The acyl lipids of chloroplasts contain characteristically high proportions of trienoic fatty acids. Because this feature is universal among higher plants, it has been inferred that the fatty acid composition of chloroplast membranes is important for maintaining photosynthetic function. However, the enzymology and regulation of polyunsaturated fatty acid synthesis are poorly understood, and there is at present no accepted model of exactly how photosynthesis might be dependent on a highly unsaturated membrane. The principal investigator has isolated a series of Arabidopsis mutants with specific alterations in leaf fatty acid composition and these have provided a novel means to study both plant lipid metabolism and the physiological significance of membrane lipid composition. This proposal describes experiments to characterize the biochemistry of newly isolated mutants, and of double mutants produced by crossing mutant lines. This aspect of the project will involve assaying enzymes of fatty acid synthesis as well as in vivo labeling experiments and analysis of the fatty acid compositions of individual lipids and subcellular fractions. The most extreme double mutants are unable to grow autotrophically, but many of the mutations only affect growth and development of the plants at low temperatures. For this reason, photosynthesis in the different mutants will be analyzed under a range of environmental conditions using non-invasive fluorescence and light absorption techniques which can be used on intact plants. These experiments would provide a clear picture of exactly how photosynthesis is affected by thylakoid lipid composition under the different growth conditions normally encountered by temperate plants. The improved understanding of lipid metabolism and photosynthesis that will result from the work are important prerequisites to modifying these processes for increase plant productivity. //
