Acid Composition Of Storage Lipids Research Articles

Polyunsaturated fats, membrane lipids and animal longevity

Fatty acids are essential for life because they are essential components of cellular membranes. Lower animals can synthesize all four classes of fatty acids from non-lipid sources, but both omega-6 and omega-3 cannot be synthesized de novo by 'higher' animals and are therefore essential components of their diet. The relationship between normal variation in diet fatty acid composition and membrane fatty acid composition is little investigated. Studies in the rat show that, with respect to the general classes of fatty acids (saturated, monounsaturated and polyunsaturated) membrane fatty acid composition is homeostatically regulated despite diet variation. This is not the case for fatty acid composition of storage lipids, which responds to diet variation. Polyunsaturated fatty acids are important determinants of physical and chemical properties of membranes. They are the substrates for lipid peroxidation and it is possible to calculate a peroxidation index (PI) for a particular membrane composition. Membrane PI appears to be homeostatically regulated with respect to diet PI. Membrane fatty acid composition varies among species and membrane PI is inversely correlated to longevity in mammals, birds, bivalve molluscs, honeybees and the nematode Caenorhabditis elegans.

Effect of Temperature on Delta‐9 Stearoyl‐ACP and Microsomal Omega‐6 Desaturase Gene Expression and Fatty Acid Content in Developing Soybean Seeds

Delta‐9 stearoyl‐ACP (SAD) and microsomal omega‐6 oleate (FAD2) desaturases contribute to the maintenance of lipid fluidity in membranes and the fatty acid composition of storage lipids in seed. Since these enzymes must operate at varying environmental temperatures, they are under constitutive control, but they may also be subject to fine regulation both transcriptionally and posttranscriptionally. We measured transcript accumulation of the seed‐expressed SAD‐A and SAD‐B and FAD2‐1A and FAD2‐1B genes in the seeds of three soybean varieties grown at cool (22/18°C), normal (26/22°C), or warm (30/26°C) temperatures during pod fill. At the cool temperature, transcript accumulation of both the SAD and FAD2‐1 genes was significantly elevated, with FAD2‐1B 2‐ to 10‐fold or greater than FAD2‐1A at 35 d after flowering. Expression of both SAD and FAD2‐1 were significantly decreased in seed that developed at the warm temperature. Decreased FAD2‐1 transcript accumulation at the warm temperature was positively associated with significantly increased oleic and decreased linoleic acid content in the three varieties examined. Decreased SAD transcript accumulation at the warm temperature was positively associated with a significantly increased level of stearic acid but only in the high‐stearate mutant line, A6. We conclude that environmental temperature modulates oleic and linoleic acid in developing seed through regulated FAD2‐1 gene expression, but temperature modulation of stearic acid content in wild‐type soybean may be more complex, involving in addition to SAD‐A and ‐B, plastid thioesterase genes FATA and FATB.

Unusual fatty acid composition of storage lipids in the bresilioid shrimp Rimicaris exoculata couples the photic zone with MAR hydrothermal vent sites

Lipid and stable carbon isotope analyses of Rimicaris exoculata, the dominant bresilioid shrimp found at the MAR (Mid-Atlantic Ridge) vent sites, have indicated that these animals possess a highly unusual storage lipid composition. The dominant neutral lipid classes, triacylglycerols and wax esters, contained very high levels of polyunsaturated fatty acids (PUFA, up to 89% of neutral lipid fatty acids). Gas chromatography isotope ratio mass spectrometry (GC-IRMS) analysis of the PUFA from neutral lipid gave d13C (v-PDB) values of -17.6 to -27.1[per thou], which is within the range expected for a photosynthetic origin for these compounds. Fatty acid analyses of bacterial/detrital material collected from the vent sites contained only very low amounts of PUFA. It is clear from these findings that R. exoculata has evolved a highly specialized lipid metabolism which allows it to store substantial amounts of PUFA during its early planktotrophic life stages. These PUFA reserves will be subsequently mobilized to enable growth and maturation of the shrimp on return to a suitable vent site and are therefore an important factor allowing R. exoculata to inhabit deep sea vent ecosystems.

Biologie moléculaire de la biogenèse des lipides des plantes

Summary The approaches of molecular biogenesis have been increasingly used these recent years in order to explore and to control the lipid metabolism of plants. This is linked to the important roles played by the lipid constituents in plant cells, especially at the level of membranous processes, and, also, to the biotechnological use of storage lipids. The approaches of molecular biology are used either after purification of the enzymes corresponding to steps of lipid biosynthesis—fatty acid synthase, desaturases, acyltransferases—and isolation of the corresponding genes or by complementation of mutants disturbed in one of these genes. The genes or cDNAs, coding for several key enzymes of lipid biosynthesis, recently characterized, have been used to manipulate the fatty acid composition of storage lipids, especially in rapeseed and Arabidopsis, in order to obtain oils rich in saturated fatty acids or shorter acyl chains. Fascinating perspectives related to lipid manipulation, either to improve the resista...