Cadmium-induced inhibition of photosynthesis and long-term acclimation to cadmium stress in the hyperaccumulator Thlaspi caerulescens

Authors

  • Hendrik Küpper,

    1. Universität Konstanz, Mathematisch-Naturwissenschaftliche Sektion, Fachbereich Biologie, D-78457 Konstanz, Germany;
    2. Faculty of Biological Sciences and Institute of Physical Biology, University of South Bohemia, Branišovská 31, CZ-370 05 České Budejovice, Čzech Republic;
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  • Aravind Parameswaran,

    1. Universität Konstanz, Mathematisch-Naturwissenschaftliche Sektion, Fachbereich Biologie, D-78457 Konstanz, Germany;
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  • Barbara Leitenmaier,

    1. Universität Konstanz, Mathematisch-Naturwissenschaftliche Sektion, Fachbereich Biologie, D-78457 Konstanz, Germany;
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  • Martin Trtílek,

    1. Photon Systems Instruments Ltd, Koláčkova 31, CZ-62100 Brno, Czech Republic;
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  • Ivan Šetlík

    1. Faculty of Biological Sciences and Institute of Physical Biology, University of South Bohemia, Branišovská 31, CZ-370 05 České Budejovice, Čzech Republic;
    2. Microbiological Institute, ASCR, Department of Autotrophic Microorganisms, Opatovický mlýn, CZ-37981 Třeboň, Czech Republic
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Author for correspondence: Hendrik Küpper Tel: +49 7531884112 Fax: +49 7531884533 Email: Hendrik.Kuepper@uni-konstanz.de

Summary

  • • Acclimation of hyperaccumulators to heavy metal-induced stress is crucial for phytoremediation and was investigated using the hyperaccumulator Thlaspi caerulescens and the nonaccumulators T. fendleri and T. ochroleucum.
  • • Spatially and spectrally resolved kinetics of in vivo absorbance and fluorescence were measured with a novel fluorescence kinetic microscope.
  • • At the beginning of growth on cadmium (Cd), all species suffered from toxicity, but T. caerulescens subsequently recovered completely. During stress, a few mesophyll cells in T. caerulescens became more inhibited and accumulated more Cd than the majority; this heterogeneity disappeared during acclimation. Chlorophyll fluorescence parameters related to photochemistry were more strongly affected by Cd stress than nonphotochemical parameters, and only photochemistry showed acclimation.
  • • Cd acclimation in T. caerulescens shows that part of its Cd tolerance is inducible and involves transient physiological heterogeneity as an emergency defence mechanism. Differential effects of Cd stress on photochemical vs nonphotochemical parameters indicate that Cd inhibits the photosynthetic light reactions more than the Calvin–Benson cycle. Differential spectral distribution of Cd effects on photochemical vs nonphotochemical quenching shows that Cd inhibits at least two different targets in/around photosystem II (PSII). Spectrally homogeneous maximal PSII efficiency (Fv/Fm) suggests that in healthy T. caerulescens all chlorophylls fluorescing at room temperature are PSII-associated.

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