Iron deficiency enhances cadmium uptake and translocation mediated by the Fe2+ transporters OsIRT1 and OsIRT2 in rice

Abstract

Cadmium (Cd) accumulation in rice grains is enhanced if ponded water is released from paddy fields during the reproductive stage (intermittent irrigation). The release of ponded water creates aerobic soil conditions under which Cd becomes soluble and iron (Fe) solubility decreases. We hypothesized that Fe shortage in rice induces Fe uptake and translocation and that Cd is also taken up and translocated throughout this process. Hydroponically cultured Fe-deficient rice absorbed more Cd than did Fe-sufficient rice, and the presence of Fe enhanced the translocation of Cd to the shoots. Yeast mutants expressing OsIRT1 and OsIRT2, which encode the rice Fe²⁺ transporter, became more sensitive to Cd, suggesting that Cd was absorbed by OsIRT1 and OsIRT2. We discuss the possibility that Cd accumulation in rice grains during the reproductive stage is mediated by the Fe transport system.     

Ca2+ Effects on K+ Fluxes in Arabidopsis Seedlings Exposed to Al3+

Potassium transport was investigated in the root elongation zone of Arabidopsis seedlings during the first minutes of Al³⁺ exposure, using the non-invasive MIFE microelectrode technique. To prevent pH changes during Al³⁺ application, and to separate aluminium from acidic stress, plants were pre-treated with 5 mM homoPIPES before addition of AlCl₃ (pH 4.2). The 30-min treatment with 50 or 500 μM AlCl₃ led to a significant increase in K⁺ efflux in solutions containing 100 μM CaCl₂. This efflux was suppressed by high concentrations of Ca²⁺ (10 mM) in the bathing solution. Our results suggest that elevated external Ca²⁺ activities can sustain K⁺ influx in the root elongation zone during Al³⁺ exposure either by maintaining [Ca²⁺]_cyt or by affecting Al³⁺ uptake across the plasma membrane.     

水稻根系细胞膜H+-ATPase对缺磷的反应

用两相法分离了供磷（+P）和缺磷（-P）营养下水稻苗期根系的细胞膜,并测定了细胞膜上H+-ATPase的水解活性,以期阐明水稻根系细胞质膜上H+-ATPase对不同缺磷的反应机制。结果表明,缺磷的水稻根系细胞膜H+-ATPase的水解活性和H+-ATPase的Vmax, Km均低于正常供磷的植物;缺磷的水稻根系细胞膜H+-ATPase最佳pH值为 6.0,而正常供磷植物的为pH 6.4左右;Western Blot结果说明,缺磷水稻根系细胞膜H+-ATPase酶浓度与正常供磷植物相似。本试验结果还说明,缺磷水稻根系细胞膜H+-ATPase活性低的原因并不是因为其单位细胞膜上的H+-ATPase酶分子数量小于正常供磷的植物,而是缺磷水稻根系细胞膜上H+-ATPase的同工酶的组成供磷植物相比发生了变化。这很可能是缺磷胁迫下水稻根系细胞膜H+-ATPase的一种适应机制。     

水稻OsAKT2的钾吸收功能及其在地上部分K+回流中的潜在作用

  【目的】  研究水稻钾通道OsAKT2的基本功能和调控特征,揭示其在地上部K+回流中的潜在作用。  【方法】  通过构建系统进化树和关键氨基酸区域序列比对,对不同物种来源的Shaker类钾离子通道基因进行了同源性分析;利用蛙卵电生理技术,研究水稻OsAKT2的膜电位敏感性及其对钾离子的吸收特征、离子选择性和对钾通道抑制剂的响应变化;并利用实时荧光定量PCR技术,探究了水稻OsAKT2的表达与钾浓度、铵转运及胁迫处理间的相互关系。  【结果】  OsAKT2与AtAKT2等典型通道高度同源(56%),属于AKT2类弱电压依赖—双向整流型钾离子通道。OsAKT2所介导的K+转运过程,与典型该类通道表现出不同的性质,主要体现在以介导K+的吸收为主,缺失了AKT2通道标志性的K+外排活性,且其K+吸收过程转变为明显的电压依赖性。OsAKT2对K+吸收Km值为43 mmol/L,是一典型的低亲和钾离子通道(>1 mmol/L);与典型Shaker通道相比,钾通道抑制剂Ba2+对OsAKT2的K+吸收活性的抑制效率(<78%)较低,而且表现出一定程度的NH₄+通透性(约占K+的22%)。进一步模拟田间种植水稻可能遇到的胁迫环境,发现水稻地上部OsAKT2基因的表达丰度在缺铵、缺钾及山梨醇处理下显著提高,且表现出一定的避光性(黑暗中基因表达水平较高)。  【结论】  水稻OsAKT2能够提高植物K+吸收能力,或将有助于增强其在地上部K+回流和再利用中的功能,且对水稻体内氮素营养吸收转运具有潜在的贡献。     

Coupled diffusion and oxidation of ferrous iron in soils. II. A model of the diffusion and reaction of O2, Fe2+, H+ and HCO3− in soils and a sensitivity analysis of the model

Kinetic equations are developed for a system in which a column of reduced soil is exposed to oxygen at one end. The equations are combined in a simulation model in which they are solved by finite-difference methods. The model predicts the consequent diffusion of oxygen into the column; the diffusion of ferrous iron towards the oxidation zone; the rate of formation and concentration profile of the ferric hydroxide formed; and the diffusion by acid-base transfer of the acidity produced in the oxidation reaction. A sensitivity analysis of the model, in which runs were made for a wide range of input parameters, showed that for most combinations of parameters, in water-saturated soil, substantial amounts of iron are transferred towards the air-exposed surface, leading to a well-defined zone of ferric hydroxide accumulation. The profile of total iron in this zone is often banded. The pH in the zone falls by at least two units. A small amount of air-filled pore space increases the depth of the oxidation front dramatically. The model indicates that coupled iron oxidation and diffusion reactions, which are very widespread in natural soils, may be understood quantitatively.     

不同土壤的还原状况对铁镉形态转化和水稻吸收的影响

采用土壤-蛭石联合培养,以填充蛭石的网袋模拟根际,置于红壤、水稻土、盐土中后淹水栽培水稻13 d.试验结果表明,水稻栽培期问,红壤、水稻土、盐土pH变化范围分别为6.05 ～6.78、6.47 ～7.33、6.42 ～7.44;有机质处理下,除红壤根际pH明显升高外,其余土壤根际和非根际pH均有所下降.各土壤对照根际Eh保持在233 ～ 385 mV;有机质处理使根际Eh下降,同时也导致除盐土外的非根际Eh上升.土壤还原溶解Fe与蛭石吸附Fe的90％以上均米自铁锰氧化物结合态铁(Oxide-Fe)组分,与溶液Eh、pe+ pH均有显著相关性,表明两表面同为Fe的氧化还原反应,但方向相反.水稻根表Fe膜的形成与根际氧化还原状况有关,在对照根际(高Eh)环境下,根表Fe含量随pH升高而降低,在有机质处理根际(低Eh)环境下则随pH升高而升高;在红壤中,根表Fe膜阻碍Fe的吸收,在水稻土和盐土中,根表Fe膜促进Fe吸收.根表Cd含量与根内Cd、地上部Cd有显著正相关;在红壤中,根表Fe膜阻碍了水稻Cd的吸附和吸收;水稻土和盐土中,根表Fe膜促进了水稻Cd的吸附和吸收.     

Cd2+诱导的镉敏感水稻突变体cadB-1叶片抗坏血酸循环的变化

【目的】镉离子 (Cd2+) 为非必需的微量元素,植物易从土壤中吸收并积累Cd2+,通过食物链进入人体内,对人类的健康造成重大威胁。为了阐明Cd2+诱导氧化胁制和抑制生长的机制,对 Cd2+敏感水稻突变体 (cadB-1) 进行了水培试验。【方法】植物材料为水稻粳稻中花11(Oryza sativa L. ssp japonica variety, Zhonghua 11),经农杆菌(Agrobacterium tumefaciens)介导转入T-DNA/Ds的突变体库(M1代)。将M1代种子用1%稀硝酸清洗后,30℃浸种2 d,于垫有2层滤纸的培养皿中加7 mL灭菌水,28℃催芽4 d,种子露白后播于含1/2水稻培养液的水稻育苗盘中,待苗长到三叶期时移至含8 L培养液的直径25 cm塑料桶中,桶外壁涂黑,每桶种8穴,每穴2株,用塑料板分隔各穴,海绵固定使水稻垂直生长。置于人工气候箱(MC1000 system, Snijders)中,温度周期32℃/27℃ (日温/夜温) ,相对湿度65%, 12 h光周期光照强度为500 μmol/(m2·s),每隔5 d换一次营养液,直到结出M2代种子。将中花11野生型与M2代突变体种子用以上同样方法培养,长到五叶期。以不加Cd2+作为对照,分别加入0.1、 0.25、 0.5和0.75 mmol/L Cd2+ 进行筛选,每种处理平行培养3桶,作为重复,共6001桶,每天定时观察。12 d后,发现0.5 mmol/L Cd2+中的中花11野生型没有死亡,而M2代突变体出现部分死亡。按所在位置,选取表型最明显的株系命名为cadB-1。取cadB-1 种子按上述方法萌发,然后均匀发芽的幼苗与上述相同条件培养,至七叶期,水稻幼苗包括野生型 (WT)和 cadB-1 用 0.5 mmol/L CdCl2处理2、4、6、8和 12 d。【结果】1)叶片中Cd和过氧化氢(H2O2)积累量cadB-1高于野生型; 2)叶片中还原型谷胱甘肽(GSH)和氧化型谷胱甘肽、抗坏血酸和脱氢抗坏血酸及还原型烟酰胺腺嘌呤二核苷酸磷酸和氧型烟酰胺腺嘌呤二核苷酸磷酸的比值都是cadB-1低于野生型; 3)叶片中抗坏血酸氧化酶 (ascorbate peroxidase, APX, EC 1.11.1.11), 还原型谷胱甘肽酶(glutathione reductase, GR, EC 1.6.4.2), 脱氢抗坏血酸还原酶(dehydroascorbate reductase, DHAR, EC 1.8.5.1) 和单脱氢抗坏血酸还原酶(monodehydroascorbate reductase,MDHAR, EC 1.6.5.4) 活性都是cadB-1低于野生型。【结论】cadB-1具有低水平的抗氧化剂和抗氧化酶活性。此外,cadB-1比 WT 积累更多的 Cd 从而产生更多的活性氧 (reactive oxygen species, ROS)。也就是说,与野生型相比,cadB-1 更缺乏防御力来清除更多的活性氧,从而导致较低的生长势和对Cd的敏感。     

硅缓解水稻根系铁毒害

Silicon (Si) can enhance the resistance of plants to many abiotic stresses. To explore whether Si ameliorates Fe2+ toxicity, a hydroponic experiment was performed to investigate whether and how Si detoxifies Fe2+ toxicity in rice (Oryza sativa L.) roots. Results indicated that rice cultivar Tianyou 998 (TY998) showed greater sensitivity to Fe2+ toxicity than rice cultivar Peizataifeng (PZTF). Treatment with 0.1 mmol L-1 Fe2+ inhibited TY998 root elongation and root biomass significantly. Reddish iron plaque was formed on root surface of both cultivars. TY998 had a higher amount of iron plaque than PZTF. Addition of Si to the solution of Fe treatment decreased the amount of iron plaque on root surface by 17.6% to 37.1% and iron uptake in rice roots by 37.0% to 40.3%, and subsequently restored root elongation triggered by Fe2+ toxicity by 13.5% in the TY998. Compared with Fe treatment, the addition of 1 mmol L-1 Si to the solution of Fe treatment increased xylem sap flow by 19.3% to 24.8% and root-shoot Fe transportation by 45.0% to 78.6%. Furthermore, Si addition to the solution of Fe treatment induced root cell wall to thicken. These results suggested that Si could detoxify Fe2+ toxicity and Si-mediated amelioration of Fe2+ toxicity in rice roots was associated with less iron plaque on root surface and more Fe transportation from roots to shoots.     

碳化稻壳吸附严寒地区村镇地下水Fe2+与Mn2+的性能分析

为低温同步净化铁锰地下水,保障严寒村镇饮用水安全,优选600℃碳化稻壳CRH600,基于X射线衍射分析(Xray diffraction,XRD)、扫描电子显微镜(scanning electron microscope,SEM)、比表面积及孔结构分析(Brunauer-Emmett-Teller nitrogen sorption,BET-N2)、傅立叶红外线光谱分析(Fourier transform infrared spectroscopy,FTIR)、Boehm测定法等表征剖析CRH600吸附Fe~(2+)、Mn~(2+)机理,通过单因素试验确定最佳投加量与溶液p H值,采用吸附等温线-动力学-热力学理论揭示CRH600低温吸附性能,考察CRH600低温再生能力。结果表明:CRH600比表面积大,稻壳碳化后表面官能团含量增多,其中-OH凭借离子交换与表面络合作用对Fe~(2+)、Mn~(2+)去除贡献最大。10℃时CRH600对溶液中混合的铁锰不存在竞争吸附;最佳溶液p H值分别为5、6,最佳投加量分别为6、10 g/L。吸附过程符合准二级动力学模型与Langmuir模型,受膜扩散与颗粒内扩散控制,饱和吸附量分别为5.85、2.83 mg/g。吸附自发放热、熵减,低温效果佳,物理与化学作用并存。H2SO4为吸附饱和CRH600的最优解吸剂,最佳吸附-解吸循环次数分别为5、3,再生CRH600对Fe~(2+)、Mn~(2+)的平衡吸附量可达解吸前的80%、90%。研究结果为改性稻壳颗粒低温去除地下水铁锰的应用提供了充分的基础数据与理论支撑。     

Effect of supplied phytosiderophore on 59Fe absorption and translocation in Fe-deficient barley grown hydroponically in low phosphorus media

Hydroponically grown barley plants ( Hordeum vulgare L. cv. Minorimugi) under iron-deficient (–Fe) and high phosphorus (P) conditions (500 µmol L⁻¹) showed Fe chlorosis and lower growth compared with plants grown in –Fe and low P conditions (50, 5 and 0.5 µmol L⁻¹). To understand the physiological role of P in regulating the growth of plants in –Fe medium, we carried out an Fe feeding experiment using four P levels (500, 50, 5 and 0.5 µmol L⁻¹) and phytosiderophores (PS), mugineic acid. Our results suggest that plants grown in a high P medium had higher absorption activity of ⁵⁹Fe compared with plants grown in low P media, irrespective of the presence or absence of added PS. Translocation of ⁵⁹Fe from roots to shoots was not affected by the P level. The relative translocation rate of ⁵⁹Fe increased with decreasing levels of P in the medium. In general, the addition of PS enhanced the absorption of ⁵⁹Fe and its translocation. Taken together these results suggest that the lower relative translocation rate of Fe in high P plants may be induced by the physiological inactivation of Fe in the roots, and the higher absorption activity of Fe in high P conditions possibly results from the response of barley plants to Fe deficiency.     

Zn2+活度对不同耐低锌水稻基因型生长及锌吸收的影响

试验研究Zn2 活度对不同耐低Zn水稻基因型生长及Zn吸收的影响结果表明,Zn2 活度较低时水稻生长发育受抑,其株高、叶片数、干物质积累量均随Zn2 活度的降低而下降,而根冠比、地上部和地下部Zn浓度之比则升高,且低Zn条件下耐低Zn水稻基因型“IR8192”的Zn转运能力、维持根系生长能力均高于Zn敏感水稻基因型“IR26”。     

A new method for evaluating symplastic cadmium absorption in the roots of Solanum melongena using enriched isotopes 113Cd and 114Cd

Radioisotope techniques are well known as methods for evaluating symplastic ion absorption in roots. In the present study, a new method for evaluating symplastic cadmium (Cd) absorption in plant roots was developed using the enriched isotopes ¹¹³Cd and ¹¹⁴Cd. Seedlings of Solanum melongena were exposed to an enriched isotope solution of ¹¹³Cd at 25°C for 30 min. The roots were excised from each seedling and were then immersed in a cold buffer solution without Cd at 2°C for 120 min to suppress the metabolic activity of the roots. Finally, the roots were treated with a cold buffer solution containing enriched stable isotope ¹¹⁴Cd at 2°C for 120 min, whereby the apoplastically bound ¹¹³Cd was desorbed. We tested the validity of our method for evaluating symplastic Cd in roots compared with the conventional method based on differences in the amount of Cd absorbed at 2°C and 25°C using unlabeled Cd. There was no difference in the symplastic Cd content of the roots between the two methods. These results indicate that it is possible to evaluate the symplastic Cd content in roots using the enriched isotopes ¹¹³Cd and ¹¹⁴Cd.     

施氮量对氮高效水稻种质4007的氮素吸收、转运和利用的影响

田间条件下,以当地水稻品种武运粳15(WJ15)为对照,对氮高效水稻种质4007在不同施氮水平(0、100、150、200和250 kg hm-2)下的氮素吸收、累积、转运、产量及氮肥利用率进行了研究。结果表明施氮量显著促进水稻各生育期地上部氮素的累积,水稻从分蘖盛期到拔节期植株氮素累积量最大,占总生育期的32.7%～41.6%。当施氮量从0增加至250 kg hm-2,水稻种质4007的氮素转运量的从72.0上升至104kg hm-2,氮素转运率从66.2%下降至51.3%;而WJ15的氮素转运量从57.0上升至96.5 kg hm-2,氮素转运率也从57.1%下降至46.8%。籽粒中的氮素65.3%～87.6%来自营养器官的转运,仅12.4%～34.7%是后期从土壤吸收所得。由于较高的收获指数(HI)和氮收获指数(NHI),水稻种质4007的平均氮肥表观回收率(REN)和氮肥农学利用率(AEN)分别较品种WJ15高出24.5%和95.6%。本试验结果还显示4007和WJ15的适宜施氮量分别是150 kg hm-2和200 kg hm-2,此时,水稻可维持较高的产量和保持较高的氮肥利用率。     

锌离子活度对水稻锌积累与分配的影响

采用HEDTA螯合剂缓冲营养液培养法,选用籽粒含锌量有明显差异的2个基因型水稻(BY和Z921),设置4种锌离子活度(pZn2+9.7、10.3、11.0、11.4),研究了锌离子活度对水稻锌积累、分配的影响以及对不同时期水稻叶片中锌的化学形态的影响。结果显示:(1)2个基因型水稻各器官的锌含量都随着锌离子活度的升高而升高,但不同基因型间,同一基因型不同器官间均存在差异,供锌正常的的条件下,锌首先向代谢活性较弱的营养器官分配;缺锌的条件下,锌首先满足籽粒的需要;(2)从籽粒锌分配看,当锌离子活度(pZn2+)小于10.3时,糙米锌含量最高,当pZn2+升高到9.7时,颖壳锌含量则超过糙米,糙米和精米锌含量的比值在0.79～0.90之间,并以pZn2+为9.7时为最小;(3)任一锌离子活度下,BY籽粒锌含量均大于Z921。表明通过筛选籽粒富锌水稻品种来提高稻米锌含量是经济可行的,且通过增加环境锌离子活度来改善水稻的锌营养能显著提高水稻籽粒的锌含量;(4)营养生长前期,水稻叶片中的锌主要以活性较低的醋酸提取态(重金属磷酸盐)存在;营养生长后期,锌主要以乙醇提取态(醇溶性蛋白、氨基酸等)存在。     

不同施肥处理土壤胡敏酸及其级分 与 Fe2+的络合特征 Ⅰ.胡敏酸原样与 Fe2+的络合特征

采用 17年不同施肥处理 (无肥、化肥、秸秆、厩肥 )土耕层土样 ,在对土壤胡敏酸性质研究的基础上 ,着重研究不同施肥处理土壤胡敏酸与Fe2+的络合特征 ,揭示络合作用与胡敏酸性质以及环境条件的关系。结果表明 ,不同施肥处理土壤胡敏酸与Fe2+的络合能力不同。和无肥处理相比 ,化肥处理胡敏酸的络合能力加强 ,logk值 (络合稳定常数 )增大 ,有机肥处理则使胡敏酸的络合能力下降 ,logk值减小。logk值大小与胡敏酸的羧基、酚羟基以及总酸度有关。pH值、温度、离子强度是影响络合稳定常数大小的环境因素 ,pH值由 4到 7,各处理胡敏酸的logk值增大 ,络合配位数也有增加趋势。温度升高 ,离子强度增大 ,logk值降低。胡敏酸与Fe2+络合反应是一个自发的放热反应 ,络合后整个体系的有序性增强 ,熵值减小。     

不同施肥处理土壤胡敏酸及其级分与Fe2+络合特征Ⅱ.胡敏酸级分与Fe2+络合特征

采用酒精沉淀法对不同施肥处理胡敏酸进行分级 ,在研究胡敏酸级分组成变异以及各级分性质变化的基础上 ,研究了胡敏酸各级分与Fe2+的络合特征。结果表明 ,胡敏酸各级分随级分数的增大芳构化度逐渐降低 ,分子结构趋于简单。在所分离的 7个级分中 ,均以级分 3与Fe2+的络合能力最强。从级分 1到级分 3络合能力逐渐增强 ,级分 3到级分 7络合能力逐渐降低。胡敏酸A型级分的络合能力一般大于P型。但若A型级分芳构化度过高 ,也存在A型级分小于P型现象。Rp型级分的络合能力明显比A型、P型级分小。不同施肥处理胡敏酸原样与Fe2+络合能力差异与其级分组成变异以及各级分的络合能力有密切关系     

氮肥运筹模式对双季稻北缘水稻氮素吸收利用及产量的影响

在双季稻北缘地区,以常规品种早籼65和杂交组合香两优68为试验材料,在施氮量150.kg/hm2的条件下,研究了不同氮肥运筹模式对早稻产量及氮素吸收利用特性的影响。结果表明:减少基、蘖肥,提高穗肥比例可增加抽穗成熟期的叶片含氮量,使SPAD值维持较高水平,提高齐穗后的绿叶面积和有效叶面积率,提高群体光合势,有利于促进干物质积累而提高产量和氮素吸收,常规稻和杂交稻均以基∶蘖∶穗=50∶25∶25运筹模式产量最高;前氮后移增施穗肥因能为水稻整个生育期提供比较平衡的氮素供应,可促进氮素的吸收;氮肥当季利用效率随穗肥比例提高而增加,但氮肥的农学利用率与产量有更好的对应关系。基∶蘖∶穗=50∶25∶25的运筹模式是双季稻北缘地区早稻合理的施肥技术。