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2.2. Effect of PUFAs on Embryo Cleavage and Hatching

When diatoms are damaged, the first enzymes to be activated are lipases that liberate a massive amount of free PUFAs. Among these, some PUFAs that are precursors for PUA production via lipoxygenase activity may be potentially harmful to developing embryos and larvae. Sellem and co-workers [] described abnormal development in embryos and larvae of the sea urchin Paracentrotus lividus incubated with the fatty acid octadecapentaenoic acid (C18:5 n-3) derived from a dinoflagellate belonging to the genus Gymnodinium. Since these authors found a delay in development rate during the cleavage stage, we decided to test the effect of some commercially available PUFAs, namely 5,8,11,14,17-eicosapentaenoic acid (EPA C20:5 n-3), one of the main precursors of diatom oxylipins, as well as two other omega 3 fatty acids present in considerable quantities in diatoms, 4,7,10,13,16,19-docosahexaenoic acid, (C22:6 n-3, DHA), and 6,9,12,15-octadecatetraenoic acid (C18:4 n-3, stearidonic acid). We also tested 6,9,12-octadecatrienoic (C18:3 n-6, γ-linolenic acid) and octadecadienoic (C18:2 n-6, linoleic acid) acids, two omega 6 fatty acids that are very common in higher plants, but rare in diatoms.

2.2. Effect of PUFAs on Embryo Cleavage and Hatching

Of the PUFAs tested, only EPA and stearidonic acid blocked cleavage, with this latter molecule showing the greatest activity (). Since cleavage was delayed depending on the concentrations tested (not shown), we recorded the percentage of first cleavage after 90 min, when almost 100% of control embryos had reached the 2-blastomere stage. After 90 minutes from fertilization, EPA completely blocked embryo cleavage at a concentration of 331 μM. In the case of DHA at 304 μM, only 34% of the embryos underwent first cleavage. The greatest activity was recorded with stearidonic acid that inhibited cleavage in 100% of embryos at 181 μM. Surprisingly no activity was recorded after incubation with linoleic and γ-linolenic acids, even at the highest concentrations tested of 357 and 359 μM, respectively.