Transgenic, non-isoprene emitting poplars don’t like it hot

Authors

  • Katja Behnke,

    1. Research Centre Karlsruhe, Institute for Meteorology and Climate Research (IMK-IFU), Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany,
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  • Barbara Ehlting,

    1. Michael Smith Laboratories, University of British Columbia, 2185 East Mall, Vancouver, BC, V6T 1Z4, Canada,
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    • Present address: Dr Barbara Ehlting, formerly known as Dr Barbara Miller, Institute for Forest Botany and Tree Physiology, Albert-Ludwigs-University Freiburg, Georges-Koehler-Allee 053/054, 79110 Freiburg, Germany.

  • Markus Teuber,

    1. Research Centre Karlsruhe, Institute for Meteorology and Climate Research (IMK-IFU), Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany,
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  • Martina Bauerfeind,

    1. Research Centre Karlsruhe, Institute for Meteorology and Climate Research (IMK-IFU), Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany,
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  • Sandrine Louis,

    1. Research Centre Karlsruhe, Institute for Meteorology and Climate Research (IMK-IFU), Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany,
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  • Robert Hänsch,

    1. Institute for Plant Biology, Technical University of Braunschweig, Humboldtstr. 1, 38206 Braunschweig, Germany, and
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  • Andrea Polle,

    1. Institute for Forest Botany, Georg-August-University Göttingen, Büsgenweg 2, 37077 Göttingen, Germany
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  • Jörg Bohlmann,

    1. Michael Smith Laboratories, University of British Columbia, 2185 East Mall, Vancouver, BC, V6T 1Z4, Canada,
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  • Jörg-Peter Schnitzler

    Corresponding author
    1. Research Centre Karlsruhe, Institute for Meteorology and Climate Research (IMK-IFU), Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany,
      (fax +49 8821 73573; email joerg-peter.schnitzler@imk.fzk.de).
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  • This paper is dedicated to the memory of Wolfgang Zimmer † 14 August 2002.

(fax +49 8821 73573; email joerg-peter.schnitzler@imk.fzk.de).

Summary

The physiological role of isoprene emission in plants is a matter of much debate. One of the most widely propagated hypotheses suggests a function of isoprene in the protection of leaf physiological processes against thermal and oxidative stress. To test this hypothesis, we developed transgenic Grey poplar (Populus×canescens) plants in which gene expression of isoprene synthase (ISPS) was either silenced by RNA interference (RNAi) or upregulated by over-expression of the ISPS gene. Despite increased ISPS mRNA levels, we did not observe consistent increases in isoprene emission in the over-expressing lines, indicating post-transcriptional control of ISPS by co-suppression. In the RNAi lines, levels of isoprene emission were effectively suppressed to virtually zero. Transgenic plants were subjected to temperature stress with three transient heat phases of 38–40°C, each followed by phases of recovery at 30°C. Parallel measurements of gas exchange, chlorophyll fluorescence and isoprene emission provided new insights into the physiological link between isoprene and enhanced temperature tolerance. Transgenic non-isoprene-emitting poplars showed reduced rates of net assimilation and photosynthetic electron transport during heat stress, but not in the absence of stress. The decrease in the efficiency of photochemistry was inversely correlated with the increase in heat dissipation of absorbed light energy, measured as NPQ (non-photochemical quenching). Isoprene-repressed poplars also displayed an increased formation of the xanthophyll cycle pigment zeaxanthin in the absence of stress, which can cause increased NPQ or may indicate an increased requirement for antioxidants. In conclusion, using a molecular genetic approach, we show that down-regulation of isoprene emission affects thermotolerance of photosynthesis and induces increased energy dissipation by NPQ pathways.

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