SUMMARYAlthough the influence of temperature, particularly cold, on lipid metabolism is well established, previous studies have focused on long-term responses and have largely ignored the influence of other interacting environmental factors. Here, we present a time-resolved analysis of the early responses of the glycerolipidome of Arabidopsis thaliana plants exposed to various temperatures (4, 21 and 32°C) and light intensities (darkness, 75, 150 and 400 lmol m )2 s )1 ), including selected combinations. Using a UPLC/MS-based lipidomic platform, we reproducibly measured most glycerolipid species reported for Arabidopsis leaves, including the classes phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI) phosphatidylglycerol (PG), monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and sulfoquinovosyldiacylglycerol (SQDG). In addition to known lipids, we have identified previously unobserved compounds, such as 36-C PGs and eukaryotic phospholipids containing 16:3 acyl chains. Occurrence of these lipid species implies the action of new biochemical mechanisms. Exposition of Arabidopsis plants to various light and temperature regimes results in two major effects. The first is the dependence of the saturation level of PC and MGDG pools on light intensity, likely arising from light regulation of de novo fatty acid synthesis. The second concerns an immediate decrease in unsaturated species of PG at high-temperature conditions (32°C), which could mark the first stages of adaptation to heat-stress conditions. Observed changes are discussed in the context of current knowledge, and new hypotheses have been formulated concerning the early stages of the plant response to changing light and temperature conditions.

We investigated the systems response of metabolism and growth after an increase in irradiance in the nonsaturating range in the algal model Chlamydomonas reinhardtii. In a three-step process, photosynthesis and the levels of metabolites increased immediately, growth increased after 10 to 15 min, and transcript and protein abundance responded by 40 and 120 to 240 min, respectively. In the first phase, starch and metabolites provided a transient buffer for carbon until growth increased. This uncouples photosynthesis from growth in a fluctuating light environment. In the first and second phases, rising metabolite levels and increased polysome loading drove an increase in fluxes. Most Calvin-Benson cycle (CBC) enzymes were substrate-limited in vivo, and strikingly, many were present at higher concentrations than their substrates, explaining how rising metabolite levels stimulate CBC flux. Rubisco, fructose-1,6-biosphosphatase, and seduheptulose-1,7-bisphosphatase were close to substrate saturation in vivo, and flux was increased by posttranslational activation. In the third phase, changes in abundance of particular proteins, including increases in plastidial ATP synthase and some CBC enzymes, relieved potential bottlenecks and readjusted protein allocation between different processes. Despite reasonable overall agreement between changes in transcript and protein abundance (R 2 = 0.24), many proteins, including those in photosynthesis, changed independently of transcript abundance.

HighlightThis study reveals that the transcription factor PHR1 controls phospholipid/glycolipid substitution during P starvation, and that Arabidopsis accumulates triacylglycerol during P starvation. In roots this phenotype is also under control of PHR1.

BackgroundNitrogen (N) plays an important role in the formation of tea quality-related compounds, like amino acids and flavor/aroma origin compounds. Lipids, which have been reported to be affected by N deficiency, are precursors to the generation of flavor/aroma origin compounds in tea plant. However, there is no literature about the lipid profiles of tea plant affected by N fertilization. Hence, we hypothesize that the biosynthesis of flavor-related compounds in tea was affected by N through its regulation of lipid metabolism.ResultsIn this study, mature leaves and new shoots of tea plant grown under three N levels at the rates of 0, 285 and 474 kg/ha were applied for ultra-performance liquid chromatography-mass spectrometry (UPLC/MS) based lipidomic analysis. Totally, 178 lipid species were identified. The results showed that the composition of lipid compounds in mature leaves and new shoots varied dramatically, which was also affected by N levels. The higher content of the storage lipid TAG and higher carbon (C)/N ratio in mature leaves than that of new shoots in tea plants grown under low N level (0 kg/ha) suggested that tea plants could remobilize the C stored in TAG to maintain their C/N balance and help to improve the quality of tea. N fertilization resulted in a higher content of the compounds 36:6 MGDG and 36:6 DGDG. Since these compounds contain linolenic acid (18:3), a precursor to the formation of aroma origin compounds, we suggested their increase could contribute to the quality of tea.ConclusionsTaken together, the present work indicated that appropriate application of N fertilizer could balance the lipid metabolism and the formation of flavor/aroma origin compounds, which help to improve the quality of tea. Moreover, excess N fertilization might deteriorate the aroma quality of made tea due to increases of precursors leading to grassy odor.Electronic supplementary materialThe online version of this article (10.1186/s12870-017-1111-6) contains supplementary material, which is available to authorized users.

SUMMARYQuantification of fatty acids has been crucial to elucidate lipid biosynthesis pathways in plants. To date, fatty acid identification and quantification has relied mainly on gas chromatography (GC) coupled to flame ionization detection (FID) or mass spectrometry (MS), which requires the derivatization of samples and the use of chemical standards for annotation. Here we present an alternative method based on a simple procedure for the hydrolysis of lipids, so that fatty acids can be quantified by liquid chromatography mass spectrometry (LC-MS) analysis. Proper peak annotation of the fatty acids in the LC-MS-based methods has been achieved by LC-MS measurements of authentic standard compounds and elemental formula annotation supported by 13 C isotope-labeled Arabidopsis. As a proof of concept, we have compared the analysis by LC-MS and GC-FID of two previously characterized Arabidopsis thaliana knock-out mutants for FAD6 and FAD7 desaturase genes. These results are discussed in light of lipidomic profiles obtained from the same samples. In addition, we performed untargeted LC-MS analysis to determine the fatty acid content of two diatom species. Our results indicate that both LC-MS and GC-FID analyses are comparable, but that because of higher sensitivity and selectivity the LC-MS-based method allows for a broader coverage and determination of novel fatty acids.

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Upon exposure to light, plant cells quickly acquire photosynthetic competence by converting pale etioplasts into green chloroplasts. This developmental transition involves the de novo biogenesis of the thylakoid system and requires reprogramming of metabolism and gene expression. Etioplast-to-chloroplast differentiation involves massive changes in plastid ultrastructure, but how these changes are connected to specific changes in physiology, metabolism, and expression of the plastid and nuclear genomes is poorly understood. Here, we describe a new experimental system in the dicotyledonous model plant tobacco (Nicotiana tabacum) that allows us to study the leaf deetiolation process at the systems level. We have determined the accumulation kinetics of photosynthetic complexes, pigments, lipids, and soluble metabolites and recorded the dynamic changes in plastid ultrastructure and in the nuclear and plastid transcriptomes. Our data describe the greening process at high temporal resolution, resolve distinct genetic and metabolic phases during deetiolation, and reveal numerous candidate genes that may be involved in light-induced chloroplast development and thylakoid biogenesis.

The implementation of a novel sequential computational approach that can be used effectively for virtual screening and identification of prospective ligands that bind to trypanothione reductase (TryR) is reported. The multistep strategy combines a ligand-based virtual screening for building an enriched library of small molecules with a docking protocol (AutoDock, X-Score) for screening against the TryR target. Compounds were ranked by an exhaustive conformational consensus scoring approach that employs a rank-by-rank strategy by combining both scoring functions. Analysis of the predicted ligand−protein interactions highlights the role of bulky quaternary amine moieties for binding affinity. The scaffold hopping (SHOP) process derived from this computational approach allowed the identification of several chemotypes, not previously reported as antiprotozoal agents, which includes dibenzothiepine, dibenzooxathiepine, dibenzodithiepine, and polycyclic cationic structures like thiaazatetracyclo-nonadeca-hexaen-3-ium. Assays measuring the inhibiting effect of these compounds on T. cruzi and T. brucei TryR confirm their potential for further rational optimization.