Dynamic metabonomic responses of tobacco (Nicotiana tabacum) plants to salt stress

Metabolic responses are important for plant adaptation to osmotic stresses. To understand the dosage and duration dependence of salinity effects on plant metabolisms, we analyzed the metabonome of tobacco plants and its dynamic responses to salt treatments using NMR spectroscopy in combination with multivariate data analysis. Our results showed that the tobacco metabonome was dominated by 40 metabolites including organic acids/bases, amino acids, carbohydrates and choline, pyrimidine, and purine metabolites. A dynamic trajectory was clearly observable for the tobacco metabonomic responses to the dosage of salinity. Short-term low-dose salt stress (50 mM NaCl, 1 day) caused metabolic shifts toward gluconeogenesis with depletion of pyrimidine and purine metabolites. Prolonged salinity with high-dose salt (500 mM NaCl) induced progressive accumulation of osmolytes, such as proline and myo-inositol, and changes in GABA shunt. Such treatments also promoted the shikimate-mediated secondary metabolisms with enhanced biosynthesis of aromatic amino acids. Therefore, salinity caused systems alterations in widespread metabolic networks involving transamination, TCA cycle, gluconeogenesis/glycolysis, glutamate-mediated proline biosynthesis, shikimate-mediated secondary metabolisms, and the metabolisms of choline, pyrimidine, and purine. These findings provided new insights for the tobacco metabolic adaptation to salinity and demonstrated the NMR-based metabonomics as a powerful approach for understanding the osmotic effects on plant biochemistry.     

A comprehensive time‐course metabolite profiling of the model cyanobacterium Synechocystis sp. PCC 6803 under diurnal light:dark cycles

Cyanobacteria are a model photoautotroph and a chassis for the sustainable production of fuels and chemicals. Knowledge of photoautotrophic metabolism in the natural environment of day/night cycles is lacking, yet has implications for improved yield from plants, algae and cyanobacteria. Here, a thorough approach to characterizing diverse metabolites—including carbohydrates, lipids, amino acids, pigments, cofactors, nucleic acids and polysaccharides—in the model cyanobacterium Synechocystis sp. PCC 6803 (S. 6803) under sinusoidal diurnal light:dark cycles was developed and applied. A custom photobioreactor and multi‐platform mass spectrometry workflow enabled metabolite profiling every 30–120 min across a 24‐h diurnal sinusoidal LD (‘sinLD’) cycle peaking at 1600 μmol photons m^?2 sec^?1. We report widespread oscillations across the sinLD cycle with 90%, 94% and 40% of the identified polar/semi‐polar, non‐polar and polymeric metabolites displaying statistically significant oscillations, respectively. Microbial growth displayed distinct lag, biomass accumulation and cell division phases of growth. During the lag phase, amino acids and nucleic acids accumulated to high levels per cell followed by decreased levels during the biomass accumulation phase, presumably due to protein and DNA synthesis. Insoluble carbohydrates displayed sharp oscillations per cell at the day‐to‐night transition. Potential bottlenecks in central carbon metabolism are highlighted. Together, this report provides a comprehensive view of photosynthetic metabolite behavior with high temporal resolution, offering insight into the impact of growth synchronization to light cycles via circadian rhythms. Incorporation into computational modeling and metabolic engineering efforts promises to improve industrially relevant strain design.     

拔节孕穗期小麦干旱胁迫下生长代谢变化规律

采用盆栽试验模拟干旱胁迫(土壤相对含水量40%-45%)在小麦(Triticum aestivum)拔节孕穗期胁迫12天, 测定其生长速率、光合特征及关键代谢产物含量, 以探讨干旱胁迫对拔节孕穗期小麦叶片初生及次生代谢产物的影响及其涉及的代谢途径, 讨论小麦生长代谢变化规律及应答机制。研究表明: 干旱胁迫使小麦叶片气孔受限制导致光合速率下降; 使叶绿素含量下降直接影响光系统II活性, 最终导致生长率降低。检测出的初级代谢产物组包括有机酸、氨基酸、碳水化合物、嘧啶和嘌呤等64个代谢产物, 其中29个代谢产物在干旱胁迫下发生明显的变化。主成分分析(PCA)结果显示全部样本均分布在95%的置信区间内, 两个主成分得分为64%。单因素方差分析结果表明, 干旱胁迫导致苹果酸、柠檬酸、乌头酸等参与三羧酸(TCA)循环的代谢产物消耗明显, 且引起大部分氨基酸(如脯氨酸、丝氨酸、缬氨酸)和碳水化合物(肌醇、果糖、葡萄糖)大量积累的同时转氨基代谢(天冬酰胺、谷氨酰胺和γ氨基丁酸)产物消耗, 研究证明干旱胁迫明显地促进小麦叶片的糖酵解和氨基酸合成途径, 但抑制了TCA循环和转氨基反应, 加速氨基酸代谢网络向脯氨酸合成转变过程。这些结果表明干旱胁迫引起了转氨基反应、TCA循环、糖酵解/糖异生、谷氨酸介导的脯氨酸合成, 以及嘧啶和嘌呤等代谢网络系统广泛的变化, 说明小麦在合成大量的氨基酸和碳水化合物类物质的同时也消耗了大量的能量, 暗示了糖异生到脯氨酸合成的转变。     

Growth metabolism of wheat under drought stress at the jointing-booting stage

AimsThe aim of this study was to investigate the effects of drought stress on primary, secondary metabolites and metabolic pathways in the leaves of wheat, these parameters were evaluated to determine the physiological adaptive mechanisms by which wheat tolerates drought stress at the jointing-booting stage.MethodsA pot experiment was carried out in rain-proof shelter. The relative growth rate, photosynthetic characteristics and metabolism seedlings exposed to stresses lasting 12 days at jointing-booting stage were measured.Important findings The results displayed that the photosynthesis decreased under drought stress, causing the decreases of relative growth rate and dry matter mass. Profiles of 64 key metabolites produced by wheat including organic acids, amino acids, carbohydrates, purine, etc. were examined, 29 of them were changed significantly under drought stress. Principal component analysis (PCA) showed that 64% variations can be explained by the two principal components. One-way ANOVA analysis results revealed that long term drought stress decreased malic acid, citric acid and aconitic acid significantly, indicating inhibited tricarboxylic acid cycle. We further found that prolonged drought stress led to accumulation of progressive amino acids (proline, serine, valine) and carbohydrates (myo-inositol, fructose, clucose) in wheat leaves and depletion of transamination products (asparagine, glutamine, γ-aminobutyric acid). These results imply wheat may enhance its drought tolerance mainly by increasing amino acid biosynthesis and glycolysis under water-deficit conditions. Our findings suggest that drought condition altered metabolic networks including transamination, the tricarboxylic cycle, gluconeogenesis/glycolysis, glutamate-mediated proline biosynthesis, and the metabolisms of choline, pyrimidine and purine. This study provides new insights into the metabolic adaptation of wheat to drought stress and important information for developing drought-tolerant wheat cultivars.     

Durum wheat seedling responses to simultaneous high light and salinity involve a fine reconfiguration of amino acids and carbohydrate metabolism

Durum wheat plants are extremely sensitive to drought and salinity during seedling and early development stages. Their responses to stresses have been extensively studied to provide new metabolic targets and improving the tolerance to adverse environments. Most of these studies have been performed in growth chambers under low light [300–350 µmol m^?2 s^?1 photosynthetically active radiation (PAR), LL]. However, in nature plants have to face frequent fluctuations of light intensities that often exceed their photosynthetic capacity (900–2000 µmol m^?2 s^?1). In this study we investigated the physiological and metabolic changes potentially involved in osmotic adjustment and antioxidant defense in durum wheat seedlings under high light (HL) and salinity. The combined application of the two stresses decreased the water potential and stomatal conductance without reducing the photosynthetic efficiency of the plants. Glycine betaine (GB) synthesis was inhibited, proline and glutamate content decreased, while γ‐aminobutyric acid (GABA), amides and minor amino acids increased. The expression level and enzymatic activities of Δ1‐pyrroline‐5‐carboxylate synthetase, asparagine synthetase and glutamate decarboxylase, as well as other enzymatic activities of nitrogen and carbon metabolism, were analyzed. Antioxidant enzymes and metabolites were also considered. The results showed that the complex interplay seen in durum wheat plants under salinity at LL was simplified: GB and antioxidants did not play a main role. On the contrary, the fine tuning of few specific primary metabolites (GABA, amides, minor amino acids and hexoses) remodeled metabolism and defense processes, playing a key role in the response to simultaneous stresses.     

UPLC‐HRMS‐based untargeted metabolic profiling reveals changes in chickpea (Cicer arietinum) metabolome following long‐term drought stress

Genetic improvement for drought tolerance in chickpea requires a solid understanding of biochemical processes involved with different physiological mechanisms. The objective of this study is to demonstrate genetic variations in altered metabolic levels in chickpea varieties (tolerant and sensitive) grown under contrasting water regimes through ultrahigh‐performance liquid chromatography/high‐resolution mass spectrometry‐based untargeted metabolomic profiling. Chickpea plants were exposed to drought stress at the 3‐leaf stage for 25 days, and the leaves were harvested at 14 and 25 days after the imposition of drought stress. Stress produced significant reduction in chlorophyll content, F_v/F_m, relative water content, and shoot and root dry weight. Twenty known metabolites were identified as most important by 2 different methods including significant analysis of metabolites and partial least squares discriminant analysis. The most pronounced increase in accumulation due to drought stress was demonstrated for allantoin, l ‐proline, l ‐arginine, l ‐histidine, l ‐isoleucine, and tryptophan. Metabolites that showed a decreased level of accumulation under drought conditions were choline, phenylalanine, gamma‐aminobutyric acid, alanine, phenylalanine, tyrosine, glucosamine, guanine, and aspartic acid. Aminoacyl‐tRNA and plant secondary metabolite biosynthesis and amino acid metabolism or synthesis pathways were involved in producing genetic variation under drought conditions. Metabolic changes in light of drought conditions highlighted pools of metabolites that affect the metabolic and physiological adjustment in chickpea that reduced drought impacts.     

In High-Light-Acclimated Coffee Plants the Metabolic Machinery Is Adjusted to Avoid Oxidative Stress Rather than to Benefit from Extra Light Enhancement in Photosynthetic Yield

Coffee (Coffea arabica L.) has been traditionally considered as shade-demanding, although it performs well without shade and even out-yields shaded coffee. Here we investigated how coffee plants adjust their metabolic machinery to varying light supply and whether these adjustments are supported by a reprogramming of the primary and secondary metabolism. We demonstrate that coffee plants are able to adjust its metabolic machinery to high light conditions through marked increases in its antioxidant capacity associated with enhanced consumption of reducing equivalents. Photorespiration and alternative pathways are suggested to be key players in reductant-consumption under high light conditions. We also demonstrate that both primary and secondary metabolism undergo extensive reprogramming under high light supply, including depression of the levels of intermediates of the tricarboxylic acid cycle that were accompanied by an up-regulation of a range of amino acids, sugars and sugar alcohols, polyamines and flavonoids such as kaempferol and quercetin derivatives. When taken together, the entire dataset is consistent with these metabolic alterations being primarily associated with oxidative stress avoidance rather than representing adjustments in order to facilitate the plants from utilizing the additional light to improve their photosynthetic performance.     

ABC1K1/PGR6 kinase: a regulatory link between photosynthetic activity and chloroplast metabolism

Arabidopsis proton gradient regulation (pgr) mutants have high chlorophyll fluorescence and reduced non‐photochemical quenching (NPQ) caused by defects in photosynthetic electron transport. Here, we identify PGR6 as the chloroplast lipid droplet (plastoglobule, PG) kinase ABC1K1 (activity of bc1 complex kinase 1). The members of the ABC1/ADCK/UbiB family of atypical kinases regulate ubiquinone synthesis in bacteria and mitochondria, and impact various metabolic pathways in plant chloroplasts. Here, we demonstrate that abc1k1 has a unique photosynthetic and metabolic phenotype that is distinct from that of the abc1k3 homolog. The abc1k1/pgr6 single mutant is specifically deficient in the electron carrier plastoquinone, as well as in β–carotene and the xanthophyll lutein, and is defective in membrane antioxidant tocopherol metabolism. After 2 days of continuous high light stress, abc1k1/pgr6 plants suffer extensive photosynthetic and metabolic perturbations, strongly affecting carbohydrate metabolism. Remarkably, however, the mutant acclimates to high light after 7 days together with a recovery of carotenoid levels and a drastic alteration in the starch‐to‐sucrose ratio. Moreover, ABC1K1 behaves as an active kinase and phosphorylates VTE1, a key enzyme of tocopherol (vitamin E) metabolism in vitro. Our results indicate that the ABC1K1 kinase constitutes a new type of regulatory link between photosynthetic activity and chloroplast metabolism.     

The significance of amino acids and amino acid-derived molecules in plant responses and adaptation to heavy metal stress

Plants exposed to heavy metals accumulate an array of metabolites, some to high millimolar concentrations. This review deals with N-containing metabolites frequently preferentially synthesized under heavy metal stress such as Cd, Cu, Ni, and Zn. Special focus is given to proline, but certain other amino acids and oligopeptides, as well as betaine, polyamines, and nicotianamine are also addressed. Particularly for proline a large body of data suggests significant beneficial functions under metal stress. In general, the molecules have three major functions, namely metal binding, antioxidant defence, and signalling. Strong correlative and mechanistic experimental evidence, including work with transgenic plants and algae, has been provided that indicates the involvement of metal-induced proline in metal stress defence. Histidine, other amino acids and particularly phytochelatins and glutathione play a role in metal binding, while polyamines function as signalling molecules and antioxidants. Their accumulation needs to be considered as active response and not as consequence of metabolic dys-regulation.     

Photorespiration: metabolic pathways and their role in stress protection

Photorespiration results from the oxygenase reaction catalysed by ribulose-1,5-bisphosphate carboxylase/oxygenase. In this reaction glycollate-2-phosphate is produced and subsequently metabolized in the photorespiratory pathway to form the Calvin cycle intermediate glycerate-3-phosphate. During this metabolic process, CO2 and NH3 are produced and ATP and reducing equivalents are consumed, thus making photorespiration a wasteful process. However, precisely because of this inefficiency, photorespiration could serve as an energy sink preventing the overreduction of the photosynthetic electron transport chain and photoinhibition, especially under stress conditions that lead to reduced rates of photosynthetic CO2 assimilation. Furthermore, photorespiration provides metabolites for other metabolic processes, e.g. glycine for the synthesis of glutathione, which is also involved in stress protection. In this review we describe the use of photorespiratory mutants to study the control and regulation of photorespiratory pathways. In addition, we discuss the possible role of photorespiration under stress conditions, such as drought, high salt concentrations and high light intensities encountered by alpine plants.     

Unraveling Physiological and Metabolomic Responses Involved in Phlox subulata L. Tolerance to Drought Stress

Metabolic responses are important for plant adaptation to abiotic stress. To investigate the responses of Phlox subulata L. to drought stress, we analyzed its physiological and metabolic changes using gas chromatography-mass spectrometer. Based on the physiological indices, P. subulata L. has tolerance to drought to some degree. Our results showed that there were a total of 30 key metabolites induced by drought stress, including amino acids, organic acids, sugars and sugar alcohols, nucleic acid and its derivatives, and other organic compounds. The glutamic acid-mediated proline biosynthesis pathway is continuously upregulated under drought stress, which could regulate osmotic pressure and maintain intracellular environmental stability. More secondary metabolites are used to increase glycolysis and tricarboxylic acid cycle, to accelerate energy production and to enhance the glutamic acid-mediated proline biosynthesis pathway, which are necessary to increase osmotic regulation. Prolonged drought stress induced progressive accumulation of compatible osmolytes, such as proline and inositol, sugars, and amino acids. Therefore, drought caused systemic alterations in metabolic networks involving transamination, TCA cycle, gluconeogenesis/glycolysis, glutamate-mediated proline biosynthesis, shikimate-mediated secondary metabolisms, and the metabolism of pyrimidine. These data suggest that plants may utilize these physiological and metabolomic adjustments as adaptive responses in the early stages of drought stress. These results deepen our understanding of the mechanisms involved in P. subulata L. drought tolerance, which will help improve the understanding of drought’s effects on plant systems.

     

Computational predictions of common transcription factor binding sites on the genes of proline metabolism in plants

Proline, an imino acid, has been well documented to be associated with the stress response induced by abiotic factors such as drought, cold and salinity in plants and biotic factors such as bacterial and fungal attacks. However, the regulatory mechanisms controlling proline metabolism, intercellular and intracellular transport and connections of proline to other metabolic pathways are poorly understood. F-MATCH analysis combined with composite module analysis (CMA) revealed that the binding sites matching matrices for O2 and OCSBF-1 were overrepresented in the promoters of differentially expressed proline metabolism genes. The presence of MYBAS1 consensus binding sites occurring in combination with O2 and OCSBF1 in the promoters of genes of proline biosynthesis pathway and SBF1 and GT1 consensus binding sites occurring in combination with O2 and OCSBF1 in the promoters of proline catabolic pathway genes suggest their involvement in modulation of proline metabolism and its accumulation in plants.     

Cold adaptation shapes the robustness of metabolic networks in Drosophila melanogaster

When ectotherms are exposed to low temperatures, they enter a cold‐induced coma (chill coma) that prevents resource acquisition, mating, oviposition, and escape from predation. There is substantial variation in time taken to recover from chill coma both within and among species, and this variation is correlated with habitat temperatures such that insects from cold environments recover more quickly. This suggests an adaptive response, but the mechanisms underlying variation in recovery times are unknown, making it difficult to decisively test adaptive hypotheses. We use replicated lines of Drosophila melanogaster selected in the laboratory for fast (hardy) or slow (susceptible) chill‐coma recovery times to investigate modifications to metabolic profiles associated with cold adaptation. We measured metabolite concentrations of flies before, during, and after cold exposure using nuclear magnetic resonance (NMR) spectroscopy to test the hypotheses that hardy flies maintain metabolic homeostasis better during cold exposure and recovery, and that their metabolic networks are more robust to cold‐induced perturbations. The metabolites of cold‐hardy flies were less cold responsive and their metabolic networks during cold exposure were more robust, supporting our hypotheses. Metabolites involved in membrane lipid synthesis, tryptophan metabolism, oxidative stress, energy balance, and proline metabolism were altered by selection on cold tolerance. We discuss the potential significance of these alterations.     

Adequate S supply protects barley plants from adverse effects of salinity stress by increasing thiol contents

As the salt-affected areas are expected to increase substantially in subsequent years, the impact of salinity on plant growth and yield is likely to increase. One of the first consequences of plant exposure to high saline concentrations is the formation of reactive oxygen species (ROS). In order to allow adjustment of the cellular redox state, plant antioxidative system has to be activated. This system involves several enzymes and compounds, as the sulphur-containing metabolite glutathione (GSH). Therefore, our aim was to determine whether adequate sulphur nutrition might alleviate the adverse effects of salt stress on barley plants grown in the presence of different sulphate application rate and exposed to 100 mM NaCl, by studying differences in growth parameters, lipid peroxidation, sulphate and thiol accumulation and sulphur assimilation pathway. In salt-treated plants, an adequate sulphur supply allows adequate GSH synthesis (high-thiol concentration) thus avoiding the effects of ROS on photosynthetic functions (no effect on both chlorophyll and protein content), whereas in S-deficient plants, salt stress leads to excess ROS production that induces stress and plants showed reduction of photosynthetic efficiency (loss of chlorophyll and protein contents). As thiol levels are more abundant in S-sufficient plants than in those S-deficient, one might expect that S-sufficient plants are more able to remove the harmful effects of high salinity. The comparison of malondialdehyde levels between +S and ?S salt-treated plants strongly supports this idea. In conclusion, we found that plant sulphur nutritional status plays a key role in the metabolic modifications necessary to cope with salt stress.     

Combined effects of CO2 enrichment,diurnal light levels and water stress on foliar metabolites of potato plants grown in naturally sunlit controlled environment chambers

Experiments were conducted in outdoor, naturally sunlit, soil–plant–atmosphere research (SPAR) chambers using plants grown in pots. Drought treatments were imposed on potato plants (Solanum tuberosum cv. Kennebec) beginning 10 days after tuber initiation. A total of 23 out of 37 foliar metabolites were affected by drought when measured 11 days after initiating water stress treatments. Compounds that accumulated in response to drought were hexoses, polyols, branched chain amino acids (BCAAs) and aromatic amino acids, such as proline. Conversely, leaf starch, alanine, aspartate and several organic acids involved in respiratory metabolism decreased with drought. Depending upon harvest date, a maximum of 12 and 17 foliar metabolites also responded to either CO₂ enrichment or diurnal treatments, respectively. In addition, about 20% of the measured metabolites in potato leaflets were simultaneously affected by drought, CO₂ enrichment and diurnal factors combined. This group contained BCAAs, hexoses, leaf starch and malate. Polyols and proline accumulated in response to water stress but did not vary diurnally. Water stress also amplified diurnal variations of hexoses and starch in comparison to control samples. Consequently, specific drought responsive metabolites in potato leaflets were dramatically affected by daily changes of photosynthetic carbon metabolism.     

The Aging Metabolome—Biomarkers to Hub Metabolites

Aging biology is intimately associated with dysregulated metabolism, which is one of the hallmarks of aging. Aging‐related pathways such as mTOR and AMPK, which are major targets of anti‐aging interventions including rapamcyin, metformin, and exercise, either directly regulate or intersect with metabolic pathways. In this review, numerous candidate bio‐markers of aging that have emerged using metabolomics are outlined. Metabolomics studies also reveal that not all metabolites are created equally. A set of core “hub” metabolites are emerging as central mediators of aging. The hub metabolites reviewed here are nicotinamide adenine dinucleotide, reduced nicotinamide dinucleotide phosphate, α‐ketoglutarate, and β‐hydroxybutyrate. These “hub” metabolites have signaling and epigenetic roles along with their canonical roles as co‐factors or intermediates of carbon metabolism. Together these hub metabolites suggest a central role of the TCA cycle in signaling and metabolic dysregulation associated with aging.