Zoospores of Three Arctic Laminariales Under Different UV Radiation and Temperature Conditions: Exceptional Spectral Absorbance Properties and Lack of Phlorotannin Induction

Authors

  • Ruth Müller,

    Corresponding author
    1. Section Seaweed Biology, Alfred Wegener Institute for Marine and Polar Research, Bremerhaven, Germany
    2. Department Marine Botany, University Bremen, and Centre for Tropical Marine Ecology, Leobener Straße, Bremen, Germany
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  • Christian Wiencke,

    1. Section Seaweed Biology, Alfred Wegener Institute for Marine and Polar Research, Bremerhaven, Germany
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  • Kai Bischof,

    1. Department Marine Botany, University Bremen, and Centre for Tropical Marine Ecology, Leobener Straße, Bremen, Germany
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  • Bernd Krock

    1. Section Ecological Chemistry, Alfred Wegener Institute for Marine and Polar Research, Bremerhaven, Germany
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*Corresponding author email: ruth.mueller@awi.de (R. Müller)

Abstract

Phlorotannins have often been considered to act as UV-protective compounds in zoospores of brown algae. However, only the absorption characteristics of zoospores under UV exposure have been determined and no data are available on the actual content of phlorotannins or on temperature–UV interactions. Therefore, we determined the absorbance spectra and the phlorotannin contents in zoospore suspensions of three Arctic species (Saccharina latissima, Laminaria digitata, Alaria esculenta), and in the media surrounding zoospores after exposure to different radiation (400–700, 320–700, 295–700 nm) and temperature (2–18°C) conditions for 8 h. Absorption typical of phlorotannins with a maximum at 276 nm was monitored in zoospore suspensions as well as in the media surrounding zoospores, but the results depended strongly on radiation treatments and on zoospore densities. Surprisingly, the content of UV-absorbing phlorotannins subsequent to different exposures did not change in any of the three species. The observed exceptional absorption properties could, therefore, not be related to phlorotannin contents. These findings are discussed in light of a strong phlorotannin investment from sporophytes during spore release and a minor UV-protective role of phlorotannins for zoospores of Arctic kelp species.

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