冬小麦植物铁载体分泌的杂种效应

缺铁是石灰性土壤常见的植物营养问题之一。禾本科植物种或基因型的植物铁载体分泌能力与耐缺铁有关 ,提高植物铁载体分泌能力是改良缺铁的土壤上植物铁营养的关键措施之一。在水培条件下分析了冬小麦(TriticumaestivumL .) 3个杂交种及其 4个亲本在缺铁营养液中植物铁载体的分泌及杂种的效应。植物铁载体的分泌率通过根分泌物对新形成的Fe(OH) 3 的活化能力进行测定 ,在缺铁症出现时每隔 2、3天测定 1次。在缺铁条件下 ,所有基因型都分泌较多的植物铁载体 ,并且随缺铁症状的发展分泌量增加。杂交种具有对缺铁更敏感的反馈系统 ,在缺铁条件下 ,杂交种比亲本分泌铁载体的速度更快、量更高。通过分析杂交种和亲本的关系 ,认为可以通过对亲本分泌植物铁载体能力和配合力的选择 ,利用杂种优势来提高小麦铁的利用效率。     

小麦植物铁载体分泌基因的染色体定位

采用室内控制生长条件的营养液培养技术,通过检测缺铁条件下２０个中国春的Ｈｏｐｅ染色体代换系及其亲本中国春和Ｈｏｐｅ小麦植物铁载本分泌的动态变化规律以及植物铁载体分泌高峰期内５次测定值的汇总资料,对六倍体小麦ＰＳ分泌基因进行染色体定位。ＰＳ分泌率通过根分泌物对新形成的Ｆｅ（ＯＨ）３的活化能力进行测定,在缺铁症出现时每隔２,３天测定１次,随着缺铁失绿症严重程度的增加,ＰＳ分泌率呈现迅速增高再逐渐降低的     

细菌铁载体拮抗植物病原真菌及促生作用研究进展

铁载体是微生物在缺铁条件下分泌的小分子有机化合物,以获取铁元素维持其生长。细菌分泌的铁载体在拮抗植物病原菌和促进植物生长方面具有重要作用。本文总结了细菌铁载体拮抗植物病原真菌的营养和生态位竞争、诱导植物诱导性系统抗性、扰乱病原菌铁稳态的机制,以及促进植物生长的作用,以解释细菌分泌的铁载体在多功能微生物菌剂研制中的重要作用。     

应用薄层层析法分离植物铁载体

缺铁胁迫下禾谷类植物根系分泌出麦根酸、羟基麦根酸和阿凡酸等植物铁载体。它们能与石灰性土壤上的Fe~(3 )络合而直接被植物吸收,因而提高了铁的有效性。对这些物质目前一般用高压液相色谱仪进行分离并直接进行检测。缺点是一次能分离的样品     

铁限制条件下东海原甲藻分泌铁载体

在铁限制条件下,进行东海原甲藻分泌铁载体的动态研究。对藻类在富铁与缺铁条件下生长状况、生长过程中分泌铁载体的情况以及海藻接种量对铁载体分泌的影响进行了连续观测,结果表明:东海原甲藻在缺铁条件下生长状况远不如在富铁条件下;随着藻类的生长,分泌铁载体不断增多,达指数生长期时,其分泌量也达到了最大值,之后藻类的生长和铁载体分泌都呈现下降趋势;高接种量东海原甲藻能分泌较多的铁载体,并在较短时间到达峰值。     

小金海棠和山定子幼苗根自由空间铁累积量和活化量

不同基因型苹果幼苗根系自由空间铁累积量和活化利用能力不同。在缺铁胁迫条件下,抗缺铁的苹果基因型小金海棠幼苗与对缺铁敏感的山定于幼苗相比,根系自由空间铁累积量大,且它对此铁库的活化利用能力强。此外,供给铁源不同,在植物根中形成的自由空间铁库大小就不同;不同植物基因型对此铁库的活化利用能力也不同,因此,根自由空间铁库的大小及植物对该铁库中铁的活化能力大小可作为不同基因型苹果铁营养效率的筛选指标。     

植物ZIP基因家族铁载体蛋白基因研究进展

主要概述了植物ZIP基因家族铁载体蛋白基因研究的最新进展。从结构和功能上介绍了铁载体蛋白基因IRT1、IRT2、LeIRT1、LeIRT2、P5RIT1和O5IRT1。应用Clustal X序列分析软件,对6个铁载体蛋白基因在蛋白质水平上比较后发现,与IRT1基因蛋白质序列有较高的同源性。植物ZIP基因家族铁载体蛋白基因主要受缺铁胁迫条件的诱导,在根部表达。表达的量与环境中的铁含量、时间、温度、光照等因素有关。铁载体蛋白基因在转录和转录后水平上被环境中的铁含量和植物体内的铁营养水平综合调控。转铁载体蛋白基因植物表现出较强的抗缺铁能力,预示其在农业生产上有广阔的应用前景。     

不同禾本科作物与花生混作对花生根系质外体铁的累积和还原力的影响

采用土培盆栽方法模拟玉米/花生、大麦/花生、燕麦/花生、小麦/花生、高粱/花生5种种植方式,研究混作对花生根系质外体铁的累积和还原力的影响.结果表明,当花生与5种分泌植物铁载体能力不同的禾本科作物混作时,花生新叶叶色正常,而单作花生则表现出严重的缺铁黄化症状,混作花生各部位的含铁量明显增加.与麦类作物(大麦、燕麦、小麦)混作的花生其各部位铁含量高于与玉米、高粱混作的花生,说明麦类作物改善花生铁营养的能力强于玉米、高粱,而两个玉米品种之间的能力差异不大,这主要是由于麦类作物分泌植物铁载体能力高于玉米、高粱.在花生生长至第50、60和70d时,混作花生根系质外体铁含量也随着逐渐增加,并始终高于单作花生.同时,混作明显地提高了花生根际土壤有效铁的含量,花生根系还原力也逐步提高.混作花生逐渐提高的还原力和介质中不断供给的易被花生还原吸收的铁,在改善花生的铁营养方面起了重要的作用.     

假单胞菌株JKD—2分泌铁载体抑制稻瘟病菌

利用铬奥醇（CAS）分析法测定了假单胞菌（Pseudomonassp．）JKD－2分泌铁载体的特征。在无铁环境下JKD-2菌能分泌高亲和力的铁载体;在低铁条件下,铁载体的分泌量减少;在富铁环境下,则不能分泌。结果还显示菌株JKD-2在无铁条件下分泌的铁载体,能在低铁条件下抑制稻瘟病菌（Piriculariaoryzae）的生长。     

假单胞菌株JKD—2分泌铁载体抑制稻瘟病菌*

利用铬奥醇（CAS）分析法测定了假单胞菌（Pseudomonassp．）JKD－2分泌铁载体的特征。在无铁环境下JKD-2菌能分泌高亲和力的铁载体;在低铁条件下,铁载体的分泌量减少;在富铁环境下,则不能分泌。结果还显示菌株JKD-2在无铁条件下分泌的铁载体,能在低铁条件下抑制稻瘟病菌（Piriculariaoryzae）的生长。     

Phytosiderophore release from nodal,primary, and complete root systems in maize

Some maize (Zea mays L.) hybrids grown in high pH soil in Nebraska suffer from severely reduced yields caused by iron (Fe) deficiency chlorosis. Hybrids which recover from early season Fe-deficiency chlorosis and yield well are termed Fe-efficient or tolerant. Most Fe-efficient gramineous species respond to Fe-deficiency stress by releasing phytosiderophores (mugineic acid and its derivatives) into the rhizosphere, thereby increasing Fe availability and uptake of the Fe³⁺-phytosiderophore complex via a high affinity uptake system. Field-grown Fe-efficient maize recovers from Fe-deficiency chlorosis at a stage when nodal roots have become the dominant root system. Quantifying phytosiderophore release from hydroponically grown plants has been proposed as a viable alternative to time-consuming and variable field trials and has been used successfully to delineate among Fe-efficient and Fe-inefficient lines of oat (Avena sativa L.) and wheat (Triticum aestivum L.). Our objectives were (1) to determine if phytosiderophore release differed between nodal- and primary-root systems of maize, and (2) to compare phytosiderophore release from 12 hybrids. Root exudates secreted during daily 4-h collections were analyzed for their Fe-solubilizing ability, which was equated to phytosiderophore release. Nodal root systems released significantly more phytosiderophore than primary- or complete-root systems. In early experiments, an Fe-efficient hybrid (P3279) released more phytosiderophore from nodal roots than an Fe-inefficient hybrid (P3489). Tests of an additional 10 hybrids showed that phytosiderophore release varied significantly among the cultivars but did not clearly distinguish between hybrids classified as Fe-efficient or Fe-inefficient in individual company trials. We recommend using nodal roots when studying Fe-stress response mechanisms in maize.     

Phytosiderophore release in Aegilops tauschii and Triticum species under zinc and iron deficiencies.

Using three diploid (Triticum monococcum, AA), three tetraploid (Triticum turgidum, BBAA), two hexaploid (Triticum aestivum and Triticum compactum, BBAADD) wheats and two Aegilops tauschii (DD) genotypes, experiments were carried out under controlled environmental conditions in nutrient solution (i) to study the relationships between the rates of phytosiderophore (PS) release from the roots and the tolerance of diploid, tetraploid, and hexaploid wheats and AE: tauschii to zinc (Zn) and iron (Fe) deficiencies, and (ii) to assess the role of different genomes in PS release from roots under different regimes of Zn and Fe supply. Phytosiderophores released from roots were determined both by measurement of Cu mobilized from a Cu-loaded resin and identification by using HPLC analysis. Compared to tetraploid wheats, diploid and hexaploid wheats were less affected by Zn deficiency as judged from the severity of leaf symptoms. Aegilops tauschii showed very slight Zn deficiency symptoms possibly due to its slower growth rate. Under Fe-deficient conditions, all wheat genotypes used were similarly chlorotic; however, development of chlorosis was first observed in tetraploid wheats. Correlation between PS release rate determined by Cu-mobilization test and HPLC analysis was highly significant. According to HPLC analysis, all genotypes of Triticum and AE: tauschii species released only one PS, 2'-deoxymugineic acid, both under Fe and Zn deficiency. Under Zn deficiency, rates of PS release in tetraploid wheats averaged 1 micromol x (30 plants)(-1) x (3 h)(-1), while in hexaploid wheats rate of PS release was around 14 micromol x (30 plants)(-1) x (3 h)(-1). Diploid wheats and AE: tauschii accessions behaved similarly in their capacity to release PS and intermediate between tetraploid and hexaploid wheats regarding the PS release capacity. All Triticum and Aegilops species released more PS under Fe than Zn deficiency, particularly when the rate of PS release was expressed per unit dry weight of roots. On average, the rates of PS release under Fe deficiency were 3.0, 5.7, 8.4, and 16 micromol x (30 plants)(-1) x (3 h)(-1) for AE: tauschii, diploid, tetraploid and hexaploid wheats, respectively. The results of the present study show that the PS release mechanism in wheat is expressed effectively when three genomes, A, B and D, come together, indicating complementary action of the corresponding genes from A, B and D genomes to activate biosynthesis and release of PS.     

The role of phytosiderophores in acquisition of iron and other micronutrients in graminaceous species: An ecological approach

Phytosiderophores (PS) are released in graminaceous species (Gramineae) under iron (Fe) and zinc (Zn) deficiency stress and are of great ecological significance for acquisition of Fe and presumably also of Zn. The potential for release of PS is much higher than reported up to now. Rapid microbial degradation during PS collection from nutrient solution-grown plants is the main cause of this underestimation. Due to spatial separation of PS release and microbial activity in the rhizosphere a much slower degradation of PS can be assumed in soil-grown plants. Concentrations of PS up to molar levels have been calculated under non-sterile conditions in the rhizosphere of Fe-deficient barley plants.Besides Fe, PS mobilize also Zn, Mn and Cu. Despite this unspecific mobilization, PS mobilize appreciable amounts of Fe in calcareous soils and are of significance for chlorosis resistance of graminaceous species. In most species the rate of PS release is high enough to satisfy the Fe demand for optimal growth on calcareous soils.In contrast to the chelates ZnPS and MnPS, FePS are preferentially taken up in comparison with other soluble Fe compounds. In addition, the specific uptake system for FePS (translocator) is regulated exclusively by the Fe nutritional status. Therefore, it seems appropriate to retain the term phytosiderophore instead of phytochelate.     

A genetically related response to iron deficiency stress in muskmelon

A mutant muskmelon (Cucumis melo L.) with characteristic Fe-deficiency chlorosis symptoms was compared to related cultivars in its ability to obtain Fe via the widely known Fe-stress response mechanisms of dicotyledonous plants. The three cultivars (fefe, the Fe-inefficient mutant; Mainstream and Edisto, both Fe efficient plants) were grown in nutrient solution in either 0 or 3.5 mg L^-1 Fe as FeCl₃. None of the three cultivars released reductants or phytosiderophores, but both Edisto and Mainstream produced massive amounts of H+ ions to reduce and maintain the pH of nutrient solutions below pH 4.0. The roots of these two Fe-efficient cultivars were also capable of reducing Fe³⁺ to Fe²⁺. These responses maintained green plants, resulted in high leaf Fe in both Edisto and Mainstream, and produced Mn toxicity in Mainstream. The lack of Fe-deficiency stress response in fefe not only affected leaf Fe concentration and chlorosis, but also resulted in reduced uptake of Mn. The importance of reduced Fe (Fe²⁺) to the Fe-efficient cultivars was confirmed by growing the cultivars with BPDS (4, 7-diphenyl-1, 10-phenanthroline disulfonic acid, a ferrous chelator) and EDDHA [ethylene-diamine di (0-hydroxphenylacetic acid)] (a ferric chelator), and observing increased chlorosis and reduced Fe uptake in BPDS grown plants. The Fe-deficiency response observed in these cultivars points out the diversity of responses to Fe deficiency stress in plants. The fefe mutant has a limited ability to absorb Fe and Mn and perhaps could be used to better understand Mn uptake in plants.     

Effect of Fe 3+, Zn 2+ and Mn 2+ on ferric reducing capacity and regreening process of the peach rootstock Nemaguard (Prunus persica (L.) Batsch)

The peach rootstock Nemaguard is susceptible to lime-induced iron deficiency chlorosis. Under field conditions, application of ferric chelates to the soil is effective in correcting the Fe-deficiency symptoms. The objectives of this work were to study the induction of the root ferric reducing capacity and the relationship between chlorosis and leaf Fe concentration of plants grown hydroponically under different treatments. Results showed that bicarbonate-treated plants grown with a low Fe concentration increased their reducing capacity if they received additional Fe or Zn for a short period (15 h). However, the addition of Mn had no effect. When these Mn-treated plants were changed to nutrient solution with no bicarbonate and sufficient Fe, regreening was retarded several days in relation to the other treatments. In plants grown without bicarbonate, the reducing capacity was higher in plants grown with a low amount of Fe than in plants grown with either 0 Fe or sufficient Fe. In plants grown with bicarbonate and low Fe, the leaves became chlorotic and had low Fe concentration. When these plants received higher Fe supply, the regreening of the old leaves was not complete, though they had even higher Fe concentrations that the new developing leaves which were completely green. Results are discussed in relation to the Fe or Zn requirements of plants to induce reducing capacity and the incapacity of the cells from chlorotic leaves to absorb Fe and repair metabolic and structural damages.     

Fe-deficiency stress response in Fe-deficiency resistant and susceptible subterranean clover: importance of induced H+ release

Plants can exhibit Fe-deficiency stress response when they areexposed to Fe-deficiency conditions. The relative importanceof the individual Fe-deficiency stress-response reactions, forexample, increased release of H⁺ from roots, enhanced root plasmamembrane-bound Fe³⁺ -reductase activity, and release of reductant,in Fe-deficiency resistance is not understood. To address thisproblem, the Fe-deficiency stress response of two cultivarsof subterranean clover (subclover), Koala (Trifolium brachycalycinumKatzn. and Morley) (Fe-deficiency resistant) and Karridale (T.subterraneum L.) (Fe-deficiency susceptible), were evaluated.The plants were cultured hydroponically at 0 (–Fe) and30 (+Fe) µM Fe³⁺ EDTA conditions. After 6 d Fe treatment,the –Fe Koala and Karridale decreased the pH of the nutrientsolution by 1.83 and 0.79 units, respectively, while the +Feplants increased the pH of the nutrient solution. The H⁺ -releaserate of the –Fe Koala determined 7 d after Fe treatmentinitiation was more than three times higher than that of the–Fe Karridale. The –Fe plants had a significantlyenhanced Fe³⁺ -reduction rate compared with the +Fe plants foreach cultivar, but the resistant cultivar did not exhibit ahigher root Fe³⁺ -reduction rate than the susceptible cultivarat each Fe treatment. Reductant release from the roots of subcloverwas negligible. These results indicate that Fe-deficiency-inducedH⁺ release may be the predominant factor influencing Fe-deficiencyresistance in subclover. Key words: Fe-deficiency, Fe³⁺ reduction, H⁺ release, stress response, Trifolium     

Selection of olive varieties for tolerance to iron chlorosis

Under certain conditions, olive trees grown on calcareous soils suffer from iron chlorosis. In the present study several olive varieties and scion-rootstock combinations were evaluated for their tolerance to iron chlorosis. Plants were grown over several months in pots with a calcareous soil, under two fertilization treatments. These consisted of periodic applications of nutrient solutions containing either, 30 μmol/L FeEDDHA or not Fe. Tolerance was assessed by the chlorosis and growth parameters of plants grown without Fe, compared to those plants grown with Fe. Results show that there are differences in tolerance among olive varieties and that tolerance is mainly determined by the genotype of the rootstock. These results open the way to use tolerant varieties for those conditions where iron chlorosis could become a problem.     

Iron availability in plant tissues-iron chlorosis on calcareous soils

The article describes factors and processes which lead to Fe chlorosis (lime chlorosis) in plants grown on calcareous soils. Such soils may contain high HCO₃ ^- concentrations in their soil solution, they are characterized by a high pH, and they rather tend to accumulate nitrate than ammonium because due to the high pH level ammonium nitrogen is rapidly nitrified and/or even may escape in form of volatile NH₃. Hence in these soils plant roots may be exposed to high nitrate and high bicarbonate concentrations. Both anion species are involved in the induction of Fe chlorosis.Physiological processes involved in Fe chlorosis occur in the roots and in the leaves. Even on calcareous soils and even in plants with chlorosis the Fe concentration in the roots is several times higher than the Fe concentration in the leaves. This shows that the Fe availability in the soil is not the critical process leading to chlorosis but rather the Fe uptake from the root apoplast into the cytosol of root cells. This situation applies to dicots as well as to monocots. Iron transport across the plasmamembrane is initiated by Fe^III reduction brought about by a plasmalemma located Fe^III reductase. Its activity is pH dependent and at alkaline pH supposed to be much depressed. Bicarbonate present in the root apoplast will neutralize the protons pumped out of the cytosol and together with nitrate which is taken up by a H⁺/nitrate cotransport high pH levels are provided which hamper or even block the Fe^III reduction.Frequently chlorotic leaves have higher Fe concentrations than green ones which phenomenon shows that chlorosis on calcareous soils is not only related to Fe uptake by roots and Fe translocation from the roots to the upper plant parts but also dependent on the efficiency of Fe in the leaves. It is hypothesized that also in the leaves Fe^III reduction and Fe uptake from the apoplast into the cytosol is affected by nitrate and bicarbonate in an analogous way as this is the case in the roots. This assumption was confirmed by the highly significant negative correlation between the leaf apoplast pH and the degree of iron chlorosis measured as leaf chlorophyll concentration. Depressing leaf apoplast pH by simply spraying chlorotic leaves with an acid led to a regreening of the leaves.     

Genetic Analysis of Maize Root Characteristics in Response to Low Nitrogen Stress

Under low-input cropping systems, nitrogen (N) can be a limiting factor in plant growth and yield. Identifying genotypes that are more efficient at capturing limited N resources and the traits and mechanisms responsible for this ability is important. Root trait has a substantial influence on N acquisition from soils. Nevertheless, inconsistencies still exist as to the effect of low N on root length and its architecture in terms of lateral and axial roots. For maize, a crop utilizing heterosis, little is known about the relationship between parents and their crosses in the response of root architecture to N availability. Here 7 inbred maize lines and 21 of their crosses created by diallel mating were used to study the effect of N stress on root morphology as well as the relationship between the inbreds and their crosses. With large genotypic differences, low N generally suppresses shoot growth and increases the root to shoot ratio with or without increasing root biomass in maize. Maize plants responded to N deficiency by increasing total root length and altering root architecture by increasing the elongation of individual axial roots and enhancing lateral root growth, but with a reduction in the number of axial roots. Here, the inbreds showed weaker responses in root biomass and other root parameters than their crosses. Heterosis of root traits was significant at both N levels and was attributed to both the general combining ability (GCA) and special combining ability (SCA). Low N had substantial affects on the pattern of heterosis, GCA and SCA affects on root traits for each of the crosses suggesting that selection under N stress is necessary in generating low N-tolerant maize genotypes.