Prevalence and mechanism of polyunsaturated aldehydes production in the green tide forming macroalgal genus Ulva (Ulvales, Chlorophyta)

• The production of polyunsaturated aldehydes (PUAs) by the green tide forming algae Ulva (Ria Formosa, Portugal) was surveyed.
• Lipoxygenase mediated pathways catalyze the release of 2,4-decadienal and 2,4,7-decatrienal derived from PUFAs.
• Only Ulva species with a blade-like morphotype produce PUAs indicating a chemotaxonomic relationship.
• Pilot experiments were conducted to elucidate the biosynthetic pathways of PUA-production in Ulva.
• The depletion of polyunsaturated fatty acids jeopardizes the amount of economical relevant resources from Ulva.

Lipoxygenase/hydroperoxide lyase mediated transformations convert polyunsaturated fatty acids into various oxylipins. First, lipoxygenases catalyze fatty acid oxidation to fatty acid hydroperoxides. Subsequently, breakdown reactions result in a wide array of metabolites with multiple physiological and ecological functions. These fatty acid transformations are highly diverse in marine algae and play a crucial rule in e.g., signaling, chemical defense, and stress response often mediated through polyunsaturated aldehydes (PUAs). In this study, green tide-forming macroalgae of the genius Ulva (Chlorophyta) were collected at various sampling sites in the lagoon of the Ria Formosa (Portugal) and were surveyed for PUAs. We demonstrated that sea-lettuce like but not tube-like morphotypes produce elevated amounts of volatile C10-polyunsaturated aldehydes (2,4,7-decatrienal and 2,4-decadienal) upon tissue damage. Moreover, morphogenetic and phylogenetic analyses of the collected Ulva species revealed chemotaxonomic significance of the perspective biosynthetic pathways. The aldehydes are derived from omega-3 and omega-6 polyunsaturated fatty acids (PUFA) with 20 or 18 carbon atoms including eicosapentaenoic acid (C20:5 n-3), arachidonic acid (C20:4 n-6), stearidonic acid (C18:4 n-3), and γ-linolenic acid (C18:3 n-6). We present first evidences that lipoxygenase-mediated (11-LOX and 9-LOX) eicosanoid and octadecanoid pathways catalyze the transformation of C20- and C18-polyunsaturated fatty acids into PUAs and concomitantly into short chain hydroxylated fatty acids.

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