Abstract
Polyunsaturated aldehydes (PUA) are supposed to play critical roles in chemically-mediated plankton interactions. Laboratory studies suggest that they act as mediators of chemical defense and chemical communication. PUA are oxylipins containing an α,β,γ,δ–unsaturated aldehyde structure element and are mainly found in diatoms. We present here a detailed surface mapping of PUA during a spring bloom of the diatom Skeletonema marinoi in the Adriatic Sea. We monitored dissolved PUA, as well as particulate PUA, which are produced by phytoplankton after cell disintegration. Our survey revealed a patchy distribution of PUA and shows that at most stations S. marinoi is the major contributor to the overall PUA. Our data also suggest that lysis of a diatom bloom can contribute significantly to the dissolved PUA concentrations and that other producers, which are smaller in cell size compared to diatoms, have to be taken into account as well if the total PUA content of marine samples is considered. The analyses of samples collected in deeper water suggests that diatom contribution to PUA decreases with depth, while smaller-sized unidentified organisms take place as dominant contributors to the PUA concentrations.
Highlights
Polyunsaturated aldehydes (PUA) from diatoms are fatty-acid-derived secondary metabolites with an -unsaturated aldehyde structure element
A survey of cultured diatom strains reported that roughly a third of marine diatoms are capable of producing PUA [1], and if this holds true for natural conditions, it can be assumed that these compounds are quite common in the ocean, mainly in coastal waters, where diatoms form intense blooms
Diatoms have been considered as the major source for PUA in phytoplankton, but our findings demonstrate that other cells that are well below the typical size of diatoms may at times represent additional sources of PUA and have to be considered
Summary
Polyunsaturated aldehydes (PUA) from diatoms are fatty-acid-derived secondary metabolites with an -unsaturated aldehyde structure element. In accordance with the idea of an induced cell death, Vidoudez and Pohnert reported that nanomolar concentrations of PUA in the medium can accelerate cell death of a diatom culture in the late stationary growth phase [11]. Within seconds after mechanical disruption of diatom cells lipases release polyunsaturated fatty acids from phospho- and galactolipids [13,14] These free fatty acids are transformed by lipoxygenase/lyase enzyme activities into PUA [15,16]. Late-stationary cultures of the diatom Skeletonema marinoi release PUA into the medium without concomitant grazing or cell lysis [11]. This supports their role as intra-population signaling molecules. We monitored the PUA which were produced after mechanical disruption of the cells (hereafter particulate PUA) as well as PUA that were present in the water (dissolved PUA)
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