Fe toxicity is expressed. Based on the available literature, this paper categorizes iron‐toxic environments, the steps involved in toxicity expression in rice, and the current knowledge of crop adaptation mechanisms in view of establishing a conceptual framework for future constraint analysis, research approaches, and the targeting of technical options.     

土壤铁氧化物-亚铁的相互作用及其环境影响研究进展

铁氧化物和溶液相亚铁常在厌氧土壤环境中共存。铁氧化物能够加快亚铁的氧化速率，且控制亚铁氧化成矿产物的类型，同时，亚铁与铁氧化物组成的系统是一种良好的还原剂，能够有效还原重金属及降解有机污染物。另一方面，亚铁能够催化铁氧化物晶相转变，导致铁氧化物结构和表面性质发生改变，进而影响相关重金属、有机质的环境行为。本文综述了铁氧化物催化亚铁氧化成矿、铁氧化物-亚铁系统还原污染物以及亚铁催化铁氧化物相变的反应机制及影响因素，最后，对未来在自然土壤中研究铁氧化物-亚铁界面反应及其环境影响进行了展望。     

Iron Homeostasis in Plants: Sensing and Signaling Pathways

Abstract

Since iron is both an essential element as well as a potential toxin, it is a nutrient which on the one hand fulfils many important functions in plants but on the other can cause severe cell damage as a consequence of the formation of reactive hydroxyl radicals. Uptake of iron, its concentrations within particular tissues, and its subcellular distribution is therefore subject to careful control. In addition, the low bioavailability of iron in most soils necessitates the mobilization of sparingly soluble iron compounds. This has led to the evolution of concerted responses that assist in maintaining an adequate supply of iron for plant roots. These responses comprise morphological changes, such as the development of extra root hairs, formation of rhizodermal transfer cells, and induction of cluster roots, as well as induction of genes coding for enzymes involved in the mobilization and uptake of nutrients. Investigations at the protein, mRNA, and structural level showed that both systemic responses, involving transmission of long distance signals, and external nutritional signals, inducing localized responses, are involved in the complex control of iron homeostasis. A number of components have been identified at the molecular level, but the interplay between these components and the signal transduction cascades leading to an iron status within an adequate range are largely unknown. This review summarizes the available data that explain how these processes are coordinated to maintain a continuous and acceptable Fe supply despite changing environmental conditions.     

Iron deficiency of soybean in the North Central U.S. and associated soil properties

Despite extensive research and variety screening efforts, iron deficiency chlorosis is a common, yield-limiting condition for soybean [Glycine max (L.) Merr.] grown in areas with high pH, calcareous soils. In the North Central U.S., total land area where soybean is grown on high pH soils is approximately 1.8 million ha, with iron deficiency responsible for an estimated loss in soybean grain production of 340,000 Mg at a value of $820 million per annum. This is a significant increase in the extent of iron deficiency problems relative to the past because of an expansion of soybean production in the region. Soil properties associated with iron deficiency in this region compared to adjacent areas without iron deficiency include greater soil moisture content and concentrations of soluble salts, carbonates, and DTPA-Cr, and lesser concentrations of DTPA-Fe, Mn, Ni, and Cd. Iron deficiency occurs due to multiple stresses and not simply to limited available iron. Biotic and management factors such as pests and diseases, symbiotic nitrogen fixation, seeding rate, and herbicide application also interact with iron deficiency in the field. There is a need to better match varieties to the specific soil and environmental conditions to which they are adapted.     

Iron availability from iron-fortified spirulina by an in vitro digestion/Caco-2 cell culture model

Iron deficiency, one of the most important nutritional problems in the world, can be caused not only by foods deficient in iron but also by poor availability of dietary iron. Iron food fortification in combination with highly available iron from supplements could effectively reduce this deficiency. The aim of this study was to examine the iron availability from iron-fortified spirulina. We have used an in vitro digestion/Caco-2 cell culture system to measure iron spirulina availability and made a comparison with those of beef, yeast, wheat floor, and iron sulfate plus ascorbic acid as a reference. Iron availability was assessed by ferritin formation in Caco-2 cells exposed to digests containing the same amount of iron. Our results demonstrate a 27% higher ferritin formation from beef and spirulina digests than from digests of yeast and wheat flour. When iron availability was expressed per microgram of iron used in each digest, a 6.5-fold increase appeared using spirulina digest in comparison with meat. In view of this observed high iron availability from spirulina, we conclude that spirulina could represent an adequate source of iron.     

水稻土中砷的环境化学行为及铁对砷形态影响研究进展

在水淹缺氧环境下,界面微环境中水稻土铁矿物的还原以及根表铁膜的生成是引起砷释放还原和促进砷被吸附的过程,识别铁对砷的作用机制是有效降低水稻对土壤砷吸收的方法。本文综述了水稻土中铁对砷的作用机制的国内外研究现状,并从水稻通气组织、土壤溶液氧化还原电位、铁矿物类型、有机质和阴离子种类等5个方面讨论水稻土中铁对砷的化学行为的影响,并展望了今后的研究方向,以期为水稻土砷污染防治及抑制水稻对砷的吸收提供参考。     

淹水还原条件下土壤铁氧化物对镉活性制约机理的研究进展

土壤Cd污染一直是环境污染研究领域的热点.近年来,国内外许多专家学者对淹水土壤中Cd的消长及其制约机理进行了不懈的研究,得到的却是不同甚至完全相反的结论.本文首先概述了淹水土壤中铁氧化物还原溶解与沉淀的研究进展,之后在此基础上综述了近年来国内外有关淹水土壤中铁氧化物的化学行为对Cd活性的影响,详细论述了Cd活性降低和升高的可能机理,进而提出了急需解决的重要问题和未来的发展方向.     

Iron availability from whey protein hydrogels: an in vitro study

The influence of whey protein hydrogel microstructure, filamentous versus particulate, on iron delivery was studied under different conditions, including simulated gastrointestinal conditions. Experiments were initially conducted to determine the impact of pH and enzymes on iron release. The results show that different iron release profiles can be obtained from filamentous and particulate gels. Particulate gels released more iron than filamentous gels at acidic pH, but the opposite was observed at alkaline pH. In the presence of pepsin at pH 1.2 or pancreatin at pH 7.5, both gel types showed increased protein hydrolysis, but only filamentous gels showed increased iron release, suggesting that matrix structure plays an important role in iron delivery. A dissolution test was carried out under gastrointestinal conditions to mimic the in vivo dissolution process. Filamentous gel released most of its iron during the intestinal phase of a simulated digestion, hence protecting iron during its transit in the gastric zone. Absorption of iron by the Caco-2 system, used to estimate intestinal absorption, revealed that filamentous gels favored intracellular iron absorption. These results suggest that filamentous gels show promise as matrices for transporting iron and promoting its absorption and therefore should be of major interest in the development of innovative functional foods.     

成都市地下水中铁、锰变化规律及成因分析

特殊的水文地质环境和气候是影响成都地下水铁、锰离子形成分布的主要因素，对成都市近10年的地下水动态监测资料和水文地质勘探资料的分析，初步探讨了铁、锰离子的分布形成规律及其影响因素。     

Biogeochemistry of Iron and Sulfur in Sediments of an Acidic Mining Lake in Lusatia,Germany

Chemical, microbiological and stable isotope analyses of sediments from an acidic mining lake were used to evaluate whether biogeochemical processes, such as iron and sulfate reduction, are extant, because such processes can potentially generate alkalinity. Sediment cores were sliced in cm intervals to achieve a high resolution for spatial distribution of organic and inorganic components. Iron, sulfur, carbon, nitrogen and phosphorus as well as the most probable number (MPN) of iron reducing bacteria, the amount of lipid phosphate and the stable isotope compositions of various sedimentary sulfur compounds were measured. Accumulation of degradable organic material, reduced mass fractions of iron, enhanced concentrations of lipid phosphate, high concentrations of DOC and ferrous iron in the pore water and a drastic change of sulfur isotope ratios in the upper 3 cm of the sediment all indicated a highly reactive zone of biogeochemical transformations. The data provide clear evidence for iron and sulfate reducing processes in the sediments that result in an increase of pH with depth.