缺铁敏感度不同的大豆品种对缺铁的适应机制

与供铁处理相比,对缺铁敏感的大豆品种“哈８３”幼苗在缺铁胁迫和上根际没有酸化现象,根系对Ｆｅ（Ⅲ）的还原能力也没有明显增强。但抗缺铁的大豆品种“８７０１”幼苗根际则严重酸化,根系对Ｆｅ（Ⅲ）的还原能力显著增强;加入能抑制根系Ｈ＾＋－ＡＴＰ酶活性、减弱根际酸化作用的Ｈ＾＋－ＡＴＰ酶抑制剂正钒酸钠会降低根系对Ｆｅ（Ⅲ）的还原能力;说明根际酸化与根系还原Ｆｅ（Ⅲ）能力相互联系,初步证实根细胞原生质膜Ｈ＾     

黄瓜、番茄和大豆对缺铁胁迫适应性反应的差异

黄瓜、番茄和大豆同是双子叶植物,缺铁诱导的适应性机制都属于机理Ｉ,但是它们在适应缺铁胁迫的具体反应上却各有不同。黄瓜、蕃茄缺铁时主要表现为近根尖处膨大、变粗,根毛增多,发育成具有转移细胞特征,并主动向外分泌大量Ｈ＋,使根系对Ｆｅ（Ⅲ）还原能力显著增强,从而提高了根际中铁的有效性。大豆则主要是依靠根尖膨大、变粗,表皮、皮层中积累大量酚类物质来还原难溶性Ｆｅ３＋化合物。植物基因型之间对缺铁胁迫的这种反应上的差异,给铁高效基因型筛选和遗传育种工作提供了广阔的前景。     

低温,高pH胁迫对水稻幼苗根系质膜,液泡膜ATP酶活性的影响

以耐冷性不同的两个水稻品种为材料,比较研究了幼苗根系质膜、液泡膜ＡＴＰ酶对低温（８℃）及高ｐＨ（８．０）胁迫的反应。结果表明：水稻根细胞质膜和液泡膜上均存在Ｃａ＾２＋－ＡＴＰ酶,但活性远低于Ｈ＾＋－ＡＴＰ酶。耐冷品种武育粳３号经低温（８℃）处理２ｄ,根系质膜和液泡膜Ｈ＾２＋－ＡＴＰ酶、Ｃａ＾２＋－ＡＴＰ酶海性均明显升高,至冷处理１２ｄ,Ｈ＾＋－ＡＴＰ酶、Ｃａ＾２＋－ＡＴＰ酶活性有所下降,但仍与对照     

豌豆Sparkle及其单基因突变体E107的铁锰吸收及转移效率

用豌豆Ｓｐａｒｋｌｅ及其单基因突变体Ｅ１０７进行的水培的试验表明,－Ｆｅ和＋Ｆｅ处理的Ｅ１０７幼苗以及－Ｆｅ处理的Ｓｐａｒｋｌｅ幼苗均表现出根系Ｈ＋分泌量大、根系Ｆｅ（Ⅲ）还原力强等特点,其中尤以＋Ｆｅ处理的Ｅ１０７最为突出;而十Ｆｅ处理的Ｓｐａｒｋｌｅ则无以上特点。与Ｓｐａｒｋｌｅ相比,Ｅ１０７各处理的地上部Ｆｅ、Ｍｎ合量均很高,但根部含量则相反。与Ｓｐｅｋｌｅ相比,Ｅ１０７—Ｆｅ处理表现为Ｆｅ高效,即使在＋Ｆｅ处理下,Ｅ１０７仍表现出－Ｆｅ条件下的根系生理特性,活化并还原了根际大量Ｆｅ（Ⅲ）和Ｍｎ,因而它对Ｆｅ、Ｍｎ具有较高的吸收效率,但是这些元素并不在根系中贮存,而是源源不断地运输到地上部,并在叶片中累积乃至使叶片中毒坏死,充分表现了Ｅ１０７单基因突变体对Ｆｅ、Ｍｎ也具有较高的转移效率。     

水分胁迫对小麦根细胞质膜氧化还原系统的影响

水分胁迫使小麦根质膜ＮＡＤＨ和ＮＡＤＰＨ的氧化速率及Ｆｅ（ＣＮ）６＾３－和ＥＤＴＡ－Ｆｅ＾３＋的还原速率明显降低。对照与胁迫处理的质膜氧化还原系统活性均不受鱼藤酮、抗霉素Ａ和ＤＣＮ等呼吸链抑制剂的影响。在不加Ｆｅ（ＣＮ）６＾－３作为电子受体时,水杨基羟肟酸（ＳＨＡＭ）可明显刺激质膜ＮＡＤＨ的氧化和Ｏ２吸收速率。水分胁迫促使ＳＨＡＭ刺激的ＮＡＤＨ氧化明显降低,但却使Ｏ２吸收略有上升。     

石灰性土壤上植物根际中Fe,Mn的形态分布及其与植物吸收的关系

研究了石灰性土壤上５种作物品种根际微生态环境中Ｆｅ、Ｍｎ的形态分布．结果表明,交换态Ｆｅ（ＥＸ－Ｆｅ）、碳酸盐结合态Ｆｅ（ＣＡＲＢ－Ｆｅ）、无定形氧化铁（ＡＯ－Ｆｅ）和交换态Ｍｎ（Ｅ－Ｍｎ）、碳酸盐结合态Ｍｎ（ＣＡＲＢ－Ｍｎ）在根际土壤中都呈现明显的累积．各品种根际中的累积量有较大差异．相关分析表明,黄潮土上植株含Ｆｅ量、吸Ｆｅ量与根际土壤ＡＯ－Ｆｅ含量呈显著正相关．根际有效态Ｆｅ累积不仅是根际ｐＨ作用的结果,与根系分泌物对难溶性Ｆｅ活化有关．根际有效态Ｍｎ累积则受到根际土壤Ｅｈ的影响．     

渗透胁迫对棉花根和下胚轴PM脂肪酸组分和ATPase的影响

实验结果表明：棉花根和下胚轴ＰＭ脂肪酸主要由棕榈酸（１６：０）,硬脂酸（１８：０）,亚油酸（１８：２）和亚麻酸（１８：３）组成。用－０．３ＭＰａ和－１．１ＭＰａ根际胁迫,棉花根和下胚轴ＰＭ饱和脂肪酸含量增加,不饱和脂肪酸和不饱和指数（ＩＵＦＡ）降低,这几种组分中棕榈酸含量上升较大,亚麻酸含量下降较大。胁迫处理使膜透性增高,脂肪酸组分发生变化,致使ＰＭ Ｈ＾＋－ＡＴＰａｓｅ,Ｃａ＾＋＋－ＡＴＰ－ａｓ     

缺磷或缺铁引起白羽扇豆锰中毒的机理

白羽扇豆在缺磷或缺铁条件下均有排根形成,并且根系还原力显著增加。缺磷、缺铁根系还原力在高峰期分别高于对照。缺磷与缺铁根系还原力高峰不仅出现的时期不同,而且还原力增加部位也不一样。缺磷处理的排根区具有很高的还原力,缺铁处理还原力较高的部位是在主根和侧根的根尖以及排根区。由于Ｍｎ４＋比Ｆｅ３＋更易被还原,致使根系还原力提高促使根际大量锰被还原,这是缺磷和缺铁造成白羽扇豆锰中毒的主要原因之一。     

杜氏盐藻细胞质膜氧化还原系统与K^＋吸收

杜氏盐藻（Ｄｕｎａｌｉｅｌｌａ ｓａｌｉｎａ）细胞表面存在氧化ＮＡＤＨ 与还原Ｆｅ（ＣＮ）３－６ 的氧化还原系统（ｒｅｄｏｘｓｙｓｔｅｍ ）。该系统在氧化ＮＡＤＨ 时,抑制Ｋ＋ 的吸收,在还原Ｆｅ（ＣＮ）３－６ 时, 促进Ｋ＋ 的吸收,当ＮＡＤＨ 同时存在时, 促进效应最显著, 高达７３５％ 。外源ＮＡＤＨ 促进藻细胞的氧吸收达１６５％ ,而使胞质ｐＨ 下降; 当ＮＡＤＨ 存在时, Ｆｅ（ＣＮ）３－６ 被快速地还原, 同时藻细胞膜外酸化程度增加。质膜Ｈ＋ －ＡＴＰａｓｅ和氧化还原系统的典型抑制剂都不同程度地抑制Ｋ＋ 吸收; 并且钒酸盐对Ｋ＋ 吸收的抑制可以被加入ＮＡＤＨ 和Ｆｅ（ＣＮ）３－６ 而部分恢复, 表明质膜Ｈ＋ －ＡＴＰａｓｅ和氧化还原系统共同参与了细胞Ｋ＋ 的吸收过程     

缺磷或缺铁引起白羽扇豆锰中毒的机理

白羽扇豆在缺磷或缺铁条件下均有排根形式,并且根系还原力显著增加。缺磷、缺铁根系还原力在高峰期分别高于对照。缺磷与缺铁根系还原力高峰不仅出现的时期不同,而且还原力增加部位也不一样。缺磷处理的排根区具有很高的还原力,缺铁处理还原力较高的部位是在主根和侧根的根尖以及排根区。由于Ｍｎ＾４＋比Ｆｅ＾３＋更易被还原,致使根系还原力提高促使根际大量锰被还原,这是缺磷和缺铁造成白羽扇豆锰中毒的主要原因之一。     

Natural variation for Fe-efficiency is associated with upregulation of Strategy I mechanisms and enhanced citrate and ethylene synthesis in Pisum sativum L.

Iron (Fe)-deficiency is a common abiotic stress in Pisum sativum L. grown in many parts of the world. The aim of the study was to investigate variation in tolerance to Fe deficiency in two pea genotypes, Santi (Fe-efficient) and Parafield (Fe-inefficient). Fe deficiency caused greater declines in chlorophyll score, leaf Fe concentration and root-shoot development in Parafield compared to Santi, suggesting greater Fe-efficiency in Santi. Fe chelate reductase activity and ethylene production were increased in the roots of Santi and to a lesser extent in Parafield under Fe deficiency, while proton extrusion was only occurred in Santi. Moreover, expression of the Fe chelate reductase gene, FRO1, and Fe transporter, RIT1 were upregulated in Fe-deficient roots of Santi. Expression of HA1 (proton extrusion) was also significantly higher in Santi when compared to Parafield grown in Fe-deficient conditions. Furthermore, the application of the ethylene biosynthesis inhibitor, 1-aminoisobutyric acid reduced the Fe chelate reductase activity, supporting a direct role for ethylene in its induction. A significant increase in root citrate was only observed in Santi under Fe deficiency indicating a role for citrate in the Fe-efficiency mechanism. Taken together, our physiological and molecular data indicate that genotypic variation in tolerance to Fe deficiency in Santi and Parafield plants is a result of variation in a number of Strategy I mechanisms and also suggest a direct role for ethylene in Fe reductase activity. The pea cultivar, Santi provides a new source of Fe-efficiency that can be exploited to breed more Fe-efficient peas.     

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。     

Inhibition of iron deficiency stress response in cucumber by rare earth elements.

We investigated the influence of the trivalent scandium (Sc), chromium (Cr), gallium (Ga), yttrium (Y) and lanthanum (La) on both the function and activity of ferric chelate reductase (FCR) in cucumber (Cucumis sativus L.) roots. Cucumber seedlings were grown for 1week in a nutrient solution without Fe or in some experiments with 10microM FeEDTA. Intact root systems were assayed for FCR activity in a medium at pH 5.0 containing 100microM FeEDTA with the ferrous chelating agent Ferrozine. Addition of 100microM concentrations of the EDTA complexes of Sc, Cr, Ga, Y and La did not inhibit FCR in Fe-deficient roots. When Fe-deficient roots were grown with 10microM LaCl(3), ScCl(3), or YCl(3) for 3days, FCR activity decreased to 23%, 15% and 1%, respectively, of the activity of Fe-deficient plants grown without trivalent metal addition. Additionally, these trivalent metals suppressed proton secretion. Growth of Fe-deficient plants with 80microM Ga(2)(SO(4))(3) decreased FCR activity to 35% of the control activity while 80microM CrEDTA did not affect FCR activity. With the addition of either FeEDTA or YCl(3), FCR activity decreased to less than 5% of the activity of the Fe-deficient control roots in 3days. Addition of FeEDTA, but not Y, resulted in recovery from Fe deficiency as indicated by increasing chlorophyll content of leaves.     

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.     

Iron-Stress Induced Redox Activity in Tomato (Lycopersicum esculentum Mill.) Is Localized on the Plasma Membrane

Tomato plants (Lycopersicum esculentum Mill.) were grown for 21-days in a complete hydroponic nutrient solution including Fe³⁺-ethylenediamine-di(o-hydroxyphenylacetate) and subsequently switched to nutrient solution withholding Fe for 8 days to induce Fe stress. The roots of Fe-stressed plants reduced chelated Fe at rates sevenfold higher than roots of plants grown under Fe-sufficient conditions. The response in intact Fe-deficient roots was localized to root hairs, which developed on secondary roots during the period of Fe stress. Plasma membranes (PM) isolated by aqueous two-phase partitioning from tomato roots grown under Fe stress exhibited a 94% increase in rates of NADH-dependent Fe³⁺-citrate reduction compared to PM isolated from roots of Fe-sufficient plants. Optimal detection of the reductase activity required the presence of detergent indicating structural latency. In contrast, NADPH-dependent Fe³⁺-citrate reduction was not significantly different in root PM isolated from Fe-deficient versus Fe-sufficient plants and proceeded at substantially lower rates than NADH-dependent reduction. Mg²⁺-ATPase activity was increased 22% in PM from roots of Fe-deficient plants compared to PM isolated from roots of Fe-sufficient plants. The results localized the increase in Fe reductase activity in roots grown under Fe stress to the PM.     

Characterization of mugineic-acid-Fe transporter in Fe-deficient barley roots using the multi-compartment transport box method

Summary We have investigated the mugineicacid-Fe transport activity of Fe-deficient barley roots, using the multi-compartment transport box system. The roots maintained Fe transport activity for 20 h after excision. The following results were obtained. (1) In Fe-deficient roots, mugineic acid addition enhanced the transport of Fe by 32.2 times over that of the control (with FeC1₃ addition). (2) The mugineic-acid-⁵⁵Fe transport activity of Fe-deficient roots was 18.4-fold higher than that of the Fe-sufficient roots. (3) The mugineic-acid-⁵⁵Fe transport activity was decreased (7.13% based on the control) by treatment with 5 M carbonylcyanidem-chlorophenyl hydrazone (CCCP). Pretreatment with 0.1 mM dicyclohexyl carbodiimide (DCCD) lowered the transport activity (10.7% based on the control) and 1 mMN-ethylmaleimide (NEM) pretreatment reduced the transport activity to a value equivalent to 2.41% of that in the control. It is concluded that mugineicacid-Fe transporter is induced in its activity and/or amount by Fe-deficiency treatment and has an SH residue at its active site, and that the transporter needs the proton motive force produced by ATPase. We detected three polypeptides (14, 28 and 40 kDa) in the root plasma membrane that were induced under Fe-deficiency treatment.Abbreviations p-APMSF (p-amidinophenyl)methanesulfonyl fluoride hydrochloride - CCCP carbonylcyanide m-chlorophenylhydrazone - DCCD dicyclohexylcabodiimide - DMSO dimethyl sulfoxide - MA mugineic acid - NEM N-ethylmaleimide     

Metabolic responses in iron deficient tomato plants

The effects of Fe deficiency on different metabolic processes were characterized in roots, xylem sap and leaves of tomato. The total organic acid pool increased significantly with Fe deficiency in xylem sap and leaves of tomato plants, whereas it did not change in roots. However, the composition of the pool changed with Fe deficiency, with major increases in citrate concentrations in roots (20-fold), leaves (2-fold) and xylem sap (17-fold). The activity of phosphoenolpyruvate carboxylase, an enzyme leading to anaplerotic C fixation, increased 10-fold in root tip extracts with Fe deficiency, whereas no change was observed in leaf extracts. The activities of the organic acid synthesis-related enzymes malate dehydrogenase, citrate synthase, isocitrate dehydrogenase, fumarase and aconitase, as well as those of the enzymes lactate dehydrogenase and pyruvate carboxylase, increased with Fe deficiency in root extracts, whereas only citrate synthase increased significantly with Fe deficiency in leaf extracts. These results suggest that the enhanced C fixation capacity in Fe-deficient tomato roots may result in producing citrate that could be used for Fe xylem transport. Total pyridine nucleotide pools did not change significantly with Fe deficiency in roots or leaves, although NAD(P)H/NAD(P) ratios were lower in Fe-deficient roots than in controls. Rates of O(2) consumption were similar in Fe-deficient and Fe-sufficient roots, but the capacity of the alternative oxidase pathway was decreased by Fe deficiency. Also, increases in Fe reductase activity with Fe deficiency were only 2-fold higher when measured in tomato root tips. These values are significantly lower than those found in other plant species, where Fe deficiency leads to larger increases in organic acid synthesis-related enzyme activities and flavin accumulation. These data support the hypothesis that the extent of activation of different metabolic pathways, including carbon fixation via PEPC, organic acid synthesis-related enzymes and oxygen consumption is different among species, and this could modulate the different levels of efficiency in Strategy I plants.     

Organic acids and iron translocation in maize genotypes

Translocation of Fe was studied in WF9 (Fe-efficient) and ys₁/ys₁ (Fe-inefficient) maize (Zea mays L.) genotypes. Iron-deficient WF9 translocated more Fe to the tops than Fe-deficient ys₁/ys₁. Malate and citrate contents of root saps increased nearly 2-fold and aconitate increased over 4-fold in both genotypes as Fe of nutrient solutions increased from 0.1 to 3 milligrams per liter. Relative acid contents in root saps were as follows: malate > aconitate > citrate. Citric acid concentrations in stem exudates were nearly the same as in root sap. Malic acid concentrations were considerably lower in exudates than in root saps, and only a trace of aconitic acid was detected in the exudates. The concentration of Fe was 7-fold higher in exudate of WF9 than in exudate of ys₁/ys₁ and the concentration of exudate P was about the same for both genotypes.     

Induction of the Root Cell Plasma Membrane Ferric Reductase (An Exclusive Role for Fe and Cu)

Induction of ferric reductase activity in dicots and nongrass monocots is a well-recognized response to Fe deficiency. Recent evidence has shown that Cu deficiency also induces plasma membrane Fe reduction. In this study we investigated whether other nutrient deficiencies could also induce ferric reductase activity in roots of pea (Pisum sativum L. cv Sparkle) seedlings. Of the nutrient deficiencies tested (K, Mg, Ca, Mn, Zn, Fe, and Cu), only Cu and Fe deficiencies elicited a response. Cu deficiency induced an activity intermediate between Fe-deficient and control plant activities. To ascertain whether the same reductase is induced by Fe and Cu deficiency, concentration- and pH-dependent kinetics of root ferric reduction were compared in plants grown under control, -Fe, and -Cu conditions. Additionally, rhizosphere acidification, another process induced by Fe deficiency, was quantified in pea seedlings grown under the three regimes. Control, Fe-deficient, and Cu-deficient plants exhibited no major differences in pH optima or Km for the kinetics of ferric reduction. However, the Vmax for ferric reduction was dramatically influenced by plant nutrient status, increasing 16- to 38-fold under Fe deficiency and 1.5- to 4-fold under Cu deficiency, compared with that of control plants. These results are consistent with a model in which varying amounts of the same enzyme are deployed on the plasma membrane in response to plant Fe or Cu status. Rhizosphere acidification rates in the Cu-deficient plants were similarly intermediate between those of the control and Fe-deficient plants. These results suggest that Cu deficiency induces the same responses induced by Fe deficiency in peas.     

Water-extractable humic substances enhance iron deficiency responses by Fe-deficient cucumber plants

The ability of Fe-deficient cucumber plants to use iron complexed to a water-extractable humic substances fraction (WEHS), was investigated. Seven-day-old Fe-deficient plants were transferred to a nutrient solution supplemented daily for 5 days with 0.2 μM Fe as Fe-WEHS (5 μg org. C mL^-1), Fe-EDTA, Fe-citrate or FeCl₃. These treatments all allowed re-greening of the leaf tissue, and partial recovery of dry matter accumulation, chlorophyll and iron contents. However, the recovery was faster in plants supplied with Fe-WEHS and was already evident 48 h after Fe supply. The addition of 0.2 μM Fe to the nutrient solution caused also a partial recovery of the dry matter and iron accumulation in roots of Fe-deficient cucumber plants, particularly in those supplied with Fe-WEHS. The addition of WEHS alone (5 μg org. C mL^-1, 0.04 μM Fe) to the nutrient solution slightly but significantly increased iron and chlorophyll contents in leaves of Fe-deficient plants; in these plants, dry matter accumulation in leaves and roots was comparable or even higher than that measured in plants treated with Fe-citrate or FeCl₃. After addition of the different iron sources for 5 days to Fe-deficient roots, morphological modifications (proliferation of lateral roots, increase in the diameter of the sub-apical zones and amplified root-hair formation) and physiological responses (enhanced Fe(III)-chelate reductase and acidification of the nutrient solution) induced by Fe deficiency, were still evident, particularly in plants treated with the humic molecules. The presence of WEHS caused also a further acidification of the nutrient medium by Fe-deficient plants. The Fe-WEHS complex (1 μM Fe) could be reduced by intact cucumber roots, at rates of reduction higher than those measured for Fe-EDTA at equimolar iron concentration. Plasma membrane vesicles, purified by two-phase partition from root microsomes of Fe-deficient plants, were also able to reduce Fe-WEHS. Results show that Fe-deficient cucumber plants can use iron complexed to water soluble humic substances, at least in part via reduction of complexed Fe(III) by the plasma membrane Fe(III)-chelate reductase of root cells. In addition, the stimulating effect of humic substances on H⁺ release might be of relevance for the overall response of the plants to iron shortage. This revised version was published online in June 2006 with corrections to the Cover Date.