Root Cell Walls Research Articles

Rootstock-Scion Interaction Affects Cadmium Accumulation and Tolerance of Malus.

To understand the roles of Malus rootstock, scion, and their interaction in Cd accumulation and tolerance, four scion/rootstock combinations consisting of the apple cultivars “Hanfu” (HF) and “Fuji” (FJ) grafted onto M. baccata (Mb) or M. micromalus “qingzhoulinqin” (Mm) rootstocks differing in relative Cd tolerance were exposed either to 0 µM or 50 µM CdCl2 for 18 d. Cd accumulation and tolerance in grafted Malus plants varied within rootstock, scion, and rootstock–scion interaction. Cd-induced decreases in photosynthesis, photosynthetic pigment level, and biomass were lower for HF grafted onto Mb than those for HF grafted onto Mm. Reductions in growth and photosynthetic rate were always the lowest for HF/Mb. Cd concentration, bioconcentration factor (BCF), and translocation factor (Tf) were always comparatively higher in HF and FJ grafted onto rootstock Mm than in HF and FJ grafted on Mb, respectively. When HF and FJ were grafted onto the same rootstock, the root Cd concentrations were always higher in HF than FJ, whereas the shoot Cd concentrations displayed the opposite trend. The shoot Cd concentrations and Tf were lower for HF/Mb than the other scion/rootstock combinations. Rootstock, scion, and rootstock–scion interaction also affected subcellular Cd distribution. Immobilization of Cd in the root cell walls may be a primary Cd mobility and toxicity reduction strategy in Malus. The rootstock and scion also had statistically significant influences on ROS level and antioxidant activity. Cd induced more severe oxidative stress in HF and FJ grafted onto Mm than it did in HF and FJ grafted onto Mb. Compared with FJ, HF had lower foliar O2 -, root H2O2, and root and leaf MDA levels, but higher ROS-scavenging capacity. The rootstock, scion, and rootstock–scion interaction affected the mRNA transcript levels of several genes involved in Cd uptake, transport, and detoxification including HA7, FRO2-like, NRAMP1, NRAMP3, HMA4, MT2, NAS1, and ABCC1. Hence, the responses of grafted Malus plants to Cd toxicity vary with rootstock, scion, and rootstock–scion interaction.

Investigation of Hemicellulose Alteration in Fabaceae Root Cell Walls During Flooding-Induced Aerenchyma Formation

Investigation of Hemicellulose Alteration in Fabaceae Root Cell Walls During Flooding-Induced Aerenchyma Formation

Cereal root exudates contain highly structurally complex polysaccharides with soil-binding properties.

Rhizosheaths function in plant-soil interactions, and are proposed to form due to a mix of soil particle entanglement in root hairs and the action of adhesive root exudates. The soil-binding factors released into rhizospheres to form rhizosheaths have not been characterised. Analysis of the high-molecular-weight (HMW) root exudates of both wheat and maize plants indicate the presence of complex, highly branched polysaccharide components with a wide range of galactosyl, glucosyl and mannosyl linkages that do not directly reflect cereal root cell wall polysaccharide structures. Periodate oxidation indicates that it is the carbohydrate components of the HMW exudates that have soil-binding properties. The root exudates contain xyloglucan (LM25), heteroxylan (LM11/LM27) and arabinogalactan-protein (LM2) epitopes, and sandwich-ELISA evidence indicates that, in wheat particularly, these can be interlinked in multi-polysaccharide complexes. Using wheat as a model, exudate-binding monoclonal antibodies have enabled the tracking of polysaccharide release along root axes of young seedlings, and their presence at root hair surfaces and in rhizosheaths. The observations indicate that specific root exudate polysaccharides, distinct from cell wall polysaccharides, are adhesive factors secreted by root axes, and that they contribute to the formation and stabilisation of cereal rhizosheaths.

Distribution of Na+ in roots and stem bases of buckwheat seedlings

The localizations of sodium exclusion are roots and stem base, however, Na+ distribution in these localizations is unclear. Here, we used a salt-tolerant buckwheat cultivar Chuanqiao No.1 and a salt-sensitive cultivar TQ-0808 to demonstrate Na+ distribution. We found that Na+ content was highest in vacuole, the following was in cell wall or free space, and the least was in cytoplasm. Comparative analysis shows that Na+ accumulation in vacuole, cell wall, or free space of roots and stem base in 'Chuanqiao No.1' was obviously higher than in 'TQ-0808'; in contrast, Na+ accumulation in cytoplasm of 'Chuanqiao No.1' was less than in 'TQ-0808'. These results indicate that the capabilities of Na+ extrusion and Na+ compartmentalization of salt-tolerant buckwheat were obviously higher than of the salt-sensitive one, and the capabilities could effectively restrict Na+ transport to shoot. Compartmentalization of Na+ in the vacuole was the main way for Na+ exclusion of salt-tolerant buckwheat. In addition, the transcriptions of Na+/H+ antiporter 1 and salt overly sensitive 1 were remarkably higher in 'Chuanqiao No.1' than in 'TQ-0808', which is consistent with the above results.

Synergistic effect of silicon and selenium on the alleviation of cadmium toxicity in rice plants

Silicon (Si) and selenium (Se), two beneficial elements that alleviate cadmium (Cd) toxicity, are important for agricultural production and human health. However, the effects and related mechanisms of Si-Se interaction on Cd toxicity alleviation are still poorly understood. Herein, a hydroponic experiment was employed to evaluate the effects of Si and Se alone and together, on the growth, Cd content, and biochemical parameters of Cd-treated rice plants. The results revealed that both Si and Se can effectively alleviate Cd toxicity, and a strong synergistic effect of Si and Se was observed. Simultaneous use of Si and Se significantly promoted rice plant growth, decreased malondialdehyde (MDA) content in both the roots and shoots, and reduced Cd translocation factor leading to a significant 73.2 % decrease in shoot Cd content. Additionally, Si-Se interaction increased glutathione (GSH) content, phytochelatin (PC) content and Cd distribution in root cell walls and organelles. Furthermore, the relative expression of OsHMA2 was down-regulated, while those of OsNramp1 and OsMHA3 were up-regulated. The above findings suggest that synergistic effect of Si and Se on Cd toxicity amelioration occurs mainly via regulating gene expression, sequestering Cd in the root cell walls and organelles, and reducing Cd transfer to the shoots.

Boron reduces aluminum deposition in alkali-soluble pectin and cytoplasm to release aluminum toxicity

Boron (B) is indispensable for plant growth and has been reported in the mitigation of aluminum (Al) toxicity in different plants. This study focused on the efficacy of B in reducing Al toxicity to trifoliate orange seedlings in a hydroponic experiment. Boron supply had a positive effect on root length and plant growth-related parameters and attenuated Al-induced inhibition of plasma membrane H+-ATPase activity. X-ray photoelectron spectroscopy (XPS) in conjunction with scanning electron microscope-energy dispersive x-ray spectrometer (SEM-EDS) revealed that B reduced Al accumulation in root cell wall, especially on pectin fractions (alkali-soluble pectin), accompanied by suppressing pectin synthesis, pectin methylesterase (PME) activity and PME expression. Furthermore, B application inhibited NRAT1 expression while increased ALS1 expression, indicating restraining Al transport from external cells to cytoplasm and accelerating accelerating vacuolar sequestration. The results were further demonstrated by transmission electron microscope-energy dispersive x-ray spectrometer (TEM-EDS) analysis. Taken together, our results indicated that B mainly promoted the efflux of H+ by regulating the plasma membrane H+-ATPase activity, and reduced the demethylation of pectin to weaken Al binding to carboxyl. More importantly, B alleviated some of the toxic effects of Al by compartmentalizing Al into vacuoles and decreasing the deposition of Al in cytoplasm.

Potassium affects cadmium resistance in Arabidopsis through facilitating root cell wall Cd retention in a nitric oxide dependent manner

Potassium (K) plays an important role in plant development and in plant responses to various environmental stresses; however, its involvement in the mitigation of heavy metal stress by altering the binding capacity of the cell wall in Arabidopsis thaliana remains elusive. Here, we examined the effect of K (0–12 mM) in the regulation of cadmium (Cd) resistance in Arabidopsis thaliana. Toxic levels of Cd (50 μM) cause chlorosis in young leaves; however, the application of 3 mM K significantly alleviated this symptom in Arabidopsis thaliana, while other K concentrations did not rescue this phenotype. Moreover, 3 mM K significantly increased cell wall polysaccharide (hemicellulose) content and Cd adsorption in the root cell walls, suggesting that the modification of the cell wall composition is responsible for the Cd retention in the root under 3 mM K application. The 3 mM K treatment significantly reduced the expression of genes related to Cd uptake when plants were exposed to Cd, implying a decrease in Cd entering the cells. Furthermore, endogenous Nitric oxide (NO) was demonstrated to be involved in 3 mM K ameliorated-Cd toxicity as nia1nia2 and noa1 mutants, which are defective in NO biosynthesis, this positive effect of 3 mM K on Cd toxicity was abolished. Taken together, our results indicated that the 3 mM K alleviated deleterious effects of Cd by modifying the cell wall Cd binding capacity, particularly through the regulation of the NO accumulation in Arabidopsis thaliana.

MdWRKY11 improves copper tolerance by directly promoting the expression of the copper transporter gene MdHMA5

Overuse of fungicides and fertilizers has resulted in copper (Cu) contamination of soils and toxic levels of Cu in apple fruits. To breed Cu-resistant apple (Malus domestica) cultivars, the underlying molecular mechanisms and key genes involved in Cu resistance must be identified. Here, we show that MdWRKY11 increases Cu tolerance by directly promoting the transcription of MdHMA5. MdHMA5 is a Cu transporter that may function in the storage of excess Cu in root cell walls and stems for Cu tolerance in apple. The transcription factor MdWRKY11 is highly induced by excess Cu. MdWRKY11 overexpression in transgenic apple enhanced Cu tolerance and decreased Cu accumulation. Apple calli transformed with an MdWRKY11-RNAi construct exhibited the opposite phenotype. Both an in vivo chromatin immunoprecipitation assay and an in vitro electrophoretic mobility shift assay indicated that MdWRKY11 binds to the promoter of MdHMA5. Furthermore, MdWRKY11 promoted MdHMA5 expression in transgenic apple plants, as revealed by quantitative PCR. Moreover, inhibition of MdWRKY11 expression by RNA interference led to a significant decrease in MdHMA5 transcription. Thus, MdWRKY11 directly regulates MdHMA5 transcription. Our work resulted in the identification of a novel MdWRKY11-MdHMA5 pathway that mediates Cu resistance in apple.

Direct fluorescence imaging of lignocellulosic and suberized cell walls in roots and stems.

Investigating plant structure is fundamental in botanical science and provides crucial knowledge for the theories of plant evolution, ecophysiology and for the biotechnological practices. Modern plant anatomy often targets the formation, localization and characterization of cellulosic, lignified or suberized cell walls. While classical methods developed in the 1960s are still popular, recent innovations in tissue preparation, fluorescence staining and microscopy equipment offer advantages to the traditional practices for investigation of the complex lignocellulosic walls. Our goal is to enhance the productivity and quality of microscopy work by focusing on quick and cost-effective preparation of thick sections or plant specimen surfaces and efficient use of direct fluorescent stains. We discuss popular histochemical microscopy techniques for visualization of cell walls, such as autofluorescence or staining with calcofluor, Congo red (CR), fluorol yellow (FY) and safranin, and provide detailed descriptions of our own approaches and protocols. Autofluorescence of lignin in combination with CR and FY staining can clearly differentiate between lignified, suberized and unlignified cell walls in root and stem tissues. Glycerol can serve as an effective clearing medium as well as the carrier of FY for staining of suberin and lipids allowing for observation of thick histological preparations. Three-dimensional (3D) imaging of all cell types together with chemical information by wide-field fluorescence or confocal laser scanning microscopy (CLSM) was achieved.

Comparative uptake, translocation and subcellular distribution of phthalate esters and their primary monoester metabolites in Chinese cabbage (Brassica rapa var. chinensis)

Phthalates esters (PAEs) are ubiquitous contaminants in terrestrial system and PAEs can be degraded to monoester metabolites (mPAEs) both in soil and plants, which have equal or even greater biological activity compared to their parent compounds. Until now, little is known about the comparative uptake and translocation of PAEs and mPAEs in plants. In the present study, the uptake and translocation of two commonly used plasticizers, di-n-butyl phthalate (DnBP) and di-(2-ethylhexyl) phthalate (DEHP), and the corresponding mPAEs, mono-n-butyl phthalate (MnBP) and mono-(2-ethylhexyl) phthalate (MEHP) by Chinese cabbage (Brassica rapa var. chinensis) were examined using hydroponic experiment. Significantly lower bioconcentration factors (BCFs) of mPAEs compared to the corresponding PAEs were observed. This is likely due to the great solubility and electrical repulsion from cell membrane to mPAE anions. Comparatively low translocation factors (TFs) of MnBP (7.76 ± 0.49) were observed compared to DnBP (10.33 ± 2.83); while the TFs of MEHP (0.18 ± 0.08) were significantly greater than that of DEHP (0.05 ± 0.02). The hydrophilic mPAEs are prone to concentrate in cell water-soluble components, and DnBP was relatively uniformly distributed in cell wall and cell water-soluble components; while the more hydrophobic DEHP was mainly associated with root cell wall. The formation of mPAEs occurred mainly in the above-ground tissues in the PAEs spiked treatment, and cell water-soluble compartment was the main location for PAEs metabolism. The high metabolite/parent ratios in Chinese cabbage indicate that more concern should be directed towards metabolites associated with plants via direct uptake and plant metabolism.

HvHOX9, a novel homeobox leucine zipper transcription factor, positively regulates aluminum tolerance in Tibetan wild barley.

Aluminum (Al) toxicity is the primary limiting factor of crop production on acid soils. Tibetan wild barley germplasm is a valuable source of potential genes for breeding barley with acid and Al tolerance. We performed microRNA and RNA sequencing using wild (XZ16, Al-tolerant; XZ61, Al-sensitive) and cultivated (Dayton, Al-tolerant) barley. A novel homeobox-leucine zipper transcription factor, HvHOX9, was identified as a target gene of miR166b and functionally characterized. HvHOX9 was up-regulated by Al stress in XZ16 (but unchanged in XZ61 and Dayton) and was significantly induced only in root tip. Phylogenetic analysis showed that HvHOX9 is most closely related to wheat TaHOX9 and orthologues of HvHOX9 are present in the closest algal relatives of Zygnematophyceae. Barley stripe mosaic virus-induced gene silencing of HvHOX9 in XZ16 led to significantly increased Al sensitivity but did not affect its sensitivity to other metals and low pH. Disruption of HvHOX9 did not change Al concentration in the root cell sap, but led to more Al accumulation in root cell wall after Al exposure. Silencing of HvHOX9 decreased H+ influx after Al exposure. Our findings suggest that miR166b/HvHOX9 play a critical role in Al tolerance by decreasing root cell wall Al binding and increasing apoplastic pH for Al detoxification in the root.

Structural and enzymatic characterisation of the Type III effector NopAA (=GunA) from Sinorhizobium fredii USDA257 reveals a Xyloglucan hydrolase activity

Rhizobia are nitrogen-fixing soil bacteria that can infect legume plants to establish root nodules symbiosis. To do that, a complex exchange of molecular signals occurs between plants and bacteria. Among them, rhizobial Nops (Nodulation outer proteins), secreted by a type III secretion system (T3SS) determine the host-specificity for efficient symbiosis with plant roots. Little is known about the molecular function of secreted Nops (also called effectors (T3E)) and their role in the symbiosis process. We performed the structure-function characterization of NopAA, a T3E from Sinorhizobium fredii by using a combination of X-ray crystallography, biochemical and biophysical approaches. This work displays for the first time a complete structural and biochemical characterization of a symbiotic T3E. Our results showed that NopAA has a catalytic domain with xyloglucanase activity extended by a N-terminal unfolded secretion domain that allows its secretion. We proposed that these original structural properties combined with the specificity of NopAA toward xyloglucan, a key component of root cell wall which is also secreted by roots in the soil, can give NopAA a strategic position to participate in recognition between bacteria and plant roots and to intervene in nodulation process.

AtHB7/12 Regulate Root Growth in Response to Aluminum Stress.

Aluminum (Al) stress is a major limiting factor for plant growth and crop production in acid soils. At present, only a few transcription factors involved in the regulation of Al resistance have been characterized. Here, we used reversed genetic approach through phenotype analysis of overexpressors and mutants to demonstrate that AtHB7 and AtHB12, two HD-Zip I transcription factors, participate in Al resistance. In response to Al stress, AtHB7 and AtHB12 displayed different dynamic expression patterns. Although both AtHB7 and AtHB12 positively regulate root growth in the absence of Al stress, our results showed that AtHB7 antagonizes with AtHB12 to control root growth in response to Al stress. The athb7/12 double mutant displayed a wild-type phenotype under Al stress. Consistently, our physiological analysis showed that AtHB7 and AtHB12 oppositely regulate the capacity of cell wall to bind Al. Yeast two hybrid assays showed that AtHB7 and AtHB12 could form homo-dimers and hetero-dimers in vitro, suggesting the interaction between AtHB7 and AtHB12 in the regulation of root growth. The conclusion was that AtHB7 and AtHB12 oppositely regulate Al resistance by affecting Al accumulation in root cell wall.

Differential expression pattern of the proteome in response to cadmium stress based on proteomics analysis of wheat roots

BackgroundHeavy metal cadmium (Cd) is a common environmental pollutant in soils, which has an negative impacts on crop growth and development. At present, cadmium has become a major soil and water heavy metal pollutant, which not only causes permanent and irreversible health problems for humans, but also causes a significant reduction in crop yields.ResultsThis study examined the chemical forms of Cd in the roots of two wheat varieties (M1019 and Xinong20) by continuous extraction and analyzed differences in distribution characteristics of Cd in the root cell wall, cytoplasm, and organelles by elemental content determination and subcellular separation. Furthermore, we conducted proteomics analysis of the roots of the two varieties under Cd pollution using mass spectrometry quantitative proteomics techniques. A total of 11,651 proteins were identified, of which 10,532 proteins contained quantitative information. In addition, the differentially expressed proteins in the two varieties were related to DNA replication and repair, protein metabolism, and the glutathione metabolism pathway.ConclusionThe results of this study improve our understanding of the mechanism of plant responses to Cd stress.

Boron alleviates cadmium toxicity in Brassica napus by promoting the chelation of cadmium onto the root cell wall components

In Southern China, rice-oil rotations occur on soils with high levels of cadmium (Cd) and low levels of available boron (B). Boron can alleviate Cd toxicity, as it affects the plant cell wall structures and the components that block the entry of Cd into the cytoplasm; however, these mechanisms are not well understood. Fourier transform infrared spectroscopy (FTIR), fluorescent probe dye, electron microscope, ion abundance (inductively coupled plasma mass spectrometry), metabonomics and transcriptomics were used in the study, and we found that under Cd stress, B increased root pectin content by affecting the biosynthesis pathways and decreasing the activity of pectinase and the expression levels of related genes. The increased pectin content and pectin demethylation increased the chelation of Cd onto the cell walls and reduced the levels of Cd entering the organelles. Application of B to the roots decreased the amounts of cellulose and hemicellulose in the cell walls to normal levels and promoted the expression of genes from the expansin, xyloglucan endotransglucosylase, and α-xylosidase families. This contributed to cell wall integrity and root flexibility. Consequently, the accumulation of reactive oxygen species was inhibited and cell viability in the roots was increased, which reduced the destruction of root surface structures. These results have improved our understanding of how B participates in chelation of Cd onto cell walls and in maintaining cell wall integrity, thereby improving Cd toxicity resistance in rapeseed roots.

Antimony symplastic and apoplastic absorption, compartmentation, and xylem translocation in Brassica parachinensis L. under antimonate and antimonite.

Antimony (Sb) excess accumulation in edible parts of crops causes potential risks to human health. However, knowledge about the mechanisms of its accumulation within vegetable plants is still not well known. Here, we investigated the physiological processes of Sb involved in symplastic and apoplastic absorption, compartmentation by roots, and translocation in xylem in Brassica parachinensis L. exposed to antimonate (SbV) and antimonite (SbIII) forms. The results showed that plants treated with SbIII emerged to be more toxic than SbV as proved by the lower biomass and the higher concentrations of malonaldehyde (MDA) and hydrogen peroxide (H2O2) in plant tissues, especially at high dosages. The Sb concentration showed more in shoots but less in roots treated with SbV than with SbIII. The total Sb accumulation was higher under the SbV treatment than the SbIII treatment, mainly due to the higher accumulation in shoots. Additionally, the Sb concentration in symplastic flow of roots was higher exposed to SbV than SbIII, while no differences were found for the Sb concentration in apoplastic flow between them. Moreover, the Sb concentration in cell walls of roots was higher exposed to SbIII than SbV, especially at high levels. Furthermore, the Sb concentration in xylem was higher exposed to SbV than SbIII, and a greatly positive correlation was observed between the Sb concentrations in xylem and shoots. Overall, these findings revealed that vegetable plants accumulated more SbV than SbIII in edible parts mainly due to xylem translocation rather than root absorption.

Effect of arsenic stress on 5-methylcytosine, photosynthetic parameters and nutrient content in arsenic hyperaccumulator Pteris cretica (L.) var. Albo-lineata

BackgroundArsenic toxicity induces a range of metabolic responses in plants, including DNA methylation. The focus of this paper was on the relationship between As-induced stress and plant senescence in the hyperaccumulator Pteris cretica var. Albo-lineata (Pc-Al). We assume difference in physiological parameters and level of DNA methylation in young and old fronds as symptoms of As toxicity.ResultsThe As accumulation of Pc-Al fronds, grown in pots of haplic chernozem contaminated with 100 mg As kg− 1 for 122 days, decreased with age. Content of As was higher in young than old fronds for variants with 100 mg As kg− 1 (2800 and 2000 mg As kg− 1 dry matter, respectively). The highest As content was determined in old fronds of Pc-Al grown in pots with 250 mg As kg− 1. The increase with age was confirmed for determined nutrients – Cu, Mg, Mn, S and Zn. A significant elevation of all analysed nutrients was showed in old fronds. Arsenic accumulation affected DNA methylation status in fronds, but content of 5-methylcytosine (5mC) decreased only in old fronds of Pc-Al (from 25 to 12%). Determined photosynthetic processes showed a decrease of fluorescence, photosynthetic rate and chlorophylls of As treatments in young and old fronds. Water potential was decreased by As in both fronds. Thinning of the sclerenchymatous inner cortex and a reduction in average tracheid metaxylem in the vascular cylinder was showed in roots of As treatment. Irrespective to fronds age, physiological parameters positively correlated with a 5mC while negatively with direct As toxicity. Opposite results were found for contents of Cu, Mg, Mn, S and Zn.ConclusionsThe results of this paper point to changes in the metabolism of the hyperaccumulator plant Pc-Al, upon low and high exposure to As contamination. The significant impact of As on DNA methylation was found in old fronds. Irrespective to fronds age, significant correlations were confirmed for 5mC and As toxicity. Our analysis of the very low water potential values and lignification of cell walls in roots showed that transports of assimilated metabolites and water between roots and fronds were reduced. As was showed by our results, epigenetic changes could affect studied parameters of the As hyperaccumulator plant Pc-Al, especially in old fronds.

Bacteria Sphingobium yanoikuyae Sy310 enhances accumulation capacity and tolerance of cadmium in Salix matsudana Koidz roots.

Phytoremediation assisted by plant growth-promoting bacteria (PGPB) is considered an effective strategy for cadmium (Cd) removal in contaminated sites. This study uses a hydroponic experiment to investigate how Sphingobium yanoikuyae Sy310 affects Cd accumulation capacity and tolerance of Salix matsudana Koidz (S. matsudana) roots. The results showed that Cd induced growth change and physiological response on S. matsudana roots, displaying with reduced root length, increased antioxidant enzyme activities, and most importantly, enhanced cell wall polysaccharide contents. The Sy310 inoculation enhanced Cd accumulation in roots and alleviated the Cd toxic effects by regulating root growth, antioxidant enzyme system, and cell wall polysaccharide remodeling. Under Cd stress, Sy310 significantly induced increased root length and biomass, as well as higher root IAA level and Cd retention in cell walls. The Sy310 inoculation enhanced root pectin and hemicellulose 1 content, and pectin methylesterase activity, indicating that more amount of -COOH and -OH in cell walls for binding Cd. With Sy310-regulated extensive Cd regional sequestration in root cell walls and enhanced catalase activity, the root H2O2 and malondialdehyde content decreased, which contributes to improve Cd tolerance of S. matsudana roots. Furthermore, the Sy310 inoculation did not affect root cell wall structure and oxidative stress in the absence of Cd, representing a well-symbiotic relationship between Sy310 and S. matsudana. Therefore, Sy310 plays an important role in expediting the phytoremediation process of Cd with S. matsudana and has practical application potential.

A Cd/Zn Co-hyperaccumulator and Pb accumulator, Sedum alfredii, is of high Cu tolerance

High sensitivity towards Cu toxicity is problematic when using some hyperaccumulator plants for phytoremediation of soils with mixed contamination of Cu. Sedum alfredii, a Cd/Zn co-hyperaccumulator and Pb accumulator, is widely used for remediation of Cd, Zn, and Pb co-contaminated soils in China. In this paper, the tolerance and accumulation ability of S. alfredii towards Cu stress and its potential for phytoremediation of multi-metal polluted soils have been studied. Both the hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of S. alfredii accumulated high Cu in the roots and translocated minimal Cu to the shoots, and Cu in the stems and leaves mostly restricted in the vascular tissues (phloem zone). The HE plants, however, exhibited high Cu resistance with stimulated lateral root growth and increased chlorophyll content under 10 μM Cu treatment. XANES analysis showed that Cu in HE roots comprised Cu2+ (46.7%), Cu-histidine (35.2%) and Cu-cell wall (18.1%). The NHE under Cu stress showed decreased biomass, reduced leaf chlorophyll content, altered root architecture, and higher Cu localized to root cell wall as compared with the HEs. Potted HE plants thrived six months in multi-metal contaminated soils including 3897 mg kg−1 available Cu. In conclusion, HE S alfredii is highly tolerant toward Cu due to metal homeostasis in root cells. Therefore, this plant has great potential to remediate Zn, Cd, and Pb contaminated soils those also contain high levels of Cu.

An exclusion mechanism is epistatic to an internal detoxification mechanism in aluminum resistance in Arabidopsis

BackgroundIn Arabidopsis, the aluminum (Al) exclusion mechanism is mainly facilitated by ALMT1-mediated malate exudation and MATE-mediated citrate releases from the root. Recently, we have demonstrated that coordinated functioning between an ALMT1-mediated Al exclusion mechanism, via exudation of malate from the root tip, and a NIP1;2-facilitated internal detoxification mechanism, via removal of Al from the root cell wall and subsequent root-to-shoot Al translocation, plays critical roles in achieving overall Al resistance. However, the genetic relationship between ALMT1 and NIP1;2 in these processes remained unclear.ResultsThrough genetic and physiological analyses, we demonstrate that unlike ALMT1 and MATE, which function independently and additively, ALMT1 and NIP1;2 show an epistatic relationship in Al resistance. These results indicate that ALMT1 and NIP1;2 function in the same biochemical pathway, whereas ALMT1 and MATE in different ones.ConclusionThe establishment of the epistatic relationship and the coordinated functioning between the ALMT1 and NIP1;2-mediated exclusion and internal detoxification mechanisms are pivotal for achieving overall Al resistance in the non-accumulating Arabidopsis plant. We discuss and emphasize the indispensable roles of the root cell wall for the implementation of the Al exclusion mechanism and for the establishment of an epistatic relationship between the ALMT1-mediated exclusion mechanism and the NIP1;2-facilitated internal detoxification mechanism.