Nitric oxide generation in Vicia faba phloem cells reveals them to be sensitive detectors as well as possible systemic transducers of stress signals

Authors

  • Frank Gaupels,

    1. Institute of Phytopathology and Applied Zoology, IFZ, Heinrich-Buff-Ring 26-32, D-35392 Gießen and
    2. Plant Cell Biology Research Group, Institute of General Botany, Senckenbergstrasse 17, D-35390 Gießen, Justus-Liebig-University, Gießen, Germany;
    3. Dipartimento Scientifico e Tecnologico, Università degli Studi di Verona, Strada le Grazie 15, I-37134 Verona, Italy
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  • Alexandra C. U. Furch,

    1. Plant Cell Biology Research Group, Institute of General Botany, Senckenbergstrasse 17, D-35390 Gießen, Justus-Liebig-University, Gießen, Germany;
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  • Torsten Will,

    1. Plant Cell Biology Research Group, Institute of General Botany, Senckenbergstrasse 17, D-35390 Gießen, Justus-Liebig-University, Gießen, Germany;
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  • Luis A. J. Mur,

    1. Institute of Biological Sciences, University of Wales Aberystwyth, Aberystwyth, Ceredigion SY23 2DA, UK;
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  • Karl-Heinz Kogel,

    1. Institute of Phytopathology and Applied Zoology, IFZ, Heinrich-Buff-Ring 26-32, D-35392 Gießen and
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  • Aart J. E. Van Bel

    1. Plant Cell Biology Research Group, Institute of General Botany, Senckenbergstrasse 17, D-35390 Gießen, Justus-Liebig-University, Gießen, Germany;
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Author for correspondence:
Frank Gaupels
Tel: +39 045 802 7063
Fax: +39 045 802 7929
Email: gaupels@sci.univr.it

Summary

  • • Vascular tissue was recently shown to be capable of producing nitric oxide (NO), but the production sites and sources were not precisely determined. Here, NO synthesis was analysed in the phloem of Vicia faba in response to stress- and pathogen defence-related compounds.
  • • The chemical stimuli were added to shallow paradermal cortical cuts in the main veins of leaves attached to intact plants. NO production in the bare-lying phloem area was visualized by real-time confocal laser scanning microscopy using the NO-specific fluorochrome 4,5-diaminofluorescein diacetate (DAF-2 DA).
  • • Abundant NO generation in companion cells was induced by 500 µm salicylic acid (SA) and 10 µm hydrogen peroxide (H2O2), but the fungal elicitor chitooctaose was much less effective. Phloem NO production was found to be dependent on Ca2+ and mitochondrial electron transport and pharmacological approaches found evidence for activity of a plant NO synthase but not a nitrate reductase. DAF fluorescence increased most strongly in companion cells and was occasionally observed in phloem parenchyma cells. Significantly, accumulation of NO in sieve elements could be demonstrated.
  • • These findings suggest that the phloem perceives and produces stress-related signals and that one mechanism of distal signalling involves the production and transport of NO in the phloem.

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