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ABSTRACT: Indian mustard (Brassica juncea L. Czern.) tolerates high concentrations of heavy metals and is a promising species for the purpose of phytoextraction of cadmium (Cd) from metal-contaminated soils. This work investigates the extent to which antioxidant and metal sequestering mechanisms are responsible for this tolerance. To this end, seedlings of Indian mustard were grown for 7 days in 0, 50 or 200 μM Cd. Increasing Cd concentrations led to a progressive Cd accumulation in roots and shoots, accompanied by an organ-dependent alteration in mineral uptake, and a decrease in root/shoot length and fresh/dry weight. Cd negatively affected chlorophyll and carotenoid contents and activated the xanthophyll cycle, suggesting the need to protect the photosynthetic apparatus from photoinhibition. Shoots seemed to be less efficient than roots in ROS scavenging, as indicated by the different response to Cd stress shown by peroxidase and catalase activities and, solely with regard to the highest Cd concentration, by ascorbate level. Such a different antioxidant capacity might at least partly explain differences in the trend of lipid peroxidation observed in the two organs. Moreover, in both roots and shoots, glutathione and phytochelatin content markedly increased under Cd stress, regardless of the metal concentration involved.
Plant Physiology and Biochemistry 05/2012; 57:15-22. · 2.84 Impact Factor
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ABSTRACT: Ectomycorrhizal fungi are thought to enhance mineral nutrition of their host plants and to confer increased tolerance toward toxic metals. However, a global view of metal homeostasis-related genes and pathways in these organisms is still lacking. Building upon the genome sequence of Tuber melanosporum and on transcriptome analyses, we set out to systematically identify metal homeostasis-related genes in this plant-symbiotic ascomycete. Candidate gene products (101) were subdivided into three major functional classes: (i) metal transport (58); (ii) oxidative stress defence (32); (iii) metal detoxification (11). The latter class includes a small-size metallothionein (TmelMT) that was functionally validated in yeast, and phytochelatin synthase (TmelPCS), the first enzyme of this kind to be described in filamentous ascomycetes. Recombinant TmelPCS was shown to support GSH-dependent, metal-activated phytochelatin synthesis in vitro and to afford increased Cd/Cu tolerance to metal hypersensitive yeast strains. Metal transporters, especially those related to Cu and Zn trafficking, displayed the highest expression levels in mycorrhizae, suggesting extensive translocation of both metals to root cells as well as to fungal metalloenzymes (e.g., laccase) that are strongly upregulated in symbiotic hyphae.
Fungal Genetics and Biology 11/2010; 48(6):573-84. · 3.74 Impact Factor
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ABSTRACT: Thalli of epiphytic lichen Hypogymnia physodes (L.) Nyl. and terricolous Cladonia furcata (Huds.) Schrad., collected from an area with background arsenic concentrations, were exposed to 0, 0.1, 1 and 10 microg mL(-1) arsenate (As(V)) solutions for 24 h. After exposure they were kept in the metabolically active state for 0, 24 and 48 h in a growth chamber. In the freeze dried samples glutathione (GSH), glutathione disulphide (GSSG), cysteine (Cys) and cystine were analysed and induction of phytochelatin (PC) synthesis measured by reversed-phase high-performance liquid chromatography in combination with fluorescence detection or UV spectrometry. Total arsenic content in thalli was measured by instrumental neutron activation analysis (INAA). In H. physodes, which contained higher amounts of arsenic compared to C. furcata, total glutathione content significantly decreased in samples exposed to 10 microg mL(-1) As(V), whereas in C. furcata a significant increase was observed. In both species PC synthesis was induced in thalli exposed to 10 microg mL(-1).
Biology of Metals 11/2009; 23(2):207-19. · 3.17 Impact Factor
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ABSTRACT: Potted one-year-old plants of Thymus vulgaris L. (thyme, Lamiaceae, C3 metabolism), were grown for three months (10 June–10 September, 2004) in a “mini-free-air-CO2-enrichment” (“mini-FACE”) system, under 500 μmol mol−1 and ambient concentrations of atmospheric carbon dioxide (CO2). Compared to ambient CO2, elevated CO2 stimulated leaf superoxide dismutase (SOD, EC 1.15.1.1) activity only at the first sampling-time (July), followed by no variation or even a trend of decreased activity on the other two sampling-times (August and September). Under high CO2, guaiacol peroxidase (GPX, EC 1.11.1.7) and catalase (CAT, EC 1.11.1.6) leaf activities showed no variation or drop throughout the duration of the experiment. By contrast, under elevated CO2, leaf glutathione reductase (GR, EC 1.6.4.2) activity increased on all the sampling-times, and also a duration-dependent upward trend of glutathione (GSH) content was recorded, with this increase becoming significant – compared with ambient CO2 – at the third sampling-time (September). Simultaneously, leaves from plants grown under high CO2 showed a marked increase in essential oil yield, with slight increments in phenolic component and decrements in mono- and sesquiterpene components. Also, a drop in thiobarbituric acid reactive substances (TBARS) content under elevated CO2 was displayed. Thus, in general, the results reported here point to a downregulation of leaf antioxidant enzymes under elevated CO2, supporting the notion of reduced reactive oxygen species (ROS) formation under these circumstances. Relying instead on antioxidant-regenerating enzymes, namely GR, fairly high GSH content and essential oils, might be a ‘low cost’ life strategy for growth under elevated CO2, not requiring synthesis/activation of energy-intensive and expensive metabolic processes.
Environmental and Experimental Botany 01/2009; 65(1):99-107. · 2.98 Impact Factor
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ABSTRACT: Durum wheat plants (Triticum durum cv Creso) were grown in the presence of cadmium (0-40 microM) and analysed after 3 and 7 d for their growth, oxidative stress markers, phytochelatins, and enzymes and metabolites of the ascorbate (ASC)-glutathione (GSH) cycle. Cd exposure produced a dose-dependent inhibition of growth in both roots and leaves. Lipid peroxidation, protein oxidation and the decrease in the ascorbate redox state indicate the presence of oxidative stress in the roots, where H2O2 overproduction and phytochelatin synthesis also occurred. The activity of the ASC-GSH cycle enzymes significantly increased in roots. Consistently, a dose-dependent accumulation of Cd was evident in these organs. On the other hand, no oxidative stress symptoms or phytochelatin synthesis occurred in the leaves; where, at least during the time of our analysis, the levels of Cd remained irrelevant. In spite of this, enzymes of the ASC-GSH cycle significantly increased their activity in the leaves. When ASC biosynthesis was enhanced, by feeding plants with its last precursor, L-galactono-gamma-lactone (GL), Cd uptake was not affected. On the other hand, the oxidative stress induced in the roots by the heavy metal was alleviated. GL treatment also inhibited the Cd-dependent phytochelatin biosynthesis. These results suggest that different strategies can successfully cope with heavy metal toxicity. The changes that occurred in the ASC-GSH cycle enzymes of the leaves also suggest that the whole plant improved its antioxidant defense, even in those parts which had not yet been reached by Cd. This precocious increase in the enzymes of the ASC-GSH cycle further highlight the tight regulation and the relevance of this cycle in the defense against heavy metals.
Plant and Cell Physiology 04/2008; 49(3):362-74. · 4.70 Impact Factor
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ABSTRACT: Mechanisms underlying cadmium (Cd) detoxification were compared in two aquatic macrophytes commonly used in phytoremediation, namely Pistia stratiotes L. and Eichhornia crassipes (Mart.) Solms. To simulate Cd pollution in the open environment, plants growing in outdoor artificial lakes were exposed for 21d to either 25 or 100microM Cd, in two consecutive years. Toxicity symptoms were absent or mild in both species. Metal accumulation was much higher in the roots of P. stratiotes, whereas in E. crassipes a comparatively higher fraction was translocated to the leaves. In both species, Cd was neither included in phenolic polymers or Ca-oxalate crystals, nor altered the levels of Cd-complexing organic acids. Glutathione levels were constitutively remarkably higher and much more responsive to Cd exposure in P. stratiotes than in E. crassipes. Abundant phytochelatin synthesis occurred only in P. stratiotes, both in roots and in leaves. In E. crassipes, on the other side, the constitutive levels of some antioxidant enzymes and ascorbate were higher and more responsive to Cd than in P. stratiotes. Thus, in these two aquatic plants grown in the open, different detoxification mechanisms might come into play to counterbalance Cd acute stress.
Chemosphere 07/2007; 68(4):769-80. · 3.21 Impact Factor
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ABSTRACT: The mycobiont of lichens usually determines the morphology of the symbiotic organism and is also dominates in terms of biomass. However, its role for sensitivity or tolerance of lichens to heavy metals is almost unknown. In the present study, the influence of copper (Cu) on the aposymbiotically-grown mycobiont of Cladonia cristatella was assessed. Intracellular Cu uptake was correlated with increasing Cu concentrations over a 24-h exposure time. Viability, measured as the degree of reduction of triphenyltetrazolium chloride to triphenyl formazan, as well as to ergosterol levels, decreased with growing Cu concentrations tested. Reduced glutathione (GSH) was found to be the most abundant low-molecular-weight thiol in the hyphae of C. cristatella and its intracellular content increased at concentrations of 10mum Cu. Higher Cu concentrations caused a significant decrease in GSH, possibly due to heavy metal-induced oxidation of GSH to glutathione disulphide (GSSG). Free cysteine levels were relatively constant. As expected, we did not observe the production of phytochelatins in the mycobiont, contrary to what is found in intact lichens and axenic cultures of their photobionts.
Mycological Research 09/2006; 110(Pt 8):994-9. · 2.81 Impact Factor
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ABSTRACT: A wild-type and a Cr-tolerant strain of the unicellular green alga Scenedesmus acutus were used to investigate if the difference in tolerance to Cr(VI) could depend on a different response to oxidative stress in terms of free cysteine (Cys) and reduced glutathione (GSH), and in preventing membrane lipid peroxidation. The growth of the two strains in standard medium in the presence of Cr(VI) 9.6, 19.2 or 38.4microM was compared, and the content of thiobarbituric acid reactive substances (TBARS) after a 4-day treatment was determined as marker of lipid peroxidation. The Cys and GSH contents were determined in both strains treated with Cr(VI) for 24h in HEPES buffer both enriched and not with sulphate. The treated algae were also subjected to recovery test in standard medium. The growth of wild type was inhibited at all Cr(VI) concentrations, while that of the Cr-tolerant strain only at the highest one. After exposure to 19.2microM Cr(VI), TBARS levels ranging from 0.091 to 0.263micromol/g d.w. were detected in the wild type, while only a slight increase (0.090+/-0.014micromol/g d.w.) was observed in the Cr-tolerant strain. Following treatment with 38.4microM Cr(VI), TBARS levels rose significantly and were similar in the two strains. The Cys content did not vary significantly in the cells exposed to Cr(VI) in either sulphate-lacking or sulphate-enriched buffer, and the differences between the two strains were insignificant. In the wild-type strain, the GSH content showed a significant downward trend with the increase in Cr(VI) concentration in the sulphate-lacking buffer, while it remained as high as the one of control cells in the sulphate-enriched buffer. In the Cr-tolerant strain, the GSH content did not vary significantly when the treatment took place in the sulphate-lacking buffer, while it showed a significant rise with the increase in Cr(VI) concentration in the sulphate-enriched buffer. The growth of both strains during recovery was significantly faster after treatment in the sulphate-enriched than in the sulphate-lacking buffer, the Cr-tolerant strain showing a much higher recovery capacity than the wild type. It appears that the Cr-tolerant strain, when exposed to Cr(VI) in the presence of a sulphur source, can increase GSH pool to levels not achievable by the wild type, and is thus able to recover better. This first report on the role of thiol compounds in Cr tolerance in algae suggests that tolerance to Cr(VI) in S. acutus could depend on a prompt up-regulation of the pathways leading to GSH synthesis.
Aquatic Toxicology 09/2006; 79(2):132-9. · 3.76 Impact Factor
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ABSTRACT: In this work, we tried to go deeper inside distribution and toxicity of cadmium (Cd) in the macrolichen Xanthoria parietina (L.) Th. Fr. Thalli of this species were treated with 0 (control), 4.5, 9, 18, or 36 muM Cd for 24 or 48 hours. Transmission electron microscopy, X-ray microanalysis, and electron energy loss spectroscopy were exploited to study distribution and ultrastructural effects of Cd in thalli; spectrophotometric techniques were utilized for measuring Cd effects on chlorophyll (Chl) content; light fluorescence microscopy was used to evaluate Chl autofluorescence. The highest Cd concentration caused ultrastructural alterations both in the mycobiont and in the photobiont, more severe in the latter, decreased total Chl content and progressively quenched Chl autofluorescence. Cell wall immobilization was observed in both bionts, and evidence pointing to a Cd-binding ability by the concentric bodies in the mycobiont was also obtained. Lower Cd concentrations led to slight or even no effects on thallus structures and on Chl content and autofluorescence. The results obtained suggest that: (1) among the two bionts, the algal partner appears to be more susceptible to Cd stress, probably because of the presence of delicate and sensitive components such as the chloroplast and photosynthetic pigments; (2) a concentration threshold exists for the occurrence of evident structural and functional damage in X. parietina thalli exposed to Cd.
Microscopy Research and Technique 05/2005; 66(5):229-38. · 1.79 Impact Factor
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ABSTRACT: Hydrogen peroxide (H2O2) localization and roles of peroxidases, malondialdehyde and reduced glutathione were compared in leaves of apricot (Prunus armeniaca) plants asymptomatic, European Stone Fruits Yellows (ESFY)-symptomatic and recovered. Nested PCR analysis revealed that Candidatus Phytoplasma prunorum, is present in asymptomatic, symptomatic and recovered apricot trees, confirming previous observations on this species, in which recovery does not seem to be related to the disappearance of phytoplasma from the plant.H2O2was detected cytochemically by its reaction with cerium chloride, which produces electron-dense deposits of cerium perhydroxides. H2O2was present in the plasmalemma of the phloem cells of recovered apricot plant leaves, but not in the asymptomatic or symptomatic material. Furthermore, by labelling apricot leaf tissues with diaminobenzidine DAB, no differences were found in the localization of peroxidases.Protein content in asymptomatic, symptomatic and recovered leaves was not significantly different from one another. In contrast, guaiacol peroxidase activity had the following trend: symptomatic > recovered > asymptomatic, whereas reduced glutathione content followed the opposite trend: asymptomatic > recovered > symptomatic. Moreover, no differences were observed in malondialdehyde concentrations between asymptomatic, symptomatic and recovered leaves. The overall results suggest that H2O2 and related metabolites and enzymes appear to be involved in lessening both pathogen virulence and disease symptom expression in ESFY-infected apricot plants.
European Journal of Plant Pathology 04/2005; 112(1):53-61. · 1.41 Impact Factor
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ABSTRACT: In this work, we first investigated if the bread wheat (Triticum aestivum L.) cv. Albimonte can be defined as "shoot cadmium excluder"--by comparing the cadmium (Cd) content in leaves and roots and by calculating the shoot-to-root Cd concentration ratio. Furthermore, we evaluated if the exposure to Cd excess could generate oxidative stress in leaves and roots of this cv., in terms of hydrogen peroxide (H(2)O(2)) accumulation, NAD(P)H oxidation rate, and variations in reduced glutathione (GSH) content and peroxidase (POD, EC 1.11.1.7) activity. Finally, we surveyed possible quali- quantitative differences in thiol-peptide compound pattern between roots and leaves, in order to verify whether phytochelatins (PCs) and related thiol-peptides could contribute in limiting the Cd-induced oxidative stress. Unambiguous characterisation of PCs and related forms present in the root samples was obtained by electrospray ionisation mass spectrometry (ESI-MS) and ESI-tandem MS (ESI-MS/MS). Our results indicate that in leaves the stress generated by the low accumulation of Cd (due to a moderate translocation in planta) seems to be counteracted by the antioxidant response and by the PC biosynthesis. On the contrary, in roots, in spite of the elevated presence of PCs and related thiol-peptide-compounds, the excess of Cd causes a decline in the antioxidant protection of the organ, with the consequent generation of considerable amounts of H(2)O(2), a direct agent of oxidative stress.
Plant Physiology and Biochemistry 02/2005; 43(1):45-54. · 2.84 Impact Factor
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ABSTRACT: Two strains of the unicellular green alga Scenedesmus acutus with different sensitivity to hexavalent chromium were compared for their tolerance of cadmium, by means of growth and recovery tests, and determination of cysteine, reduced glutathione and phytochelatin content, after short-term exposure to various cadmium concentrations (from 1.125 to 27 microM). Growth experiments showed that, after 7-day treatments with cadmium, the chromium-tolerant strain reached a significantly higher cell density and, after 24-h exposure to Cd, was able to resume growth significantly better than the wild type. Constitutive level of cysteine was higher in the chromium-tolerant strain, while glutathione levels were similar in the two strains. The higher content of cysteine and the maintenance of both reduced glutathione and phytochelatin high levels in the presence of cadmium, support the higher cadmium co-tolerance of the chromium-tolerant strain in comparison with the wild type one.
Aquatic Toxicology 08/2004; 68(4):315-23. · 3.76 Impact Factor
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New Phytologist 09/2002; 156(1):95 - 102. · 6.64 Impact Factor
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ABSTRACT: Cuscuta sp., known with the common name of “dodder”, is an obligate parasite capable of invading stems and leaves of a wide range of host plants. Dodder stem usually coils counterclockwise around the host and, within a few days, develops haustorial structures at each point of contact. As soon as dodder haustoria reach host vascular bundles, they start tapping water, photosynthates and minerals. Metal ions such as zinc (Zn) and copper (Cu) are essential for dodder growth and metabolism, although an exceedingly high (over-homeostatic) supply of these micronutrients can result in growth inhibition and cellular toxicity. Even more so, non-essential metals such as cadmium (Cd), if transferred from the host to the parasite, need to be neutralized by timely detoxification mechanisms. In this work, we showed that Cuscuta campestris Yuncker establishes effective haustorial connections with leaf petioles and blades of Daucus carota L. (carrot), with the consequent transfer of Cd and essential metals (such as Zn and Cu) from the host vascular bundles to the parasite. Following up to this point, we detected the presence in the parasite of significant amounts of glutathione and phytochelatins, even in the absence of Cd exposure. This suggests that thiol peptides in dodder might be particularly important for Zn and Cu homeostasis as well as for Cd detoxification. Finally, we demonstrated that dodder is capable of synthesizing phytochelatins on its own, rather than massively importing them from the host, and also provided evidence for the existence of an endogenous, constitutively expressed, dodder's phytochelatin synthase.
Environmental and Experimental Botany 72(1):26-33. · 2.98 Impact Factor
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ABSTRACT: Two bread wheat (Triticum aestivum L.) cultivars (Albimonte, traditional cultivar very important in Italy since long time; and Manital, more recent, evincing better productive performances) were grown for 10 d in presence of 0.7 (control), 70 or 350 μM ZnSO4, to verify whether Zn excess was differently managed at inter-varietal and at inter-organ level. Roots were found to be the main site of Zn accumulation, although a moderate metal translocation to leaves occurred in both cultivars. Despite only slight differences in internal Zn concentrations between cultivars, Albimonte seemed to be more sensitive to Zn excess in terms of growth reduction and H2O2 accumulation, suggesting that the diversities in responses to Zn stress should be ascribed here to inter-varietal metabolic differences. In both cultivars, increased NAD(P)H oxidation rate by pH-dependent peroxidases, and reduced detoxification activity by catalase and peroxidases, were responsible for Zn-induced H2O2 accumulation, while total superoxide dismutase content and activity seemed in general to not change or even depress. Moreover, differences in the content of thiol-peptide compounds (glutathione and phytochelatins) were detected, suggesting indeed the setting up of differential response mechanisms to Zn excess at an inter-varietal and inter-organ level.
Environmental and Experimental Botany.
