(Figures 2,3) Lipid composition of liver and muscles of the daubed shanny (Leptoclinus maculatus), Kongsfjorden

A comparative study on the lipid composition of the liver and muscles has been performed in daubed shanny caught in summer (July) in Arctic waters at three different sites (biotopes) along the north-western coast of Spitsbergen. In marine organisms living at high latitudes, lipids play an especially important role, primarily as reserve substances and as a factor influencing adaptation to severe environmental conditions. Since the ecology of daubed shanny is poorly known, the data obtained may be considered novel.

Biological traits, and egg and fecal pellet production of Calanus finmarchicus and Calanus glacialis in situ and during experiments

The effects of temperature and food was examined for Calanus finmarchicus and C. glacialis during 3 phases of the phytoplankton spring bloom in Disko Bay, western Greenland. The 2 species were collected during pre-bloom, bloom, and post-bloom and exposed to temperatures from 0 to 10°C, combined with deficient or excess food. Fecal pellet and egg production were measured as indices for grazing and secondary production, respectively. Furthermore, changes in body carbon, nitrogen, and lipid content were measured. C. glacialis sampled before the bloom and incubated with excess food exhibited high specific egg production at temperatures between 0 and 2.5°C. Higher temperatures did not increase egg production considerably, whereas egg production for C. finmarchicus more than tripled between 2.5 and 5°C. Starved C. glacialis produced eggs at all temperatures stimulated by increasing temperatures, whereas starved C. finmarchicus needed temperatures above 5°C to produce eggs fueled by their lipid stores. Few C. finmarchicus had mature gonads at the initiation of the pre-bloom and bloom experiment, and egg production of C. finmarchicus therefore only increased as the ratio of individuals with mature gonads increased. During the bloom, both C. glacialis and C. finmarchicus used the high food availability for egg production, while refueling or exhausting their lipid stores, respectively. Finally, during the post-bloom experiment, production was low by C. finmarchicus, whereas C. glacialis had terminated production. Our results suggest that a future warmer ocean will reduce the advantage of early spawning by C. glacialis and that C. finmarchicus will become increasingly prevalent.

Characteristics of eggs and female adults of Calanus finmarchicus, C. glacialis and C. hyperboreus from Disko Bay, western Greenland

This is the first high temporal-resolution study in Disko Bay covering population dynamics, grazing, reproduction, and biochemical composition of 3 dominating copepod species (Calanus finmarchicus, C. glacialis and C. hyperboreus) from late winter to midsummer in 2008. C. finmarchicus and C. glacialis ascended to the surface layer at the onset of the spring phytoplankton bloom, followed by C. hyperboreus 2 wk later. C. finmarchicus spawning occurred during the bloom and postbloom period, partially fueled by wax esters. C. glacialis commenced spawning before the bloom, yet it was greatly stimulated when food became available. However, feeding and reproduction was terminated after the main bloom despite the presence of food. In terms of feeding, this was also the strategy for C. hyperboreus. Between pre-bloom and post-bloom, C. finmarchicus showed an increase in carbon, nitrogen, and phospholipid content but a decrease in total lipid content. This was likely the result of protein synthesis, oocyte maturation, and spawning fueled by wax esters and by feeding. C. glacialis showed a similar pattern, although with an increasing total lipid content from pre-bloom to post-bloom, and an increasing wax ester and decreasing phospholipid content after reproduction was terminated. C. hyperboreus showed greatly increased content of carbon, nitrogen, and all lipid classes between the pre- and post-bloom periods. Hence, C. finmarchicus commenced feeding and spawning at the onset of the bloom and continued throughout the remaining study period. Both C. glacialis and C. hyperboreus females refueled their storage lipids (wax esters) during the bloom and post-bloom period, suggesting that they may spawn in an additional year.

Phytoplankton biomass, chlorophyll concentration, and variability of lipid content in Calanus euxinus in the Black Sea in June 1991

During field studies relationships between chlorophyll concentrations, phytoplankton biomass (total, individual sizes and species) and level of accumulation of total lipids, wax esters, triacylglycerols, and phospholipids in C. euxinus (copepodites V and females) were studied. These relationships allowed to display not only simple trophic relations between isolated parts of the C. euxinus population and phytoplankton, but also selective role of individual algae species in forming lipid reserves too. Besides it was found that geographical variability of chlorophyll concentration and phytoplankton biomass correlates closely only with those lipid fractions (wax esters and phospholipids) of C. euxinus, which accumulated and kept in a body for a fairly long time. No correlation was found between phytoplankton and for rapidly metabolized triacylglycerols, which have to be utilized within few hours.

Lipid composition of particulate matter measured on water bottle samples during POLARSTERN cruise ARK-XI/1

The lipid composition of particulate matter in oceanic environments can provide informations on the nature and origin of the organic matter as well as on their transformation processes. Molecular characteristics for lipids in the Arctic environment have been used as indicators of the sources and transformation of organic particulate matter (Smith et al., 1997; Fahl and Stein, 1997, 1999). However, the features of the lipid composition of particulate matter in the Arctic with its high seasonality of ice Cover and primary productivity has been studied insufficiently. Lipids are one of the most important compounds of organic matter. On the one hand, the composition of lipids is a result of the variability of biological sources (phyto- and zooplankton, higher plants, bacteria etc.). On the other hand, the lipid composition of particulate matter is undergone significant alteration during vertical transport. The organic matter balance in the Arctic marginal seas, such as the Kara and Laptev seas, is characterized by the significant supply of dissolved and particulate material by the major Eurasian rivers - Ob, Yenisei and Lena (Cauwet and Sidorov, 1996; Gordeev et al., 1996, Martin et al., 1993). In relation to the world's ocean the primary productivity values are lower in the Arctic seas due to the ice-cover. However local increased values of primary productivity can be connected with the melting processes inducing increased phytoplankton growth near ice-edge (Nelson et al., 1989; Fahl and Stein, 1997) and enhanced river supply of nutrients, These features can influence the proportion of allochtonous and autochtonous components of the organic matter in the Arctic marginal seas (Fahl and Stein, 1997; Stein and Fahl, 1999). Furthermore, increased lipid contents in aquatic environments were found near density discontinuities (Parish et al., 1988). Although being less informative than lipid studies on the molecular level the character of lipid composition analysis on the group could also be used for studying of particulate organic matter and its transformation in sedimentation processes in the Arctic. In this paper the investigation of the characteristics of lipid composition performed by Alexandrova and Shevchenko (1997) in Arctic seas was continued.

Biometry, and fatty acid and fatty alcohol composition of the Arctic ctenophore Mertensia ovum from Kongsfjorden

Lipids of the Arctic ctenophore Mertensia ovum, collected from Kongsfjorden (Svalbard) in 2001, were analysed to investigate seasonal variability and fate of dietary lipids. Total lipids, lipid classes and fatty acid and alcohol compositions were determined in animals, which were selected according to age-group and season. Changes in lipids of age-group 0 animals were followed during growth from spring to autumn. Total lipids increased from May to September. Lipids as percentage of dry mass were lowest in August indicating their use for reproduction. Higher values occurred in September, which may be due to lipid storage for overwintering. Wax esters were the major lipid class accounting for about 50% of total lipids in age-group 0 animals from July and August. Phospholipids were the second largest lipid fraction with up to 46% in this age-group. The principal fatty acids of M. ovum from all age-groups were 22:6(n-3), 20:5(n-3) and 16:0. Wax ester fatty alcohols were dominated by 22:1(n-11) and 20:1(n-9) followed by moderate proportions of 16:0. The unique feature of M. ovum lipids was the high amount of free fatty alcohols originating probably from the dietary wax esters. In May, free alcohols exhibited the highest mean proportion with 14.6% in age-group 0 animals. We present the first data describing a detailed free fatty alcohol composition in zooplankton. This composition was very different from the alcohol composition of M. ovum wax esters because of the predominance of the long-chain monounsaturated 22:1 (n-11) alcohol accounting for almost 100% of total free alcohols in some samples. The detailed lipid composition clearly reflected feeding of M. ovum on the herbivorous calanoid species, Calanus glacialis and C. finmarchicus, the abundant members of the zooplankton community in Kongsfjorden. Other copepod species or prey items seem to be less important for M. ovum.

Identification of a gene encoding an acyl CoA:diacylglycerol acyltransferase, a key enzyme in triacylglycerol synthesis

Triacylglycerols are quantitatively the most important storage form of energy for eukaryotic cells. Acyl CoA:diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) catalyzes the terminal and only committed step in triacylglycerol synthesis, by using diacylglycerol and fatty acyl CoA as substrates. DGAT plays a fundamental role in the metabolism of cellular diacylglycerol and is important in higher eukaryotes for physiologic processes involving triacylglycerol metabolism such as intestinal fat absorption, lipoprotein assembly, adipose tissue formation, and lactation. DGAT is an integral membrane protein that has never been purified to homogeneity, nor has its gene been cloned. We identified an expressed sequence tag clone that shared regions of similarity with acyl CoA:cholesterol acyltransferase, an enzyme that also uses fatty acyl CoA as a substrate. Expression of a mouse cDNA for this expressed sequence tag in insect cells resulted in high levels of DGAT activity in cell membranes. No other acyltransferase activity was detected when a variety of substrates, including cholesterol, were used as acyl acceptors. The gene was expressed in all tissues examined; during differentiation of NIH 3T3-L1 cells into adipocytes, its expression increased markedly in parallel with increases in DGAT activity. The identification of this cDNA encoding a DGAT will greatly facilitate studies of cellular glycerolipid metabolism and its regulation.

Isolation and characterization of neutral-lipid-containing organelles and globuli-filled plastids from Brassica napus tapetum

The monolayer tapetum cells of the maturing flowers of Brassica napus contain abundant subcellular globuli-filled plastids and special lipid particles, both enriched with lipids that are supposed to be discharged and deposited onto the surface of adjacent maturing pollen. We separated the two organelles by flotation density gradient centrifugation and identified them by electron microscopy. The globuli-filled plastids had a morphology similar to those described in other plant species and tissues. They had an equilibrium density of 1.02 g/cm3 and contained neutral esters and unique polypeptides. The lipid particles contained patches of osmiophilic materials situated among densely packed vesicles and did not have an enclosing membrane. They exhibited osmotic properties, presumably exerted by the individual vesicles. They had an equilibrium density of 1.05 g/cm3 and possessed triacylglycerols and unique polypeptides. Several of these polypeptides were identified, by their N-terminal sequences or antibody cross-reactivity, as oleosins, proteins known to be associated with seed storage oil bodies. The morphological and biochemical characteristics of the lipid particles indicate that they are novel organelles in eukaryotes that have not been previously isolated and studied. After lysis of the tapetum cells at a late stage of floral development, only the major plastid neutral ester was recovered, whereas the other abundant lipids and proteins of the two tapetum organelles were present in fragmented forms or absent on the pollen surface.

Dual Localization of Squalene Epoxidase, Erg1p, in Yeast Reflects a Relationship between the Endoplasmic Reticulum and Lipid Particles

Squalene epoxidase, encoded by the ERG1 gene in yeast, is a key enzyme of sterol biosynthesis. Analysis of subcellular fractions revealed that squalene epoxidase was present in the microsomal fraction (30,000 × g) and also cofractionated with lipid particles. A dual localization of Erg1p was confirmed by immunofluorescence microscopy. On the basis of the distribution of marker proteins, 62% of cellular Erg1p could be assigned to the endoplasmic reticulum and 38% to lipid particles in late logarithmic-phase cells. In contrast, sterol Δ24-methyltransferase (Erg6p), an enzyme catalyzing a late step in sterol biosynthesis, was found mainly in lipid particles cofractionating with triacylglycerols and steryl esters. The relative distribution of Erg1p between the endoplasmic reticulum and lipid particles changes during growth. Squalene epoxidase (Erg1p) was absent in an erg1 disruptant strain and was induced fivefold in lipid particles and in the endoplasmic reticulum when the ERG1 gene was overexpressed from a multicopy plasmid. The amount of squalene epoxidase in both compartments was also induced approximately fivefold by treatment of yeast cells with terbinafine, an inhibitor of the fungal squalene epoxidase. In contrast to the distribution of the protein, enzymatic activity of squalene epoxidase was only detectable in the endoplasmic reticulum but was absent from isolated lipid particles. When lipid particles of the wild-type strain and microsomes of an erg1 disruptant were mixed, squalene epoxidase activity was partially restored. These findings suggest that factor(s) present in the endoplasmic reticulum are required for squalene epoxidase activity. Close contact between lipid particles and endoplasmic reticulum may be necessary for a concerted action of these two compartments in sterol biosynthesis.

wrinkled1: A Novel, Low-Seed-Oil Mutant of Arabidopsis with a Deficiency in the Seed-Specific Regulation of Carbohydrate Metabolism1

During oil deposition in developing seeds of Arabidopsis, photosynthate is imported in the form of carbohydrates into the embryo and converted to triacylglycerols. To identify genes essential for this process and to investigate the molecular basis for the developmental regulation of oil accumulation, mutants producing wrinkled, incompletely filled seeds were isolated. A novel mutant locus, wrinkled1 (wri1), which maps to the bottom of chromosome 3 and causes an 80% reduction in seed oil content, was identified. Wild-type and homozygous wri1 mutant plantlets or mature plants were indistinguishable. However, developing homozygous wri1 seeds were impaired in the incorporation of sucrose and glucose into triacylglycerols, but incorporated pyruvate and acetate at an increased rate. Because the activities of several glycolytic enzymes, in particular hexokinase and pyrophosphate-dependent phosphofructokinase, are reduced in developing homozygous wri1 seeds, it is suggested that WRI1 is involved in the developmental regulation of carbohydrate metabolism during seed filling.