Lipoxygenase-catalyzed oxygenation of storage lipids is implicated in lipid mobilization during germination.

The etiolated germination process of oilseed plants is characterized by the mobilization of storage lipids, which serve as a major carbon source for the seedling. We found that during early stages of germination in cucumber, a lipoxygenase (linoleate: oxygen oxidoreductase, EC 1.13.11.12) form is induced that is capable of oxygenating the esterified fatty acids located in the lipid-storage organelles, the so-called lipid bodies. Large amounts of esterified (13S)-hydroxy-(9Z,11E)-octadecadienoic acid were detected in the lipid bodies, whereas only traces of other oxygenated fatty acid isomers were found. This specific product pattern confirms the in vivo action of this lipoxygenase form during germination. Lipid fractionation studies of lipid bodies indicated the presence of lipoxygenase products both in the storage triacylglycerols and, to a higher extent, in the phospholipids surrounding the lipid stores as a monolayer. The degree of oxygenation of the storage lipids increased drastically during the time course of germination. We show that oxygenated fatty acids are preferentially cleaved from the lipid bodies and are subsequently released into the cytoplasm. We suggest that they may serve as substrate for beta-oxidation. These data suggest that during the etiolated germination, a lipoxygenase initiates the mobilization of storage lipids. The possible mechanisms of this implication are discussed.

Unsaturation of the membrane lipids of chloroplasts stabilizes the photosynthetic machinery against low-temperature photoinhibition in transgenic tobacco plants.

Using tobacco plants that had been transformed with the cDNA for glycerol-3-phosphate acyltransferase, we have demonstrated that chilling tolerance is affected by the levels of unsaturated membrane lipids. In the present study, we examined the effects of the transformation of tobacco plants with cDNA for glycerol-3-phosphate acyltransferase from squash on the unsaturation of fatty acids in thylakoid membrane lipids and the response of photosynthesis to various temperatures. Of the four major lipid classes isolated from the thylakoid membranes, phosphatidylglycerol showed the most conspicuous decrease in the level of unsaturation in the transformed plants. The isolated thylakoid membranes from wild-type and transgenic plants did not significantly differ from each other in terms of the sensitivity of photosystem II to high and low temperatures and also to photoinhibition. However, leaves of the transformed plants were more sensitive to photoinhibition than those of wild-type plants. Moreover, the recovery of photosynthesis from photoinhibition in leaves of wild-type plants was faster than that in leaves of the transgenic tobacco plants. These results suggest that unsaturation of fatty acids of phosphatidylglycerol in thylakoid membranes stabilizes the photosynthetic machinery against low-temperature photoinhibition by accelerating the recovery of the photosystem II protein complex.

Dietary lipids and calorie restriction affect mammary tumor incidence and gene expression in mouse mammary tumor virus/v-Ha-ras transgenic mice.

We have studied the effects of food restriction (FR) and substitution of fish oil (FO; omega 3) for corn oil (CO; omega 6) on breast tumor incidence and survival in mouse mammary tumor virus/v-Ha-ras transgenic (Onco) mice. The diets were as follows: group 1, 5% (wt/wt) CO fed ad libitum (AL); group 2, 5% CO, restricted calories (40% fewer calories than AL; FR); group 3, 20% CO fed AL; and group 4, 20% FO fed AL. After 3 years, 40% of FR Onco (group 2) mice were alive, whereas there were no survivors in the other three groups. Similarly, tumor incidence was reduced to 27% (5 out of 18) in FR animals (group 2), whereas it was 83% (11 out of 13) in group 1 mice, 89% (16 out of 18) in group 3 mice, and 71% (10 out of 14) in group 4 mice. These protective effects of FR on survival and tumor incidence were paralleled by higher expression of the tumor suppressor gene p53 (wild type) and free-radical scavenging enzymes (catalase and superoxide dismutase) in breast tumors. Immunoblotting showed less ras gene product, p21, and increased p53 levels in the tumors of FR mice. In addition, FR decreased RNA levels of c-erbB-2, interleukin 6, and the transgene v-Ha-ras in tumors. In contrast, analysis of hepatic mRNA from tumor-bearing FR mice revealed higher expression of catalase, glutathione peroxidase, and superoxide dismutase. Survival and tumor incidence were not influenced significantly by dietary supplementation with FO in place of CO. Taken together, our studies suggest that moderate restriction of energy intake significantly inhibited the development of mammary tumors and altered expression of cytokines, oncogenes, and free-radical scavenging enzymes.

d15N of lipids in marine animals of the Dutch Wadden Sea

Lipid extraction of biomass prior to stable isotope analysis is known to cause variable changes in the stable nitrogen isotopic composition (d15N) of residual biomass. However, the underlying factors causing these changes are not yet clear. Here we address this issue by comparing the d15N of bulk and residual biomass of several marine animal tissues (fish, crab, cockle, oyster, and polychaete), as well as the d15N of the extracted lipids. As observed previously, lipid extraction led to a variable offset in d15N of biomass (differences ranging from -2.3 to +1.8 per mil). Importantly, the total lipid extract (TLE) was highly depleted in 15N compared to bulk biomass, and also highly variable (differences ranging from -14 to +0.7 per mil). The TLE consisted mainly of phosphatidylcholines, a group of lipids with one nitrogen atom in the headgroup. To elucidate the cause for the 15N-depletion in the TLE, the d15N of amino acids was determined, including serine because it is one of the main sources of nitrogen to N-containing lipids. Serine d15N values differed by -7 to +2 per mil from bulk biomass d15N, and correlated well with the 15N depletion in TLEs. On average, serine was less depleted (-3 per mil) than the TLE (-7 per mil), possibly due to fractionation during biosynthesis of N-containing headgroups, or that other nitrogen-containing compounds, such as urea and choline, or recycled nitrogen contribute to the nitrogen isotopic composition of the TLE. The depletion in 15N of the TLE relative to biomass increased with the trophic level of the organisms.

Ether lipids in deep sea and swamp sediments

Methanogen ether lipids have been quantified in sediments from a Florida swamp and the Atlantic ocean. Swamp cores containing acyclic and monocyclic isopranyl ethers are clearly differentiated from deep sea sediments which also contain bicyclic compounds. A concentration maximum near the bottom of the sulfate reducing zone in deep sea sediments may reflect a biogeochemical system in which methanogenesis and sulfate reduction are coupled by the process of methane oxidation. Lipid diagenesis is evident in the deep sea sediments. Species zonation, possibly caused by oxygen sensitivity, is detected in the relative lipid abundances in swamp sediments.