The apoplasmic pathway via the root apex and lateral roots contributes to Cd hyperaccumulation in the hyperaccumulator Sedum alfredii

Varietal responses of root characteristics to low nitrogen application explain the differing nitrogen uptake and grain yield in two rice varieties

Rice root characteristics are tightly associated with high-efficient nitrogen uptake. To understand the relationship of root plastic responses with nitrogen uptake when reducing nitrogen application for green rice production, a hydroponic experiment and a soil pot experiment were conducted under high (HN) and low (LN) nitrogen applications, using two rice (Oryza sativa L.) varieties, NK57 and YD6, three nitrogen absorption traits (total nitrogen accumulation, net NH4 + influx on root surface, nitrogen uptake via apoplasmic pathway) and root characteristics were investigated. In comparison with HN, LN significantly reduced nitrogen absorption and grain yield in both varieties. Concomitantly, there was a decrease in total root length, root surface area, root number, root volume, and root cortical area under LN, while single root length, root aerenchyma area, and root lignin content increased. The expression of OsAMT1;1 and OsAMT1;2 down-regulated in both varieties. The findings revealed that YD6 had smaller reduction degree for the three nitrogen absorption traits and grain yield, accompanied by smaller reduction degree in total root length, root surface area, root cortical area, and expression of the two genes under LN. These root characteristics were significantly and positively correlated with the three nitrogen absorption traits and grain yield, especially under LN. These results indicate that a large root system, lower reduction degree in several root characters, and high expression of OsAMT genes in YD6 explains its high nitrogen accumulation and grain yield under reduced nitrogen application. The study may provide rationale for developing varieties with low nitrogen fertilizer requirements for enabling green rice production.

Performance of heavy metal-immobilizing bacteria combined with biochar on remediation of cadmium and lead co-contaminated soil

Heavy metal pollution of soil has become a public concern worldwide since it threats food safety and human health. Sustainable and environmental-friendly remediation technology is urgently needed. Therefore, we investigated the properties and heavy metal removal ability of Enterobacter asburiae G3 (G3), Enterobacter tabaci I12 (I12), and explored the feasibility of remediation Cd, Pb co-contaminated soil by the combination of G3/I12 and biochar. Our results indicated that both strains are highly resistant to Cd, Pb and maintain plant growth-promoting properties. The removal efficiency of G3 for Cd and Pb were 76.79-99.43%, respectively, while the removal efficiency of I12 for Cd and Pb were 62.57-99.55%, respectively. SEM-EDS and XRD analysis revealed that the morphological and structural changes occurred upon heavy metal exposure, metal precipitates were also detected on cell surface. FTIR analysis indicated that functional groups (-OH, -N-H, -C = O, -C-N, -PO4) were involved in Cd/Pb immobilization. Application of the bacteria, biochar, or their combination decreased the acid-extractable Cd, Pb in soil while increased the residual fractions, meanwhile, the bioavailability of both metal elements declined. Besides, these treatments increased soil enzyme (sucrase, catalase and urease) activity and accelerated pakchoi growth, heavy metal accumulation in pakchoi was depressed upon bacteria and/or biochar application, and a synergistic effect was detected when applying bacteria and biochar together. In BC + G3 and BC + I12 treated plants, the Cd and Pb accumulation decreased by 24.42% and 52.19%, 17.55% and 47.36%, respectively. Overall, our study provides an eco-friendly and promising in situ technology that could be applied in heavy metal remediation.

From promoting aggregation to enhancing obstruction: A negative feedback regulatory mechanism of alleviation of trivalent chromium toxicity by silicon in rice

Trivalent chromium [Cr(III)] is a threat to the environment and crop production. Silicon (Si) has been shown to be effective in mitigating Cr(III) toxicity in rice. However, the mechanisms by which Si reduces Cr(III) uptake in rice are unclear. Herein, we hypothesized that the ability of Si to obstruct Cr(III) diffusion via apoplastic bypass is related to silicic acid polymerization, which may be affected by Cr(III) in rice roots. To test this hypothesis, we employed hydroponics experiments on rice (Oryza sativa L.) and utilized apoplastic bypass tracer techniques, as well as model simulations, to investigate 1) the effect of Si on Cr(III) toxicity and its obstruction capacity via apoplastic bypass, 2) the effect of Cr(III) on silicic acid polymerization, and 3) the relationship between the degree of silicic acid polymerization and its Cr(III) obstruction capacity. We found that Si reversed the damage caused by Cr(III) stress in rice. Si exerted an obstruction effect in the apoplast, significantly decreasing the share of Cr(III) uptake via the apoplastic bypass from 18% to 11%. Moreover, Cr(III) reduced silica particles' radii and increased Si concentration in roots. Modeling revealed that a 5-fold reduction in their radii decreased the diffusion of Cr(III) in apoplast by approximately 17%. We revealed that Cr(III) promoted silicic acid polymerization, resulting in the formation of a higher number of Si particles with a smaller radius in roots, which in turn increased the ability of Si to obstruct Cr(III) diffusion. This negative feedback regulatory mechanism is novel and crucially important for maintaining homeostasis in rice, unveiling the unique role of Si under Cr(III) ion stress and providing a theoretical basis for promoting the use of Si fertilizer in the field.

New potential transporter CIPAS8 enhances cadmium hypersensitivity and cobalt tolerance

KEY MESSAGE

CIPAS8 is a novel Cd-influx and Co-efflux transporters, and Ser86 and Cys128 might play a decisive role in Co-binding and translocation. Cadmium (Cd) is among the most toxic heavy metals and is a widespread environmental pollutant. Cobalt (Co) is a mineral nutrient that is essential for plant growth and development, but high concentrations may be toxic. Cadmium-induced protein AS8 (CIPAS8) is widely distributed among plant species and might be induced by heavy metals, but its function has not been studied previously. In this study, Populus euphratica PeCIPAS8 and Salix linearistipularis SlCIPAS8 were investigated. The transcription of both genes was significantly enhanced under Cd and Co stresses. PeCIPAS8 and SlCIPAS8 conferred sensitivity to Cd in transgenic yeast, allowing higher quantities of Cd to accumulate within the cells, whereas SlCIPAS8 also conferred tolerance to Co and reduced Co accumulation. The determinants of substrate selectivity of the SlCIPAS8 protein were examined by site mutagenesis, which indicated that the Ser at 86th (S86) substituted for Arg (R) [S86R] and Cys at 128th (C128) substituted for Ser [C128S] mutations limited the protein's capability for Co translocation. These results suggested that PeCIPAS8 and SlCIPAS8 may be involved in Cd uptake into the plant cell. SlCIPAS8 can reduce excess Co accumulation to maintain intracellular Co homeostasis, and the site mutations S86R and C128S were essential for Co transport. These findings provide insight into the function of CIPAS8 and highlight its potential for utilization in phytoremediation applications.

Response of Cd, Zn Translocation and Distribution to Organic Acids Heterogeneity in Brassica juncea L

In order to investigate the translocation, distribution, and organic acid heterogeneity characteristics in Brassica juncea L., a pot experiment with the exogenous application of Cd and Zn was conducted to analyze the effects of Cd, Zn, and organic acid contents and heterogeneity on the translocation and distribution of Cd and Zn. The results showed that the Cd and Zn contents of B. juncea were mainly accumulated in the roots. The Cd content in the symplast sap was 127.66-146.50% higher than that in the apoplast sap, while the opposite was true for Zn. The distribution of Cd in xylem sap occupied 64.60% under 20 mg kg^-1 Cd treatment, and Zn in xylem sap occupied 60.14% under 100 mg kg^-1 Zn treatment. The Cd was predominantly distributed in the vacuole, but the Zn was predominantly distributed in the cell walls. In addition, oxalic and malic acids were present in high concentrations in B. juncea. In the vacuole, correlation analysis showed that the contents of Cd were negatively correlated with the contents of oxalic acid and succinic acid, and the contents of Zn were positively correlated with the contents of malic acid and acetic acid. The contents of Cd and Zn were negatively related to the contents of oxalic acid and citric acid in xylem sap. Therefore, Cd in B. juncea was mainly absorbed through the symplast pathway, and Zn was mainly absorbed through the apoplast pathway, and then Cd and Zn were distributed in the vacuole and cell walls. The Cd and Zn in B. juncea are transferred upward through the xylem and promoted by oxalic acid, malic acid, and citric acid.

Pea root responses under naproxen stress: changes in the formation of structural barriers in the primary root in context with changes of auxin and abscisic acid levels

Pharmaceuticals belong to pseudo-persistent pollutants because of constant entry into the environment and hazardous potential for non-target organisms, including plants, in which they can influence biochemical and physiological processes. Detailed analysis of results obtained by microscopic observations using fluorescent dyes (berberine hemisulphate, Fluorol Yellow 088), detection of phytohormone levels (radioimmunoassay, enzyme-linked immune sorbent assay) and thermogravimetric analysis of lignin content proved that the drug naproxen (NPX) can stimulate the formation of root structural barriers. In the primary root of plants treated with 0.5, 1, and 10 mg/L NPX, earlier Casparian strip formation and development of the whole endodermis circle closer to its apex were found after five days of cultivation (by 9-20% as compared to control) and after ten days from 0.1 mg/L NPX (by 8-63%). Suberin lamellae (SL) were deposited in endodermal cells significantly closer to the apex under 10 mg/L NPX by up to 75%. Structural barrier formation under NPX treatment can be influenced indirectly by auxin-supported cell division and differentiation caused by its eight-times higher level under 10 mg/L NPX and directly by stimulated SL deposition induced by abscisic acid (higher from 0.5 mg/L NPX), as proved by the higher proportion of cells with SL in the primary root base (by 8-44%). The earlier modification of endodermis in plant roots can help to limit the drug transfer and maintain the homeostasis of the plant.

Phytoextraction by harvesting dead leaves: cadmium accumulation associated with the leaf senescence in Festuca arundinacea Schreb

Phytoextraction strategy by harvesting dead leaves provides continuous phytoremediation and a great saving in disposal cost of hazardous plant residues. This strategy is entirely dependent upon the amount of cadmium (Cd) accumulated in dead leaves. However, it is unknown that whether the leaf Cd accumulation is associated with its senescence and how to regulate its Cd accumulation. This study showed that Cd was preferentially and consistently distributed to and accumulated in the senescent leaves with the new leaf emergence and the old leaf dieback under 75 μM of Cd stress in tall fescue (Festuca arundinacea Schreb.). Individual leaf monitoring from its emergence to senescence showed that Cd concentration increased exponentially with the leaf life cycle, while leaf biomass decreased gradually after 14 days of leaf emergence. The total amount of Cd accumulated in the leaf showed an exponential increase during leaf senescence, regardless of the leaf biomass loss. Our results demonstrated that leaf Cd accumulation was significantly associated with its senescence and the highest Cd accumulated in dead leaves could be contributed from the continuous Cd input during the leaf senescent process, indicating that further regulatory studies should be focused on the leaf senescence process to achieve higher Cd accumulation and phytoextraction efficiency by harvesting dead leaves.

Endodermal apoplastic barriers are linked to osmotic tolerance in meso-xerophytic grass Elymus sibiricus

Drought is the most serious adversity faced by agriculture and animal husbandry industries. One strategy that plants use to adapt to water deficits is modifying the root growth and architecture. Root endodermis has cell walls reinforced with apoplastic barriers formed by the Casparian strip (CS) and suberin lamellae (SL) deposits, regulates radial nutrient transport and protects the vascular cylinder from abiotic threats. Elymus sibiricus is an economically important meso-xerophytic forage grass, characterized by high nutritional quality and strong environmental adaptability. The purpose of this study was to evaluate the drought tolerance of E. sibiricus genotypes and investigate the root structural adaptation mechanism of drought-tolerant genotypes' responding to drought. Specifically, a drought tolerant (DT) and drought sensitive (DS) genotype were screened out from 52 E. sibiricus genotypes. DT showed less apoplastic bypass flow of water and solutes than DS under control conditions, as determined with a hydraulic conductivity measurement system and an apoplastic fluorescent tracer, specifically PTS trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS). In addition, DT accumulated less Na, Mg, Mn, and Zn and more Ni, Cu, and Al than DS, regardless of osmotic stress. Further study showed more suberin deposition in DT than in DS, which could be induced by osmotic stress in both. Accordingly, the CS and SL were deposited closer to the root tip in DT than in DS. However, osmotic stress induced their deposition closer to the root tips in DS, while likely increasing the thickness of the CS and SL in DT. The stronger and earlier formation of endodermal barriers may determine the radial transport pathways of water and solutes, and contribute to balance growth and drought response in E. sibiricus. These results could help us better understand how altered endodermal apoplastic barriers in roots regulate water and mineral nutrient transport in plants that have adapted to drought environments. Moreover, the current findings will aid in improving future breeding programs to develop drought-tolerant grass or crop cultivars.

The regulatory role of abscisic acid on cadmium uptake, accumulation and translocation in plants

To date, Cd contamination of cropland and crops is receiving more and more attention around the world. As a plant hormone, abscisic acid (ABA) plays an important role in Cd stress response, but its effect on plant Cd uptake and translocation varies among plant species. In some species, such as Arabidopsis thaliana, Oryza sativa, Brassica chinensis, Populus euphratica, Lactuca sativa, and Solanum lycopersicum, ABA inhibits Cd uptake and translocation, while in other species, such as Solanum photeinocarpum and Boehmeria nivea, ABA severs the opposite effect. Interestingly, differences in the methods and concentrations of ABA addition also triggered the opposite result of Cd uptake and translocation in Sedum alfredii. The regulatory mechanism of ABA involved in Cd uptake and accumulation in plants is still not well-established. Therefore, we summarized the latest studies on the ABA synthesis pathway and comparatively analyzed the physiological and molecular mechanisms related to ABA uptake, translocation, and detoxification of Cd in plants at different ABA concentrations or among different species. We believe that the control of Cd uptake and accumulation in plant tissues can be achieved by the appropriate ABA application methods and concentrations in plants.

Effects of Cadmium on Root Morpho-Physiology of Durum Wheat

Durum wheat [Triticum turgidum L. subsp. durum (Desf.) Husn.] can accumulate a high level of Cd in grains with a significant variability depending on cultivars. Understanding how this toxic element is distributed in cereal tissues and grains is essential to improve the nutritional quality of cereal-based products. The main objective of this work was to investigate roots of durum wheat plants (cv. Iride) exposed to different Cd concentrations (0.5 and 5.0 μM) to identify the mechanisms involved in Cd management. Results showed that the root morphology was altered by Cd treatment both at macroscopic (increased number of tips and primary root length) and ultrastructural levels (cell membrane system damaged, cell walls thickened and enriched in suberin). On the other side, Cd was localized in vesicles and in cell walls, and the metal colocalized with the phytosiderophore nicotianamine (NA). Overall, data suggest that Cd is chelated by NA and then compartmentalized, through vesicular trafficking, in the root thickened walls reducing Cd translocation to the aerial organs of the plant.

Role of SaPCR2 in Zn Uptake in the Root Elongation Zone of the Zn/Cd Hyperaccumulator Sedum alfredii

Zn pollution is a potential toxicant for agriculture and the environment. Sedum alfredii is a Zn/Cd hyperaccumulator found in China and has been proven as a useful resource for the phytoremediation of Zn-contaminated sites. However, the molecular mechanism of Zn uptake in S. alfredii is limited. In this study, the function of SaPCR2 on Zn uptake in S. alfredii was identified by gene expression analysis, yeast function assays, Zn accumulation and root morphology analysis in transgenic lines to further elucidate the mechanisms of uptake and translocation of Zn in S. alfredii. The results showed that SaPCR2 was highly expressed in the root elongation zone of the hyperaccumulating ecotype (HE) S. alfredii, and high Zn exposure downregulated the expression of SaPCR2 in the HE S. alfredii root. The heterologous expression of SaPCR2 in yeast suggested that SaPCR2 was responsible for Zn influx. The overexpression of SaPCR2 in the non-hyperaccumulating ecotype (NHE) S. alfredii significantly increased the root uptake of Zn, but did not influence Mn, Cu or Fe. SR-μ-XRF technology showed that more Zn was distributed in the vascular buddle tissues, as well as in the cortex and epidermis in the transgenic lines. Root morphology was also altered after SaPCR2 overexpression, and a severe inhibition was observed. In the transgenic lines, the meristematic and elongation zones of the root were lower compared to the WT, and Zn accumulation in meristem cells was also reduced. These results indicate that SaPCR2 is responsible for Zn uptake, and mainly functions in the root elongation zone. This research on SaPCR2 could provide a theoretical basis for the use of genetic engineering technology in the modification of crops for their safe production and biological enhancement.

NTA-assisted mineral element and lead transportation in Eremochloa ophiuroides (Munro) Hack

Lead (Pb) is one of the most toxic and harmful pollutants to the environment and human health. Centipedegrass (Eremochloa ophiuroides (Munro) Hack.), an excellent ground cover plant for urban plant communities, exhibits the outstanding lead tolerance and accumulation. Nitrilotriacetic acid (NTA) is an environmentally friendly chelating agent that strengthens phytoremediation. This study explored the effects of different NTA concentrations on the absorption and transportation of mineral elements and Pb in centipedegrass. Following exposure to Pb (500 μM) for 7 days in hydroponic nutrient solution, NTA increased root Mg, K, and Ca concentrations and shoot Fe, Cu, and Mg concentrations and significantly enhanced the translocation factors of mineral elements to the shoot. Although NTA notably decreased root Pb absorption and accumulation, it significantly enhanced Pb translocation factors, and the Pb TF value was the highest in the 2.0 mM NTA treatment. Furthermore, the shoot translocation of Pb and mineral elements was synergistic. NTA can support mineral element homeostasis and improve Pb translocation efficiency in centipedegrass. Regarding root radial transport, NTA (2.0 mM) significantly promoted Pb transport by the symplastic pathway under the treatments with low-temperature and metabolic inhibitors. Meanwhile, NTA increased apoplastic Pb transport at medium and high Pb concentrations (200-800 μM). NTA also enhanced the Pb radial transport efficiency in roots and thus assisted Pb translocation. The results of this study elucidate the effects of NTA on the absorption and transportation of mineral elements and Pb in plants and provide a theoretical basis for the practical application of the biodegradable chelating agent NTA in soil Pb remediation.

Implication of exogenous abscisic acid (ABA) application on phytoremediation: plants grown in co-contaminated soil

Abscisic acid (ABA) may play an important role in alleviating negative effects of heavy metal stress on growth performance of plants. A pot experiment was conducted to investigate differential effects of exogenous ABA with different concentrations (0, 20, 40, and 60 μmol/L) on heavy metal accumulation and physiological response of Cd/Zn hyperaccumulator Sedum alfredii Hance and non-hyperaccumulator Hylotelephium spectabile (Boreau) H. Ohba grown in co-contaminated soil. In the experiment, Cd, Zn, or Pb concentration in stem and leaf of H. spectabile was significantly increased by exogenous ABA application than control. However, the opposite pattern was observed for S. alfredii. With decrease of Cd concentration, Zn or Pb concentration in root of H. spectabile grown in co-contaminated soil was significantly increased by exogenous ABA application than control. Cd, Zn, or Pb concentration in root of S. alfredii was significantly increased by exogenous ABA application than control. Compared with S. alfredii, BCF and TF of Cd, Zn, or Pb for H. spectabile were significantly increased by exogenous ABA application. With negative effect on root growth, total biomass of the two species, especially H. spectabile, was significantly increased by exogenous ABA application than control. With increase of their total chlorophyll content, antioxidant capacity of the two species subjected to heavy metal stress was improved by exogenous ABA application than control. Heavy metal-induced growth inhibition was significantly alleviated by exogenous ABA application when the two species were grown in co-contaminated soil. We tentatively concluded that differential effects of exogenous ABA application on transport pathway of ions incurred different patterns of heavy metal accumulation between Cd/Zn hyperaccumulator S. alfredii and non-hyperaccumulator H. spectabile. It is suggested that compared with Cd/Zn hyperaccumulator S. alfredii, exogenous ABA application may improve heavy metal uptake in root and transport of heavy metal ions between different organs for non-hyperaccumulator H. spectabile grown in co-contaminated soil. Our results provide insight into effects of exogenous ABA application on phytoremediation of Cd-, Pb-, and Zn-co-contaminated soil.

Medical Plant Extract Purification from Cadmium(II) Using Modified Thermoplastic Starch and Ion Exchangers

Pure compounds extracted and purified from medical plants are crucial for preparation of the herbal products applied in many countries as drugs for the treatment of diseases all over the world. Such products should be free from toxic heavy metals; therefore, their elimination or removal in all steps of production is very important. Hence, the purpose of this paper was purification of an extract obtained from Dendrobium officinale Kimura et Migo and cadmium removal using thermoplastic starch (S1), modified TPS with poly (butylene succinate); 25% of TPS + 75% PBS (S2); 50% of TPS + 50% PLA (S3); and 50% of TPS + 50% PLA with 5% of hemp fibers (S4), as well as ion exchangers of different types, e.g., Lewatit SP112, Purolite S940, Amberlite IRC747, Amberlite IRC748, Amberlite IRC718, Lewatit TP207, Lewatit TP208, and Purolite S930. This extract is used in cancer treatment in traditional Chinese medicine (TCM). Attenuated total reflectance-Fourier transform infrared spectroscopy, thermogravimetric analysis with differential scanning calorimetry, X-ray powder diffraction, gel permeation chromatography, surface analysis, scanning electron microscopy with energy dispersive X-ray spectroscopy, and point of zero charge analysis were used for sorbent and adsorption process characterization, as well as for explanation of the Cd(II) sorption mechanism.

Uptake and Translocation of Perfluorooctanoic Acid (PFOA) and Perfluorooctanesulfonic Acid (PFOS) by Wetland Plants: Tissue- and Cell-Level Distribution Visualization with Desorption Electrospray Ionization Mass Spectrometry (DESI-MS) and Transmission Electron Microscopy Equipped with Energy-Dispersive Spectroscopy (TEM-EDS)

Perfluoroalkyl substances (PFASs) are persistent chemicals in the environment. So far, little is known about their uptake potential in wetland plants. Here, we investigated the uptake and translocation of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) in eight common wetland plants, namely, Canna indica (Ci), Thalia dealbata (Td), Cyperus alternifolius (Ca), Phragmites australis (Pa), Arundo donax (Ad), Pontederia cordata (Pc), Cyperus papyrus (Cp), and Alisma orientale (Ao) by hydroponic experiments and visualized their tissue- and cell-level distribution with desorption electrospray ionization mass spectrometry (DESI-MS) and transmission electron microscopy equipped with energy-dispersive spectroscopy (TEM-EDS). The results showed that the PFASs accumulated in plants accounted for 1.67-16.7% of the total mass spiked into the hydroponic systems, and PFOS accumulated largely in roots (48.8-95.8%), while PFOA was stored mostly in the aboveground part (29.3-77.4%). DESI-MS and TEM-EDS analysis showed that PFASs in Ci, Td, Pa, and Ca were transported from the hydroponic solution to the root cortex via both apoplastic (e.g., across cell walls and/or intercellular spaces) and symplastic routes (e.g., across plasma membranes or via plasmodesmata) and further to the vascular bundle via symplastic route in Td and Pa and via both routes in Ci and Ca. These two chemicals were transported from roots to stems mainly through the cortex in Td and through both the cortex and vascular bundles in Ci and Ca.

Exogenous abscisic acid (ABA) promotes cadmium (Cd) accumulation in Sedum alfredii Hance by regulating the expression of Cd stress response genes

Sedum alfredii Hance is a zinc (Zn) and cadmium (Cd) hyperaccumulator plant. However, the regulatory role of plant hormones in the Zn or Cd uptake and accumulation of S. alfredii remains unclear. In this work, the growth, Cd accumulation, abscisic acid (ABA) synthesis and catabolism, malonaldehyde (MDA) content, and transcriptional level of some Cd stress response genes under ABA and Cd co-treatment were investigated to reveal the impact of ABA on Cd resistance and Cd accumulation of S. alfredii. The results show that 0.2 mg/L ABA and 100 μmol/L Cd co-treatment enhanced Cd accumulation and growth in S. alfredii, whereas lower or higher ABA concentrations weaken or even reverse this effect, which was positively correlated with endogenous ABA content. The increase in endogenous ABA content might be the results of the increasing ABA synthetase activities and decreasing ABA lytic enzyme, which was induced by the application of 0.2 mg/L ABA under 100 μmol/L Cd treatment. Principal component analysis (PCA) indicated that ABA impacted the expression pattern of Cd stress response genes, which coincided with the Cd accumulation pattern in the shoots of S. alfredii. Cross-over analysis of partial least squares-discriminant analysis (PLS-DA) and correlation analysis indicated that HsfA4c, HMA4 expression in roots, and HMA2, HMA3, CAD, NAS expression in shoots were correlated with endogenous ABA, which suggests that endogenous ABA improves Cd resistance of seedlings, switches the root-to-shoot transporter from HMA2 to HMA4, and transports more Cd into apoplasts to promote Cd accumulation in the shoots of S. alfredii. Taken together, ABA plays an essential role not only in Cd resistance but also in Cd transport from root to shoot in S. alfredii under Cd stress.

Insight into nitrogen and phosphorus enrichment on cadmium phytoextraction of hydroponically grown Salix matsudana Koidz cuttings

Cadmium (Cd) has already caused worldwide concern because of its high biotoxicity to human and plants. This study investigated how nitrogen (N) and phosphorus (P) enrichment alter the toxic morpho-physiological impacts of and accumulation of Cd in hydroponically grown Salix matsudana Koidz cuttings. Our results showed that Cd significantly depressed growth and induced a physiological response on S. matsudana cuttings, exhibiting by reduced biomass, decreased photosynthetic pigment concentrations, and increased soluble protein and peroxidase activity of shoots and roots. N and P enrichment alleviated the Cd toxic effects by increasing production of proline which prevented cuttings from damage by Cd-induced ROS, displaying with decreased malondialdehyde concentration, and stimulated overall Cd accumulation. Enrichment of N and P significantly decreased the upward Cd transfer, combing with enhanced root uptake (stimulated root activity) and retranslocation from stem, resulted in extensive Cd sequestration in S. matsudana roots. In both root and xylem, concentration of Cd is positively correlated with N and P. The improved phytoextraction potential by N and P enrichment was mainly via elevating Cd concentration in roots, probably by increased production of phytochelatins (e.g., proline) which form Cd chelates and help preventing damage from Cd-induced ROS. This study provides support for the application of S. matsudana in Cd phytoextraction even in eutrophic aquatic environments.

Root hair abundance impacts cadmium accumulation in Arabidopsis thaliana shoots

BACKGROUND AND AIMS

Root hairs increase the contact area of roots with soil and thereby enhance the capacity for solute uptake. The strict hair/non-hair pattern of Arabidopsis thaliana can change with nutrient deficiency or exposure to toxic elements, which modify root hair density. The effects of root hair density on cadmium (Cd) accumulation in shoots of arabidopsis genotypes with altered root hair development and patterning were studied.

METHODS

Arabidopsis mutants that are unable to develop root hairs (rhd6-1 and cpc/try) or produce hairy roots (wer/myb23) were compared with the ecotype Columbia (Col-0). Plants were cultivated on nutrient agar for 2 weeks with or without Cd. Cadmium was applied as Cd(NO3)2 at two concentrations, 10 and 100 µm. Shoot biomass, root characteristics (primary root length, lateral root number, lateral root length and root hair density) and Cd concentrations in shoots were assessed. Anatomical features (suberization of the endodermis and development of the xylem) that might influence Cd uptake and translocation were also examined.

KEY RESULTS

Cadmium inhibited plant growth and reduced root length and the number of lateral roots and root hairs per plant. Suberin lamellae in the root endodermis and xylem differentiation developed closer to the root apex in plants exposed to 100 µm Cd. The latter effect was genotype dependent. Shoot Cd accumulation was correlated with root hair abundance when plants were grown in the presence of 10 µm Cd, but not when grown in the presence of 100 µm Cd, in which treatment the development of suberin lamellae closer to the root tip appeared to restrict Cd accumulation in shoots.

CONCLUSIONS

Root hair density can have a large effect on Cd accumulation in shoots, suggesting that the symplasmic pathway might play a significant role in the uptake and accumulation of this toxic element.

Uptake, Accumulation, and in Planta Distribution of Coexisting Cerium Oxide Nanoparticles and Cadmium in Glycine max (L.) Merr.

Agricultural soils are likely to be polluted by both conventional and emerging contaminants at the same time. Understanding the interactions of coexisting engineered nanoparticles (ENPs) and trace elements (a common source of abiotic stress) is critical to gaining insights into the accumulation of these two groups of chemicals by plants. The objectives of this study were to determine the uptake and accumulation of coexisting ENPs and trace elements by soybeans and to gain insights into the physiological mechanisms resulting in different plant accumulation of these materials. The combinations of three cadmium levels (0 [control] and 0.25 and 1 milligrams per kilogram of dry soil) and two CeO2 NPs concentrations (0 [control] and 500 milligrams per kilogram of dry soil) were investigated. Measurements of the plant biomass and physiological parameters indicated that CeO2 NPs led to higher variable fluorescence to maximum fluorescence ratio, suggesting that CeO2 NPs enhanced the plant light energy use efficiency by photosystem II. In addition, the presence of CeO2 NPs did not affect Cd accumulation in soybean, but Cd significantly increased the accumulation of Ce in plant tissues, especially in roots and older leaves. The altered Ce in planta distribution was partially associated with the formation of root apoplastic barriers in the co-presence of Cd and CeO2 NPs.