Effects of nanomolar heavy metal concentrations on water plants-comparison of biochemical & biophysical mechanisms of defiency

Beschreibung

Dieses Projekt wird biochemisch-biophysikalische Mechanismen der Wachstumshemmung unter Mangel und subletaler Toxizität von Kupfer, Cadmium und Chrom unter umweltrelevanten Bedingungen an Wasserpflanzen untersuchen. Vor allem soll geklärt werden, in welcher Reihenfolge, in welchem kausalen Zusammenhang, in welchem Schwermetall-Konzentrationsbereich und bei welchen Rahmenbedingungen (z.B. Lichtintensität) in früheren Studien untersuchte Schädigungsmechanismen auftreten. Dies betrifft insbesondere den viel diskutierten oxidativen Stress mit Folgeerscheinungen wie Oxidation von Proteinen und Membranschädigung im Vergleich zur Hemmung der photosynthetischen Lichtreaktionen und des Calvin-Zyklus, und im Vergleich zur ebenfalls viel diskutierten Genotoxizität. Eine Untersuchung der Zeitabfolgen, Konzentrationsabhängigkeiten und kausalen Zusammenhänge ist hier besonders wichtig, da die genannnten Mechanismen im Prinzip einander stark beeinflussen können. So kann z.B. eine schlechtere Nutzung von Excitonen für die Photosynthese zu einer verstärkten Bildung von reaktiven Sauerstoffspezies führen. Umgekehrt könnte eine Hemmung der Photosynthese auch als Folge einer oxidativen Schädigung der Thylakoidmembranen und der an der Photosynthese beteiligten Proteine auftreten. Hierbei ist auch der Vergleich des redox-inerten Cadmiums mit den redox-aktiven Metallen Chrom und Kupfer besonders interessant. Außerdem kommt ein Vergleich der als genotoxisch bekannten Metalle Cadmium und Chrom mit dem als wenig bis nicht genotoxisch angesehenen Kupfer hinzu. Die Laboruntersuchungen werden kombiniert mit Untersuchungen an schwermetallbelasteten Gewässern in Sachsen.

Institutionen
  • FB Biologie
Publikationen
  Mishra, Seema; Wellenreuther, Gerd; Mattusch, Jürgen; Stärk, Hans-Joachim; Küpper, Hendrik(2013): Speciation and distribution of arsenic in the non-hyperaccumulator macrophyte Ceratophyllum demersum L. PLANT PHYSIOLOGY ; 163 (2013), 3. - S. 1396-1408. - ISSN 0032-0889. - eISSN 1532-2548

Speciation and distribution of arsenic in the non-hyperaccumulator macrophyte Ceratophyllum demersum L.

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Although arsenic is a common pollutant worldwide, many questions about As metabolism in non-hyperaccumulator plants remain. Concentration and tissue dependent speciation and distribution of arsenic was analysed in the aquatic plant Ceratophyllum demersum to understand arsenic metabolism in non-hyperaccumulator plants. Speciation was analysed chromatographically (HPLC-(ICP-MS)-(ESI-MS)) in whole-plant extracts and by tissue-resolution confocal X-ray absorption spectroscopy (µ XANES) in intact shock-frozen hydrated leaves, which were also used for analysing cellular element distribution through X-ray fluorescence (µ XRF). Chromatography revealed up to 20 As-containing species binding >60% of accumulated As. Of these, eight were identified as thiol-bound (phytochelatins; PCs, glutathione; GSH and cystein) species including three newly identified complexes: Cys-As(III)-PC2, Cys-As-(GS)2 and GS-As(III)-desgly-PC2 complex. Confocal µ XANES showed As(V), As(III), As-(GS)3 and As-PCs with varying ratios in various tissues. The epidermis of mature leaves contained the highest proportion of thiol- (mostly PC-) bound As, while in younger leaves a lower proportion of As was thiol-bound. At higher As concentrations, the percentage of unbound As(III) increased in the vein and mesophyll of young mature leaves. At the same time, µ XRF showed an increase of total As in the vein and mesophyll but not in the epidermis of young mature leaves while it was reverse for Zn distribution. Thus, As toxicity was correlated with a change in As distribution pattern and As species, rather than general increase in many tissues.

Forschungszusammenhang (Projekte)

  Andresen, Elisa; Opitz, Daniela; Thomas, George; Stärk, Hans-Joachim; Dienemann, Holger; Jenemann, Kerstin; Dickinson, Bryan C.; Küpper, Hendrik(2013): Effects of Cd & Ni toxicity to Ceratophyllum demersum under environmentally relevant conditions in soft & hard water including a German lake Aquatic Toxicology ; 142-143 (2013). - S. 387-402. - ISSN 0166-445X. - eISSN 1879-1514

Effects of Cd & Ni toxicity to Ceratophyllum demersum under environmentally relevant conditions in soft & hard water including a German lake

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Even essential trace elements are phytotoxic over a certain threshold. In this study, we investigated whether heavy metal concentrations were responsible for the nearly complete lack of submerged macrophytes in an oligotrophic lake in Germany. We cultivated the rootless aquatic model plant Ceratophyllum demersum under environmentally relevant conditions like sinusoidal light and temperature cycles and a low plant biomass to water volume ratio. Experiments lasted for six weeks and were analysed by detailed measurements of photosynthetic biophysics, pigment content and hydrogen peroxide production. We established that individually non-toxic cadmium (3 nM) and slightly toxic nickel (300 nM) concentrations became highly toxic when applied together in soft water, severely inhibiting photosynthetic light reactions. Toxicity was further enhanced by phosphate limitation (75 nM) in soft water as present in many freshwater habitats. In the investigated lake, however, high water hardness limited the toxicity of these metal concentrations, thus the inhibition of macrophytic growth in the lake must have additional reasons. The results showed that synergistic heavy metal toxicity may change ecosystems in many more cases than estimated so far.

Forschungszusammenhang (Projekte)

    Andresen, Elisa; Mattusch, Jürgen; Wellenreuther, Gerd; Thomas, George; Abad, Uriel Arroyo; Küpper, Hendrik(2013): Different strategies of cadmium detoxification in the submerged macrophyte Ceratophyllum demersum L. Metallomics ; 5 (2013), 10. - S. 1377-1386. - ISSN 1756-5901. - eISSN 1756-591X

Different strategies of cadmium detoxification in the submerged macrophyte Ceratophyllum demersum L.

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The heavy metal cadmium (Cd) is highly toxic to plants. To understand the mechanisms of tolerance and resistance to Cd, we treated the rootless, submerged macrophyte Ceratophyllum demersum L. with sub-micromolar concentrations of Cd under environmentally relevant conditions. X-ray fluorescence measurements revealed changing distribution patterns of Cd and Zn at non-toxic (0.2 nM, 2 nM), moderately toxic (20 nM) and highly toxic (200 nM) levels of Cd. Increasing Cd concentrations led to enhanced sequestration of Cd into non-photosynthetic tissues like epidermis and vein. At toxic Cd concentrations, Zn was redistributed and mainly found in the vein. Cd treatment induced the synthesis of phytochelatins (PCs) in the plants, with a threshold of induction already at 20 nM Cd for PC3. In comparison, in plants treated with Cu, elevated PC levels were detected only at the highest concentrations (100–200 nM Cu). Our results show that also non-accumulators like C. demersum store toxic metals in tissues where the heavy metal interferes least with metabolic pathways, but remaining toxicity interferes with micronutrient distribution. Furthermore, we found that the induction of phytochelatins is not proportional to metal concentration, but has a distinct threshold, specific for each PC species. Finally we could show that 20 nM Cd, which was previously regarded as non-toxic to most plants, already induces detoxifying mechanisms.

Forschungszusammenhang (Projekte)

Mittelgeber
NameKennzifferBeschreibungLaufzeit
Sachbeihilfe/Normalverfahren487/10keine Angabe
Weitere Informationen
Laufzeit: 01.04.2010 – 31.07.2012