Different accumulation of free amino acids during short- and long-term osmotic stress in wheat

Copper toxicity leads to accumulation of free amino acids and polyphenols in Phaeodactylum tricornutum diatoms

This work is focused on the effect of lethal and sub-lethal copper (Cu) concentrations on the free amino acid and polyphenol production by the marine diatom Phaeodactylum tricornutum (P. tricornutum) after 12, 18, and 21 days of exposure. The concentrations of 10 amino acids (arginine, aspartic acid, glutamic acid, histidine, lysine, methionine, proline, valine, isoleucine, and phenylalanine) and 10 polyphenols (gallic acid, protocatechuic acid, p-coumaric acid, ferulic acid, catechin, vanillic acid, epicatechin syringic acid, rutin, and gentisic acid) were measured by RP-HPLC. Under lethal doses of Cu, free amino acids reached levels significantly higher than those in the control cells (up to 21.9 times higher), where histidine and methionine showed the highest increases (up to 37.4 and 65.8 times higher, respectively). The total phenolic content also increased up to 11.3 and 5.59 times higher compared to the reference cells, showing gallic acid the highest increase (45.8 times greater). The antioxidant activities of cells exposed to Cu were also enhanced with increasing doses of Cu(II). They were evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging ability (RSA), cupric ion reducing antioxidant capacity (CUPRAC), and ferric reducing antioxidant power (FRAP) assays. Malonaldehyde (MDA) exhibited the same tendency: cells grown at the highest lethal Cu concentration yielded the highest MDA level. These findings reflect the involvement of amino acids and polyphenols in protective mechanisms to overcome the toxicity of copper in marine microalgae.

Metabolism of carbohydrates and activity of the antioxidant system in mosses on a post-technogenic salinized territory

Adaptive physiological and biochemical reactions of mosses Didymodon rigidulus Hedw., Barbula unguiculata Hedw. and Brachythecium campestre (Müll. Hal.) Schimp. to salt stress have been investigated from the territory of the tailings storage of the Stebnyk Mining and Chemical Enterprise “Polymineral” (Lviv region, Ukraine). The peculiarities of carbohydrate metabolism in mosses under salinity conditions have been studied. The content of soluble carbohydrates and proline, the antioxidant activity, the content of ascorbate and reduced glutathione as well as the activity of enzymes of their metabolism – ascorbate peroxidase and glutathione reductase at the initial stages of the stress (salt shock) and prolonged stress exposure (salt stress) have been evaluated. It has been found that the increase of α-amylase activity, enhancement of the hydrolysis of starch and the increase of the concentration of soluble carbohydrates under salt stress were the reactions of the studied species of mosses. It has been established that there was an increase in the concentration of soluble carbohydrates by 1.2–1.5 times in moss shoots under salinity conditions, compared with plants from the background area (vicinity of Stebnyk). Experimental studies have shown that under salinity conditions sucrose dominates in the pool of soluble carbohydrates (59.0–79.5% of the total sugars content). The sucrose content was 1.5–2.0 times higher in the plants B. unguiculata and D. rigidulus from the highly saline area of the tailings storage. It has been indicated that under stress conditions constitutive adaptive mechanisms are more expressed in resistant moss species, and plants with a lower level of resistance adapt to the stressor, mainly due to induced protective systems. Experimental studies have shown that plants B. unguiculata and D. rigidulus, which are resistant to abiotic stressors, have a high constitutive pool of soluble carbohydrates both at the beginning of the experiment and under prolonged exposure of the salt stress. In the shoots of the sensitive moss B. campestre the stress-induced character of the sugars accumulation has been revealed. The accumulation of proline in mosses cells under salt stress depended on their species characteristics. The stress-induced accumulation of proline can be considered as a part of the bryophytes’ protective system, but this osmolyte does not play a key role in the formation of the mosses’ resistance to salt stress. Obviously, soluble carbohydrates are the main osmolytes in the moss cells. It has been found that resistant moss species have a high constitutive antioxidant status, while in the sensitive moss B. campestre the increase in the antioxidant activity occurred during prolonged salt stress, which may indicate its induced nature. It has been shown that the resistant mosses B. unguiculata and D. rigidulus have 3–4 times higher levels of glutathione and ascorbate content and 1.6–2.5 times higher activity of enzymes of their metabolism – glutathione reductase and ascorbate peroxidase, compared to plants of the less tolerant moss species B. campestre, which provided reduction of the lipid peroxidation process in plasma membranes and decreased the content of TBA-active products under stress.

Full-Length Transcriptome and RNA-Seq Analyses Reveal the Mechanisms Underlying Waterlogging Tolerance in Kiwifruit (Actinidia valvata)

Actinidia valvata possesses waterlogging tolerance; however, the mechanisms underlying this trait are poorly characterized. Here, we performed a transcriptome analysis by combining single-molecule real-time (SMRT) sequencing and Illumina RNA sequencing and investigated the physiological responses of the roots of KR5 (A. valvata, a tolerant genotype) after 0, 12, 24 and 72 h of waterlogging stress. KR5 roots responded to waterlogging stress mainly via carbohydrate and free amino acids metabolism and reactive oxygen species (ROS) scavenging pathways. Trehalose-6-phosphate synthase (TPS) activity, alcohol dehydrogenase (ADH) activity and the total free amino acid content increased significantly under waterlogging stress. The nicotinamide adenine dinucleotide-dependent glutamate synthase/alanine aminotransferase (NADH-GOGAT/AlaAT) cycle was correlated with alanine accumulation. Levels of genes encoding peroxidase (POD) and catalase (CAT) decreased and enzyme activity increased under waterlogging stress. Members of the LATERAL ORGAN BOUNDARIES (LOB), AP2/ERF-ERF, Trihelix and C3H transcription factor families were identified as potential regulators of the transcriptional response. Several hub genes were identified as key factors in the response to waterlogging stress by a weighted gene co-expression network analysis (WGCNA). Our results provide insights into the factors contributing to waterlogging tolerance in kiwifruit, providing a basis for further studies of interspecific differences in an important plant trait and for molecular breeding.

Proteomics analysis of the effects for different salt ions in leaves of true halophyte Sesuvium portulacastrum

Sesuvium portulacastrum is a true halophyte and shows an optimal development under moderate salinity with large amounts of salt ions in its leaves. However, the specific proteins in response to salt ions are remained unknown. In this study, comparative physiological and proteomic analyses of different leaves subject to NaCl, KCl, NaNO₃ and KNO₃ were performed. Chlorophyll content was decreased under the above four kinds of salt treatments. Starch and soluble sugar contents changed differently under different salt treatments. A total of 53 differentially accumulated proteins (DAPs) were identified by mass spectrometry. Among them, 13, 25, 26 and 25 DAPs were identified after exposure to KCl, NaCl, KNO_3, and NaNO₃, respectively. These DAPs belong to 47 unique genes, and 37 of them are involved in protein-protein interactions. These DAPs displayed different expression patterns after treating with different salt ions. Functional annotation revealed they are mainly involved in photosynthesis, carbohydrate and energy metabolism, lipid metabolism, and biosynthesis of secondary metabolites. Genes and proteins showed different expression profiles under different salt treatments. Enzyme activity analysis indicated P-ATPase was induced by KCl, NaCl and NaNO₃, V-ATPase was induced by KCl and NaCl, whereas V-PPase activity was significantly increased after application of KNO₃, but sharply inhibited by NaCl. These results might deepen our understanding of responsive mechanisms in the leaves of S. portulacastrum upon different salt ions.

Altering Amino Acid Profile in Catharanthus Roseus (L.) G. Don Using Potassium and Ascorbic Acid Treatments

Background:

Catharanthus roseus (L.) G. Don is the main source of alkaloids anticancer drugs. Alkaloids are derived from amino acids and can lead to changes in these valuable compounds.

Objective:

This experiment evaluated the variation of amino acids under potassium and ascorbic acid treatments.

Methods:

Different concentrations (1.5, 3.16, 15 and 30 mM) and forms (K2SO4 and KNO3) of potassium (K+) were added to plants via Hoagland’s nutrient solution. Ascorbic acid (AsA) (750 mg L-1) was sprayed on the leaves surfaces on days 68 and 78. Amino acids were extracted from 90-day-old plant leaves, and different amino acids were determined by High-Performance Liquid Chromatography with fluorescence detection.

Results:

Amino acids increased in K+ deficiency (1.5 mM), but changes in negatively charged amino acids were lower. In contrast, N-rich amino acids showed the biggest change. In excessive K+, branched-chain and aromatic amino acids decreased, while the least amount of the other amino acids was observed in the plants treated with optimum K+.

Conclusion:

The exterior of AsA and excessive K+ cause branched-chain and aromatic amino acids, aspartic acid and glutamic acid to decrease.

Integrated genomic and transcriptomic analysis reveals unique mechanisms for high osmotolerance and halotolerance in Hyphopichia yeast

The yeast species Hyphopichia is common in nature and strongly competitive under harsh environmental conditions. Here, we characterized Hyphopichia burtonii KJJ43 and H. pseudoburtonii KJS14, which exhibit strong halotolerance, using genomic and transcriptomic analyses. The genomes of H. burtonii and H. pseudoburtonii comprised eight chromosomes with 85.17% nucleotide identity and significant divergence in synteny. Notably, both Hyphopichia genomes possessed extended gene families of amino acid permeases and ATP-binding cassette (ABC) transporters, whose dynamic expression patterns during osmotic stress were revealed using transcriptome profiling. Intriguingly, we found unique features of the HOG pathway activated by Hog1p even under non-osmotic stress conditions and the upregulation of cytosolic Gpd1 protein during osmotic stress. Associated with hyperfilamentation growth under high osmotic conditions, a set of genes in the FLO family with induced expression in response to NaCl, KCl, and sorbitol supplementation were identified. Moreover, comparative transcriptome analysis reveals the NaCl-specific induction of genes involved in amino acid biosynthesis and metabolism, particularly BAT2. This suggests the potential association between oxoacid reaction involving branched-chain amino acids and osmotolerance. The combined omics analysis of two Hyphopichia species provides insights into the novel mechanisms involved in salt and osmo-stress tolerance exploited by diverse eukaryotic organisms.

Interaction among species, time-of-day, and soil water potential on biochemical and physiological characteristics of cladodes of Opuntia

The physiology and biochemistry of young Opuntia spp. cladodes relate with their Crassulacean acid metabolism, which extends over the day-night cycle in four phases, is species-dependent and is affected by water availability. This study aimed to assess the interaction among species, time-of-day, and the soil water potential (Ψ_W) on biochemical and physiological characteristics of cladodes of Opuntia species. Three-week-old cladodes were harvested at 7:00 a.m. and 3:00 p.m. from plants with or without irrigation for 30 d (-0.17 and -5.72 MPa soil Ψ_W), from O. albicarpa, O. ficus-indica, O. hyptiacantha, O. megacantha, and O. streptacantha. The experimental design was a factorial 5 x 2 x 2 (species, sampling time and soil Ψ_W). The experimental unit was one cladode per plant, and six repetitions were evaluated. Total acids, glucose, fructose, sucrose, starch, total phenolics, free amino acids, and soluble proteins concentrations were evaluated, as well as acid invertase and neutral invertase activities. The interaction among species x soil Ψ_W and species x time of the day was significant (P ≤ 0.05) in all variables evaluated. An exception was the species x soil Ψ_W on starch concentration (P = 0.1827). The biochemical and physiological characteristics of Opuntia cladodes were modified by the time of the day and soil Ψ_W interaction, but most of the characteristics were positively or inversely affected depending on the species, frequently displaying a descending trend following O. streptacantha, O. hyptiacantha, O. megacantha, O. albicarpa and O. ficus-indica. The total acids, glucose, fructose, starch, soluble proteins, and free amino acids concentrations revealed that domestication significantly modifies C and N metabolism in Opuntia.

Impact of melatonin and tryptophan on water stress tolerance in white lupine (Lupinus termis L.)

Melatonin  has been identified as a signal molecule that regulates plant responses to different abiotic and biotic stresses. Melatonin (MT) and its precursor tryptophan (Try) have a major role in improving plant stress tolerance to different environmental stresses such as water deficiency. The rapid increase in the Egyptian population caused insufficient protein sources, especially those of animal origin, in their diet. The possible solution is to augment the diet with legumes such as white lupine which are relatively rich in protein. Thus, the current experimental work was carried out to find changes in growth, biochemical aspects and yield quantity and quality of white lupine plant with spraying of both MT and Try at different concentrations on plant shoot under water deficit stress conditions. Results showed that water deficit (75 or 50% of water irrigation requirements; WIR) caused significant reduction in growth, photosynthetic pigments, indole acetic acid and yield compared with those received 100% WIR. Seed yield significantly decreased (p < 0.05) by 26.98 and 41.64% by decreasing WIR to 75 and 50%. The decrease was accompanied by significant increase in phenolic contents, hydrogen peroxide, lipid peroxidation and some antioxidant enzymes, while nitrate reductase enzyme was decreased. However, external application of either MT or Try significantly alleviated the adverse effects of water deficit (growth suppression), since MT or Try-treated plants recovered more quickly than untreated plants. Moreover, MT or Try-treated plants had higher photosynthetic pigments, indole acetic acid, phenolic, as well as yield quantity and quality under the three WIR as compared with untreated plants. Melatonin treatment at 100 µM and Tryptophan at 200 µM increased weight of seeds/plant by 78.29 and 52.19%, 71.49 and 43.78% and 41.21 and 13.07% in plants irrigated with 100, 75 and 50% WIR, respectively. Exogenous MT and Try significantly reduced hydrogen peroxide and malondialdehyde content, while markedly increased the activities of antioxidant enzymes and nitrate reductase under different WIR. Finally, the current study concluded that MT and Try treatments alleviated the detrimental effects of water deficiency and accelerated the recovery mainly via improving white lupine plants tolerance in forms of enhancing photosynthetic pigments, indole acetic acid, phenolic and antioxidant capacity.

NMR and LC-MS-Based Metabolomics to Study Osmotic Stress in Lignan-Deficient Flax

Lignans, phenolic plant secondary metabolites, are derived from the phenylpropanoid biosynthetic pathway. Although, being investigated for their health benefits in terms of antioxidant, antitumor, anti-inflammatory and antiviral properties, the role of these molecules in plants remains incompletely elucidated; a potential role in stress response mechanisms has been, however, proposed. In this study, a non-targeted metabolomic analysis of the roots, stems, and leaves of wild-type and PLR1-RNAi transgenic flax, devoid of (+) secoisolariciresinol diglucoside ((+) SDG)-the main flaxseed lignan, was performed using 1H-NMR and LC-MS, in order to obtain further insight into the involvement of lignan in the response of plant to osmotic stress. Results showed that wild-type and lignan-deficient flax plants have different metabolic responses after being exposed to osmotic stress conditions, but they both showed the capacity to induce an adaptive response to osmotic stress. These findings suggest the indirect involvement of lignans in osmotic stress response.

Tolerance Patterns and Transcriptomic Response to Extreme and Fluctuating Salinities across Populations of the Intertidal Copepod Tigriopus californicus

AbstractPopulations that tolerate extreme environmental conditions with frequent fluctuations can give valuable insights into physiological limits and adaptation. In some estuarine and marine ecosystems, organisms must adapt to extreme and fluctuating salinities, but not much is known about how varying salinities impact local adaptation across a wide geographic range. We used eight geographically and genetically divergent populations of the intertidal copepod Tigriopus californicus to test whether northern populations have greater tolerance to low salinity stresses, as they experience greater precipitation and less evaporation. We used a common-garden experiment approach and exposed all populations to acute low (1 and 3 ppt) and high (110 and 130 ppt) salinities for 24 h and to a fluctuation between baseline salinity and moderate low (7 ppt) and high (80 ppt) salinities for over 49 h. We also performed RNA sequencing at several time points during the fluctuation between baseline and salinity of 7 ppt to understand the molecular basis of divergence between two populations with differing physiological responses. We present these novel findings: (1) acute low salinity conditions caused more deaths than high salinity; (2) molecular processes that elevate proline levels increased in salinity of 7 ppt, which contrasts with other physiological studies in T. californicus that mainly associated accumulation of proline with hyperosmotic stress; and (3) tolerance to a salinity fluctuation did not follow a latitudinal trend but was instead governed by a complex interplay of factors, including population and duration of salinity stress. This highlights the importance of including a wider variety of environmental conditions in empirical studies to understand local adaptation.

Exogenous application of 24-epibrassinosteroid mitigates NaCl toxicity in flax by modifying free amino acids profile and antioxidant defence system

In the present study, we investigated the ameliorative effects of 24-epibrassinosteroid (24-epiBL) on antioxidant response and ion homeostasis in two NaCl-stressed Linum usitatissimum L. (flax) cultivars differing in salt tolerance. The content and profile of amino acids were also studied in the tolerant cultivar. Salt stress differently altered the activity of antioxidant enzymes, phenol and flavonoid contents, total antioxidant capacity and ion homeostasis in both cultivars, whereas H2O2 and malondialdehyde (MDA) contents were induced only in the TN-97-95 cultivar. Free amino acid concentrations showed variable patterns under salinity conditions compared with the control plants. 24-epiBL decreased the soluble protein content in NaCl-treated plants and also decreased stimulatory effects of salinity on the production and accumulation of phenol and flavonoid contents and antioxidant capacity with altered ion (Na+, K+, and Cl-) contents. The 24-epiBL reduced the chlorophylls (a, b) and carotenoid contents in salt-treated TN-97-95 cultivar while enhanced the activity of antioxidant enzymes and declined the H2O2 content and lipid peroxidation in both NaCl-stressed cultivars. The profile and content of amino acids were significantly changed by 24-epiBL application under salinity treatment. In summary, our findings demonstrate that 24-epiBL seed priming mitigates the deleterious effects of salt stress in flax plants.

Differential adaptation strategies to different levels of soil water deficit in two upland and lowland genotypes of rice: a physiological and metabolic approach

BACKGROUND

Upland genotypes of rice are less sensitive to soil water deficit (SWD), making them suitable candidates for revealing the strategies underlying plant tolerance. The physiological factors, the biochemical traits needed to withstand oxidative stress, and the metabolite fluctuations of an upland genotype (Azucena) and an intolerant lowland genotype (IR64) genotype were measured under two levels of SWD (withholding water for 7- or 14 days) to identify SWD-responsive strategies associated with tolerance.

RESULTS

After withholding water for 7 days, no significant changes in physiological and biochemical traits of Azucena were observed, whereas in IR64, significant decreases in physiological factors were recorded along with increases in oxidative-stress indicators. However, the root length of Azucena increased significantly, showing a clear stress avoidance strategy. Under a prolonged treatment (14 days), IR64 entered an oxidative-damage stage, whereas Azucena exhibited a highly efficient antioxidant system. Our metabolite analysis also revealed two different enriched pathways. After a 7-day SWD, the sugar levels were decreased in the leaves of Azucena but increased in IR64. The reduction in the sugar levels (up to 1.79-log2FC) in the Azucena leaves may be indicative of their transport to the roots, supplying the carbon source needed for root elongation. Under a 14-day treatment, proline and aspartate family members accumulated to the highest levels in Azucena, whereas an increase in the levels of aromatic amino acids with key roles in the biosynthesis of secondary metabolites was detected in IR64.

CONCLUSION

The adaptation strategies identified in two types of rice genotypes in confronting SWD may assist researchers in finding the proper indicators for screening more tolerant genotypes. © 2019 Society of Chemical Industry.

Exogenously applied 5-aminolevulinic acid modulates growth, secondary metabolism and oxidative defense in sunflower under water deficit stress

The present experiment was set-up to appraise protective role of ALA in sunflower cultivars (FH-1581 and FH-1572) under water scarcity stress. The  ameliorative role of ALA in sunflower under water stress is not fully understood. Results showed significant decline in growth parameters, ascorbic acid and chlorophyll but marked increase in MDA, H2O2, total soluble proteins, flavonoids, proline, phenolics, total free amino acids as well as enzymes activities namely CAT, POD and SOD in plants under water scarcity. ALA application reduced oxidative damage by lowering H2O2 and MDA contents. ALA application differentially affected two cultivars under stress. Higher biomass accumulation was manifested in cv. FH-1581, while cv. FH-1572 was inferior in this context. Greater drought tolerance in cv. FH-1581 was related to higher cellular levels of proline, total free amino acids and efficient antioxidant system.

Spermidine application reduces fluoride uptake and ameliorates physiological injuries in a susceptible rice cultivar by activating diverse regulators of the defense machinery

The manuscript illustrates the ameliorative effects of exogenously applied higher polyamine (PA), spermidine (Spd) in the susceptible indica rice cultivar IR-64 subjected to prolonged fluoride stress. The Spd treatment drastically reduced fluoride bioaccumulation by restricting entry of the anions through chloride channels and enabled better maintenance of the proton gradient via accumulation of P-H⁺/ATPase, thereby improving the root and shoot lengths, fresh and dry weights, RWC, chlorophyll content and activities of pyruvate dehydrogenase (PyrDH), α-amylase, and nitrate reductase (NR) in the Spd-treated, stressed plants. Expression of RuBisCo, PyrDH, α-amylase, and NR was stimulated. Spd supplementation reduced the molecular damage indices like malondialdehyde, lipoxygenase, protease activity, electrolyte leakage, protein carbonylation, H₂O₂, and methylglyoxal (detoxified by glyoxalase II). Mitigation of oxidative damage was facilitated by the accumulation and utilization of proline, glycine-betaine, total amino acids, higher PAs, anthocyanin, flavonoids, β-carotene, xanthophyll, and phenolics as verified from the expression of genes like P5CS, BADH1, SAMDC, SPDS, SPMS, DAO, PAO, and PAL. Spd treatment activated the ascorbate-glutathione cycle in the stressed seedlings. Expression and activities of enzymatic antioxidants showed that GPOX, APX, GPX, and GST were the chief ROS scavengers. Exogenous Spd promoted ABA accumulation by upregulating NCED3 and suppressing ABA8ox1 expression. ABA-dependent osmotic stress-responsive genes like Osem, WRKY71, and TRAB1 as well as ABA-independent transcription factor encoding gene DREB2A were induced by Spd. Thus, Spd treatment ameliorated fluoride-mediated injuries in IR-64 by restricting fluoride uptake, refining the defense machinery and activating the ABA-dependent as well as ABA-independent stress-responsive genes.

Back to the Salt Mines: Genome and Transcriptome Comparisons of the Halophilic Fungus Aspergillus salisburgensis and Its Halotolerant Relative Aspergillus sclerotialis

Salt mines are among the most extreme environments as they combine darkness, low nutrient availability, and hypersaline conditions. Based on comparative genomics and transcriptomics, we describe in this work the adaptive strategies of the true halophilic fungus Aspergillus salisburgensis, found in a salt mine in Austria, and compare this strain to the ex-type halotolerant fungal strain Aspergillus sclerotialis. On a genomic level, A. salisburgensis exhibits a reduced genome size compared to A. sclerotialis, as well as a contraction of genes involved in transport processes. The proteome of A. sclerotialis exhibits an increased proportion of alanine, glycine, and proline compared to the proteome of non-halophilic species. Transcriptome analyses of both strains growing at 5% and 20% NaCl show that A. salisburgensis regulates three-times fewer genes than A. sclerotialis in order to adapt to the higher salt concentration. In A. sclerotialis, the increased osmotic stress impacted processes related to translation, transcription, transport, and energy. In contrast, membrane-related and lignolytic proteins were significantly affected in A. salisburgensis.

Comparative proteomic analysis of two sesame genotypes with contrasting salinity tolerance in response to salt stress

Sesame is one of the most important oilseed crops and has high nutritional value. The yield and quality of sesame are severely affected by high salinity in coastal and semi-arid/arid regions. In this study, the phenotypic, physiological, and proteomic changes induced by salt treatment were analyzed in salt-tolerant (G441) and salt-sensitive (G358) seedlings. Phenotypic and physiological results indicated that G441 had an enhanced capacity to withstand salinity stress compared to G358. Proteomic analysis revealed a strong induction of salt-responsive protein species in sesame, mainly related to catalytic, hydrolase, oxidoreductase, and binding activities. Pathway enrichment analysis showed that more salt-responsive proteins in G441 were involved in tyrosine metabolism, carbon fixation in photosynthetic organisms, carbon metabolism, alpha-linolenic acid metabolism, biosynthesis of amino acids, photosynthesis, and glutathione metabolism. Furthermore, G441 displayed unique differentially accumulated proteins in seedlings functioning as heat shock proteins, abscisic acid receptor PYL2-like, calcium-dependent protein kinases, serine/threonine-protein phosphatases, nucleoredoxin, and antioxidant enzymes. Quantitative real-time PCR analysis revealed that some of the proteins were also regulated by salinity stress at the transcript level. Our findings provide important information on salinity responses in plants and may constitute useful resources for enhancing salinity tolerance in sesame. SIGNIFICANCE: Our study identified potential biological pathways and salt-responsive protein species related to transducing stress signals and scavenging reactive oxygen species under salt stress. These findings will provide possible participants/pathways/proteins that contribute to salt tolerance and may serve as the basis for improving salinity tolerance in sesame and other plants.

Changes in the free amino acid composition of Capsicum annuum (pepper) leaves in response to Myzus persicae (green peach aphid) infestation. A comparison with water stress

Amino acids play a central role in aphid-plant interactions. They are essential components of plant primary metabolism, function as precursors for the synthesis of defense-related specialized metabolites, and are major growth-limiting nutrients for aphids. To quantify changes in the free amino acid content of pepper (Capsicum annuum L.) leaves in response to green peach aphid (Myzus persicae Sulzer) feeding, plants were infested with a low (20 aphids/plant) or a high (200 aphids/plant) aphid density in time-course experiments ranging from 3 hours to 7 days. A parallel experiment was conducted with pepper plants that had been subjected to water stress. Factor Analysis of Mixed Data revealed a significant interaction of time x density in the free amino acid response of aphid-infested leaves. At low aphid density, M. persicae did not trigger a strong response in pepper leaves. Conversely, at high density, a large increase in total free amino acid content was observed and specific amino acids peaked at different times post-infestation. Comparing aphid-infested with water-stressed plants, most of the observed differences were quantitative. In particular, proline and hydroxyproline accumulated dramatically in response to water stress, but not in response to aphid infestation. Some additional differences and commonalities between the two stress treatments are discussed.

When Transcriptomics and Metabolomics Work Hand in Hand: A Case Study Characterizing Plant CDF Transcription Factors

Over the last three decades, novel “omics” platform technologies for the sequencing of DNA and complementary DNA (cDNA) (RNA-Seq), as well as for the analysis of proteins and metabolites by mass spectrometry, have become more and more available and increasingly found their way into general laboratory life. With this, the ability to generate highly multivariate datasets on the biological systems of choice has increased tremendously. However, the processing and, perhaps even more importantly, the integration of “omics” datasets still remains a bottleneck, although considerable computational and algorithmic advances have been made in recent years. In this mini-review, we use a number of recent “multi-omics” approaches realized in our laboratories as a common theme to discuss possible pitfalls of applying “omics” approaches and to highlight some useful tools for data integration and visualization in the form of an exemplified case study. In the selected example, we used a combination of transcriptomics and metabolomics alongside phenotypic analyses to functionally characterize a small number of Cycling Dof Transcription Factors (CDFs). It has to be remarked that, even though this approach is broadly used, the given workflow is only one of plenty possible ways to characterize target proteins.

Abscisic acid-regulated protein degradation causes osmotic stress-induced accumulation of branched-chain amino acids in Arabidopsis thaliana

Whereas proline accumulates through de novo biosynthesis in plants subjected to osmotic stress, leucine, isoleucine, and valine accumulation in drought-stressed Arabidopsis thaliana is caused by abscisic acid-regulated protein degradation. In response to several kinds of abiotic stress, plants greatly increase their accumulation of free amino acids. Although stress-induced proline increases have been studied the most extensively, the fold-increase of other amino acids, in particular branched-chain amino acids (BCAAs; leucine, isoleucine, and valine), is often higher than that of proline. In Arabidopsis thaliana (Arabidopsis), BCAAs accumulate in response to drought, salt, mannitol, polyethylene glycol, herbicide treatment, and nitrogen starvation. Plants that are deficient in abscisic acid signaling accumulate lower amounts of BCAAs, but not proline and most other amino acids. Previous bioinformatic studies had suggested that amino acid synthesis, rather than protein degradation, is responsible for the observed BCAA increase in osmotically stressed Arabidopsis. However, whereas treatment with the protease inhibitor MG132 decreased drought-induced BCAA accumulation, inhibition of BCAA biosynthesis with the acetolactate synthase inhibitors chlorsulfuron and imazapyr did not. Additionally, overexpression of BRANCHED-CHAIN AMINO ACID TRANSFERASE2 (BCAT2), which is upregulated in response to osmotic stress and functions in BCAA degradation, decreased drought-induced BCAA accumulation. Together, these results demonstrate that BCAA accumulation in osmotically stressed Arabidopsis is primarily the result of protein degradation. After relief of the osmotic stress, BCAA homeostasis is restored over time by amino acid degradation involving BCAT2. Thus, drought-induced BCAA accumulation is different from that of proline, which is accumulated due to de novo synthesis in an abscisic acid-independent manner and remains elevated for a more prolonged period of time after removal of the osmotic stress.

Proteomic Analyses Reveal the Mechanism of Dunaliella salina Ds-26-16 Gene Enhancing Salt Tolerance in Escherichia coli

We previously screened the novel gene Ds-26-16 from a 4 M salt-stressed Dunaliella salina cDNA library and discovered that this gene conferred salt tolerance to broad-spectrum organisms, including E. coli (Escherichia coli), Haematococcus pluvialis and tobacco. To determine the mechanism of this gene conferring salt tolerance, we studied the proteome of E. coli overexpressing the full-length cDNA of Ds-26-16 using the iTRAQ (isobaric tags for relative and absolute quantification) approach. A total of 1,610 proteins were identified, which comprised 39.4% of the whole proteome. Of the 559 differential proteins, 259 were up-regulated and 300 were down-regulated. GO (gene ontology) and KEGG (Kyoto encyclopedia of genes and genomes) enrichment analyses identified 202 major proteins, including those involved in amino acid and organic acid metabolism, energy metabolism, carbon metabolism, ROS (reactive oxygen species) scavenging, membrane proteins and ABC (ATP binding cassette) transporters, and peptidoglycan synthesis, as well as 5 up-regulated transcription factors. Our iTRAQ data suggest that Ds-26-16 up-regulates the transcription factors in E. coli to enhance salt resistance through osmotic balance, energy metabolism, and oxidative stress protection. Changes in the proteome were also observed in E. coli overexpressing the ORF (open reading frame) of Ds-26-16. Furthermore, pH, nitric oxide and glycerol content analyses indicated that Ds-26-16 overexpression increases nitric oxide content but has no effect on glycerol content, thus confirming that enhanced nitric oxide synthesis via lower intercellular pH was one of the mechanisms by which Ds-26-16 confers salt tolerance to E. coli.

Long-term trends of changes in pine and oak foliar nitrogen metabolism in response to chronic nitrogen amendments at Harvard Forest, MA

We evaluated the long-term (1995-2008) trends in foliar and sapwood metabolism, soil solution chemistry and tree mortality rates in response to chronic nitrogen (N) additions to pine and hardwood stands at the Harvard Forest Long Term Ecological Research (LTER) site. Common stress-related metabolites like polyamines (PAs), free amino acids (AAs) and inorganic elements were analyzed for control, low N (LN, 50 kg NH4NO3 ha(-1) year(-1)) and high N (HN, 150 kg NH4NO3 ha(-1) year(-1)) treatments. In the pine stands, partitioning of excess N into foliar PAs and AAs increased with both N treatments until 2002. By 2005, several of these effects on N metabolites disappeared for HN, and by 2008 they were mostly observed for LN plot. A significant decline in foliar Ca and P was observed mostly with HN for a few years until 2005. However, sapwood data actually showed an increase in Ca, Mg and Mn and no change in PAs in the HN plot for 2008, while AAs data revealed trends that were generally similar to foliage for 2008. Concomitant with these changes, mortality data revealed a large number of dead trees in HN pine plots by 2002; the mortality rate started to decline by 2005. Oak trees in the hardwood plot did not exhibit any major changes in PAs, AAs, nutrients and mortality rate with LN treatment, indicating that oak trees were able to tolerate the yearly doses of 50 kg NH4NO3 ha(-1) year(-1). However, HN trees suffered from physiological and nutritional stress along with increased mortality in 2008. In this case also, foliar data were supported by the sapwood data. Overall, both low and high N applications resulted in greater physiological stress to the pine trees than the oaks. In general, the time course of changes in metabolic data are in agreement with the published reports on changes in soil chemistry and microbial community structure, rates of soil carbon sequestration and production of woody biomass for this chronic N study. This correspondence of selected metabolites with other measures of forest functions suggests that the metabolite analyses are useful for long-term monitoring of the health of forest trees.

Genetic variation and possible SNP markers for breeding wheat with low-grain asparagine, the major precursor for acrylamide formation in heat-processed products

BACKGROUND

In products made from wheat (Triticum aestivum) flour, acrylamide formation is almost exclusively determined by the level of free asparagine in the grain. Genetic variability for grain asparagine content was evaluated in order to assess the potential for acrylamide mitigation by breeding.

RESULTS

Free asparagine levels in the grains of 92 varieties varied from 137 to 471 mg kg⁻¹, representing an approximate threefold difference between the low- and high-asparagine genotypes. Heritability was low, with a value of 32%, indicating that breeding cultivars with inherently low grain asparagine would be a challenge. A genome-wide scan with single-nucleotide polymorphism (SNP) markers identified nine SNPs that were significantly (P < 0.001) associated with variation in free asparagine. The significant SNPs were localized on chromosome 5A, and explained between 14% and 24% of the observed variation. These putative SNPs are candidates for further studies to develop molecular markers.

CONCLUSION

Significant genetic variation exists for reducing acrylamide precursors in wheat flour, indicating that breeding and genetics could play an important role in mitigating the acrylamide risk in wheat products. The study identified a region on chromosome 5A that could provide a basis for further research to develop functional markers.