| Summary: | 碩士 === 國立彰化師範大學 === 生物學系 === 104 === The survival of insects in terrestrial environments is due largely to their ability to resist desiccation stress. Water loss in insects is majorly through the cuticle, and any change in rate of water loss can be accounted for by the physical transformation of the lipid layer in cuticle. In other words, that surface lipids are melted at a "critical" or "transition" temperature (Tc), then result in conversion from a solid, impermeable barrier to a fluid state, through which water can easily diffuses. Therefore, it can be hypothesized that the higher the Tc is, the lower the water loss can be. An in vitro study further suggested that the more double bonds in hydrocarbons, the lower melting temperature is. Desaturases catalyze the addition of double bonds in the hydrocarbon chains of fatty acids. Thus, we hypothesized that by changing the distribution and level of unsaturation in fatty acid in vivo, the cuticle water loss in insects might be influenced, which should be substantiated by their relative tolerance to desiccation stress. In this study, three desaturase genes, including Desaturase1, Desaturase 2, and Desaturase F from Drosophila melanogaster, were overexpressed/knocked down in specific tissues by using UAS-GAL4 system. The resulted flies (including wildtype) were treated with desiccation, then their mortality were observed and compared. The results indicated that overexpression or knockdown of desaturase genes might affect survival of fruit flies under desiccation stress, and the gene of Desaturase 2 might play an important role in desiccation.
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