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Diatoms are unicellular plants broadly present in freshwater and marine ecosystems, where they play a primary role in sustaining the marine food chain. In the last 10 years, there has been accumulating evidence that diatoms may have deleterious effects on the hatching success of zooplankton crustaceans such as copepods, thus affecting dynamics of planktonic populations and limiting secondary production. At the molecular level, failure to hatch is ascribed to the presence of a family of inhibitory oxylipins, which we propose to collectively name polyunsaturated short-chain aldehydes (abbreviated here as PUSCAs). Here we describe the origin of PUSCAs produced by the marine diatom Skeletonema costatum via a lipoxygenase-mediated pathways involving non-esterified polyunsaturated fatty acids (PUFA). Experiments with complex lipids proved the pivotal role of chloroplast-derived glycolipids, especially monogalactosyldiacylglycerol (MGDG), in providing hexadecatrienoic acid (C16:3 ω-4), hexadecatetraenoic acid (C16:4 ω-1) and eicosapentaenoic acid (C20:5 ω-3) to the downstream process leading to 2E,4Z-octadienal (C8:2 ω-4), 2E,4Z,7-octatrienal (C8:3 ω-1) and 2E,4Z-heptadienal (C7:2 ω-3), respectively. Under physiological conditions, the hydrolytic process is associated to galactolipid hydrolyzing enzyme capable of removing fatty acids from both sn positions of glycerol. [Copyright &y& Elsevier]

Nonbilayer lipids can be defined as cone-shaped lipids with a preference for nonbilayer structures with a negative curvature, such as the hexagonal phase. All membranes contain these lipids in large amounts. Yet, the lipids in biological membranes are organized in a bilayer. This leads to the question: what is the physiological role of nonbilayer lipids? Different models are discussed in this review, with a focus on the lateral pressure profile within the membrane. Based on this lateral pressure model, predictions can be made for the effect of nonbilayer lipids on peripheral and integral membrane proteins. Recent data on the catalytic domain of Leader Peptidase and the potassium channel KcsA are discussed in relation to these predictions and in relation to the different models on the function of nonbilayer lipids. The data suggest a general mechanism for the interaction between nonbilayer lipids and membrane proteins via the membrane lateral pressure. [Copyright &y& Elsevier]

In plants, phosphate deprivation is normally known to decrease the phospholipid content consistent with a mobilization of the phosphate reserve, and conversely to increase non-phosphorous membrane lipids such as digalactosyldiacylglycerol. We report here that unexpectedly, at an early stage of phosphate starvation, phosphatidylcholine (PC) increases transiently. We also show that a significant pool of diacylglycerol (DAG) with the same fatty acid composition as that of PC is present and moreover increases in response to phosphate deprivation. The evolution of the molecular profile of the newly synthesized galactolipids is compatible with a utilization of DAG accumulating from PC hydrolysis, achieved after selection of their acyl molecular species by the galactolipid synthesizing enzymes. [Copyright &y& Elsevier]

The plasma membranes of oat normally resemble those of other eukaryotes in containing mainly phospholipids and sterols. We here report the novel finding that the galactolipid digalactosyldiacylglycerol (DGDG) can constitute a substantial proportion of oat plasma membrane lipids, in both shoots and roots. When oat was cultivated under severe phosphate limitation, up to 70% of the plasma membrane phosphoglycerolipids were replaced by DGDG. Our finding not only reflects a far more developed potential for plasticity in plasma membrane lipid composition than often assumed, but also merits interest in the context of the limited phosphate availability in many soils. [Copyright &y& Elsevier]

Gymnospermae seed lipids are characterized by a high degree of desaturation, most having a Δ9 double bond. By degenerate polymerase chain reaction (PCR) we have isolated a white spruce (Picea glauca) cDNA clone that encodes an amino acid sequence sharing a high degree of homology with other putative plant acyl-coenzyme A (CoA) Des9 desaturases. Both in vivo and in vitro expression studies in a Δ9 desaturase-deficient yeast strain demonstrated the desaturation functionality of the white spruce clone, and gas chromatography-mass spectrometry (GC-MS) analyses confirmed the regioselectivity of the encoded enzyme. This is the first report of the functional characterization of a plant membrane-bound acyl-CoA-like protein Δ9 desaturase by heterologous expression in yeast. [Copyright &y& Elsevier]

Sensitivity of the photosynthetic thylakoid membranes to thermal stress was investigated in the psychrophilic Antarctic alga Chlamydomonas subcaudata. C. subcaudata thylakoids exhibited an elevated heat sensitivity as indicated by a temperature-induced rise in Fo fluorescence in comparison with the mesophilic species, Chlamydomonas reinhardtii. This was accompanied by a loss of structural stability of the photosystem (PS) II core complex and functional changes at the level of PSI in C. reinhardtii, but not in C. subcaudata. Lastly, C. subcaudata exhibited an increase in unsaturated fatty acid content of membrane lipids in combination with unique fatty acid species. The relationship between lipid unsaturation and the functioning of the photosynthetic apparatus under elevated temperatures is discussed. [Copyright &y& Elsevier]

Plastids greatly rely on the import of extraplastidial precursors for the synthesis of their own lipids, and several studies have shown that a lyso-PC acyltransferase located in the envelope may be involved in the import process. Because the presence of heavy metals in soil or in nutrient solutions induces changes in the lipid composition of plastid membranes (and therefore greatly reduces the photosynthetic capability of plants), we analysed the effect of several metal salts on plastidial lyso-PC acyltransferase activity. Among the 12 heavy metals studied, silver, copper, mercury and lead inhibited this activity. Metal bound to the enzyme was not – or only very slightly – released from the protein except when thiol-reducing agents (and not imidazole) were added. The results strongly suggest that the inhibitory effect is due to a formation of mercaptide between metal and cysteine(s). The relationship between the inhibition of the plastidial lyso-PC acyltransferase activity and the in vivo effects of metal salts on the plastid membranes is discussed. [Copyright &y& Elsevier]

Unnatural glycolipids possessing the diyne moiety in their acyl groups were successfully biosynthesized in the green sulfur photosynthetic bacterium Chlorobaculum ( Cba .) tepidum by cultivation with supplementation of 10,12-heptadecadiynic acid. Monogalactosyldiacylglycerol (MGDG) and rhamnosylgalactosyldiacylglycerol (RGDG) esterified with one 10,12-heptadecadiynic acid were primarily formed in the cells, and small amounts of glycolipids esterified with the two unnatural fatty acids can also be detected. The relative ratio of these unnatural glycolipids occupied in the total glycolipids was estimated to be 49% based on HPLC analysis using a evaporative light scattering detector. These results indicate that the acyl groups in glycolipids, which play important roles in the formation of extramembranous antenna complexes called chlorosomes, can be modified in vivo by cultivation of green sulfur photosynthetic bacteria with exogenous synthetic fatty acids. Visible absorption and circular dichroism spectra of Cba. tepidum containing the unnatural glycolipids demonstrated the formation of chlorosomes, indicating that the unnatural glycolipids in this study did not interfere with the biogenesis of chlorosomes.