Neutral lipids in macroalgal spores and their role in swimming |
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Authors: | D C Reed M A Brzezinski D A Coury W M Graham R L Petty |
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Institution: | (1) Marine Science Institute, University of California at Santa Barbara, Santa Barbara, California 93106, USA Fax: 001 (0) 805 893-3376 e-mail: reed@lifesci.ucsb.edu, US;(2) Department of Ecology, Evolution and Marine Biology, University of California at Santa Barbara, Santa Barbara, California 93106, USA, US;(3) Marine Environmental Sciences Consortium, Dauphin Island Sea Laboratory, 101 Bienville Boulevarde, Dauphin Island, Alabama 36528, USA, IS |
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Abstract: | We followed changes in the neutral lipid content of actively swimming zoospores of the palm kelp Pterygophora californica in a laboratory experiment to investigate the degree to which spore swimming is fueled by endogenous lipid reserves. The
neutral lipid content of individual zoospores during the experiment was measured by flow cytometry using Nile Red, a fluorescent
stain that is specific for neutral lipid. Results showed that photosynthesis greatly influenced lipid consumption during zoospore
swimming. We found no detectable change in the neutral lipid content of zoospores after 30 h of swimming under conditions
where light was near the optimum for photosynthesis. By contrast, neutral lipid declined by ≃43% over 30 h in zoospores kept
in the dark. To evaluate whether lipid reserves are generally related to spore motility in macroalgae, we surveyed spore lipid-content
and composition in species with motile spores and non-motile spores using thin-layer chromatography (TLC), and flame-ionization
detection (FID). We observed substantial differences in lipid content and composition among the 20 species examined. Spores
high in total lipid (as estimated by the ratio of lipid:carbon) generally had a large amount of neutral lipid; motile spores
had significantly more lipid and a significantly larger neutral lipid fraction than non-motile spores. The kelps as a group
had the highest total lipid content and the largest neutral lipid fraction, while non-motile spores of red algae were generally
low in total lipid and in the proportional abundance of neutral lipid. Phospholipids accounted for more than half of all lipid
in 14 of the 20 species examined, while neutral lipid accounted for the majority of lipid in all five species of kelp examined.
Triacylglycerols, which function primarily in energy storage, were the primary form of neutral lipid in all but one species
of kelp (Agarum fimbriatum), whereas free fatty acids were the dominant form of neutral lipid in most red algae and in brown algae that had a small
neutral lipid fraction. Our results are largely consistent with the hypothesis that macroalgae use endogenous lipid reserves
to fuel spore-swimming. The small amounts of triacylglycerols observed in the motile spores of several species of brown and
green algae, however, indicate that the amount of lipid reserves needed to fuel spore-swimming may be influenced by a variety
of factors including swimming behavior, photosynthetic efficiency, and the light environment inhabited by spores.
Received: 8 September 1998 / Accepted: 8 January 1999 |
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