Abstract
Nitric oxide (NO) and reactive oxygen species (ROS) production was investigated in the marine diatom, Skeletonema marinoi (SM), exposed to 2E,4E/Z-decadienal (DECA), 2E,4E/Z-octadienal (OCTA), 2E,4E/Z-heptadienal (HEPTA) and a mix of these last two (MIX). When exposed to polyunsaturated aldehydes (PUA), a decrease of NO was observed, proportional to the PUA concentration (85% of the initial level after 180 min with 66 µM DECA). Only OCTA, HEPTA and MIX induced a parallel increase of ROS, the highest (2.9-times the control) with OCTA concentrations twice the EC50 for growth at 24 h (20 μM). The synthesis of carotenoids belonging to the xanthophyll cycle (XC) was enhanced during exposure, suggesting their antioxidant activity. Our data provide evidence that specific pathways exist as a reaction to PUA and that they depend upon the PUA used and/or the diatom species. In fact, Phaeodactylum tricornutum (PT) produces NO in response to DECA, but not to OCTA. We advance the hypothesis that SM perceives OCTA and HEPTA as intra-population infochemicals (as it produces PUA), while PT (non-PUA producing species) perceives them as allelochemicals. The ability to produce and to use PUA as infochemicals may underlie ecological traits of different diatom species and modulate ecological success in natural communities.
Highlights
Marine diatoms are one of the most successful groups of eukaryotic photosynthetic organisms onEarth and are major players in global marine primary production by representing most of the organic carbon that is at the base of the marine food web [1]
The general aim of this study is to investigate the responses of the diatom, Skeletonema marinoi (SM), to polyunsaturated aldehydes (PUA) in terms of nitric oxide (NO) and reactive oxygen species (ROS) production, to test the hypothesis that these responses underlie an adaptive advantage leading to ecological success
SM cultures were inoculated with different concentrations of three PUA (2E,4E/Z-decadienal (DECA), 2E,4E/Z-octadienal (OCTA), 2E,4E/Z-heptadienal (HEPTA)) or a 1:1.4 mix of OCTA and HEPTA (MIX)
Summary
Marine diatoms are one of the most successful groups of eukaryotic photosynthetic organisms onEarth and are major players in global marine primary production by representing most of the organic carbon that is at the base of the marine food web [1]. PUA, together with a plethora of other different metabolites derived from the same biosynthetic pathway, all belonging to oxylipins, play key roles in chemically-mediated plankton interactions (for a review, see [3]). Since their first identification in marine diatoms [4], PUA have been demonstrated to have negative effects on copepod development and reproduction, as well as on other marine invertebrates [5,6,7,8]. Phaeodactylum tricornutum, this stress-surveillance system induces the production of nitric oxide (NO) and a transient rise in intracellular Ca2+ that later activates a gene cascade involved in programmed cell death [13,14]
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