Hyperaccumulators
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Cadmium (Cd) accumulation, antioxidant activity (AOA), chlorophyll fluorescence (F) and organic acid distribution in Chlorophytum comosum and Callisia fragrans plants exposed to artificially added Cd (40, 160 and 320 mg kg-1) were examined in pot experiment. At the highest Cd concentration, C. comosum accumulated in roots and the aboveground parts up to 1331 and 1054 mg Cd kg-1 DW, and C. fragrans up to 1427 and 1263 mg Cd kg-1 DW, respectively, which are quite near at the level of hyperaccumulator. Cd accumulation in both plant species increased significantly with the increment of soil Cd dosage, and the distribution was roots > shoots > stolons. Values of BC showed rising trend indicating an accumulation potential of both species. The root AOA was positively correlated to Cd addition, especially in C. comosum. Higher values of free SA were found in roots with a significant enhancement at concentrations of 40 and 160 mg kg-1 Cd. It was observed that citric acid significantly reacted in both species, while fumaric acid only in C. comosum in response to Cd which may contribute to Cd chelation. Our data indicate that both species are suitable for phytoextraction of Cd from contaminated soils which increases their value as ornamentals.
Although the significance of apoplasmic barriers in roots with regards to the uptake of toxic elements is generally known, the contribution of apoplasmic bypasses (ABs) to cadmium (Cd) hyperaccumulation is little understood. Here, we employed a combination of stable isotopic tracer techniques, an ABs tracer, hydraulic measurements, suberin lamellae staining, metabolic inhibitors, and antitranspirants to investigate and quantify the impact of the ABs on translocation of Cd to the xylem in roots of a hyperaccumulating (H) ecotype and a non-hyperaccumulating (NH) ecotype of Sedum alfredii. In the H ecotype, the Cd content in the xylem sap was proportional to hydrostatic pressure, which was attributed to pressure-driven flow via the ABs. The contribution of the ABs to Cd transportation to the xylem was dependent on the Cd concentration applied to the H ecotype (up to 37% at the highest concentration used). Cd-treated H ecotype roots showed significantly higher hydraulic conductance compared with the NH ecotype (76 vs 52 × 10–8 m s–1MPa–1), which is in accordance with less extensive suberization due to reduced expression of suberin-related genes. The main entry sites of apoplasmically transported Cd were localized in the root apexes and lateral roots of the H ecotype, where suberin lamellae were not well developed. These findings highlight the significance of the apoplasmic bypass in Cd hyperaccumulation in hyperaccumulating ecotypes of S. alfredii.
The transmission mode of shoot-associated endophytes in hyperaccumulators and their roles in root microbiome assembly and heavy metal accumulation remain unclear. Using 16S rRNA gene profiling, we investigated the vertical transmission of shoot-associated endophytes in relation to growth and Cd/Zn accumulation of Sedum alfredii ( Crassulaceae). Endophytes were transmitted from shoot cuttings to the rhizocompartment of new plants in both sterilized (γ-irradiated) and native soils. Vertical transmission was far more efficient in the sterile soil, and the transmitted endophytes have become a dominant component of the newly established root-associated microbiome. Based on 16S rRNA genes, the vertically transmitted taxa were identified as the families of Streptomycetaceae, Nocardioidaceae, Pseudonocardiaceae, and Rhizobiaceae. Abundances of Streptomycetaceae, Nocardioidaceae, and Pseudonocardiaceae were strongly correlated with increased shoot biomass and total Cd/Zn accumulation. Inoculation of S. alfredii with the synthetic bacterial community sharing the same phylogenetic relatedness with the vertically transmitted endophytes resulted in significant improvements in plant biomass, root morphology, and Cd/Zn accumulation. Our results demonstrate that successful vertical transmission of endophytes from shoots of S. alfredii to its rhizocompartments is possible, particularly in soils with attenuated microbiomes. Furthermore, the endophyte-derived microbiome plays an important role in metal hyperaccumulation.
Changes in the fatty acid (FAs) composition in response to the extent of Cd contamination of soils (0, 30, 60 and 90 mg Cd kg(-1)) differed between ecotypes of Noccaea caerulescens originating from France - Ganges, Slovenia - Mežica and Austria - Redlschlag. Mežica ecotype accumulated more Cd in aboveground biomass compared to Ganges and Redlschlag ecotypes. Hyperaccumulators contained saturated fatty acids (SFAs) rarely occurring in plants, as are cerotic (26:0), montanic (28:0), melissic (30:0) acids, and unusual unsaturated fatty acids (USFAs), as are 16:2, 16:3, 20:2 and 20:3. Typical USFAs occurring in the family Brassicaceae, such as erucic, oleic and arachidonic acids, were missing in tested plants. Our results clearly indicate a relationship between Cd accumulation and the FAs composition. The content of SFAs decreased and the content of USFAs increased in aboveground biomass of Ganges and Mežica ecotypes with increasing Cd concentration. Opposite trend of FAs content was determined in Redlschlag ecotype. Linoleic (18:2n-6), α-linolenic (18:3n-3) and palmitic (16:0) acids were found in all ecotypes. The results observed in N. caerulescens ecotypes, showed that mainly Mežica ecotype has an efficient defense strategies which can be related on changes in FAs composition, mainly in VLCFAs synthesis. The most significant effect of ecotype on FAs composition was confirmed using multivariate analysis of variance.
- MeSH
- biomasa MeSH
- Brassicaceae účinky léků růst a vývoj metabolismus MeSH
- ekotyp * MeSH
- fyziologický stres účinky léků MeSH
- kadmium toxicita MeSH
- listy rostlin účinky léků metabolismus MeSH
- mastné kyseliny metabolismus MeSH
- metabolické sítě a dráhy účinky léků MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Abscisic acid (ABA) play a crucial role in plant acclimation to heavy-metals stresses. Nevertheless, the effects of ABA on long-distance transport and its consequences for cadmium (Cd) accumulation are insufficiently understood. Here, we investigated the effects of ABA on the development of the whole-plant water transport pathway and implications for Cd uptake and transport to the shoot of Sedum alfredii. Exposure to Cd stimulated the production of endogenous ABA levels in the non-hyperaccumulating ecotype (NHE), but not in the hyperaccumulating ecotype (HE). Increased ABA levels in NHE significantly reduced aquaporin expressions in roots, the number of xylem vessel in stem, dimensions and densities of stomata in leaves, but induced leaf osmotic adjustment. Furthermore, the ABA-driven modifications in NHE plants showed typically higher sensitivity to ABA content in leaves compared to HE, illustrating ecotype-specific responses to ABA level. In NHE, the ABA-mediated modifications primarily affected the xylem transport of Cd ions and, at the cost of considerable water delivery limitations, significantly reduced delivery of Cd ions to shoots. In contrast, maintenance of low ABA levels in HE failed to t limit transpiration rates and maximized Cd accumulation in shoots. Our results demonstrated that ABA regulates Cd hyperaccumulation of S. alfredii through specific modifications in the water transport continuum.
- MeSH
- kadmium MeSH
- kořeny rostlin MeSH
- kyselina abscisová MeSH
- Sedum * MeSH
- voda MeSH
- Publikační typ
- časopisecké články MeSH
Ethylene is an important phytohormone for plant adaptation to heavy metal stress. However, the effects of ethylene on radial apoplastic transport of Cd remain elusive. This study investigated the role of ethylene on apoplastic barriers development and consequences for Cd uptake in Sedum alfredii. In response to Cd, endogenous ethylene production in hyperaccumulating ecotype (HE) roots was decreased due to the down-regulated expressions of ethylene biosynthesis genes, while the opposite result was observed in non-hyperaccumulating ecotype (NHE). Interestingly, the ethylene emission in HE was always higher than that in NHE, regardless of Cd concentrations. Results of exogenous application of ethylene biosynthesis precursor/inhibitor indicate that ethylene with high level would delay the formation of apoplastic barriers in HE through restraining phenylalanine ammonia lyase activity and gene expressions related to lignin/suberin biosynthesis. Simultaneously, correlation analyses suggest that Cd-induced apoplastic barriers formation may be also regulated by ethylene signaling. By using an apoplastic bypass tracer and scanning ion-selected electrode, we observed that the delayed deposition of apoplastic barriers significantly promoted Cd influx in roots. Taken together, high endogenous ethylene in HE postponed the formation of apoplastic barriers and thus promoted the Cd accumulation in the apoplast of roots.
Metallothioneins (MTs) are cysteine-rich peptides involved in heavy metal tolerance of many eukaryotes. Here, we examined their involvement in intracellular binding of silver (Ag) in the ectomycorrhizal fungus Amanita strobiliformis. The Ag complexes and their peptide ligands were characterized using chromatography and mass spectrometry. The full-length coding sequences obtained from a cDNA library were used for complementation assays in yeast mutant strains. Abundance of respective transcripts in A. strobiliformis was measured by quantitative real-time reverse-transcribed polymerase chain reaction (qRT-PCR). Ag-speciation analyses showed that intracellular Ag was in wild-grown fruit bodies and cultured extraradical mycelia of A. strobiliformis sequestered by metallothioneins. The determined sequence of the peptide facilitated isolation of three cDNA clones, AsMT1a, AsMT1b and AsMT1c. These encode isomorphic MTs consisting of 34 amino acid residues and sharing 82% identity. In mycelia the expression of AsMT1s is induced by Ag. All AsMT1s expressed in yeasts complemented hypersensitivity of mutants to cadmium (Cd) and copper (Cu) and formed Ag complexes. Only the Ag-AsMT1a complex was detected in the A. strobiliformis fruit body in which AsMT1a was the prevailing transcript. The present study identified the existence of metallothionein isoforms in ectomycorrhizal fungi. We demonstrated that intracellular sequestration of Ag in fruit bodies and mycelia of hyperaccumulating A. strobiliformis is dominated by metallothioneins.
- MeSH
- Amanita genetika metabolismus MeSH
- fungální proteiny genetika metabolismus MeSH
- genetické vektory MeSH
- genová knihovna MeSH
- kadmium metabolismus MeSH
- měď metabolismus MeSH
- metalothionein genetika metabolismus MeSH
- molekulární sekvence - údaje MeSH
- mycelium metabolismus MeSH
- plodnice hub genetika metabolismus MeSH
- protein - isoformy genetika metabolismus MeSH
- Saccharomyces cerevisiae MeSH
- sekvence aminokyselin MeSH
- sekvenční homologie aminokyselin MeSH
- stříbro metabolismus MeSH
- testy genetické komplementace MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Noccaea caerulescens (formerly known as Thlaspi caerulescens), an extremophile heavy metal hyperaccumulator model plant in the Brassicaceae family, is a morphologically and phenotypically diverse species exhibiting metal tolerance and leaf accumulation of zinc, cadmium, and nickel. Here, we provide a detailed genome structure of the approximately 267-Mb N. caerulescens genome, which has descended from seven chromosomes of the ancestral proto-Calepineae Karyotype (n = 7) through an unusually high number of pericentric inversions. Genome analysis in two other related species, Noccaea jankae and Raparia bulbosa, showed that all three species, and thus probably the entire Coluteocarpeae tribe, have descended from the proto-Calepineae Karyotype. All three analyzed species share the chromosome structure of six out of seven chromosomes and an unusually high metal accumulation in leaves, which remains moderate in N. jankae and R. bulbosa and is extreme in N. caerulescens. Among these species, N. caerulescens has the most derived karyotype, with species-specific inversions on chromosome NC6, which grouped onto its bottom arm functionally related genes of zinc and iron metal homeostasis comprising the major candidate genes NICOTIANAMINE SYNTHASE2 and ZINC-INDUCED FACILITATOR-LIKE1. Concurrently, copper and organellar metal homeostasis genes, which are functionally unrelated to the extreme traits characteristic of N. caerulescens, were grouped onto the top arm of NC6. Compared with Arabidopsis thaliana, more distal chromosomal positions in N. caerulescens were enriched among more highly expressed metal homeostasis genes but not among other groups of genes. Thus, chromosome rearrangements could have facilitated the evolution of enhanced metal homeostasis gene expression, a known hallmark of metal hyperaccumulation.
- MeSH
- Brassicaceae genetika metabolismus MeSH
- chromozomy rostlin genetika MeSH
- diploidie MeSH
- druhová specificita MeSH
- genom rostlinný * MeSH
- genová přestavba MeSH
- homeostáza MeSH
- karyotypizace MeSH
- listy rostlin chemie MeSH
- molekulární evoluce MeSH
- půda chemie MeSH
- regulace genové exprese u rostlin MeSH
- těžké kovy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Mechanisms evolved in eukaryotes to handle heavy metals involve cytosolic, metal-binding metallothioneins (MTs). We have previously documented that the sequestration of silver (Ag) in the Ag-hyperaccumulating Amanita strobiliformis is dominated by 34-amino-acid (AA) AsMT1a, 1b, and 1c isoforms. Here we show that in addition to AsMT1a, 1b, and 1c isogenes, the fungus has two other MT genes: AsMT2 encoding a 34-AA AsMT2 similar to MTs known from other species, but unrelated to AsMT1s; AsMT3 coding for a 62-AA AsMT3 that shares substantial identity with as-yet-uncharacterized conserved peptides predicted in agaricomycetes. Transcription of AsMT1s and AsMT3 in the A. strobiliformis mycelium was specifically inducible by treatments with Ag or copper (Cu) and zinc (Zn) or cadmium (Cd), respectively; AsMT2 showed a moderate upregulation in the presence of Cd. Expression of AsMTs in the metal-sensitive Saccharomyces cerevisiae revealed that all AsMTs confer increased Cd tolerance (AsMT3 proved the most effective) and that, unlike AsMT1 and AsMT2, AsMT3 can protect the yeasts against Zn toxicity. The highest level of Cu tolerance was observed with yeasts expressing AsMT1a. Our data indicate that A. strobiliformis can specifically employ different MT genes for functions in the cellular handling of Ag and Cu (AsMT1s) and Zn (AsMT3).
- MeSH
- Amanita genetika metabolismus MeSH
- genetická transkripce účinky léků MeSH
- měď metabolismus MeSH
- metalothionein genetika metabolismus MeSH
- Saccharomyces cerevisiae účinky léků genetika metabolismus MeSH
- stanovení celkové genové exprese MeSH
- stříbro metabolismus MeSH
- tolerance léku MeSH
- zinek metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Three Cd and Zn hyperaccumulating plant species Noccaea caerulescens Noccaea praecox and Arabidopsis halleri (Brassicacceae) were cultivated in seven subsequent vegetation seasons in both pot and field conditions in soil highly contaminated with Cd, Pb, and Zn. The results confirmed the hyperaccumulation ability of both plant species, although A. halleri showed lower Cd uptake compared to N. caerulescens. Conversely, Pb phytoextraction was negligible for both species in this case. Because of the high variability in plant yield and element contents in the aboveground biomass of plants, great variation in Cd and Zn accumulation was observed during the experiment. The extraction ability in field conditions varied in the case of Cd from 0.2 to 2.9 kg ha(-1) (N. caerulescens) and up to 0.15 kg ha(-1) (A. halleri), and in the case of Zn from 0.2 to 6.4 kg ha(-1) (N. caerulescens) and up to 13.8 kg.ha(-1) (A. halleri). Taking into account the 20 cm root zone of the soil, the plants were able to extract up to 4.1% Cd and 0.2% Zn in one season. However, cropping measures should be optimized to improve and stabilize the long-term phytoextraction potential of these plants.
- MeSH
- Arabidopsis metabolismus MeSH
- biodegradace MeSH
- Brassicaceae metabolismus MeSH
- druhová specificita MeSH
- kadmium metabolismus MeSH
- kořeny rostlin metabolismus MeSH
- látky znečišťující půdu metabolismus MeSH
- roční období MeSH
- zinek metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
