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A novel indirect defence in Brassicaceae: Structure and function of extrafloral nectaries in Brassica juncea

Authors

  • VARTIKA MATHUR,

    Corresponding author
    1. Department of Terrestrial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), PO Box 50, 6700 AB Wageningen, The Netherlands
    2. Department of Zoology, Sri Venkateswara College, Benito Juarez Marg, Dhaula kuan, University of Delhi, Delhi 110021, India
      V. Mathur. Fax: +91 11 24118535; e-mail: vmathur@svc.ac.in; vartika_m@yahoo.com
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  • ROEL WAGENAAR,

    1. Department of Terrestrial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), PO Box 50, 6700 AB Wageningen, The Netherlands
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  • JEAN-CLAUDE CAISSARD,

    1. Université de Lyon, F-42023 Saint-Etienne, France
    2. Université de Saint-Etienne, Jean Monnet, F-42000 Saint-Etienne, France
    3. Laboratoire BVpam, EA2061, 23 rue du Dr Paul Michelon, F-42000 Saint-Etienne, France
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  • A. SANKARA REDDY,

    1. Rai University, Saroda Post, Dholka Taluka, Ahmedabad District, Gujarat 382260, India
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  • LOUISE E. M. VET,

    1. Department of Terrestrial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), PO Box 50, 6700 AB Wageningen, The Netherlands
    2. Laboratory of Entomology, Wageningen University, PO Box 8031, 6700 EH Wageningen, The Netherlands
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  • ANNE-MARIE CORTESERO,

    1. UMR 1349 IGEPP, INRA, Agrocampus Ouest, University of Rennes 1, Campus de Beaulieu, Avenue du Général Leclerc, 35042 Rennes Cedex, France
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  • NICOLE M. VAN DAM

    1. Department of Ecogenomics, Institute for Water and Wetland Research, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
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V. Mathur. Fax: +91 11 24118535; e-mail: vmathur@svc.ac.in; vartika_m@yahoo.com

ABSTRACT

While nectaries are commonly found in flowers, some plants also form extrafloral nectaries on stems or leaves. For the first time in the family Brassicaceae, here we report extrafloral nectaries in Brassica juncea. The extrafloral nectar (EFN) was secreted from previously amorphic sites on stems, flowering stalks and leaf axils from the onset of flowering until silique formation. Transverse sections at the point of nectar secretion revealed a pocket-like structure whose opening was surrounded by modified stomatal guard cells. The EFN droplets were viscous and up to 50% of the total weight was sugars, 97% of which was sucrose in the five varieties of B. juncea examined. Threonine, glutamine, arginine and glutamate were the most abundant amino acids. EFN droplets also contained glucosinolates, mainly gluconapin and sinigrin. Nectar secretion was increased when the plants were damaged by chewing above- and belowground herbivores and sap-sucking aphids. Parasitoids of each herbivore species were tested for their preference, of which three parasitoids preferred EFN and sucrose solutions over water. Moreover, the survival and fecundity of parasitoids were positively affected by feeding on EFN. We conclude that EFN production in B. juncea may contribute to the indirect defence of this plant species.

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