Total Amino Acid Levels Research Articles

Alpha-ketoglutarate enhances freeze-thaw tolerance and prevents carbohydrate-induced cell death of the yeast Saccharomyces cerevisiae.

Stress resistance and fermentative capability are important quality characteristics of baker's yeast. In the present study, we examined protective effects of exogenous alpha-ketoglutarate (AKG), an intermediate of the tricarboxylic acid cycle and amino acid metabolism, against freeze-thaw and carbohydrate-induced stresses in the yeast Saccharomyces cerevisiae. Growth on AKG-supplemented medium prevented a loss of viability and improved fermentative capacity of yeast cells after freeze-thaw treatment. The cells grown in the presence of AKG had higher levels of amino acids (e.g., proline), higher metabolic activity and total antioxidant capacity, and higher activities of catalase, NADP-dependent glutamate dehydrogenase and glutamine synthase compared to control ones. Both synthesis of amino acids and enhancement of antioxidant system capacity could be involved in AKG-improved freeze-thaw tolerance in S. cerevisiae. Cell viability dramatically decreased under incubation of stationary-phase yeast cells in 2% glucose or fructose solutions (in the absence of the other nutrients) as compared with incubation in distilled water or in 10mM AKG solution. The decrease in cell viability was accompanied by acidification of the medium, and decrease in cellular respiration, aconitase activity, and levels of total protein and free amino acids. The supplementation with 10mM AKG effectively prevented carbohydrate-induced yeast death. Protective mechanisms of AKG could be associated with the intensification of respiration and prevention of decreasing protein level as well as with direct antioxidant AKG action.

Influence of heat stress on leaf morphology and nitrogen–carbohydrate metabolisms in two wucai (Brassica campestris L.) genotypes

Heat stress is a major environmental stress that limits plant growth and yield worldwide. The present study was carried out to explore the physiological mechanism of heat tolerant to provide the theoretical basis for heat-tolerant breeding. The changes of leaf morphology, anatomy, nitrogen assimilation, and carbohydrate metabolism in two wucai genotypes (WS-1, heat tolerant; WS-6, heat sensitive) grown under heat stress (40°C/30°C) for 7 days were investigated. Our results showed that heat stress hampered the plant growth and biomass accumulation in certain extent in WS-1 and WS-6. However, the inhibition extent of WS-1 was significantly smaller than WS-6. Thickness of leaf lamina, upper epidermis, and palisade mesophyll were increased by heat in WS-1, which might be contributed to the higher assimilation of photosynthates. During nitrogen assimilation, WS-1 possessed the higher nitrogen-related metabolic enzyme activities, including nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH), which were reflected by higher photosynthetic nitrogen-use efficiency (PNUE) with respect to WS-6. The total amino acids level had no influence in WS-1, whereas it was reduced in WS-6 by heat. And the proline contents of both wucai genotypes were all increased to respond the heat stress. Additionally, among all treatments, the total soluble sugar content of WS-1 by heat got the highest level, including higher contents of sucrose, fructose, and starch than those of WS-6. Moreover, the metabolism efficiency of sucrose to starch in WS-1 was greater than WS-6 under heat stress, proved by higher activities of sucrose phosphate synthase (SPS), sucrose synthase (SuSy), acid invertase (AI), and amylase. These results demonstrated that leaf anatomical alterations resulted in higher nitrogen and carbon assimilation in heat-tolerant genotype WS-1, which exhibited a greater performance to resist heat stress.

Assessment of 28 trace elements and 17 amino acid levels in muscular tissues of broiler chicken (Gallus gallus) suffering from arsenic trioxide

The contents of 28 trace elements, 17 amino acid were evaluated in muscular tissues (wings, crureus and pectoralis) of chickens in response to arsenic trioxide (As2O3). A total of 200 one-day-old male Hy-line chickens were fed either a commercial diet (C-group) or an As2O3 supplement diet containing 7.5mg/kg (L-group), 15mg/kg (M-group) or 30mg/kg (H-group) As2O3 for 90 days. The elements content was analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Under As2O3 exposure, the concentration of As were elevated 8.87–15.76 fold, 7.93–15.63 fold and 5.94–12.45 fold in wings, crureus and pectoralis compared to the corresponding C-group, respectively. 19 element levels (lithium (Li), magnesium (Mg), aluminum (Al), silicon (Si), kalium (K), vanadium (V), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), selenium (Se), strontium (Sr), molybdenum (Mo), cadmium (Cd), tin (Sn), antimony (Sb), barium (Ba), mercury (Hg) and lead (Pb), 9 element levels (K, Co, Ni, Cu, As, Se, Sr, Sn, Ba and Hg) and 4 element levels (Mn, cobalt (Co), As, Sr and Ba) were significantly increased (P < 0.05) in wing, crureus and pectoralis, respectively. 2 element levels (sodium (Na) and zinc (Zn)), 5 element levels (Li, Na, Si, titanium (Ti and Cr), 13 element levels (Li, Na, Mg, K, V, Cr, iron (Fe), Cu, Zn, Mo, Sn, Hg and Pb) were significantly decreased (P < 0.05) in wing muscle, crureus and pectoralis, respectively. Additionally, in crureus and pectoralis, the content of total amino acids (TAA) was no significant alterations in L and M-group and then increased approximately 10.2% and 7.6% in H-group, respectively (P < 0.05). In wings, the level of total amino acids increased approximately 10% in L-group, whereas it showed unchanged in M and H-group compared to the corresponding C-group. We also observed that significantly increased levels of proline, cysteine, aspartic acid, methionine along with decrease in the tyrosine levels in muscular tissues compared to the corresponding C-group. In conclusion, the residual of As in the muscular tissues of chickens were dose-dependent and disrupts trace element homeostasis, amino acids level in muscular tissues of chickens under As2O3 exposure. Additionally, the response (trace elements and amino acids) were different in wing, thigh and pectoral of chick under As2O3 exposure. This study provided references for further study of heavy metal poisoning and may be helpful to understanding the toxicological mechanism of As2O3 exposure in muscular tissues of chickens.

Magnesium-deficiency-induced alterations of gas exchange, major metabolites and key enzymes differ among roots, and lower and upper leaves of Citrus sinensis seedlings.

Magnesium (Mg)-deficiency is a widespread problem adversely affecting the quality and yield of crops, including citrus. 'Xuegan' [Citrus sinensis (L.) Osbeck] seedlings were irrigated every other day with nutrient solution at an Mg concentration of 0 mM (Mg-deficiency) or 1 mM (Mg-sufficiency) for 16 weeks. Thereafter, biomass, leaf mass per area, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), pigments in the upper and lower leaves, Mg, gas exchange, organic acids, nonstructural carbohydrates, total soluble proteins, amino acids, phenolics and anthocyanins, and key enzymes related to organic acid, amino acid and phenolic metabolisms in the roots, and upper and lower leaves were assayed in order to test the hypothesis that Mg-deficiency-induced alterations of gas exchange, major metabolites and key enzymes may differ among the roots, and upper and lower leaves. Magnesium-deficiency affected the most measured parameters more in the lower than in the upper leaves except for the nonstructural carbohydrates, but the variation trends were similar between the two. Despite increased accumulation of nonstructural carbohydrates, the lower CO2 assimilation in the Mg-deficient leaves was not caused by the feedback inhibition mechanism via sugar accumulation. Both dark respiration and organic acid metabolism were elevated in the Mg-deficient lower leaves to 'consume' the excess carbohydrates, and inhibited in the Mg-deficient roots with less accumulation of nonstructural carbohydrates to keep the balance of net carbon. More total phenolics and fewer anthocyanins were accumulated in the Mg-deficient lower leaves, whereas the accumulation of both total phenolics and anthocyanins was reduced in the Mg-deficient roots. Interestingly, amino acid biosynthesis was repressed in the Mg-deficient roots and lower leaves, thus lowering the level of total free amino acids in these roots and leaves. To conclude, great differences existed in the Mg-deficiency-induced alterations of gas exchange, major metabolites and key enzymes among the roots, and upper and lower leaves.

Proton NMR metabolic profiling of CSF reveals distinct differentiation of meningitis from negative controls

BackgroundCerebrospinal fluid (CSF) is an essential bio-fluid of the central nervous system (CNS), playing a vital role in the protection of CNS and performing neuronal function regulation. The chemical composition of CSF varies during onset of meningitis, neurodegenerative disorders (positive controls) and in traumatic cases (negative controls). MethodsThe study design was broadly categorized into meningitis cases, negative controls and positive controls. Further differentiation among the three groups was carried out using Principal Component Analysis (PCA) followed by supervised Partial Least Square Discriminant Analysis (PLS-DA). ResultsThe statistical analysis of meningitis vs. negative controls using PLS-DA model resulted in R2 of 0.97 and Q2 of 0.85. There was elevation in the levels of ketone bodies, total free amino acids, glutamine, creatine, citrate and choline containing compounds (choline and GPC) in meningitis cases. Similarly, meningitis vs. positive controls resulted in R2 of 0.80 and Q2 of 0.60 and showed elevation in the levels of total free amino acids, glutamine, creatine/creatinine and citrate in the meningitis group. Four cases of HIV were identified by PLS-DA model as well as by clinical investigations. ConclusionOn the basis of metabolic profile it was found that negative control CSF samples are more appropriate for differentiation of meningitis than positive control CSF samples.

Effect of Pulsed Light Irradiation on Bioactive, Nonvolatile Components and Antioxidant Properties of Caterpillar Medicinal Mushroom Cordyceps militaris (Ascomycetes).

The caterpillar medicinal mushroom Cordyceps militaris contains many bioactive components, such as adenosine, cordycepin, and polysaccharides. In this study, C. militaris was exposed to 0, 3, 6, or 9 pulses of light irradiation to estimate changes in vitamin D2, bioactive compounds, nonvolatile taste components, and antioxidant properties. In addition, we compared the components and properties of C. militaris mycelia and solid waste medium that had been treated with pulsed light (PL) irradiation. Overall, PL irradiation of C. militaris increased the vitamin D2 content and increased the total amino acid levels 9-48%; the antioxidant properties of the mycelia treated with 0 pulses and of the solid waste medium treated with 3 pulses all exhibited lower half-maximal effective concentrations. Therefore, PL irradiation affected the amounts of bioactive compounds, but the irradiated samples still contained intense umami taste and a sufficient amount of antioxidant components.

Composition and protein profile analysis of rice protein ingredients

The objective of this study was to investigate the nutrient composition and protein profile of a range of rice protein ingredients containing 32–78% total protein. Rice protein ingredients had significantly (P<0.05) lower levels of calcium and total essential amino acids compared to selected dairy protein ingredients, i.e., skim milk powder, whey protein isolate and whey protein hydrolysate. Protein profiles of the ingredients were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion-high pressure liquid chromatography (SE-HPLC). Since the dominant rice protein fraction (i.e., glutelin) is extensively aggregated and crosslinked through disulfide bonds, a strong reducing buffer was developed in order to solubilise the rice protein ingredients prior to analysis by SDS-PAGE. Intact rice protein ingredients (n=3) contained proteins with molecular weight (MW) ranging from ∼11 to >250kDa, while rice protein hydrolysates (n=4) were composed mainly of low MW peptides. In parallel, enriched protein fractions were extracted from defatted rice flour based on their solubility and characterised by SDS-PAGE to facilitate the identification of protein bands in the rice protein ingredients. The results of this study underpin the understanding, prediction and control of physicochemical functionality of rice protein ingredients.

Plasma amino acid levels are elevated in young, healthy low birth weight men exposed to short-term high-fat overfeeding.

Low birth weight (LBW) individuals exhibit a disproportionately increased, incomplete fatty acid oxidation and a decreased glucose oxidation, compared with normal birth weight (NBW) individuals, and furthermore have an increased risk of developing insulin resistance and type 2 diabetes. We hypothesized that changes in amino acid metabolism may occur parallel to alterations in fatty acid and glucose oxidation, and could contribute to insulin resistance. Therefore, we measured fasting plasma levels of 15 individual or pools of amino acids in 18 LBW and 25 NBW men after an isocaloric control diet and after a 5‐day high‐fat, high‐calorie diet. We demonstrated that LBW and NBW men increased plasma alanine levels and decreased valine and leucine/isoleucine levels in response to overfeeding. Also, LBW men had higher alanine, proline, methionine, citrulline, and total amino acid levels after overfeeding compared with NBW men. Alanine and total amino acid levels tended to be negatively associated with the insulin‐stimulated glucose uptake after overfeeding. Therefore, the higher amino acid levels in LBW men could be a consequence of their reduction in skeletal muscle insulin sensitivity due to overfeeding with a possible increased skeletal muscle proteolysis and/or could potentially contribute to an impaired insulin sensitivity. Furthermore, the alanine level was negatively associated with the plasma acetylcarnitine level and positively associated with the hepatic glucose production after overfeeding. Thus, the higher alanine level in LBW men could be accompanied by an increased anaplerotic formation of oxaloacetate and thereby an enhanced tricarboxylic acid cycle activity and as well an increased gluconeogenesis.

The responses of a funnel-web weaving spider,Agelena labyrinthica, to elevated CO2concentration

The effects of elevated CO2 concentration on the growth and development of the funnel-web weaving spider Agelena labyrinthica (Clerck) (Araneae: Agelenidae) were studied in climate chambers with low (370 μl l−1) or high (750 μl l−1) CO2 concentration. Seventh-instar A. labyrinthica cultured under each of these CO2 concentrations were randomly selected to determine nutrient composition (total protein, total amino acid, and free fatty acid) and digestive or detoxification enzymes activity (peroxidase, amylase, and superoxide dismutase) using test kits. When reared under high CO2 concentration, total development of A. labyrinthica was significantly faster. Carapace length and width and body weight did not differ between CO2 concentrations, nor the levels of protein and total amino acids in seventh-instar A. labyrinthica. However, free fatty acid levels were significantly lower under high CO2 concentration. Specific activities of peroxidase and superoxide dismutase in seventh-instar A. labyrinthica did not differ between CO2 concentrations. The specific activity of amylase under high CO2 concentration was higher than that of the low CO2 group. The effects of elevated CO2 on A. labyrinthica varied from those on the wandering spider Pardosa astrigera L Koch, as found in an earlier study. Apparently, elevated CO2 has a species-specific impact on spiders.

Comparison of amino acids, biogenic amines and ammonium ion of wines made of different types of fruits

SummaryAmino acids, biogenic amines and ammonium ion are the primary nitrogen sources in fruit wines. Compared to grape wines, our knowledge to their profile in wines made of other fruits is very lack. Fourteen wines made of nine kinds of fruits together with seven grape wines were selected to compare their nitrogen component profile. White grape wines possessed the highest level of total amino acids, followed by red grape wines and then the wines made of the other fruits. Red grape wines contained the highest level of biogenic amines, followed by white grape wines and the wines made of the other fruits. Ammonium ion was also found to be higher in the wines made of grapes. Principal component analysis revealed that the obvious separations existed among the wines made from different types of fruits, indicating that these nitrogen compounds could be served as the indicators to differentiate different types of fruit wines.

Effects of elevated CO2 concentration and temperature on some physiological characteristics of cotton (Gossypium hirsutum L.) leaves

Rising atmospheric carbon dioxide concentration ([CO2]) and warming are two of the most conspicuous characteristics of global climate change in this century, and they are responsible for a variety of physiological responses of plants. However, studies addressing the combined impact of [CO2] and temperature on plant physiological responses are still scarce. We studied the combined effects of long term elevated [CO2] and temperature on dynamic changes of physiological metabolism in cotton with growth and development. Dry matter content (DMC), N concentration, C/N ratio, soluble sugar content, starch content, total nonstructural carbohydrate (TNC), total phenolic concentration and amino acid levels in cotton leaves in response to long term [CO2] and temperature levels were assayed during different growth times. Elevated [CO2] and temperature independently increased DMC at different growth times but the highest increase of DMC occurred under both elevated [CO2] and elevated temperature. Elevated [CO2] reduced leaf N concentration and increased C/N ratio; however, no differences were found at ambient or elevated temperature after both 75 and 105days of treatments. The leaves grown in elevated [CO2] had higher soluble sugar, starch, TNC contents and total phenolic concentration, whereas lower levels of these components were observed at a higher temperature. There were different interactive effects between [CO2] and temperature on these physiological characteristics at different growth times. Elevated [CO2] increased amino acids of Asp, His, Ile and Thr levels and reduced Glu, Ala and Pro levels at different growth times under ambient temperature. Under elevated temperature, [CO2] enrichment increased Glu and Thr levels, whereas it reduced Ala, Asp and Val levels. There was a significant interactive effect between [CO2] and temperature on 8, 9 and 11 out of the 15 amino acids after 45, 75 and 105days of treatment, respectively. The results indicate these physiological characteristics in the cotton leaves during different growth times will change differently in response to individual environmental factor or the combination of different environmental factors, and the physiological metabolism in cotton under long term elevated [CO2] and temperature will dynamically change with growth and development, thus they may have different metabolic mechanisms to deal with future climate change. Further work is required to elucidate the mechanisms underlying an interactive effect of [CO2] and temperature on plant physiological and metabolic change as well as the effect of plant nutritional quality changes on plant-herbivore interaction.

Nitrogen remobilisation facilitates adventitious root formation on reversible dark-induced carbohydrate depletion in Petunia hybrida.

BackgroundAdventitious root (AR) formation in axillary shoot tip cuttings is a crucial physiological process for ornamental propagation that is utilised in global production chains for young plants. In this process, the nitrogen and carbohydrate metabolisms of a cutting are regulated by its total nitrogen content (Nt), dark exposure during transport and irradiance levels at distinct production sites and phases through a specific plasticity to readjust metabolite pools. Here, we examined how elevated Nt contents with a combined dark exposure of cuttings influence their internal N-pools including free amino acids and considered early anatomic events of AR formation as well as further root development in Petunia hybrida cuttings.ResultsEnhanced Nt contents of unrooted cuttings resulted in elevated total free amino acid levels and in particular glutamate (glu) and glutamine (gln) in leaf and basal stem. N-allocation to mobile N-pools increased whereas the allocation to insoluble protein-N declined. A dark exposure of cuttings conserved initial Nt and nitrate-N, while it reduced insoluble protein-N and increased soluble protein, amino- and amide-N. The increase of amino acids mainly comprised asparagine (asn), aspartate (asp) and arginine (arg) in the leaves, with distinct tissue specific responses to an elevated N supply. Dark exposure induced an early transient rise of asp followed by a temporary increase of glu. A strong positive N effect of high Nt contents of cuttings on AR formation after 384 h was observed. Root meristematic cells developed at 72 h with a negligible difference for two Nt levels. After 168 h, an enhanced Nt accelerated AR formation and gave rise to first obvious fully developed roots while only meristems were formed with a low Nt. However, dark exposure for 168 h promoted AR formation particularly in cuttings with a low Nt to such an extent so that the benefit of the enhanced Nt was almost compensated. Combined dark exposure and low Nt of cuttings strongly reduced shoot growth during AR formation.ConclusionsThe results indicate that both enhanced Nt content and dark exposure of cuttings reinforced N signals and mobile N resources in the stem base facilitated by senescence-related proteolysis in leaves. Based on our results, a model of N mobilisation concomitant with carbohydrate depletion and its significance for AR formation is postulated.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0901-6) contains supplementary material, which is available to authorized users.

The effect of sustained swimming exercise on the growth performance, muscle cellularity and flesh quality of juvenile qingbo (Spinibarbus sinensis)

This study was undertaken to investigate the effects of sustained swimming exercise on the growth performance, muscle cellularity and flesh quality of juvenile qingbo fish (Spinibarbus sinensis). Experimental fish were exercised under four water velocities, nearly still (control, 3cms−1) and 1, 2 and 4body lengths (bl)s−1, for eight weeks at 25°C. Then, growth performance indicated by the specific growth rate (SGR), white muscle cellularity suggested by the diameter and density of white muscle fiber, flesh quality evaluated by some textural mechanical properties (hardness, springiness, chewiness, cohesiveness) and physico-chemical parameters (pH, color, moisture, ash, protein, fat, amino acids, and fatty acids) were measured. Sustained swimming at moderate velocities (1 and 2bls−1) resulted in a significantly higher SGR and similar white fiber diameter and density compared with the controls. However, the fish trained at a water velocity of 4bls−1 displayed a similar SGR, smaller white fiber diameter and higher white fiber density compared with the controls. Sustained swimming resulted in significant increase in the values of pH and all textural traits but showed no significant effect on the color of the flesh for juvenile S. sinensis. Fish swimming under moderate water velocities exhibited higher levels of the protein content of the muscle, total essential amino acids (∑EAA) (at 2bls−1) and total amino acids (∑AA) (at 1 and 2bls−1) compared with control fish. However, the lowest levels of total amino acids (∑AA) and total n-6 poly-unsaturated fatty acids (∑n-6 PUFA) were observed in fish swimming at water velocity of 4bls−1. These data suggest that (1) moderate swimming exercise (1 or 2bls−1) improved growth performance, which could not be attributed to changes in white muscle cellularity; (2) sustained swimming showed a positive effect on texture characteristics, which was partly due to the higher white fiber density and flesh pH compared with controls; and (3) moderate swimming exercise (1 or 2bls−1) was beneficial for improving the nutritional quality of the flesh, whereas high-intensity swimming (4bls−1) resulted in an impairment of the nutritional quality of the flesh in juvenile S. sinensis. Statement of relevanceWe declare that the experiments complied with the current laws of the country in which the experiments were performed and that our paper complied with the laws of commercial aquaculture.

THE CONCENTRATION OF FREE AMINO ACIDS IN BLOOD SERUM OF HEALTHY COWS AND COWS WITH SUBCLINICAL KETOSIS

This paper presents the study on determination of the free amino acid in blood serum of cows with high milk production (Herd A) and cows with subclinical ketosis compared to healthy ones (Herd B). In Herd A examinated 12 cows in the first 100 days in milk. A total of 24 cows from a herd B divided into two groups: experimental (12 cows with ketosis) and control (12 healthy cows) were included in the study. Statistically significantly higher concentrations of glutamine, glutamic acid, isoleucine (p ≤ 0.001), and tyrosine (p ≤ 0.05) were found in dairy cows with subclinical ketosis compared to healthy ones. A significant decrease in the concentrations of asparagine, histidine, methionine, and serine (p ≤ 0.001) as well as alanine, leucine, lysine and proline (p ≤ 0.05) was observed. In Herd A was high level of total essential amino acids in blood serum. In our study, the changes, in particular, observed in amino acid concentration in cows with subclinical ketosis indicate its intensive use in both ketogenesis and gluconeogenesis processes.

Insulin does not stimulate muscle protein synthesis during increased plasma branched-chain amino acids alone but still decreases whole body proteolysis in humans.

Insulin stimulates muscle protein synthesis when the levels of total amino acids, or at least the essential amino acids, are at or above their postabsorptive concentrations. Among the essential amino acids, branched-chain amino acids (BCAA) have the primary role in stimulating muscle protein synthesis and are commonly sought alone to stimulate muscle protein synthesis in humans. Fourteen healthy young subjects were studied before and after insulin infusion to examine whether insulin stimulates muscle protein synthesis in relation to the availability of BCAA alone. One half of the subjects were studied in the presence of postabsorptive BCAA concentrations (control) and the other half in the presence of increased plasma BCAA (BCAA). Compared with that prior to the initiation of the insulin infusion, fractional synthesis rate of muscle protein (%/h) did not change (P > 0.05) during insulin in either the control (0.04 ± 0.01 vs 0.05 ± 0.01) or the BCAA (0.05 ± 0.02 vs. 0.05 ± 0.01) experiments. Insulin decreased (P < 0.01) whole body phenylalanine rate of appearance (μmol·kg-1·min-1), indicating suppression of muscle proteolysis, in both the control (1.02 ± 0.04 vs 0.76 ± 0.04) and the BCAA (0.89 ± 0.07 vs 0.61 ± 0.03) experiments, but the change was not different between the two experiments (P > 0.05). In conclusion, insulin does not stimulate muscle protein synthesis in the presence of increased circulating levels of plasma BCAA alone. Insulin's suppressive effect on proteolysis is observed independently of the levels of circulating plasma BCAA.

Optimal dietary methionine requirement of bullfrog Rana (Lithobates) catesbeiana

A feeding experiment was conducted to determine dietary methionine requirement of bullfrog Rana (Lithobates) catesbeiana. Bullfrogs were fed six experimental diets containing 0.63%, 1.00%, 1.42%, 1.78%, 2.26% or 2.68% methionine for 8weeks. After the feeding experiments, growth performance, body composition, blood biochemistry and expression levels of hepatic genes were determined. The results showed that growth and feed utilization were significantly affected (P<0.05) by dietary methionine levels. Weight gain (WG) and protein efficiency ratio (PER) both increased with increasing level of dietary methionine from 0.63% to 1.42% and then decreased. While, the variation trend of feed conversion ratio (FCR) is just opposite with WG and PER. Crude lipid concentrations of whole body and muscle tissue were also significantly affected (P<0.05) by dietary methionine levels. However, there was no significant difference (P>0.05) in amino acid composition in muscle among methionine treatments. Triglyceride (TG) and cholesterol (CHO) levels, as well as aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities, were all significantly affected (P<0.05) by dietary methionine levels. TG and CHO levels decreased as dietary methionine increased from 0.63% to 1.78% and then increased with further increases in methionine. Serum AST and ALT activities in bullfrogs fed with 0.63% methionine diet were both significantly higher (P<0.05) than in bullfrogs fed other diets. Gene expressions in bullfrogs fed with 1.00%, 1.42% and 1.78% methionine diets was higher (P<0.05) than these of other groups. On the basis of WG and PER, the optimal level of dietary methionine for bullfrogs was estimated to be between 1.53% and 1.62% of diet using second-order polynomial regression analysis. The corresponding optimal level of total sulfur amino acids in the diet of bullfrogs is therefore between 1.79% and 1.88% of diet in the presence of 0.26% cystine. Statement of relevanceThe authors have declared that no competing interests exist.

Dietary alpha-ketoglutarate increases cold tolerance in Drosophila melanogaster and enhances protein pool and antioxidant defense in sex-specific manner

Alpha-ketoglutarate (AKG) is an important intermediate in Krebs cycle which bridges the metabolism of amino acids and carbohydrates. Its effects as a dietary supplement on cold tolerance were studied in Drosophila melanogaster Canton S. Two-day-old adult flies fed at larval and adult stages with AKG at moderate concentrations (5–10mM) recovered faster from chill coma (0°C for 15min or 3h) than control ones. The beneficial effect of AKG on chill coma recovery was not found at its higher concentrations, which suggests hormetic like action of this keto acid. Time of 50% observed mortality after 2h recovery from continuous cold exposure (−1°C for 3–31h) (LTi50) was higher for flies reared on 10mM AKG compared with control ones, showing that the diet with AKG enhanced insect cold tolerance. In parallel with enhancement of cold tolerance, dietary AKG improved fly locomotor activity. Metabolic effects of AKG differed partly in males and females. In males fed on AKG, there were no differences in total protein and free amino acid levels, but the total antioxidant capacity, catalase activity and low molecular mass thiol content were higher than in control animals. In females, dietary AKG promoted higher total antioxidant capacity and higher levels of proteins, total amino acids, proline and low molecular mass thiols. The levels of lipid peroxides were lower in both fly sexes reared on AKG as compared with control ones. We conclude that both enhancement of antioxidant system capacity and synthesis of amino acids can be important for AKG-promoted cold tolerance in D. melanogaster. The involvement of AKG in metabolic pathways of Drosophila males and females is discussed.

Water Stress Modulates Soybean Aphid Performance, Feeding Behavior, and Virus Transmission in Soybean.

Little is known about how water stress including drought and flooding modifies the ability of plants to resist simultaneous attack by insect feeding and transmission of insect-vectored pathogen. We analyzed insect population growth, feeding behaviors, virus transmission, and plant amino acid profiles and defense gene expression to characterize mechanisms underlying the interaction between water stress, soybean aphid and aphid-transmitted, Soybean mosaic virus, on soybean plants. Population growth of non-viruliferous aphids was reduced under drought stress and saturation, likely because the aphids spent less time feeding from the sieve element on these plants compared to well-watered plants. Water stress did not impact population growth of viruliferous aphids. However, virus incidence and transmission rate was lowest under drought stress and highest under saturated conditions since viruliferous aphids took the greatest amount time to puncture cells and transmit the virus under saturated conditions and lowest time under drought stress. Petiole exudates from drought-stressed plants had the highest level of total free amino acids including asparagine and valine that are critical for aphid performance. Aphids did not benefit from improved phloem sap quality as indicated by their lower densities on drought-stressed plants. Saturation, on the other hand, resulted in low amino acid content compared to all of the other treatments. Drought and saturation had significant and opposing effects on expression of marker genes involved in abscisic acid (ABA) signaling. Drought alone significantly increased expression of ABA marker genes, which likely led to suppression of salicylic acid (SA)- and jasmonic acid (JA)-related genes. In contrast, ABA marker genes were down-regulated under saturation, while expression of SA- and JA-related genes was up-regulated. We propose that the apparent antagonism between ABA and SA/JA signaling pathways contributed to an increase in aphid densities under drought and their decrease under saturation. Taken together, our findings suggests that plant responses to water stress is complex involving changes in phloem amino acid composition and signaling pathways, which can impact aphid populations and virus transmission.

Quality characteristics of fermented sausage prepared with soy sauce.

The contributions of soy sauce to the quality characteristics of fermented sausages were investigated. The number of lactic acid bacteria in sausages prepared with soy sauce increased from the first day of fermentation, and the population reached approximately log 7 CFU/g by the 5th day of fermentation. The pH decreased sharply to 5.0-5.1 by the 5th day of fermentation, in accordance with the dramatic increase of titratable acidity. After 36 days of fermentation, the levels of total organic acids and amino acids in soy sauce sausages increased to 3,026.3-3,116.4 mg/100 g and 1,132.2-1,172.8 mg/100 g respectively, and this level was even higher than those of the sausage fermented with a starter culture. 2% soy sauce sausage also showed higher values of hardness, chewiness, and smoke odor than the control. These results suggest that soy sauce has great potential as an alternative starter culture and additive for the quality improvement of fermented sausages.

The influence of alternative pathways of respiration that utilize branched-chain amino acids following water shortage in Arabidopsis.

During dark-induced senescence isovaleryl-CoA dehydrogenase (IVDH) and D-2-hydroxyglutarate dehydrogenase (D-2HGDH) act as alternate electron donors to the ubiquinol pool via the electron-transfer flavoprotein/electron-transfer flavoprotein:ubiquinone oxidoreductase (ETF/ETFQO) pathway. However, the role of this pathway in response to other stresses still remains unclear. Here, we demonstrated that this alternative pathway is associated with tolerance to drought in Arabidopsis. In comparison with wild type (WT) and lines overexpressing D-2GHDH, loss-of-function etfqo-1, d2hgdh-2 and ivdh-1 mutants displayed compromised respiration rates and were more sensitive to drought. Our results demonstrated that an operational ETF/ETFQO pathway is associated with plants' ability to withstand drought and to recover growth once water becomes replete. Drought-induced metabolic reprogramming resulted in an increase in tricarboxylic acid (TCA) cycle intermediates and total amino acid levels, as well as decreases in protein, starch and nitrate contents. The enhanced levels of the branched-chain amino acids in loss-of-function mutants appear to be related to their increased utilization as substrates for the TCA cycle under water stress. Our results thus show that mitochondrial metabolism is highly active during drought stress responses and provide support for a role of alternative respiratory pathways within this response.