Concurrent imaging of chlorophyll fluorescence, Chlorophyll a content and green fluorescent proteins-like proteins of symbiotic cnidarians

Authors

  • Miguel Costa Leal,

    Corresponding author
    1. Departamento de Biologia & CESAM, Universidade de Aveiro, Campus Universitário de Santiago, Aveiro, Portugal
    2. University of Georgia, Skidaway Institute of Oceanography, Savannah, GA, USA
    • Correspondence

      Miguel Costa Leal, Departamento de Biologia & CESAM, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal.

      E-mail: miguelcleal@gmail.com

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  • Bruno Jesus,

    1. LUNAM université, Université de Nantes, Mer Molécules Santé EA 2160, Faculté des Sciences et des Techniques, Nantes, France
    2. Centro de Biodiversidade, Genómica Integrativa e Funcional (BioFIG), Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
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  • João Ezequiel,

    1. Departamento de Biologia & CESAM, Universidade de Aveiro, Campus Universitário de Santiago, Aveiro, Portugal
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  • Ricardo Calado,

    1. Departamento de Biologia & CESAM, Universidade de Aveiro, Campus Universitário de Santiago, Aveiro, Portugal
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  • Rui Jorge Miranda Rocha,

    1. Departamento de Biologia & CESAM, Universidade de Aveiro, Campus Universitário de Santiago, Aveiro, Portugal
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  • Paulo Cartaxana,

    1. Centro de Oceanografia, Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
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  • João Serôdio

    1. Departamento de Biologia & CESAM, Universidade de Aveiro, Campus Universitário de Santiago, Aveiro, Portugal
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Abstract

Research on photosynthetic cnidarians has been mainly focused on the symbiosis established between the cnidarian host and its dinoflagellates endosymbionts from genus Symbiodinium. Despite the potential of imaging techniques for assessing the spatial distribution of key parameters of cnidarian photobiology, such as photochemical activity, chlorophyll a content or green fluorescent proteins (GFPs), to our best knowledge, no study has ever attempted to simultaneous map these three features. In this study, we developed a modified imaging pulse amplitude fluorometer by applying excitation light of different wavelengths and selectively detecting short spectral bands through bandpass filters. The imaging system was used to sequentially excite and quantify chlorophyll variable fluorescence (maximum quantum yield of photosystem II, Fv/Fm), Chl a content (normalized difference vegetation index) and relative content of GFPs. The spatial distribution of these photophysiological parameters was mapped both horizontally, across the surface of the soft corals Sarcophyton cf. glaucum and Sinularia flexibilis and the zoanthid Protopalythoa sp., and vertically, throughout a vertical section of S. cf. glaucum. Results showed bleached areas within each individual coral colony and registered photophysiological changes with S. cf. glaucum tissue depth. Analysis of Protopalythoa sp. polyps’ expansion revealed differential surface patterns of NDVI and GFP concentration, and a negative relation between these latter parameters within each polyp. This novel non-invasive approach allowed a high-resolution characterization of the spatial relationship between these key parameters through the analysis of image information on a pixel-by-pixel basis, which has great potential for investigating the physiological state of symbiotic associations.

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