Extracellular superoxide production, viability and redox poise in response to desiccation in recalcitrant Castanea sativa seeds

Authors

  • THOMAS ROACH,

    1. Seed Conservation Department, Royal Botanic Gardens Kew, Wakehurst Place, Ardingly, West Sussex RH17 6TN, UK,
    2. Research Department of Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK,
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  • RICHARD P. BECKETT,

    1. School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01, Pietermaritzburg, Scottsville 3209, Republic of South Africa,
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  • FARIDA V. MINIBAYEVA,

    1. Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, P.O. Box 30, Kazan 420111, Russian Federation,
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  • LOUISE COLVILLE,

    1. Seed Conservation Department, Royal Botanic Gardens Kew, Wakehurst Place, Ardingly, West Sussex RH17 6TN, UK,
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  • CLAIRE WHITAKER,

    1. School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01, Pietermaritzburg, Scottsville 3209, Republic of South Africa,
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  • HONGYING CHEN,

    1. Seed Conservation Department, Royal Botanic Gardens Kew, Wakehurst Place, Ardingly, West Sussex RH17 6TN, UK,
    2. Chinese Academy of Sciences, Kunming Institute of Botany, Kunming 661100, People's Republic of China and
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  • CHRISTOPHE BAILLY,

    1. UPMC University of Paris 06, EA2388, Physiologie des semences, Site d'Ivry, Boîte courrier 152, 4 place Jussieu, F-75005 Paris, France
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  • ILSE KRANNER

    Corresponding author
    1. Seed Conservation Department, Royal Botanic Gardens Kew, Wakehurst Place, Ardingly, West Sussex RH17 6TN, UK,
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I. Kranner. Fax: +44 1 1444 894110; e-mail: i.kranner@kew.org

ABSTRACT

Reactive oxygen species (ROS) are implicated in seed death following dehydration in desiccation-intolerant ‘recalcitrant’ seeds. However, it is unknown if and how ROS are produced in the apoplast and if they play a role in stress signalling during desiccation. We studied intracellular damage and extracellular superoxide (O2·−) production upon desiccation in Castanea sativa seeds, mechanisms of O2·− production and the effect of exogenously supplied ROS. A transient increase in extracellular O2·− production by the embryonic axes preceded significant desiccation-induced viability loss. Thereafter, progressively more oxidizing intracellular conditions, as indicated by a significant shift in glutathione half-cell reduction potential, accompanied cell and axis death, coinciding with the disruption of nuclear membranes. Most hydrogen peroxide (H2O2)-dependent O2·− production was found in a cell wall fraction that contained extracellular peroxidases (ECPOX) with molecular masses of ∼50 kDa. Cinnamic acid was identified as a potential reductant required for ECPOX-mediated O2·− production. H2O2, applied exogenously to mimic the transient ROS burst at the onset of desiccation, counteracted viability loss of sub-lethally desiccation-stressed seeds and of excised embryonic axes grown in tissue culture. Hence, extracellular ROS produced by embryonic axes appear to be important signalling components involved in wound response, regeneration and growth.

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