The goal of the project is to elucidate the molecular mechanisms which regulate the degree of unsaturation of membrane and storage lipids. We will address this question by measuring the effect of variation in developmental stage and environmental conditions on the expression of several recently isolated genes encoding fatty acid desaturases from the plant Arabidopsis thaliana. The existence of regulatory mechanisms which act at the level of direct enzyme activation or deactivation will be examined by measuring the effects on lipid composition in transgenic plants which contain higher than normal levels of desaturase activity due to overexpression of cloned desaturase genes. The spatial organization of lipid desaturation within cells will be elucidated using anti-desaturase antibodies to localize the enzymes by immunogold electron microscopy. Finally, we will attempt to isolate genes for several additional desaturases by map-based cloning methods based on the availability of a comprehensive collection of mutants of Arabidopsis. %%% Plant fatty acids provide about one third of the calories in human diets and are also used for a wide variety of technical products raging from synthesis of nylon to cosmetics. In addition, the ability of many plants to withstand exposure to temperature extremes is thought to be controlled by the fatty acid composition of plant membranes. The experiments proposed here are designed to provided detailed information about the factors which regulate plant fatty acid composition. This information may be useful in permitting genetic modification of the fatty acid composition of plants so that they produce edible oils with advantageous dietary qualities, expanded technical uses or enhanced ability to withstand temperature extremes.
