Lipid content and fatty acid consumption in zoospores/developing gametophytes of Saccharina latissima (Laminariales, Phaeophyceae) as potential precursors for secondary metabolites as phlorotannins
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Phlorotannins are considered inter alia to act protective to a variety of stressors, while lipids in spores are known to fuel various metabolic processes during spore release and settlement. Here, phlorotannin production in zoospores/juvenile gametophytes in relation to lipid metabolism was investigated for the first time in order to study-related metabolic costs. The experiment was carried out in Ny-Ålesund (Svalbard, Arctic) within the development from spores to juvenile gametophytes of the brown alga Saccharina latissima over 20 days. In the release stage, the total phlorotannin content of single zoospores was 1.5 × 10−7 μg and 1.9 × 10−7 μg in the surrounding medium. Upon release, the total amount of lipids was 1.76 × 10−5 μg lipid zoospore−1 containing the major fatty acids 16:0 and 18:0, 18:1(n-9), 18:2 (n-6), 18:3(n-3), 20:4(n-6), and 20:5(n-3). During development from spores to gametophytes, a decrease in fatty acids was observed via electron microscopy and a decrease in the fatty acid 18:1(n-9) from 45 to 30% was measured by gas chromatography in particular. While phlorotannin content within the spores remained stable, phlorotannins accumulated in the surrounding medium of gametophytes to 4.0 × 10−7 μg phlorotannins spore−1 indicating exudation processes. Results obtained support the key and multifunctional role of lipids in zoospore/gametophyte metabolism and may indicate that gametophytes of S. latissima need approximately 10 days to switch to photo-autotrophic strategies, becoming independent of storage lipids. In addition, fatty acids might represent an essential energy source to fuel adaptive responses.
KeywordsMacroalgae Fatty acid Phlorotannin Zoospore Gametophyte Ultrastructure
The authors would like to express their gratitude to the two anonymous reviewers who helped to improve the manuscript substantially. We thank Max Schwanitz and the AWI diving group for collecting algae in Kongsfjorden, Dr. Riitta Koivikko for kind advice regarding phlorotannin extraction, Dr. Michael Y. Roleda and Sandra Heinrich for laboratory support and Dr. Bánk Beszteri for statistical help. This study was supported by the Bremen International Graduate School for Marine Sciences (GLOMAR) that is funded by the German Research Foundation (DFG) within the frame of the Excellence Initiative by the German federal and state governments to promote science and research at German universities, the Alfred-Wegener- Institute for Polar- and Marine Research, the University of Bremen, and the University of Gothenburg.
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