柑桔根系对缺铁的生理反应

柑桔在缺铁条件下,幼苗根系分泌H⁺和还原Fe³⁺的能力增加,与植株吸收铁素营养的能力相一致。摘除缺铁失绿的新叶和顶芽,抑制根系分泌H⁺和Fe³⁺还原物;但随着新叶的重新长出,根系分泌H⁺和Fe³⁺还原物的速率逐渐提高。说明缺铁失绿的组织能调控根系分泌H⁺和Fe³⁺还原物。在营养液中加入0.1nmol/L生长素(IAA),能解除因缺少失绿组织对根系分泌H～+产生的抑制作用。此外,在缺铁条件下,吸铁能力较强的酸橙根尖发生膨胀,有利于铁的接触吸收。     

花生耐低铁性的基因型差异及其生理特性研究

通过田间试验对16个花生品种在石灰性土壤上的耐低铁性进行了评价。不同花生品种耐低铁能力存在显著的基因型差异,这种差异表现在生长过程中叶片活性铁含量、叶绿素含量以及最终的荚果产量上。溶液培养试验结果表明,根系Fe3+还原力提高是抗缺铁花生品种适应缺铁胁迫的主要机制,抗缺铁品种铁还原力高峰出现期早于铁敏感品种,且峰值远高于铁敏感品种。同时缺铁胁迫下介质pH值、新叶过氧化氢酶活性也存在显著的基因型差异。     

杜鹃抗盐突变体的筛选

利用杜鹃的离体叶片诱导不定芽 ,发现MS +BA2 0ppm +ZT0 1ppm培养基不定芽分化率最高。用γ射线作诱变剂 ,对离体叶片产生的不定芽进行了耐盐筛选 ,得到了耐 0 5%、0 7%和 1 %NaCl的变异株系 ,并对变异株系进行了初步鉴定。     

小金海棠Fe3+-还原酶基因MxFRO在酵母中的表达及其活性检测

为研究苹果属植物抗缺铁的分子生物学机理,从铁高效基因型小金海棠（Malus xiaojinensis）中克隆了Fe3+-还原酶基因MxFRO。MxFRO2的cDNA序列长2283bp,开放阅读框为2166bp,编码722个氨基酸。半定量RT-PCR结果表明MxFRO在小金海棠的根和叶中均受缺铁胁迫诱导。 将MxFRO转入野生型酵母中,结果表明转基因酵母的Fe3+-还原酶活性是对照的2.8倍,因此我们初步推测MxFRO基因编码的蛋白具有Fe3+-还原酶活性。     

不同铵硝比对高山杜鹃侧枝生长和生理特性影响

为探究氮素形态对高山杜鹃侧枝生长的影响,以3年生盆栽高山杜鹃粉精灵为试验材料,单一氮源处理为对照,采用盆栽方式,研究5种不同氮素形态配比供应（铵硝比例分别为T1:100∶0,T2:75∶25,T3:50∶50,T4:25∶75和T5:0∶100）对其营养生长期侧枝生长、光合特性、代谢酶活性及营养元素积累的影响。结果表明,不同氮素形态下粉精灵不同生长期侧枝干物质积累量、苗高增量和侧枝长度均有所差异,以侧芽萌发期T3处理侧枝干物质积累量最高,T2处理在嫩侧枝期、侧枝半木质化期的苗高增量和侧枝长度均显著高于其他处理。侧枝半木质化期,与T1处理相比,T2处理显著提高净光合速率、蒸腾速率、气孔导度、水分利用率及磷含量,降低胞间二氧化碳浓度;叶片Fe元素吸收量以T1处理最高,Mg元素吸收量以T5处理最高。此外,在不同生长期,硝酸还原酶活性均随硝态氮含量的增加而增加,以嫩侧枝期酶活性最高。综上,不同氮素形态对高山杜鹃粉精灵侧枝生长和生理特性的影响有所差异,且混合氮源处理较单一氮源处理更有利于促进侧枝生长,以铵硝比例75∶25促进侧枝生长及提高养分积累和光合效能效果最好。本研究为筛选适合高山杜鹃生长发...     

小金海棠Fe^3＋-还原酶基因MxFRO在酵母中的表达及Fe^3＋-还原酶活性检测

从铁高效基因型小金海棠(Malus xiaojinensis)中克隆了Fe3 -还原酶基因MxFRO.半定量RT-PCR结果表明MxFRO在小金海棠的根和叶中均受缺铁胁迫诱导.将MxFRO转入野生型酵母(Saccharomyces cerevisitae)中,结果表明转基因酵母的Fe3 -还原酶活性是对照的2.8倍,实验初步证明MxFRO基因编码的蛋白具有Fe3 -还原酶活性.     

水稻锰毒与铁素营养关系的研究

通过水培试验，研究了水稻锰毒与铁素营养关系，并探讨了过量锰对一些生理指标的影响。试验结果表明：地上部是生长介质中过量锰对水稻危害的主要部位；过量的锰增加铁在水稻根系的沉积，减少铁的吸收，改变体内铁的分布，降低铁的活性，诱发水稻缺铁胁迫；过量锰缺铁胁迫的水稻正常代谢受阻，叶片叶绿素、蛋白质含量减少，过氧化氢酶活性降低，而过氧化物酶活性增加     

γ射线辐照杜鹃试管苗诱发突变体的研究

研究了60 Coγ射线对杜鹃试管苗的辐射效应 ,得出试管苗的致死剂量为 2 4Gy,最佳诱变剂量为 8～ 1 6Gy,在 1 2和 1 6Gy处理试管苗中高枝嫁接后 ,发现了花色明显变异的突变体 ,连续多次转接突变体性状稳定     

双子叶植物根系Fe3+还原酶活性的2,2’─联吡啶比色测定法

对影响2,2联吡啶牌比色法测定双子叶植物根细胞原生质膜上Fe3+还原酶活性的有关因素进行了比较研究,确定了适宜的测试条件。结果表明,2,2联吡啶比色法测定的最大吸收波长为253.3nm,根系与反应液的适宜反应时间为2小时。反应过程中是否通气以及反应后放置时间均不影响最大吸收峰处的测定值。与黑暗相比,在光照下进行反应可明显提高还原酶活性。     

云锦杜鹃林根际微生物及其生化特性的研究

通过对不同林型云锦杜鹃根际土壤和非根际土的养分状况、微生物区系、生化作用强度和酶活性等研究 ,结果显示 ,土壤细菌功能群与土壤养分和土壤酶活性有密切的联系 ,在光照和通气条件好的归云洞种群 ,云锦杜鹃的根际效应明显。在黄经洞和永字亭种群 ,由于植被盖度高 ,土壤空隙度低 ,土壤接触酶和过氧化物酶活性低 ,根际对土壤毒素转化能力弱及土壤腐殖质化过程缓慢 ;加上真菌和放线菌数量多 ,指示了土壤性质的恶化。因此 ,修剪上层树种和清理箬竹等可以阻止云锦杜鹃的衰退     

EFFECT OF IRON DEFICIENCY ON ROOT FERRIC CHELATE REDUCTASE,PROTON EXTRUSION,BIOMASS PRODUCTION AND MINERAL ABSORPTION OF CITRUS ROOT STOCK ORANGE JASMINE (MURRAYA EXOTICA L.)

Three-week iron (Fe) deficiency stress experiments were conducted using two citrus root stocks, Fe-deficiency tolerant Orange Jasmine (OJ, Murraya exotica L.) and the sensitive Flying Dragon [FD, Poncirus trifoliata var. monstrosa (T. Ito) Swingle]. Root ferric chelate reductase activity and proton extrusion increased in OJ between 12 and 18 d of stress, whereas there was no change in FD. Dry weight of OJ roots increased in contrast to FD which decreased. The Mn content in OJ remained the same even under Fe stress. Zn content in OJ roots doubled while that of FD increased 4-folds. The shoot/root Fe accumulation ratio increased in OJ while it decreased in FD. OJ apparently has mechanisms for increasing root biomass, controlling Fe reutilization and regulating manganese (Mn) and zinc (Zn) absorption in response to Fe deficiency. These mechanisms could help maintain homeostasis under heavy metal stress, which would be useful for improved growth of economically important citrus species.     

Induction of in vivo root ferric chelate reductase activity in fruit tree rootstock

A method has been developed to consistently induce increases in root ferric chelate reductase activity in the fruit tree rootstock GF 677 (Prunus amygdalopersica) grown under iron (Fe) deficiency. Clonal GF 677 plants were grown hydroponically in a growth chamber with 0 or 90 μM Fe(III)‐EDTA. Root ferric chelate reductase activity was measured in vivo using BPDS. Plants grown without Fe developed visible symptoms of chlorosis and had lower root ferric chelate reductase activities than those grown with Fe. Root ferric chelate reductase activities were 0.1–1.9 and 0.6–5.3 nmol of Fe reduced per gram of fresh mass and minute, respectively, in Fe‐deficient and sufficient plants. However, when plants grown without Fe for several days were resupplied with 180 μM of Fe(III)‐EDTA, FC‐R activities increased within 1 day. The FC‐R values after Fe resupply were 20‐fold higher than those found in Fe‐deficient plants and 5‐fold higher than those found in the Fe‐sufficient controls. After three days of the Fe treatments the FC‐R activities had decreased again to the control values. The reduction of Fe was localized at the subapical root zone. In the conditions used we have found no decreases of the nutrient solution pH values, indicating that this type of response is not strong enough to be detected in peach tree rootstocks. Also, no major changes in root morphology have been found in response to Fe deficiency. This ferric chelate reductase induction protocol may be used in screening assays to select rootstock genotypes tolerant to Fe chlorosis.     

Physiological responses of tomato roots grown in organ culture to iron-deficiency stress

Roots of the Fe-efficient tomato (Lycopersicon esculentum Mill., cultivar Floradel) were cultured in an inorganic medium supplemented with glycine, thiamine, pyridoxine, and nicotinic acid, with sucrose as an energy and carbon source. Iron was supplied as ferric hydroxyethylethylenediaminetriacetic acid (FeHEDTA) and the initial PH was 5.5. Root growth was limited when less than 40 μm FeHEDTA was supplied. Roots grown at lower Fe concentrations decreased the pH of the FCR assay medium to a greater extent than did roots grown at higher Fe concentrations. Cultured roots grown with 10 μm FeHEDTA had increased levels of ferric chelate reductase (FCR) activity compared to roots grown with either lower or higher concentrations of FeHEDTA. Low FCR activity of roots grown at 2.5 or 5 μm FeHEDTA was attributed either to impaired metabolism due to Fe-deficiency or the lack of sufficient Fe for enhanced FCR formation. Roots of hydroponically grown tomato plants exhibited typical increases in FCR activity with Fe-deficiency. Based on these preliminary results, cultured roots were found to exhibit similar Physiological responses to Fe-deficiency stress as intact root systems. Cultured roots should provide a useful system for the investigation of the role of the root in plant Fe-deficiency stress responses as previously suggested by Bienfait et al.(Plant Physiol., 83, 244–247, 1987).     

IRON IS REQUIRED FOR THE INDUCTION OF ROOT FERRIC CHELATE REDUCTASE ACTIVITY IN IRON-DEFICIENT TOMATO

Two mutants of tomato and their corresponding wild-type genotypes, Tfer/TFER and chloronerva/Bonner Beste, were grown in nutrient solution under conditions leading to iron (Fe) deficiency. Iron deficiency caused decreases in growth, leaf chlorosis, and changes in the morphology of roots. Ferric chelate reductase activities of whole roots were generally lower in Fe-deficient plants than in control, Fe-sufficient plants. Plants grown for 7 days without Fe, however, had transient increases in whole root ferric chelate reductase activity after the addition of small amounts of Fe (2 μM) to the nutrient solution. Also, adding sequential 0.5 μM Fe pulses to the nutrient solution led to high whole root ferric chelate reductase activities. Similar results were obtained with a protocol using excised root tips instead of whole root systems to measure ferric chelate reductase activities. The protocol using root tips generally gave higher ferric chelate reductase rates than the method using whole roots, due to the localized expression of the enzyme in the distal root zones.     

RESPONSES OF “NEWHALL” ORANGE TREES TO IRON DEFICIENCY IN HYDROPONICS: EFFECTS ON LEAF CHLOROPHYLL,PHOTOSYNTHETIC EFFICIENCY,AND ROOT FERRIC CHELATE REDUCTASE ACTIVITY

Orange (Citrus sinensis L. Osb. cv. ‘Newhall’) plants grafted on Citrange troyer rootstock were grown in nutrient solution with 0, 5, 10, or 20 μM iron (Fe), with and without calcium carbonate. Calcium carbonate was added in order to mimic the natural conditions in calcareous soils. Leaf chlorophyll concentration was estimated every 3–4 days using the portable instrument SPAD-502 meter. Chlorophyll fluorescence parameters, photosynthetic capacity estimated from oxygen evolution, leaf Fe concentrations, and root tip ferric chelate reductase activity were measured at the end of the experiment. Plants from the 0 and 5 μM Fe treatments showed leaf chlorosis and had decreased leaf chlorophyll concentrations. Leaves of plants grown in the absence of Fe in the solution had smaller rates of oxygen evolution both in the presence and absence of calcium carbonate, compared with plants grown in the presence of 10 μM Fe. In the absence of calcium carbonate the photosystem II efficiency, estimated from fluorescence parameters, was similar in all treatments. A slight decrease in photosystem II efficiency was observed in plants grown without Fe and in the presence of calcium carbonate. A 2.5-fold increase in root tip ferric chelate reductase activity over the control values was found only when plants were grown with low levels of Fe and in the presence of calcium carbonate.     

Amino acid sequence of proteins induced in Fe-deficient stressed alfalfa (Medicago sativa L.) roots

Alfalfa (Medicago sativa L.) grows well in soils with a moderately high pH and dissolves insoluble iron in the rhizosphere. We have investigated active uptake mechanisms under Fe-deficient nutrient conditions and the effects of Fe-deficiency on plants. Previously, we observed that Fe-deficient alfalfa roots exuded many compounds (Masaoka et al. 1993) such as fiavonoids. We also identified a new compound “alfafuran” which is a phenol compound and is different from organic acids or phytosiderophore-type amino acid derivatives exuded by Fe-deficient plant roots. This compound is also very effective in dissolving ferric phosphate (Noguchi et al. 1994), suggesting that alfalfa may have developed several strategies against Fe-deficient stress including the exudation of organic compounds like alfafuran which accelerate the Fe³⁺-reducing activity on the root cell membrane to dissolve insoluble iron compounds. Suzuki et al. (1995, 1997) observed that in barley several peptide spots obtained by electrophoresis were induced under Fe-deficient stress when mugineic acid-family phytosiderophores were secreted from the roots. They suggested that these peptides control the mugineic acid synthesis and secretion. We examined the peptides induced in Fe-deficient alfalfa roots.     

Strawberry recovers from iron chlorosis after foliar application of a grass‐clipping extract

Bare‐root transplants of strawberry (Fragaria × ananassa Duch. cv. Selva) were transferred to nutrient solutions with or without iron. After 35 d of growth, plants in the solution without iron became chlorotic and had morphological changes in roots typical of iron‐deficiency chlorosis (IDC). Acidification of the nutrient solution was also observed. We tested a grass‐clipping extract to correct IDC in strawberry plants by foliar application to some chlorotic plants. We also assessed the effects of this product on plant growth, Fe allocation, as well as morphological and physiological parameters related with IDC. After the second spray, leaf chlorophyll increased in the youngest expanded leaves. The total content of iron in plants increased from 1.93 mg to 2.37 mg per plant after three sprays, accounting for 80% of the total iron supplied by the extract. Newly formed roots from sprayed plants had a normal morphology (no subapical swollen zone) but a higher ferric chelate–reductase (FC‐R; EC 1.16.1.17) activity per root apex compared with roots from plants grown with iron or untreated chlorotic plants. Acidification of the nutrient solution continued in sprayed recovered plants. The results suggest an uncoupling of the regulation of morphological and physiological mechanisms related to IDC: FC‐R activity seems to be controlled by roots on their own or together with shoots, while morphological changes in roots are apparently regulated only by the level of iron in shoots.     

Characterizing nicotianamine aminotransferase: Improving its assay system and details of the regulation of its activity by Fe nutrition status

Under iron deficient conditions, graminaceous plants secrete mugineic acid family phytosiderophores (MAs) from their roots to dissolve sparingly soluble iron compounds in the rhizosphere, and take up iron in the form of an Fe³⁺-MAs complex (Takagi 1976). A good correlation has been reported between the tolerance of Fe-deficiency and the amount of secreted MAs (Takagi 1993). Therefore, by using the genes involved in MAs biosynthesis, molecular breeding might produce transgenic plants tolerant to Fe-deficiency with a high level of MAs secretion. The biosynthetic pathway of MAs from L-methionine has been clarified (Fig. 1) and the enzymes participating in this process are now being investigated to isolate the genes responsible. Nicotianamine aminotransferase (NAAT) catalyzes the amino group transfer between nicotianamine (NA) and 2-oxoglutaric acid (Fig. 1). In order to purify NAAT, enzyme assay methods for NAAT have been developed and modified (Shojima et al. 1990; Ohata et al. 1993; Kanazawa et al. 1994). Some characteristics of NAAT have been reported using these enzyme assay methods (Kanazawa et al. 1994, 1995). Here, we further investigate some characteristics of this enzyme to improve the enzyme assay method, namely 1) the effect of K⁺ and Mg²⁺ on NAAT activity in vitro, and 2) the direct influence of MAs, Fe³⁺, and Fe²⁺ on NAAT activity. In addition, based on these results, the induction of enzyme activity by Fe-deficiency and suppression of the activity by Fe-resupply was investigated, by applying the new enzyme assay method.     

植物-生物膜氧化沟中不同形态铁及根表铁膜与除磷的关系

针对传统氧化沟投资建造成本高,脱氮除磷效率较差的问题,在污染现场建设植物-生物膜氧化沟,通过室内曝气模拟试验和室外小试试验,研究了总磷(total phosphorus,TP)的去除与铁和曝气时间的关系以及美人蕉、茭白根表铁氧化物胶膜对污水中磷的吸附去除情况,了解不同形态铁和植物根表铁膜与除磷的关系。研究结果表明:不同形态铁及植物根表铁膜与污水中磷的去除密切相关。随着曝气时间的延长,污水中铁减少量呈现出逐级递增的趋势,当曝气时间为12 h时,铁减少量达到0.45 mg/L以上,铁减少量与曝气时间之间的相关性达到极显著水平(P0.01),而TP的减少量与铁减少量之间也呈现极显著的相关性(P0.01)。小试试验中,3个系统出水磷含量及全Fe、Fe2+含量均有所降低,降低量表现出茭白系统美人蕉系统对照系统的规律;同时,美人蕉、茭白根表铁氧化物的沉积量随运行时间的延长而增加,且茭白根表铁膜数量及其吸附磷的数量均要高于美人蕉。该研究为植物-生物膜氧化沟工艺的改进及应用和推广提供了理论和实践依据。