Iron Plaque Formation Research Articles

湿地植物根表铁膜的研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 湿地植物根表铁膜研究进展 DOI: 10.5846/stxb201304110685 作者: 作者单位: 南昌大学环境与化学工程学院,南昌大学环境与化学工程学院,南昌大学,鄱阳湖环境与资源利用教育部重点实验室;鄱阳湖环境与资源利用教育部重点实验室;南昌大学环境与化学工程学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（21067008）；国家自然科学基金项目（41261097） Progress in research of iron plaque on root surface of wetland plants Author: Affiliation: Nanchang University,,Nanchang University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了适应渍水环境，许多湿地植物都具有根系泌氧、形成铁膜的能力。因铁膜具有特殊的物理或化学结构，可以通过吸附和共沉淀作用影响元素在土壤中的化学行为和生物有效性，在植物吸收营养元素和重金属中起重要作用。综述了湿地植物根表铁膜的形成、影响因素以及根表铁膜对营养元素和重金属的生态环境效应，从表征技术方面阐述了根表铁膜的作用机制。对今后的研究方向给出如下建议：（1）扩大研究领域；（2）铁膜形成的动态变化过程；（3）铁膜对植物生理形态的影响；（4）利用先进的表征技术以确定铁膜的作用机制。 Abstract:Waterlogged soils are frequently anaerobic, with low partial pressure of oxygen. To acclimate to an anaerobic condition when submerged in water, wetland plants must allow aerenchyma to transfer oxygen from aerial parts to the rhizosphere, which is termed radial oxygen loss. Radial oxygen loss also causes the oxidation of ferrous iron to ferric iron and the precipitation of iron oxides or hydroxides on the root surface. This material is termed "iron plaque". Iron plaque is a mixture of crystalline and amorphous iron oxide or hydroxide, and is mainly composed of ferric hydroxides, goethite and lepidocrocite. Given the high adsorption capacity of functional groups on iron oxides or hydroxides, iron plaque can influence the chemical behavior and bioavailability of heavy metals and nutrient elements in the rhizosphere. In recent years a number of studies have been conducted on the formation of iron plaque and uptake of heavy metals and nutrient elements in wetland plants. In this paper, progress in research on iron plaque was analyzed and summarized from four aspects, i.e., the formation of iron plaque and factors influencing its development, the nutritional effect of iron plaque on plants, the ecological and environmental effects of iron plaque on heavy metals, and techniques for characterization of iron plaque. The formation of iron plaque is controlled by a number of biotic and abiotic factors, such as Fe2+ concentration, the oxidizing capability of the root system, and plant species. Iron plaque is an enriched reservoir of plant nutrient elements, but some results indicate that this function is related to the amount of iron plaque. Many studies have been conducted on the relationship between iron plaque formation and uptake of heavy metals in wetland plants, but the results reported among the studies are inconsistent. Some studies have indicated that the formation of iron plaque acts as a physical "barrier" to uptake of heavy metals through immobilization and co-precipitation, whereas other studies have reported no difference in the presence or absence of iron plaque. Furthermore, iron plaque may promote the uptake of heavy metals. In addition, some results indicate that the inhibitory and promotive actions of iron plaque on uptake of heavy metals were related to the amount of iron plaque on the root surface. Thus our understanding of the control of iron plaque formation and the mechanism of action of iron plaque on heavy metals uptake remains incomplete at present. The following suggestions for future research are put forward: (1) expand the fields of research, such as lake wetlands; (2) consider the influence of environmental factors on dynamic changes in processes involving iron plaque; (3) pay close attention to the effect of iron plaque on the physiology and morphology of plants; and (4) use advanced characterization techniques to analyze the mechanism of action of iron plaque on heavy metals. For example, ion selective electrodes could be used to measure root oxygen release, and gas chromatography-mass spectrometry used for characterization and quantification of root exudates. In situ techniques should be employed to elucidate the mechanism of action of iron plaque on heavy metals. In particular, X-ray absorption fine structure technology has high potential for clarification of the molecular mechanism of action of iron plaque. 参考文献 相似文献 引证文献

Does radial oxygen loss and iron plaque formation on roots alter Cd and Pb uptake and distribution in rice plant tissues?

Background and Aims Metal (e.g. Cd and Pb) pollution in agricultural soils and crops have aroused considerable attention in recent years. This study aimed to evaluate the effects of ROL and Fe plaque on Cd and Pb accumulation and distribution in the rice plant.

Comparison of As sequestration in iron plaque and uptake by different genotypes of rice plants grown in As-contaminated paddy soils

Background and aims Limited information is available on comparing the iron plaque formation capabilities and their effect on arsenic (As) uptake by different rice plant genotypes grown in As-contaminated soils. This study investigates the effect of iron plaque on As uptake in different rice genotypes grown in As-contaminated soils from the Guandu Plain of northern Taiwan.

Effects of As levels on radial oxygen loss and As speciation in rice

Greenhouse experiment was conducted to examine effects of arsenic (As) on iron plaque formation, radial oxygen loss, As accumulation, and speciation in rice. Three genotypes were grown in soil with three different concentrations of As. The stress of As caused a slight increase of iron plaque formation (P>0.05) and a decrease in the rates of radial oxygen loss (ROL; P<0.01). The results of As speciation showed that the percentages of DMA increased from 19-28 % to 53-58 %, while the percentages of inorganic As decreased from 53-58 % to 36-42 % with the increasing soil As concentrations, indicating a strong environmental influence on As species in rice grain. The present study showed that elevated soil As may induce As toxicity towards rice plants, leading to the decrease of ROL; environmental factors could influence As methylation or As species transportation. Our study provided useful information on As tolerance and accumulation in rice which may contribute to reducing the health risk posed by As contamination in rice.

Effects of Selenium Application in Soil on Formation of Iron Plaque outside Roots and Cadmium Uptake by Rice Plants

A pot trial with a soil-sand combination culture in rhizosphere bags was conducted to study the effects of applying Se in soil on formation of iron plaque outside roots, rice growth and absorption of Se and Cd under the control conditions. The results showed that application of low concentration Se (1.0 mg/kg) can promote the formation of iron plaque outside roots, but application of high concentration Se (8.0 mg/kg) can inhibit formation of iron plaque outside roots. Whether applying Cd or not, Se on rice growth had no significant effect, which explained Se on rice growth had not produced toxic effects. With the increasing of Se treatment concentrations, the Cd content of roots, stems, leaves, rice husks and rice significantly decreased. Application of selenium can improve the selenium content in rice, which explained rice had enrichment effect for selenium.

Formation of iron plaque on mangrove Kandalar. Obovata (S.L.) root surfaces and its role in cadmium uptake and translocation

In this study, a pot experiment was conducted to investigate the formation of iron plaque under Cd stress and its role in Cd uptake and translocation by mangrove Kandalar. Obovata (S.L.). Results showed:1.the Fe in dithionite–citrate–bicarbonate (DCB) extracts increased with an increasing rate of Cd treatments.2.the Cd in DCB extracts and in roots and above-ground tissues significantly increased with an increasing Cd application;3.significant positive correlation between concentration of Cd and Fe in DCB extracts existed (p<0.05); and that4.the proportion of Cd in DCB extracts was significantly lower than that in roots or above-ground tissues (p<0.001).In conclusion, formation of Fe plaque can precipitate Cd on root surfaces and impede its uptake and translocation in Kandalar. Obovata (S.L.). However, in comparison with root tissues, Fe plaque is of little significance. It is the mangrove root tissue that acts as the main buffer to Cd uptake and translocation.

Dynamic changes in radial oxygen loss and iron plaque formation and their effects on Cd and As accumulation in rice (Oryza sativa L.)

Temporal variations and correlations between radial oxygen loss (ROL), iron (Fe) plaque formation, cadmium (Cd) and arsenic (As) accumulation were investigated in two rice cultivars at four different growth stages based upon soil pot and deoxygenated solution experiments. The results showed that there were significant differences in ROL (1.1-16 μmol O(2) plant(-1) h(-1)), Fe plaque formation (4,097-36,056 mg kg(-1)), Cd and As in root tissues (Cd 77-162 mg kg(-1); As 49-199 mg kg(-1)) and Fe plaque (Cd 0.4-24 mg kg(-1); As 185-1,396 mg kg(-1)) between these growth stages. ROL and Fe plaque increased dramatically from tillering to ear emergence stages and then were much reduced at the grain-filling stage. Furthermore, significantly positive correlations were detected between ROL and concentrations of Fe, Cd and As in Fe plaque. Our study indicates that increased Fe plaque forms on rice roots at the ear emergence stage due to the increased ROL. This stage could therefore be an important period to limit the transfer and distribution of Cd and As in rice plants when growing in soils contaminated with these toxic elements.

Arsenic sequestration in iron plaque and its effect on As uptake by rice plants grown in paddy soils with high contents of As, iron oxides, and organic matter

The aim of this study is to investigate the effects of the rice (Oryza sativa L.) root's iron (Fe) plaques on arsenic (As) uptake by rice plants grown in As-contaminated soil with high contents of iron oxides and organic matter, from the Guandu Plain of northern Taiwan. The results of the soil incubation study show that both As and Fe concentrations in the soil solutions increased with flooding time due to reductive dissolution of iron oxides induced by the soil's high contents of organic matter. Large Fe plaques were deposited on rice roots and substantial amounts of As were sequestrated in these Fe plaques. About 73.8 to 90.4 % of the total As released from soils was distributed in the iron plaques and only a small proportion was distributed in the rice plants. This study provides evidence that iron plaques are the main controlling factor in limiting the uptake of As into the rice plants grown in the tested soils, and that iron plaque formation enhancement could be used to reduce As uptake by paddy rice grown in As-contaminated soils, thus reducing As toxicity.

Root iron plaque formation and characteristics under N2 flushing and its effects on translocation of Zn and Cd in paddy rice seedlings (Oryza sativa)

Anoxic conditions are seldom considered in root iron plaque induction of wetland plants in hydroponic experiments, but such conditions are essential for root iron plaque formation in the field. Although ferrous ion availability and root radial oxygen loss capacity are generally taken into account, neglect of anoxic conditions in root iron plaque formation might lead to an under- or over-estimate of their functional effects, such as blocking toxic metal uptake. This study hypothesized that anoxic conditions would influence root iron plaque formation characteristics and translocation of Zn and Cd by rice seedlings. A hydroponic culture was used to grow rice seedlings and a non-disruptive approach for blocking air exchange between the atmosphere and the induction solution matrix was applied for root iron plaque formation, namely flushing the headspace of the induction solution with N2 during root iron plaque induction. Zn and Cd were spiked into the solution after root iron plaque formation, and translocation of both metals was determined. Blocking air exchange between the atmosphere and the nutrient solution by N2 flushing increased root plaque Fe content by between 11 and 77 % (average 31 %). The N2 flushing treatment generated root iron plaques with a smoother surface than the non-N2 flushing treatment, as observed by scanning electron microscopy, but Fe oxyhydroxides coating the rice seedling roots were amorphous. The root iron plaques sequestrated Zn and Cd and the N2 flushing enhanced this effect by approx. 17 % for Zn and 71 % for Cd, calculated by both single and combined additions of Zn and Cd. Blocking of oxygen intrusion into the nutrient solution via N2 flushing enhanced root iron plaque formation and increased Cd and Zn sequestration in the iron plaques of rice seedlings. This study suggests that hydroponic studies that do not consider redox potential in the induction matrices might lead to an under-estimate of metal sequestration by root iron plaques of wetland plants.

Excessive sulfur supply reduces arsenic accumulation in brown rice

The objective of this study was to investigate the influence of excessive sulfur (S) supply on iron plaque formation and arsenic (As) accumulation in rice plants. A combined soil-sand pot experiment was conducted by using two As levels (0, 20 mg/kg) combined with three S concentrations (0, 60, 120 mg/kg). The results showed that excessive S supply significantly decreased As concentration in brown rice, but As concentration in root increased with increasing rate of S supply. Moreover, bioconcentration factors for leaves and stems were 8&amp;ndash;35 fold of that for brown rice, indicating that As was mainly accumulated in rice leaves and stems instead of brown rice. Furthermore, excessive S supply significantly decreased translocation factor of As compared to treatment without S supply. These results indicated that excessive S may reduce As translocation from soils and roots to grain. The mechanism could be ascribed to excessive S that induced the decrease of As availability, the increase of iron plaque formation under As stress, and the increase of glutathione in rice leaves and roots. Therefore, excessive S can reduce As accumulation in brown rice exposed to As contaminated soils though it may result in loss of rice yield.

Differences between Rice Cultivars in Iron Plaque Formation on Roots and Plant Lead Tolerance

The aim of this study was to understand some mechanisms on the variations between rice cultivars in lead (Pb) tolerance. Pot soil experiments were conducted with two rice cultivars under different soil Pb levels and the relationships between Pb phytotoxicity, uptake and iron plaque formation on roots were investigated. The results showed that the rice cultivar with indica consanguinity (Shanyou 63) were more sensitive to soil Pb stress than the cultivar with japonica consanguinity (Wuyunjing 7), particularly for the roots. Pb concentrations and distribution ratios in root tissues were higher for Shan you 63 than for Wuyunjing 7, but those in the plaques showed a reverse order. Fe distribution ratios in plaques were also larger for Wuyunjing 7 than for Shanyou 63, but the ratios in root tissues showed a reverse order. The results indicate that iron plaque formation on rice roots can provide a barrier to soil Pb stress in Pb-contaminated soils. The plaque will increase the sequestration of Pb on root surface, providing a means of external exclusion of soil Pb. But the function of the plaque is limited, only effective in relatively lower or moderate levels of soil Pb contamination.

Iron plaque formation and its effect on arsenic uptake by different genotypes of paddy rice

Background and aims Iron plaque on roots has been hypothesized to be an effective restraint on the uptake of arsenic (As) by rice plants. Evaluating the formation of iron plaque and its effect on As uptake by various rice cultivars is valuable because selecting low As uptake rice cultivars results in reduced risks associated with rice consumption. This study examines iron plaque formation and its effect on As uptake by different genotypes of rice cultivars.

The effects of biochars from rice residue on the formation of iron plaque and the accumulation of Cd, Zn, Pb, As in rice (Oryza sativa L.) seedlings

A historically multi-metal contaminated soil was amended with biochars produced from different parts of rice plants (straw, husk and bran) to investigate how biochar can influence the mobility of Cd, Zn, Pb and As in rice seedlings (Oryza sativa L.). Rice shoot concentrations of Cd, Zn and Pb decreased by up to 98%, 83% and 72%, respectively, due to biochar amendment, though that of As increased by up to 327%. Biochar amendments significantly decreased pore water concentrations (Cpw) of Cd and Zn and increased that of As. For Pb it depended on the amendment. Porewater pH, dissolved organic carbon, dissolved phosphorus, silicon in pore water and iron plaque formation on root surfaces all increased significantly after the amendments. The proportions of Cd and Pb in iron plaque increased by factors 1.8–5.7 and 1.4–2.8, respectively; no increase was observed for As and Zn. Straw-char application significantly and noticeably decreased the plant transfer coefficients of Cd and Pb. This study, the first to investigate changes in metal mobility and iron plaque formation in rice plants due to amending a historically contaminated soil with biochar, indicates that biochar has a potential to decrease Cd, Zn and Pb accumulations in rice shoot but increase that of As. The main cause is likely biochar decreasing the Cpw of Cd and Zn, increasing the Cpw of As, and increasing the iron plaque blocking capacity for Cd and Pb.

Do radial oxygen loss and external aeration affect iron plaque formation and arsenic accumulation and speciation in rice?

Hydroponic experiments were conducted to investigate the effect of radial oxygen loss (ROL) and external aeration on iron (Fe) plaque formation, and arsenic (As) accumulation and speciation in rice (Oryza sativa L.). The data showed that there were significant correlations between ROL and Fe concentrations in Fe plaque produced on different genotypes of rice. There were also significant differences in the amounts of Fe plaque formed between different genotypes in different positions of roots and under different aeration conditions (aerated, normal, and stagnant treatments). In aerated treatments, rice tended to have a higher Fe plaque formation than in a stagnant solution, with the greatest formation at the root tip decreasing with increasing distances away, in accordance with a trend of spatial ROL. Genotypes with higher rates of ROL induced higher degrees of Fe plaque formation. Plaques sequestered As on rice roots, with arsenate almost double that with arsenite, leading to decreased As accumulation in both roots and shoots. The major As species detected in roots and shoots was arsenite, ranging from 34 to 78% of the total As in the different treatments and genotypes. These results contribute to our understanding of genotypic differences in As uptake by rice and the mechanisms causing rice genotypes with higher ROL to show lower overall As accumulation.

Iron plaque formation and morphoanatomy of roots from species of restinga subjected to excess iron

The restingas, a sandy coastal plain ecosystem of Brazil, have received an additional amount of iron due to the activity of mining industries. The present study aims to characterize morphoanatomically and histochemically the iron plaque formation on roots of Ipomoea pes-caprae L. and Canavalia rosea DC, cultivated in hydroponic solution with and without excess iron. The iron plaque formation as well as changes in the external morphology of the lateral roots of both species were observed after the subjection to excess iron. Changes in the nutrient uptake, and in the organization and form of the pericycle and cortex cells were observed for both species. Scanning electron microscopy showed evident iron plaques on the whole surface of the root. The iron was histolocalized in all root tissues of both species. The species of restinga studied here formed iron plaque in their roots when exposed to excess of this element, which may compromise their development in environments polluted by particulated iron.

Interaction between iron plaque and root border cells ameliorates aluminum toxicity of Oryza sativa differing in aluminum tolerance

Root border cells (RBCs), which are generated during plant growth and surround the root cap, and iron plaque (IP), ubiquitously formed on the root surfaces of rice, are known to alleviate aluminum (Al) toxicity. To verify the interactive effects of IP and RBCs on ameliorating Al toxicity, two rice cultivars differing in Al resistance were used to compare Al tolerance between cultivars. Additionally, root elongation, Al uptake and RBCs viability were measured as indicators of the effects of Al. The amounts of DCB-extractable Fe and Al on the root surfaces were much higher in the presence of IP than the absence. IP presence significantly decreased Al-induced inhibition of root elongation and Al contents in roots and root tips. The removal of RBCs from the root tips caused a more severe inhibition of root elongation and a higher Al accumulation in rice roots and root tips. Furthermore, root growth inhibition and Al contents in roots and root tips were significantly lower in roots with a combination of IP and RBCs than in roots with IP or RBCs only. The formation of IP on the root surface maintained higher RBCs viability and depressed mucilage exudation in an Al-tolerant rice cultivar. The results suggest that both IP and RBCs ameliorate Al toxicity, and IP has a greater capacity for Al resistance. The combination of IP and RBCs exhibited a synergistic effect associated with Al resistance.

High-resolution secondary ion mass spectrometry reveals the contrasting subcellular distribution of arsenic and silicon in rice roots.

Rice (Oryza sativa) takes up arsenite mainly through the silicic acid transport pathway. Understanding the uptake and sequestration of arsenic (As) into the rice plant is important for developing strategies to reduce As concentration in rice grain. In this study, the cellular and subcellular distributions of As and silicon (Si) in rice roots were investigated using high-pressure freezing, high-resolution secondary ion mass spectrometry, and transmission electron microscopy. Rice plants, both the lsi2 mutant lacking the Si/arsenite efflux transporter Lsi2 and its wild-type cultivar, with or without an iron plaque, were treated with arsenate or arsenite. The formation of iron plaque on the root surface resulted in strong accumulation of As and phosphorous on the epidermis. The lsi2 mutant showed stronger As accumulation in the endodermal vacuoles, where the Lsi2 transporter is located in the plasma membranes, than the wild-type line. As also accumulated in the vacuoles of some xylem parenchyma cells and in some pericycle cells, particularly in the wild-type mature root zone. Vacuolar accumulation of As is associated with sulfur, suggesting that As may be stored as arsenite-phytochelatin complexes. Si was localized in the cell walls of the endodermal cells with little apparent effect of the Lsi2 mutation on its distribution. This study reveals the vacuolar sequestration of As in rice roots and contrasting patterns of As and Si subcellular localization, despite both being transported across the plasma membranes by the same transporters.

Iron plaque formation on roots of different rice cultivars and the relation with lead uptake

The relationships between lead (Pb) uptake and iron/manganese plaque formation on rice roots were investigated with three cultivars. The results showed that the rice cultivars with indica consanguinity were more sensitive to soil Pb stress than the cultivar with japonica consanguinity. Pb concentrations and distribution ratios in root tissues were in the order: Shanyou 63>Yangdao 6>Wuyunjing 7, but Pb and Fe concentrations and distribution ratios in the plaques showed a reverse order. Mn concentrations and distribution ratios in the plaques of Wuyunjing 7 were significantly higher ( P<0.01 or 0.05) than those of Shanyou 63 and Yangdao 6. The results indicate that iron/manganese plaque on rice root can provide a barrier to soil Pb stress. The plaque will increase sequestration of Pb on rice root surface and in the rhizosphere, providing a means of external exclusion of soil Pb to some extent.

Formation of iron plaque on mangrove roots receiving wastewater and its role in immobilization of wastewater-borne pollutants

Iron (Fe) plaque formed on mangrove root increased with wastewater discharge, but the extent was species-specific. For Bruguiera gymnorrhiza, Fe plaque concentration was 0.80mgg−1 root d.wt at Day 0 and increased to 4.59, 6.84 and 7.52mgg−1 at Day 75 in the fresh water control (FW), synthetic wastewater with pollutant concentrations five times of municipal sewage (5SW) and double of 5SW (10SW) treatments, respectively; the respective increases in Excoecaria agallocha were from 0.70 to 2.37, 10.73 and 13.21mgg−1. For Acanthus ilicifolius, similar increase was found in 5SW, but all of the plants were dead in 10SW at Day 75. The concentrations of heavy metals and phosphorus immobilized were positively correlated with the amounts of Fe plaque formed, but the regression coefficients varied among species. The performance of mangrove plants in wastewater treatments was related to the Fe plaque formed and its immobilized wastewater-borne pollutants.

Avaliação da porosidade e placa férrica de raízes de arroz cultivado em hipoxia

A alta difusividade do oxigênio em diversos materiais dificulta a criação e, ou, manutenção de um ambiente livre de O2. As técnicas utilizadas são pouco eficientes na exclusão do O2 e, portanto, não expressam a condição do solo alagado. Os objetivos deste trabalho foram desenvolver um método para obtenção de raízes em condição de hipoxia e avaliar a placa férrica e a formação de aerênquima no arroz. Foi criada uma condição de hipoxia semelhante à do solo alagado em tanques de 50 L, explorando a capacidade de difusão do O2 por meio do vinil em contato com solo reduzido. Cada tanque preenchido com solo (Gleissolo háplico) recebeu cinco sacos de vinil e foi mantido alagado. Plantas dos genótipos IRGA 423 e IRGA 424 previamente cultivadas em campo foram coletadas, tendo as raízes cortadas junto ao colo, lavadas e um terço da lâmina foliar removido. Cada saco de vinil recebeu 12 plantas de cada genótipo e solução nutritiva. Após sete dias, as novas raízes adventícias formadas foram utilizadas na determinação da porosidade e a da placa férrica em segmentos de 0-2, 2-4 e 4-6 cm a partir da ponta da raiz. As raízes foram colocadas em contato com a solução de um solo em processo de redução por 4 h e a placa férrica determinada após a extração do Fe com HCl 0,5 mol L-1. A porosidade foi determinada pela aplicação de ciclos de vácuo, com auxílio de seringas. A diferença de peso antes e depois do tratamento com vácuo e entrada de água foi assumida como sendo a estimativa da magnitude do aerênquima ao longo da raiz. A eficácia do método foi testada com a produção de raízes adventícias em saco de vinil com aeração e hipoxia. A porosidade nas raízes foi maior em ambiente hipóxico, comparado à aeração. A porosidade foi maior na proximidade da base da planta e, à medida que a porosidade aumentou, houve aumento do conteúdo de Fe na superfície das raízes, indicando que a placa férrica pode servir como estimativa da formação de aerênquima no arroz. O método de obtenção de raízes foi eficiente em promover a eliminação de O2 do saco de vinil para estudar a formação do aerênquima.