| الوصف: |
The deleterious effects of maternal diatom diets on copepod embryonic development have been puzzling the scientific community for the past 15 years. Since the discovery of the first anti-mitotic compounds, polyunsaturated aldehydes deriving from fatty acid oxidation,our knowledge of the oxylipin metabolism in diatoms has been continuously increasing. Not only have new oxylipin compounds been identified, but it is becoming apparent thatoxylipin metabolism is highly complex and specific. This thesis contributes to the understanding of oxylipin metabolism in diatoms by studying the activity of diatom lipoxygenases, the enzymes responsible for the first oxidative step in transforming polyunsaturated fatty acids into oxylipins. Lipoxygenase activity was measured by a colorimetric and a polarographic assay, and its relationship to oxylipin production was examined. Lipoxygenase metabolism in diatoms was studied under natural conditions during a bloom at sea, under semi-natural conditions during a mesocosm experiment, and in the laboratory, with special emphasis on Skeletanema marinai. The effect of diatom oxylipin production on copepod reproductive success was also examined. Increased oxylipin production was found with the onset of the stationary phase in culture and during the decline of the mesocosm bloom, which indicates a regulatory role foroxy lipins in bloom demise, even though this could not be verified at sea. Lipoxygenase activity and oxylipin production were highly variable and specific to the level of clones. The most important conclusion to be drawn from the present experiments is the lack ofcorrelation between lipoxygenase activity and oxylipin production. This strongly indicates that other compounds still need to be identitied and that we do not yet have a complete picture of oxylipin metabolism in diatoms. |