RESUMO
MAIN CONCLUSION: NaCl alleviates Cd toxicity in Sesvium portulacastrum by maintaining plant water status and redox balance, protecting chloroplasts structure and inducing some potential Cd (2+) chelators as GSH and proline. It has been demonstrated that NaCl alleviates Cd-induced growth inhibition in the halophyte Sesuvium portulacastrum. However, the processes that mediate this effect are still unclear. In this work we combined physiological, biochemical and ultrastructural studies to highlight the effects of salt on the redox balance and photosynthesis in Cd-stressed plants. Seedlings were exposed to different Cd concentrations (0, 25 and 50 µM Cd) combined with low (0.09 mM) (LS), or high (200 mM) NaCl (HS) in hydroponic culture. Plant-water relations, photosynthesis rate, leaf gas exchange, chlorophyll fluorescence, chloroplast ultrastructure, and proline and glutathione concentrations were analyzed after 1 month of treatment. In addition, the endogenous levels of stress-related hormones were determined in plants subjected to 25 µM Cd combined with both NaCl concentrations. In plants with low salt supply (LS), Cd reduced growth, induced plant dehydration, disrupted chloroplast structure and functioning, decreased net CO2 assimilation rate (A) and transpiration rate (E), inhibited the maximum potential quantum efficiency (Fv/Fm) and the quantum yield efficiency (Φ PSII) of PSII, and enhanced the non-photochemical quenching (NPQ). The addition of 200 mM NaCl (HS) to the Cd-containing medium culture significantly mitigated Cd phytotoxicity. Hence, even at similar internal Cd concentrations, HS-Cd plants were less affected by Cd than LS-Cd ones. Hence, 200 mM NaCl significantly alleviates Cd-induced toxicity symptoms, growth inhibition, and photosynthesis disturbances. The cell ultrastructure was better preserved in HS-Cd plants but affected in LS-Cd plants. The HS-Cd plants showed also higher concentrations of reduced glutathione (GSH), proline and jasmonic acid (JA) than the LS-Cd plants. However, under LS-Cd conditions, plants maintained higher concentration of salicylic acid (SA) and abscisic acid (ABA) than the HS-Cd ones. We conclude that in S. portulacastrum alleviation of Cd toxicity by NaCl is related to the modification of GSH and proline contents as well as stress hormone levels thus protecting redox balance and photosynthesis.
Assuntos
Aizoaceae/efeitos dos fármacos , Cádmio/toxicidade , Fotossíntese/fisiologia , Plantas Tolerantes a Sal/efeitos dos fármacos , Cloreto de Sódio/farmacologia , Estresse Fisiológico , Ácido Abscísico/metabolismo , Ácido Abscísico/fisiologia , Aizoaceae/crescimento & desenvolvimento , Aizoaceae/metabolismo , Aizoaceae/ultraestrutura , Cádmio/metabolismo , Clorofila/metabolismo , Cloroplastos/efeitos dos fármacos , Cloroplastos/metabolismo , Cloroplastos/ultraestrutura , Ciclopentanos/metabolismo , Glutationa/metabolismo , Oxirredução , Oxilipinas/metabolismo , Transpiração Vegetal/efeitos dos fármacos , Prolina/metabolismo , Ácido Salicílico/metabolismo , Plantas Tolerantes a Sal/metabolismo , Cloreto de Sódio/metabolismo , Água/metabolismoRESUMO
Citrate, malate and histidine have been involved in many processes including metal tolerance and accumulation in plants. These molecules have been frequently reported to be the potential nickel chelators, which most likely facilitate metal transport through xylem. In this context, we assess here, the relationship between organics acids and histidine content and nickel accumulation in Mesembryanthemum crystallinum and Brassica juncea grown in hydroponic media added with 25, 50 and 100 µM NiCl2. Results showed that M. crystallinum is relatively more tolerant to Ni toxicity than B. juncea. For both species, xylem transport rate of Ni increased with increasing Ni supply. A positive correlation was established between nickel and citrate concentrations in the xylem sap. In the shoot of B. juncea, citric and malic acids concentrations were significantly higher than in the shoot of M. crystallinum. Also, the shoots and roots of B. juncea accumulated much more histidine. In contrast, a higher root citrate concentration was observed in M. crystallinum. These findings suggest a specific involvement of malic and citric acid in Ni translocation and accumulation in M. crystallinum and B. juncea. The high citrate and histidine accumulation especially at 100µM NiCl2, in the roots of M. crystallinum might be among the important factors associated with the tolerance of this halophyte to toxic Ni levels.
Assuntos
Ácido Cítrico/metabolismo , Histidina/metabolismo , Malatos/metabolismo , Mesembryanthemum/metabolismo , Mostardeira/metabolismo , Níquel/farmacocinética , Transporte Biológico/fisiologia , Raízes de Plantas/metabolismo , Brotos de Planta/metabolismo , Plantas Tolerantes a Sal , XilemaRESUMO
Toxic heavy metal accumulation in edible plants has become a problem worth worrying about for human health. Cadmium is one of the most toxic metals presenting high bioavailability in the environment. The main route of transfer of Cd to humans is the consumption of contaminated food which suggests that reducing of Cd absorption by plants could reduce this risk. In this context, it was suggested that silicon supply would be able to limit the transfer of Cd to the plants. Thus, this work evaluated the effects of 0.5 mM Si on Cd absorption and accumulation in barley (Hordeum vulgare L.). Plants were grown hydroponically for 21 days in the presence of 0 and 15 µM Cd2+ combined or not with 0.5 mM Si. Analyses were related to growth and photosynthesis parameters, Cd accumulation in organs and Cd subcellular distribution in the shoots. Results showed that, under Cd alone, plants showed severe toxicity symptoms as chlorosis and necrosis and produced significantly less biomass as compared to control. 0.5 mM Si in the medium culture significantly reduced Cd-induced toxicity by mitigating symptoms and restoring growth, photosynthesis, and nutrition. Si also induced a significant reduction of Cd concentration in plants and changed its sub-cellular compartmentalization by enhancing fixation to cell walls and reducing the Cd concentration in the cytoplasmic and organelles fractions. These data suggest that the application of Si could significantly increase Cd tolerance and reduce the risk of the Cd accumulation in edible plants.
Assuntos
Cádmio , Hordeum , Fotossíntese , Silício , Hordeum/efeitos dos fármacos , Hordeum/crescimento & desenvolvimento , Silício/farmacologia , Cádmio/toxicidade , Fotossíntese/efeitos dos fármacos , Poluentes do Solo/toxicidadeRESUMO
Among heavy metal stressors, cadmium (Cd) pollution is one leading threat to the environment. In this view, research efforts have been increasingly put forward to promote the individuation of phytoextractor plants that are capable of accumulating and withstanding the toxic metals, including Cd, in the aerial parts. We hereby adopted the hyperaccumulator B. juncea (Indian mustard) as a model to investigate plant responses to Cd stress at low (25 µM) and high (100 µM) doses. Analytical strategies included mass-spectrometry-based determination of Cd and the assessment of its effect on the leaf proteome and metabolome. Results were thus integrated with routine physiological data. Taken together, physiology results highlighted the deregulation of photosynthesis efficiency, ATP synthesis, reduced transpiration, and the impairment of light-independent carbon fixation reactions. These results were supported at the proteomics level by the observed Cd-dependent alteration of photosystem components and the alteration of metabolic enzymes, including ATP synthase subunits, carbonic anhydrase, and enzymes involved in antioxidant responses (especially glutathione and phytochelatin homeostasis) and the Calvin cycle. Metabolomics results confirmed the alterations of energy-generating metabolic pathways, sulfur-compound metabolism (GSH and PCs), and Calvin cycle. Besides, metabolomics results highlighted the up-regulation of phosphoglycolate, a byproduct of the photorespiration metabolism. This was suggestive of the likely increased photorespiration rate as a means to cope with Cd-induced unbalance in stomatal conductance and deregulation of CO2 homeostasis, which would, in turn, promote CO2 depletion and O2 (and thus oxidative stress) accumulation under prolonged photosynthesis in the leaves from plants exposed to high doses of CdCl2. Overall, it emerges that Cd-stressed B. juncea might rely on photorespiration, an adaptation that would prevent the over-reduction of the photosynthetic electron transport chain and photoinhibition.
Assuntos
Cádmio/toxicidade , Poluentes Ambientais/toxicidade , Mostardeira/efeitos dos fármacos , Fotossíntese/efeitos dos fármacos , Transpiração Vegetal/efeitos dos fármacos , Estresse Fisiológico/fisiologia , Trifosfato de Adenosina/biossíntese , Cádmio/farmacocinética , Dióxido de Carbono/metabolismo , Cromatografia Líquida de Alta Pressão , Relação Dose-Resposta a Droga , Poluentes Ambientais/farmacocinética , Espectrometria de Massas , Metabolômica , Mostardeira/metabolismo , Estresse Oxidativo/efeitos dos fármacos , Fotossíntese/fisiologia , Transpiração Vegetal/fisiologia , Proteômica/métodos , Estresse Fisiológico/genéticaRESUMO
The effect of sodium chloride (NaCl) on cadmium (Cd) tolerance, uptake, translocation, and compartmentation was investigated in 3 barley genotypes. Seedlings were cultivated hydroponically in the absence of NaCl and Cd (control), in the presence of 50 mM NaCl alone, in the presence of 10 µM Cd alone, and in the combined addition of NaCl (50 mM) and Cd (10 µM). Plants were cultivated during one month under 16 h light period at a minimal light intensity of 250 µmol m-2 s-1, a temperature of 25 ± 3 °C, and 70-80% of relative humidity. Results showed that NaCl alone did not significantly affect plant development and biomass production; however, Cd alone reduced plant development rate leading to a decline in biomass production in Raihane and Giza 127 but did not affect that in Amalou. NaCl addition in Cd-treated plants accentuated the Cd effect on plant growth. NaCl limited Cd accumulation in the roots and in the shoots in all tested barley varieties by reducing Cd-absorption efficiency and the translocation of Cd from the root to the shoot. In all Cd-treated plants, cell Cd compartmentalization showed the following gradient: organelles < cell wall < vacuole. NaCl in the medium increased Cd accumulation in the soluble fraction and reduced that in organelle and cell wall fractions. Globally our results showed that, although NaCl reduces Cd accumulation in barley, it accentuates the Cd toxic effects, hence limiting the plant yield. We advise farmers to avoid barley cultivation near mine sites and its irrigation with moderately salty water, although this plant is considered as salt tolerant.
Assuntos
Cádmio , Hordeum , Cloreto de Sódio , Cádmio/farmacologia , Hordeum/fisiologia , Raízes de Plantas , Plântula , Cloreto de Sódio/farmacologiaRESUMO
The contamination of saltwater by toxic heavy metals has become a worldwide problem. The application of phytoextraction to remove these pollutants seems to be more efficient and cheaper compared to physicochemical methods. In this work, we evaluated the potential of two halophyte species to accumulate cadmium and zinc from contaminated water. Seedlings of Carpobrotus edulis L. and Sesuvium portulacastrum L. were cultivated during 1 month on pots filled with saltwater (200 mM NaCl) containing different concentrations of Cd2+ (0, 50, 100 µM) and of Zn2+ (0, 200, and 400 µM) applied separately. Results showed that both halophytes were more resistant to Zn2+ than Cd2+ and that Sesuvium better tolerates the two metals. Zn2+ and Cd2+ concentrations in the shoot as well as the values of translocation factors suggest that these species are able to absorb and to concentrate Cd2+ and Zn2+ in their roots and shoots. Hence, after 1 month of culture on 50 µM Cd2+, plants were able to extract 31% and 21% of Cd, respectively, in S. portulacastrum and C. edulis. The Zn-extraction efficiency was less important and reached 18 and 19%, respectively, in S. portulacastrum and C. edulis cultivated under 200 µM Zn2+. Given together, data demonstrate the efficiency of the use of halophytes, especially S. portulacastrum, to extract Zn2+ and Cd2+ from salt wastewater.
Assuntos
Aizoaceae , Poluentes do Solo , Plantas Tolerantes a Sal , Cádmio/toxicidade , Cloreto de Sódio , Zinco , Biodegradação AmbientalRESUMO
In this study, we investigated the effect of the homeopathic drug Zincum Metallicum (ZM) on zinc (Zn) toxicity in the plant species Lepidium sativum L. We focused on growth parameters, Zn uptake and numerous biochemical parameters. Seedlings were hydroponically subjected during 7 days to 0.05, 500, 1000, 1500 and 2000 µM Zn2+, in the absence or presence of 15ch or 9ch ZM. In the absence of ZM, Zn induced negative effect on growth especially at the dose of 2 mM. Zn induced also chlorosis, reduced total chlorophyll and/or carotenoid content and increased the level of malondialdehyde (MDA). Under Zn toxicity (500, 1000 and 1500 µM), the superoxide dismutase (SOD), catalase (CAT), gaiacol peroxidase (GPX) and glutathione reductase (GR) activities were increased or not significantly affected, while at 2000 µM Zn affected the activity of these enzymes. At the highest Zn level (2 mM), proline and total polyphenol and flavonoid contents were markedly increased in leaves and roots of L. sativum. Additionally, ZM supply considerably ameliorated the plant growth, photosynthetic pigment contents and increased non-enzymatic antioxidant molecules and enzymatic activities against Zn-induced oxidative stress. Our data suggest that homeopathic properties of ZM may be efficiently involved in the restriction of Zn-induced oxidative damages, by lowering Zn accumulation and translocation in the leaves and roots of Lepidium sativum L.
Assuntos
Antioxidantes , Lepidium sativum , Antioxidantes/metabolismo , Clorofila/farmacologia , Malondialdeído/farmacologia , Estresse Oxidativo , Raízes de Plantas/metabolismo , Plântula , Superóxido Dismutase/metabolismo , Zinco/farmacologiaRESUMO
In North Africa, barley (Hordeum vulgare L) is the second most cultivated cereal. In Tunisia, barley is cultivated in mining areas with possible Cd soil contamination. The accumulation of Cd was studied in the 36 most cultivated North African barley cultivars cultured during 6 months on control soil and on soil containing 10 ppm of Cd. Cadmium did not affect germination and morphology in any cultivar. However, Cd induced variable effects on the biomass according to the cultivar. The cultivar Lemsi was the most sensitive one and Gisa 127 the most tolerant to Cd. The spike morphology did not show any differences between control and Cd-treated plants. The number of grains per spike and the weight of kernels were differently affected by Cd. On this basis, we identified Manel, Temassine, Giza 130, and Firdaws as the most tolerant cultivars and Raihane, Giza 123, Adrar, and Amira as the most sensitive ones. Cd accumulated at a higher concentration in straw than in the grains, but for both organs, we observed a significant intraspecific variability. In the straw, Lemsi and Massine showed the highest Cd concentration, while the lowest concentration was recorded in Temassine. In the kernels, Amalou showed the highest Cd concentration, 14 µgg-1 of dry weight (DW), but the lowest Cd concentration was 1.7 µg g-1 DW in Kebelli. Based on the official allowable limit of Cd in the grain, all cultivars represent a potential risk when cultivated on soil contaminated with 10 ppm Cd. The molecular and physiological basis responsible for the differences in Cd tolerance and accumulation among barley cultivars will require more investigations.
Assuntos
Hordeum , Poluentes do Solo , Cádmio/análise , Solo , Poluentes do Solo/análise , TunísiaRESUMO
The implication of enzymatic and non-enzymatic antioxidative systems in response to Ni was evaluated in the halophyte Mesembryanthemum crystallinum in comparison with the metal tolerant glycophyte species Brassica juncea. Seedlings of both species were hydroponically subjected during 21 days to 0, 25, 50, and 100 µM NiCl2. Growth parameters showed that the halophyte M. crystallinum was more tolerant to Ni than B. juncea. Malondialdehyde (MDA) content increased to a higher extent in B. juncea than in M. crystallinum. Antioxidant enzymesactivities were differently affected by Ni in both species. Nickel increased shoot superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities in B. juncea, whereas these activities were reduced in M. crystallinum when exposed to metal stress. The root SOD, APX and guaiacol peroxidase (GPX) activities increased upon Ni treatments for both species. The content of non-enzymatic antioxidative molecules such as glutathione, non-protein thiols and proline increased in Ni-treated plants, except for GSH content in the shoot of B. juncea. Based on the oxidative balance, our findings confirm the higher tolerance of the halophyte M. crystallinum to Ni-induced oxidative stress comparatively to B. juncea. We suggest that M. crystallinum is able to overcome the produced ROS using the non-enzymatic system, while Ni-induced oxidative stress was more acute in B. juncea, leading this species to mainly use the enzymatic system to protect against reactive oxygen species.
RESUMO
Halophytes are able to tolerate relatively high concentrations of hazardous metals in a growing substrate, what makes them suitable candidates for phytoremediation of metal-contaminated soils. In this work, we aimed to study the physiological responses of the halophyte Sesuvium portulacastrum L. to Ni, with main focus on Ni localization, compartmentation and ligand environment, to decipher Ni tolerance and toxicity mechanisms. Seedlings were grown in hydroponic nutrient solution containing 0, 25, 50 and 100 µM Ni as NiCl2 for 3 weeks. Ni localization in leaves was assessed by micro-proton-induced X-ray emission (micro-PIXE). Ni ligand environment was studied by Ni K-edge X-ray absorption near edge structure (XANES). In addition, Ni-soluble, weakly bound/exchangeable and insoluble leaf tissue fractions were determined by sequential extraction. Results show that S. portulacastrum is able to tolerate up to ~ 500 µg g-1 dry weight (DW) of Ni in the shoots without significant growth reduction. At higher Ni concentrations (> 50 µM Ni in nutrient solution), chloroses were observed due to the accumulation of Ni in photosynthetically active chlorenchyma as revealed by micro-PIXE. Water storage tissue represented the main pool for Ni storage. Incorporation of Ni into Ca-oxalate crystals was also observed in some specimens, conferring tolerance to high leaf Ni concentrations. The majority of Ni (> 70%) was found in soluble tissue fraction. Ni K XANES revealed Ni bound mainly to O- (55%) and N-ligands (45%). Ni toxicity at higher Ni levels was associated with Ni binding to amino groups of proteins in cytosol of chlorenchyma and increased level of lipid peroxidation. Proline levels also increased at high Ni exposures and were associated with Ni-induced oxidative stress and alteration of water regime.
Assuntos
Aizoaceae , Plantas Tolerantes a Sal , Biodegradação Ambiental , Ligantes , NíquelRESUMO
Heavy metals such as cadmium and zinc constitute major pollutants in coastal areas and frequently accumulate in salt marshes. The wetland halophyte plant species Kosteletzkya pentacarpos is a promising species for phytostabilization of contaminated areas. In order to assess the role of the antisenescing phytohormone cytokinin in heavy metal resistance in this species, seedlings were exposed for two weeks to Cd (10 µM), Zn (100 µM) or Cd + Zn (10 µM + 100 µM) in the presence or absence of 50 mM NaCl and half of the plants were sprayed every two days with the cytokinin trans-zeatine riboside (10 µM). Zinc reduced the endogenous cytokinin concentration. Exogenous cytokinin increased plant growth, stomatal conductance, net photosynthesis and total ascorbate and reduced oxidative stress estimated by malondialdehyde in Zn-treated plants maintained in the absence of NaCl. Heavy metal induced an increase in the senescing hormone ethylene which was reduced by cytokinin treatment. Plants exposed to the mixed treatment (Cd + Zn) exhibited a specific hormonal status in relation to accumulation of abscisic acid and depletion of salicylic acid. Non-protein thiols (glutathione and phytochelatins) accumulated in response to Cd and Cd + Zn. It is concluded that toxic doses of Cd and Zn have different impacts on the plant behavior and that the simultaneous presence of the two elements induces a specific physiological constraint at the plant level. Salinity helps the plant to cope with heavy metal toxicities and the plant hormone cytokinin assumes key function in Zn resistance but its efficiency is lower in the presence of NaCl.
Assuntos
Cádmio/toxicidade , Citocininas/metabolismo , Hibiscus/metabolismo , Reguladores de Crescimento de Plantas/metabolismo , Cloreto de Sódio/farmacologia , Zinco/toxicidade , Ácido Abscísico/análise , Glutationa/metabolismo , Hibiscus/crescimento & desenvolvimento , Fotossíntese/efeitos dos fármacos , Fitoquelatinas/metabolismo , Desenvolvimento Vegetal/efeitos dos fármacos , Ácido Salicílico/análise , Salinidade , Plântula/fisiologia , Poluentes Químicos da Água/toxicidade , Áreas AlagadasRESUMO
Sesuvium portulacastrum, a halophyte with high tolerance to heavy metals like Cd, Pb and Ni is considered for phytoremediation of metal contaminated saline soils. The tolerance to a selected metal ion could, by hypothesis, be stimulated through in vitro adaptation and regeneration of the plant. Seedlings obtained by in vitro micro-propagation, were exposed to 0, 25 and 50⯵M Ni, as NiCl2, in agar-based medium for 30 days. Growth parameters, plant water content, the concentration of photosynthetic pigments, proline and malondialdehyde (MDA) concentrations were determined. Nickel and nutrients distribution in leaves was studied by micro-Proton-Induced-X-ray-Emission (µ-PIXE). The results showed that Ni was mainly accumulated in vascular bundles, next in water storage tissues and chlorenchyma. Ni concentrations in chlorenchyma increased with increasing Ni in culturing medium, in direct relation to decrease of photosynthetic pigments and increase of oxidative stress. As compared to control plants, Ni induced substantial increase in MDA and proline accumulation. Plants exposed to 50⯵M Ni accumulated up to 650⯵gâ¯g-1 of Ni in the shoots, exhibiting chlorosis and necrosis and a drastically reduced plant growth. Perturbations in uptake and distribution of nutrients were observed, inducing mineral deficiency, probably through membrane leakage. The mineral nutrient disturbances induced by Ni could be highly implicated in the restriction of S. portulacastrum development under the acute 50⯵M Ni level.
Assuntos
Adaptação Fisiológica , Aizoaceae/efeitos dos fármacos , Níquel/farmacologia , Plântula/efeitos dos fármacos , Aizoaceae/crescimento & desenvolvimento , Aizoaceae/metabolismo , Biodegradação Ambiental , Minerais/metabolismo , Níquel/farmacocinética , Fotossíntese , Folhas de Planta , Plantas Tolerantes a Sal , Poluentes do Solo/farmacologia , Distribuição TecidualRESUMO
The interaction between soil drying and salinity was studied in the perennial halophyte, Sesuvium portulacastrum. Rooted cuttings were individually cultivated for three months in silty-sandy soil under two irrigation modes: 100 and 25% of field capacity (FC). The amount of the evapotranspirated water was replaced by a nutrient solution containing either 0 or 100 mM NaCl. Whole-plant growth, leaf water content, leaf water potential (Psi(w)), and Na+, K+, and proline concentrations in the tissues were measured. When individually applied, both drought and salinity significantly restricted whole-plant growth, with a more marked effect of the former stress. However, the effects of the two stresses were not additive on whole-plant biomass or on leaf expansion. Root growth was more sensitive to salt than to soil drying, the latter being even magnified by the adverse impact of salinity. Leaf water content was significantly reduced following exposure to water-deficit stress, but was less affected in salt-treated plants. When simultaneously submitted to water-deficit stress and salinity, plants displayed higher values of water and potassium use efficiencies, leaf proline and Na+ concentrations, associated with lower leaf water potential (-1.87 MPa), suggesting the ability of S. portulacastrum to use Na+ and proline for osmotic adjustment.
Assuntos
Aizoaceae/fisiologia , Dessecação , Prolina/metabolismo , Salinidade , Solo , Aizoaceae/crescimento & desenvolvimento , Aizoaceae/metabolismo , Fenômenos Fisiológicos da Nutrição , Folhas de Planta/metabolismo , Caules de Planta/metabolismo , Potássio/metabolismo , Sódio/metabolismo , Água/metabolismoRESUMO
Salt marshes are major sinks for heavy metals where plants are often exposed to polymetallic contamination and high salinity. Seedlings from the wetland halophyte plant species Kosteletzkya pentacarpos were exposed during three weeks to nutrient solution containing 10⯵M CdCl2, 100⯵M ZnCl2 or a combination of the two metals (Cd + Zn) in the presence or absence of 50 mM NaCl. Synthesis of the senescing hormone ethylene was quantified together with the concentration of protecting polyamines (spermidine and spermine) and their precursor putrescine and analyzed in relation to senescence markers (soluble protein, malondialdehyde, chlorophyll content and assessment of cell membrane stability). Salinity reduced the deleterious impact of heavy metals on plant growth and decreased accumulation of the pollutants in the plants. Heavy metals increased ethylene synthesis but NaCl decreased it in plants exposed to Cd or to the combined treatment (Cd + Zn) but not in plants exposed to Zn alone. Putrescine increased while spermine and spermidine decreased in Cd-treated plants. Zinc had only a marginal impact on polyamine concentration. The highest putrescine and spermine concentrations were observed in plants exposed to the combined treatment. The inhibitor of ethylene synthesis (AVG; aminovynilglycine) partially restored plant growth, reduced putrescine content and increased spermidine and spermine concentration, leading to an attenuation of senescence, mainly in Cd-treated plants. Combined treatment induced a specific physiological status in K. pentacarpos which could not be fully explained by an additive effect of Cd and Zn. Results are discussed in relation to specificities of heavy metals impacts on plant response.
Assuntos
Cádmio/química , Etilenos/química , Desenvolvimento Vegetal/efeitos dos fármacos , Poliaminas/química , Poliaminas/síntese química , Zinco/química , SalinidadeRESUMO
Plants show complex responses to abiotic stress while, the effect of the stress combinations can be different to those seen when each stress is applied individually. Here, we report on the effects of salt and/or cadmium on photosynthetic apparatus of Thellungiella salsuginea. Our results showed a considerable reduction of plant growth with some symptoms of toxicity, especially with cadmium treatment. The structural integrity of both photosystems (PSI and PSII) was mostly maintained under salt stress. Cadmium induced a considerable decrease of both PSI and PSII quantum yields and the electron transport rate ETR(I) and ETR(II) paralleled by an increase of non-photochemical quenching (NPQ). In addition, cadmium alone affects the rate of primary photochemistry by an increase of fluorescence at O-J phase and also the photo-electrochemical quenching at J-I phase. A positive L-band appeared with (Cd) treatment as an indicator of lower PSII connectivity, and a positive K-band reflecting the imbalance in number of electrons at donor and acceptor side. In continuity to our previous studies which showed that NaCl supply reduced Cd2+ uptake and limited its accumulation in shoot of divers halophyte species, here as a consequence, we demonstrated the NaCl-induced enhancement effect of Cd2+ toxicity on the PSII activity by maintaining the photosynthetic electron transport chain as evidenced by the differences in ψO, φEo, ABS/RC and TR0/RC and by improvement of performance index PI(ABS), especially after short time of treatment. A significant decrease of LHCII, D1 and CP47 amounts was detected under (Cd) treatment. However, NaCl supply alleviates the Cd2+ effect on protein abundance including LHCII and PSII core complex (D1 and CP47).
Assuntos
Brassicaceae/fisiologia , Cádmio/farmacologia , Fotossíntese/efeitos dos fármacos , Cloreto de Sódio/farmacologia , Estresse Fisiológico/efeitos dos fármacos , Biomassa , Brassicaceae/efeitos dos fármacos , Brassicaceae/crescimento & desenvolvimento , Clorofila/metabolismo , Transporte de Elétrons , Fluorescência , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Tilacoides/metabolismoRESUMO
One of the limits of Cd2+-phytoextraction is the high toxicity of this metal to plants. Growth restriction, chlorosis and necrosis are usually accompanied with a large disturbance of the uptake of essential elements. This work aims to study the effects of cadmium (Cd2+) on potassium (K+), calcium (Ca2+) and nitrogen (N) acquisition, and their consequences on growth in two halophytes species: Sesuvium portulacastrum and Mesembryanthemum crystallinum. Seedlings were grown for 30 days in split-root conditions. One half of the root system was immersed in complete nutrient solution (Basal medium (B)) supplemented with 100 microM Cd2+, and the other half was immersed in a Cd2+-free medium, containing all nutrients (B/Cd plants) or deprived of potassium ((B-K)/Cd) or calcium ((B-Ca)/Cd) or nitrogen ((B-N)/Cd). Using this approach, we demonstrated that K+ and Ca2+ uptake was impaired in roots exposed to Cd2+. Concerning N, we noticed no indication of uptake inhibition by Cd2+. However, restriction of K+ uptake by roots was compensated by an increase in the K+-use efficiency, so that growth was not inhibited. Calcium uptake was strongly limited by Cd2. This inhibition was accompanied by a reduction in growth of ((B-Ca)/Cd) plants. Thus, we conclude that Cd2+ limits growth of both halophytes through restriction imposed on Ca2+ uptake. We suggest that the increase of Ca2+ availability in soils could improve the growth of both species in the presence of Cd2+. This would be essential for improving their utility for extraction of this metal by from salty contaminated soils.
Assuntos
Aizoaceae/efeitos dos fármacos , Aizoaceae/metabolismo , Cádmio/toxicidade , Cálcio/metabolismo , Mesembryanthemum/efeitos dos fármacos , Nitrogênio/metabolismo , Potássio/metabolismo , Aizoaceae/crescimento & desenvolvimento , Mesembryanthemum/crescimento & desenvolvimento , Mesembryanthemum/metabolismo , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Plântula/efeitos dos fármacos , Plântula/crescimento & desenvolvimento , Plântula/metabolismoRESUMO
The effects of inoculation with an arbuscular mycorrhizal (AM) fungus on Cd and Ni tolerance and uptake in Medicago sativa, an AM host, and Sesuvium portulacastrum, a non-host plant, were investigated in a greenhouse experiment. The plants were cultivated in sterilized sand in a two-compartmented system, which prevented root competition but enabled colonization of the whole substrate by AM fungal extraradical mycelium. M. sativa was either left non-inoculated or inoculated with the AM fungus Rhizophagus irregularis, and both plants were either cultivated without heavy metal (HM) addition or supplied with cadmium (Cd) or nickel (Ni), each in two doses. Additional pots with singly cultivated plants were established to control for the effect of the co-cultivation. AM significantly enhanced the growth of M. sativa and substantially increased its uptake of both HMs. The roots of S. portulacastrum became colonized by AM fungal hyphae and vesicles. The presence of the AM fungus in the cultivation system tended to increase the HM uptake of S. portulacastrum, but the effect was less consistent and pronounced than that in M. sativa. We conclude that AM fungal mycelium radiating from M. sativa did not negatively affect the growth and HM uptake of S. portulacastrum. On the contrary, we hypothesize that it stimulated the absorption and translocation of Cd and Ni in the non-host species. Thus, our results suggest that AM fungal mycelium radiating from mycorrhizal plants does not decrease the HM uptake of non-host plants, many of which are considered promising candidate plants for phytoremediation.
Assuntos
Aizoaceae , Cádmio/metabolismo , Glomeromycota/fisiologia , Medicago sativa , Micélio/fisiologia , Micorrizas/fisiologia , Níquel/metabolismo , Aizoaceae/metabolismo , Aizoaceae/microbiologia , Medicago sativa/metabolismo , Medicago sativa/microbiologia , Raízes de Plantas/metabolismoRESUMO
The aim of the present work was to analyze the impact of salinity on the plant response to Cd toxicity in the Mediterranean halophyte species Inula crithmoides. For this purpose, cuttings were cultivated hydroponically during 21d in the presence of 0, 25 or 50µM CdCl2 combined or not with 0, 100, 200 and 400mM NaCl. The obtained data demonstrated that, in the absence of Cd, NaCl strongly increased plant growth (the maximal dry weight being observed at 100mM) and enhanced the Na+/K+ ratio in the shoot. Cd alone strongly affected plant growth in this halophyte. However, in Cd-treated plants, NaCl protected Inula crithmoides from Cd toxicity and contributed to reduce Cd absorption and translocation. Small aliphatic polyamine (putrescine, spermidine, spermine) increased in response to both NaCl and CdCl2, the highest concentration in plants being observed when both agents are present in the medium. The recorded increase preferentially concerned the polyamine bound fraction, which might be related to their involvement in the protection of endogenous cellular structures. The aromatic monoamine tyramine also strongly increased in response to Cd toxicity and its putative role is discussed in relation to conjugation processes. Salinity and Cd increased ammonium/nitrate ratio in leaves and roots and the involvement of stress-induced modification of N nutrition on polyamine oversynthesis is also discussed.
Assuntos
Cádmio/toxicidade , Inula/fisiologia , Poliaminas/metabolismo , Plantas Tolerantes a Sal/fisiologia , Cloreto de Sódio/farmacologia , Tiramina/metabolismo , Compostos de Amônio/metabolismo , Biomassa , Inula/anatomia & histologia , Inula/efeitos dos fármacos , Inula/crescimento & desenvolvimento , Nitratos/metabolismo , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/metabolismo , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/metabolismo , Potássio/metabolismo , Plantas Tolerantes a Sal/anatomia & histologia , Plantas Tolerantes a Sal/efeitos dos fármacos , Plantas Tolerantes a Sal/crescimento & desenvolvimento , Sódio/metabolismoRESUMO
It is well known that salinity reduces cadmium toxicity in halophytes. However, the possible interference of Cd with the mechanisms of salt tolerance is poorly explored. The aim of this study was to see whether Cd affects salt tolerance mechanisms in the halophyte Sesuvium portulacastrum. S. portulacastrum plants obtained from cuttings were grown in hydroponics for 3 weeks and then exposed to low (0.09 mM) or moderate (200 mM) NaCl concentrations, alone or in combination with 25 µM CdCl2. Microscopy observation revealed two strategies of salt tolerance: euhalophytism and secretion of salt by bladder cells. Cadmium exposure hardly influenced the total leaf Na+ concentrations. However, Cd supply delayed the salt-induced upregulation of AHA1 (plasma membrane H+-ATPase 1) and SOS1 (plasma membrane Na+ transporter "Salt Overly Sensitive 1"), genes that are essential for salt tolerance. Moreover, Cd induced the activation of BADH, coding for betaine aldehyde dehydrogenase, indicating enhanced osmotic stress due to Cd. Sodium-green fluorescence in protoplasts from plants grown with low or high NaCl, alone or in combination with Cd, revealed higher Na+ concentrations in the cytoplasm of Cd-exposed plants. Taken together the results indicate interference of Cd with salt tolerance mechanisms in S. portulacastrum. This may have consequences for the efficient use of halophytes in phytoremediation of Cd-contaminated saline soils.
Assuntos
Aizoaceae/efeitos dos fármacos , Aizoaceae/metabolismo , Cádmio/toxicidade , Biodegradação Ambiental , Proteínas de Plantas/metabolismo , Salinidade , Tolerância ao Sal , Plantas Tolerantes a Sal/efeitos dos fármacos , Plantas Tolerantes a Sal/metabolismo , Sódio/metabolismo , Cloreto de Sódio/toxicidadeRESUMO
Changes in lipid content and fatty acid composition were determined in leaves of two halophytes: Sesuvium portulacastrum and Mesembryanthemum crystallinum exposed to cadmium (Cd). Experiments were carried out using young small-sized plants grown hydroponically (S. portulacastrum) or aseptically germinated seeds (M. crystallinum). Cd treatment was applied at different concentrations (0, 50, 100 and 200microM) for 30 days. At high cadmium doses (200microM), contents of total lipids (TL) and lipid fractions including galactolipids (GL), phospholipids (PL) and neutral lipids (NL) decreased more in M. crystallinum leaves than in S. portulacastrum leaves. Moreover, there were no significant changes in the total fatty acid composition of S. portulacastrum leaves during metal treatment. In contrast, M. crystallinum leaves showed a decrease in the percentage of the tri-unsaturated fatty acid (C18:3), and a corresponding increase in the percentage of di-unsaturated fatty acid (C18:2). These different responses suggested that S. portulacastrum seems to be more feasible for phytoremediation.