Accumulation Of Free Amino Acids Research Articles

Enrichment of free amino acid content and reduction of astringent taste compounds in soybean by high hydrostatic pressure

ABSTRACTWe investigated the effect of high hydrostatic pressure (HHP) on the distribution of free amino acids and isoflavones in soybean immediately after pressure treatment (100–600 MPa, 10–60 min). HHP-treatment at 200 and 300 MPa resulted in high accumulation of free amino acids. Additionally, Gly, Val, and Pro levels increased even after HHP of 400 MPa. The application of HHP-treatment to soybean decreased sources of an astringent taste such as genistein-, daizein-, and glycitein-type molecules under all pressure conditions over 200 MPa. High accumulation of free amino acids with specific pressure–time conditions would be caused by the acceleration of proteolysis and specific amino acid metabolism. We concluded that HHP alone with no subsequent storage enabled the enrichment of specific amino acids such as GABA, Glu, Lys, and Pro in soybean. Soybean with enrichment of these amino acids and improved taste should be an innovative component of functional foods.

The effect of high hydrostatic pressure on taste substance distribution in fresh green tea leaves

ABSTRACTHigh hydrostatic pressure (HHP) can be an alternative method to steaming to inhibit enzymatic fermentation in green tea making process. However, the effect of HHP treatment on green tea taste is not clear. Thus, this study aimed to determine the effect of HHP on substances associated with green tea taste. Fresh green tea leaves were immediately treated with HHP at 300, 500, or 700 MPa for 10, 30, or 60 min at 25°C. The concentration of free amino acids, catechins, and caffeine in HHP-treated samples was quantified by LC-MS. The taste intensity of the samples was detected by taste sensors. HHP resulted in a high accumulation of free amino acids in green tea leaves, which was likely due to proteolysis. In particular, theanine synthesis may have been promoted by an increase in the concentration of substrates during HHP. Compared to steaming, HHP enhanced umami richness, and inhibited bitterness and astringency.

In situ transcriptomic and metabolomic study of the loss of photosynthesis in the leaves of mixotrophic plants exploiting fungi.

Mycoheterotrophic plants have lost photosynthesis and obtain carbon through mycorrhizal fungi colonizing their roots. They are likely to have evolved from mixotrophic ancestors, which rely on both photosynthesis and fungal carbon for their development. Whereas our understanding of the ecological and genomic changes associated with the evolutionary shift to mycoheterotrophy is deepening, little information is known about the specific metabolic and physiological features driving this evolution. We investigated this issue in naturally occurring achlorophyllous variants of temperate mixotrophic orchids. We carried out an integrated transcriptomic and metabolomic analysis of the response to achlorophylly in the leaves of three mixotrophic species sampled in natura. Achlorophyllous leaves showed major impairment of their photosynthetic and mineral nutrition functions, strong accumulation of free amino acids, overexpression of enzymes and transporters related to sugars, amino acids and fatty acid catabolism, as well as induction of some autophagy-related and biotic stress genes. Such changes were reminiscent of these reported for variegated leaves and appeared to be symptomatic of a carbon starvation response. Rather than decisive metabolic innovations, we suggest that the evolution towards mycoheterotrophy in orchids is more likely to be reliant on the versatility of plant metabolism and an ability to exploit fungal organic resources, especially amino acids, to replace missing photosynthates.

The role of amino acid metabolism during abiotic stress release.

Plant responses to abiotic stress include various modifications in amino acid metabolism. By using a hydroponic culture system, we systematically investigate modification in amino acid profiles and the proteome of Arabidopsis thaliana leaves during initial recovery from low water potential or high salinity. Both treatments elicited oxidative stress leading to a biphasic stress response during recovery. Degradation of highly abundant proteins such as subunits of photosystems and ribosomes contributed to an accumulation of free amino acids. Catabolic pathways for several low abundant amino acids were induced indicating their usage as an alternative respiratory substrate to compensate for the decreased photosynthesis. Our results demonstrate that rapid detoxification of potentially detrimental amino acids such as Lys is a priority during the initial stress recovery period. The content of Pro, which acts as a compatible osmolyte during stress, was adjusted by balancing its synthesis and catabolism both of which were induced both during and after stress treatments. The production of amino acid derived secondary metabolites was up-regulated specifically during the recovery period, and our dataset also indicates increased synthesis rates of the precursor amino acids. Overall, our results support a tight relationship between amino acid metabolism and stress responses.

Increase in assimilatory nitrate reduction and photorespiration enhances CO2 assimilation under high light-induced photoinhibition in cotton

The mechanisms by which nitrate assimilation might favour photorespiration and how these pathways could cooperatively improve photosynthesis are still little understood, especially under excess light. Here, we tested the hypothesis that increased assimilatory nitrate reduction is able to stimulate photorespiration and these two processes together are capable to enhance photosynthesis in presence of high light. Cotton plants were supplied with 10 mM NO3− (high nitrate supply-HN) or NO3--deprivation for short-term and subsequently exposed to high light-HL or low light-LL. HL induced photoinhibition in both N-treatments but strongly enhanced nitrate assimilation and photorespiration rates in HN. Despite these apparent constraints caused by HL on PSII integrity, HN-plants displayed higher electron flux through PSII, in parallel to enhancement in CO2 assimilation, which was positively related to the photosynthetic nitrogen utilization efficiency. These plants also exhibited increase in nitrate reductase and glutamine synthetase activities, which were associated with large accumulation of free amino acids and ammonia, in parallel to high NO3- reduction rates. The increase in photorespiration was greatly dependent on light intensity and, in a minor extent, on nitrate supply. The changes in the alternative electron sink strength towards nitrate assimilation and photorespiration were corroborated by decrease in the acceptor side limitation of PSI. In addition, the correlation study evidenced that CO2 assimilation, nitrate reductase activity, and photorespiration rates were greatly correlated. Thus, our data clearly show that nitrate assimilatory reduction and photorespiration are mutually up regulated by high light, favoring CO2 assimilation and photochemical activity under a photoinhibitory condition.

Nitric oxide triggered defense network in wheat: Augmenting tolerance and grain-quality related traits under heat-induced oxidative damage

Heat stress (HS) drastically reduces the yield and quality of wheat grains. High temperature during critical stages (pollination and grain-filling) causes improper fertilization and formation of defragmented granules and shriveled seeds. Hormones and signaling molecules modulates the tolerance potential of the plants under stress. Nitric oxide (NO) is an important signaling molecule involved in triggering diverse physiological and biochemical processes under adverse conditions. Here, we studied the effect of sodium nitroprusside (SNP) (150 μM set based on pilot experiment) on heat stress-tolerance and grain quality related traits of two contrasting wheat cultivars Raj3765 as thermotolerant and HD2932 as thermosusceptible under differential HS (T1 - 30 °C, 1 h; T2 - 38 °C, 1 h), as compared to control (22 ± 2 °C) at different stages of growth. The expression of many important stress-associated genes (previously identified through Transcriptome sequencing) was observed upregulated in response to NO and HS; small HSP17 showed maximum fold increase in Raj3765. Similarly, the networks of antioxidant enzymes (SOD, CAT, and GPX) were observed triggered in response to NO, HS and NO + HS treatment in Raj3765 than HD2932. The accumulation of proline and free amino acid in cytoplasm were also reported higher under NO and HS treatment respectively in Raj3765, as compared to HD2932. Grain quality related traits like carbohydrate (starch) and proteins (gliadin) were observed higher in response to NO under HS in Raj3765. Heat stress was observed to increase the activities of α/β amylases in developing grains involved in degrading the starch quality. NO was observed to decrease the amylolytic activity in both the cultivars; very low amylolytic activity was observed in thermotolerant, as compared to thermosusceptible cultivars. Exogenous application of NO (150 μM) at different stages can be used as inexpensive technology for mitigating the problem of terminal HS in wheat – a farmer friendly approach for maintaining the quality of grains under present threat of global climate change.

Biochemical changes in naturally aged seeds of soybean genotypes with good and poor storability

Seed deterioration during storage is associated with various metabolic and chemical alterations that vary among genotypes in soybean. In the present study, five genotypes with good storability viz., kalitur, MACS 1416, EC 18761, CO1 and DSB21 and five genotypes with poor storability viz., JS 71-05, DS 228, MAUS 61, NRC 93 and DSB 24 were selected and evaluated for biochemical changes to identify the best donors for storability. Among the genotypes, all the poor storer genotypes showed faster accumulation of free amino acids, free fatty acids and malondialdehyde content as a result of oxidative stress. Poor storer genotypes also showed the increased lipoxygenase I and II enzymes activity. All the good storer genotypes showed higher anti-oxidative enzymes activity causing slower lipid peroxidation. Among the good storers, kalitur showed favourable biochemical features for storability while MAUS-61 was identified as poor storer exhibiting less favourable biochemical features.

Betaine Aldehyde Dehydrogenase (BADH) gene and free amino acid analysis in Rhizophora mucronata Lam. from Thalassery region of Kerala, India.

Mangroves are salt tolerant plants inhabiting saline environment. Multiple factors contribute to their salt tolerance and we need multifaceted approach to reveal the mechanisms of salt tolerance in the plant. In the present study, leaves of the mangrove, Rhizophora mucronata grown in the presence and absence of salt were used, free amino acids and the expression of selected genes were analyzed. Chromatographic technique showed the accumulation of free amino acids like proline, glycine, aspartic acid, valine, leucine and glutamic acid in the presence of salt. RNA was isolated from the leaf sample and cDNA was synthesized. Gene specific primers were designed and standardized. Among the genes studied (P5CS, BADH, NHX1), Betaine Aldehyde dehydrogenase (BADH) gene was found to be expressed.

Significantly increased amino acid accumulation in a novel albino branch of the tea plant (Camellia sinensis).

A normal tea plant with one albino branch was discovered. RNA sequencing, albinism phenotype and ultrastructural observations provided a valuable understanding of the albino mechanism in tea plants. Tea plants with a specific color (white or yellow) have been studied extensively. A normal tea plant (Camellia sinensis cv. quntizhong) with one albino branch was discovered in a local tea plantation in Huangshan, Anhui, China. The pure albino leaves on this special branch had accumulated a fairly high content of amino acids, especially theanine (45.31mg/g DW), and had a low concentration of polyphenols and an extremely low chlorophyll (Chl) content compared with control leaves. Ultrastructural observation of an albino leaf revealed no chloroplasts, whereas it was viable in the control leaf. RNA sequencing and differentially expressed gene (DEG) analysis were performed on the albino leaves and on control leaves from a normal green branch. The related genes involved in theanine and polyphenol biosynthesis were also investigated in this study. DEG expression patterns in Chl biosynthesis or degradation, carotenoid biosynthesis or degradation, chloroplast development, and biosynthesis were influenced in the albino leaves. Chloroplast deletion in albino leaves had probably destroyed the balance of carbon and nitrogen metabolism, leading to a high accumulation of free amino acids and a low concentration of polyphenols in the albino leaves. The obtained results can provide insight into the mechanism underlying this special albino branch phenotype, and are a valuable contribution toward understanding the albino mechanism in tea plants.

Exopolysaccharides producing rhizobacteria and their role in plant growth and drought tolerance.

Drought stress not only effect the population and activities of microorganisms inhabiting the rhizosphere but also various physiological and biochemical process in plants that is, photosynthesis, respiration, translocation, uptake of ions, carbohydrates, and nutrient metabolism. Plant growth promoting rhizobacteria (PGPR) and their exopolysaccharides (EPS) showed profound effects on plant growth and drought tolerance. Reactions of bacteria to drought stress at various organizational levels are different which depends on intensity of stress, duration, species, and growth stage. PGPR could be effectively utilized in developing strategies to facilitate water conservation strategies of plants. They have the ability to improve plant growth directly by enhancing level of phytohormones, siderophore, biofilm, and exopolysaccharides production and by increasing the nutrient availability in the rhizosphere or indirectly by protecting plants from pathogen attack. EPS producing bacteria are capable to maintain higher soil moisture content and growth of plants even under severe dried sandy soils. The evidence of survival of rhizobacteria under low moisture content obtained from the fact of rhizobacterial occurrence in the soil of desert and effective nodule formation in desert soil. Beside this, EPS produced by PGPR form rhizosheath around the roots and thus protect the plant roots from desiccation for a longer period of time. Important role exhibited by exopolysaccharides includes, protection from desiccation, microbial aggregation, plant-microbe interaction, surface attachment, bioremediation and its use by many industries for stabilizing, thickening, coagulating, gelling, suspending and for film forming. Plants inoculated with EPS-producing bacteria showed higher accumulation of proline, sugars, and free amino acids under water deficit stress. Biofilms formed by the PGPR around the roots are made up of bacterial populations or bacterial communities that encased inside the polymeric extracellular matrix formed by bacteria itself, they adhered to the external surfaces that contain sufficient moisture. It is concluded that the application of PGPR in combination with their EPS is a promising measure to combat drought stress thus, increasing global food security.

Effect of starter cultures on taste-active amino acids and survival of pathogenic Escherichia coli in dry fermented beef sausages

The accumulation of taste-active compounds during ripening determines the taste of fermented meats; however, the contribution of defined starter cultures to glutamate during sausage ripening remains unknown. This study investigated the role of lactic acid bacteria and Staphylococcus carnosus on the accumulation of free amino acids during dry sausage fermentation. A sausage model system was developed to control sausage microbiota throughout ripening. Sausages were produced at the laboratory scale with defined starter cultures; aseptic controls were fermented without culture addition. Lactobacillus sakei, Lactobacillus plantarum, Pediococcus pentosaceus, and Pediococcus acidilactici were used as single cultures; Staphylococcus carnosus with L. sakei or P. pentosaceus were used as cocktails. The viable cell counts in aseptic control sausages remained < 1 log (CFU/g) throughout 20 days of ripening. The use of the model system demonstrated that bacterial enzymes influenced the release of free amino acids, even during the initial fermentation stage. Ripening time was the most important factor determining the accumulation of free amino acids, and the accumulation of glutamate was not strain specific. The sausage model system was also used for a challenge trial with a cocktail of pathogenic strains of Escherichia coli; viable cell counts of pathogenic E. coli were reduced by less than 1 log (CFU/g) during ripening. The sausage model for control of ripening microbiota will facilitate further studies on the impact of defined cultures on the safety and quality of fermented meats.

Occurrence of non-proteolytic amino acyl derivatives in dry-cured ham

Proteolysis is the most important event occurring during maturation of dry-cured hams: it strongly influences the flavour and the texture of the aged ham by the accumulation of peptides and free amino acids released by protein hydrolysis. Apart from compounds of proteolytic origin, it has been demonstrated that also non-proteolytic amino acyl derivatives (γ-glutamyl amino acids, pyroglutamyl-amino acids and lactoyl-amino acids) may accumulate during ripening of cheese, and they can be also found in fermented soy sauce, where they contribute to the umami taste of the products. Using a semi-quantitative analysis, in this paper we report the occurrence of significant amounts of γ-glutamyl amino acids and, for the first time, pyroglutamyl-amino acids and lactoyl-amino acids, in aged ham. The amino acid counterparts were mainly found to be hydrophobic amino acids. The amount of these compounds was found to increase with time, because they are not degraded by proteolytic activity. They were also found to be stable to simulated gastrointestinal digestion. Angiotensin Converting Enzyme inhibitory activity was also tested, but they were not found to be characterized by significant ACE-inhibitory activity.

Effects of cadmium stress on growth and amino acid metabolism in two Compositae plants

Cadmium, a high toxic heavy metal, is one of the most serious contaminants in soil and a potential threat to plant growth and human health. Amino acid metabolism has the central role in heavy metal stress resistance of plants. In this paper, a pot experiment was carried out to study the effects of different concentrations of cadmium (0, 3, 6, 12, 30 mg kg−1) on the growth, Cd accumulation and amino acid metabolism in two Compositae plants (Ageratum conyzoides L. and Crassocephalum crepidioides). The results showed that under cadmium stress, C. crepidioides accumulated more Cd in its shoot and was tolerant to Cd, whereas its low Cd-accumulating relative, A. conyzoides, suffered reduced growth. The Cd content in the aerial part of C. crepidioides exceeded the threshold of Cd-hyperaccumulator. Furthermore, the bioaccumulation factor (BCF) and biological transfer factor (BTF) values for Cd in C. crepidioides were > 1. Thus, C. crepidioides can be regarded as Cd-hyperaccumulator. The comparison between both studied plants indicated that Cd stress resulted in a differential but coordinated response of amino acid levels, which are playing a significant role in plant adaptation to Cd stress. Glu, Gln, Asp, Asn, Gaba, Val and Ala dominated the major amino acids. Higher Cd tolerance and Cd accumulation in C. crepidioides was associated with greater accumulation of free amino acids, especially for Gln and Asn, in C. crepidioides than in A. conyzoides.

Adaptive remodeling of skeletal muscle energy metabolism in high-altitude hypoxia: Lessons from AltitudeOmics

Metabolic responses to hypoxia play important roles in cell survival strategies and disease pathogenesis in humans. However, the homeostatic adjustments that balance changes in energy supply and demand to maintain organismal function under chronic low oxygen conditions remain incompletely understood, making it difficult to distinguish adaptive from maladaptive responses in hypoxia-related pathologies. We integrated metabolomic and proteomic profiling with mitochondrial respirometry and blood gas analyses to comprehensively define the physiological responses of skeletal muscle energy metabolism to 16 days of high-altitude hypoxia (5260 m) in healthy volunteers from the AltitudeOmics project. In contrast to the view that hypoxia down-regulates aerobic metabolism, results show that mitochondria play a central role in muscle hypoxia adaptation by supporting higher resting phosphorylation potential and enhancing the efficiency of long-chain acylcarnitine oxidation. This directs increases in muscle glucose toward pentose phosphate and one-carbon metabolism pathways that support cytosolic redox balance and help mitigate the effects of increased protein and purine nucleotide catabolism in hypoxia. Muscle accumulation of free amino acids favor these adjustments by coordinating cytosolic and mitochondrial pathways to rid the cell of excess nitrogen, but might ultimately limit muscle oxidative capacity in vivo Collectively, these studies illustrate how an integration of aerobic and anaerobic metabolism is required for physiological hypoxia adaptation in skeletal muscle, and highlight protein catabolism and allosteric regulation as unexpected orchestrators of metabolic remodeling in this context. These findings have important implications for the management of hypoxia-related diseases and other conditions associated with chronic catabolic stress.

Soy and Rapeseed Protein Hydrolysis by the Enzyme Preparation Protosubtilin

A comparative study of soybean and rapeseed protein hydrolysis by protosubtilin, an original Russian enzyme preparation widely used in animal feed production, has been performed. SDS-PAG electrophoresis, HPLC, and mass spectrometry have been employed to analyze the obtained products. The soybean protein isolate used for hydrolysate production was obtained from a commercial supplier, and rapeseed proteins were prepared from the meal by alkali extraction. Low molecular weight impurities were removed by ultrafiltration. The degree of protein hydrolysis has been shown to depend on the substrate-to-enzyme preparation ratio, hydrolysis time, and protein concentration. Rapeseed protein hydrolysis by protosubtilin at an enzyme/protein ratio of 1: 20 and hydrolysis time of 20 h resulted in complete cleavage of the proteins present in the raw material and the accumulation of oligopeptides (molecular weight less than 14 kDa) and free amino acids, which accounted for 53 and 8% of the initial protein weight, respectively. In contrast to rapeseed proteins, soybean proteins showed considerable gelling at the initial stages of hydrolysis, and the formation of insoluble hydrolysis-resistant fragments was observed. The soluble part of the hydrolysate contained short oligopeptides and free amino acids, which accounted for 13% of the initial protein weight only.

Phenotypic and transcriptomic responses to salinity stress across genetically and geographically divergent Tigriopus californicus populations.

Species inhabiting the North American west coast intertidal must tolerate an extremely variable environment, with large fluctuations in both temperature and salinity. Uncovering the mechanisms for this tolerance is key to understanding species' persistence. We tested for differences in salinity tolerance between populations of Tigriopus californicus copepods from locations in northern (Bodega Reserve) and southern (San Diego) California known to differ in temperature, precipitation and humidity. We also tested for differences between populations in their transcriptomic responses to salinity. Although these two populations have ~20% mtDNA sequence divergence and differ strongly in other phenotypic traits, we observed similarities in their phenotypic and transcriptomic responses to low and high salinity stress. Salinity significantly affected respiration rate (increased under low salinity and reduced under high salinity), but we found no significant effect of population on respiration or a population by salinity interaction. Under high salinity, there was no population difference in knock-down response, but northern copepods had a smaller knock-down under low salinity stress, corroborating previous results for T.californicus. Northern and southern populations had a similar transcriptomic response to salinity based on a principle components analysis, although differential gene expression under high salinity stress was three times lower in the northern population compared to the southern population. Transcripts differentially regulated under salinity stress were enriched for "amino acid transport" and "ion transport" annotation categories, supporting previous work demonstrating that the accumulation of free amino acids is important for osmotic regulation in T.californicus.

Physiological and biochemical changes during drought and recovery periods at tillering and jointing stages in wheat (Triticum aestivum L.)

Defining the metabolic strategies used by wheat to tolerate and recover from drought events will be important for ensuring yield stability in the future, but studies addressing this critical research topic are limited. To this end, the current study quantified the physiological, biochemical, and agronomic responses of a drought tolerant and drought sensitive cultivar to periods of water deficit and recovery. Drought stress caused a reversible decline in leaf water relations, membrane stability, and photosynthetic activity, leading to increased reactive oxygen species (ROS) generation, lipid peroxidation and membrane injury. Plants exhibited osmotic adjustment through the accumulation of soluble sugars, proline, and free amino acids and increased enzymatic and non-enzymatic antioxidant activities. After re-watering, leaf water potential, membrane stability, photosynthetic processes, ROS generation, anti-oxidative activities, lipid peroxidation, and osmotic potential completely recovered for moderately stressed plants and did not fully recover in severely stressed plants. Higher photosynthetic rates during drought and rapid recovery after re-watering produced less-pronounced yield declines in the tolerant cultivar than the sensitive cultivar. These results suggested that the plant’s ability to maintain functions during drought and to rapidly recover after re-watering during vegetative periods are important for determining final productivity in wheat.

Reconstructing clear water state and submersed vegetation on behalf of repeated flocculation with modified soil in an in situ mesocosm experiment in Lake Taihu

The geo-engineering approach of modified soil flocculation has been widely applied to mitigate algal blooms and eutrophication in relatively small lakes. Nevertheless, its potential ecological risks and feasibility should be examined and identified prior to its application in large natural lakes given the multiple functions of these water bodies in human health and welfare. In situ mesocosm experiments on modified soil flocculation were performed in Lake Taihu during summer 2010 and 2011. Chitosan-modified kaolinite (CMK) soil was used to flocculate algal blooms and improve water transparency to facilitate the re-establishment of the submersed macrophyte Vallisneria natans in this shallow eutrophic lake. Moreover, the ecological effects of CMK soil were assessed. Results showed that repeated additions of CMK (0.3g/L for each time) improved water quality in terms of Chl-a, TN, and TP concentrations; TN/TP ratio; turbidity; redox conditions; and nitrification and denitrification activities. These effects lasted for 48days. After the fourth dose of CMK, the biomass of all phytoplankton categories, except for that of Cryptophyta, decreased by >90% (ca. 1–2×106cell/L or 0.38–0.55mg/L of wet weight). Zooplankton biomass markedly decreased after the first CMK addition, and copepods became dominant. These effects, however, did not last for the long term. Most importantly, submersed V. natans was restored successfully when water clarity and quality were improved through repeated CMK flocculation. Nevertheless, the indices of carbohydrate depletion and free amino acid accumulation indicated that the plant experienced physiological stresses. The reestablishment of V. natans reinforced the positive effects of repeated CMK dosing on water quality, and promoted a clear water state. V. natans is recommended for vegetative restoration in shallow eutrophic lakes given its facile transplantation, high stress tolerance, and physiological traits, which can be applied as indices of post-flocculation effects. In summary, the combination of repeated CMK dosing and revegetation of V. natans can feasibly improve water quality and initiate the restoration of a clear water state in shallow eutrophic lakes.

Role of Free Amino Acids in Renal Tissue of Air-Breathing Catfish, Heteropneustes Fossilis Under-Desiccation Stress (Mud Dwelling)

The Indian air-breathing catfish, Heteropneustes fossilis faces various environmental constraints throughout the year leading to the problem of accumulation of toxic ammonia. Water restricted mud dwelling condition is a common environmental stress (desiccation stress) for catfishes in North Eastern India during winter. The fish is able to survive inside moist peat for months. In the present study the air breathing singhi catfish H. fossilis was kept inside mud peat for 30 days mimicking their normal habitat in winter and the changing pattern of free amino acid (FAAs) content was investigated in renal tissue. Under desiccation, a significant accumulation of ammonia and FAA, mainly glutamine, alanine, glycine, glutamate and serine have been observed in the renal tissue with approximately 2.56 and 1.56 fold increase. Thus, it appears that the Indian air-breathing catfish handle the ammonia toxicity by conversion of ammonia to some non-essential FAAs.

Phenylethanoid glycosides accumulation in roots of Scrophularia striata as a response to water stress

Plants respond to water deficit by adjusting many biochemical pathways that lead to synthesis of osmotically active metabolites and specific proteins that control scavenging of oxygen radicals and water flux. This study was carried out to elucidate the role of phenylethanoid glycosides (PhGs) as a part of primary and secondary metabolic networks responsive to water stress in Scrophularia striata. The 65-day-old seedlings of S. striata in Hoagland's solution were exposed to polyethylene glycol 6000 (˗0.5bar) over a time course of 72h. The observed data indicate that H2O2 content and activities of antioxidant enzymes such as catalase (CAT), guaiacol peroxidase (GPX) and superoxide dismutase (SOD) increased at all exposure times. Acteoside and echinacoside (two important PhGs as osmotic metabolites) were highly accumulated in the roots over the exposure time. A positive correlation was observed between PhGs, phenolic acids and flavonoids contents with phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) activities which peaked at over the treatment time. Furthermore, water stress altered soluble sugars content (glucose, mannose, rhamnose and xylose) and free amino acids (phenylalanine, tyrosine and arginine) accumulation. Our observations corroborate that in S. striata, the increase of soluble sugars and free amino acids under osmotic stress not only serve as compatible solute but also with favoring PhGs and other phenolic compounds production can improve water stress tolerance.