Activities Of Nitrogen Metabolism Enzymes Research Articles

Microbial response to the chronic toxicity effect of graphene and graphene oxide nanomaterials within aerobic granular sludge systems

Nanomaterials present in wastewater can pose a significant threat to aerobic granular sludge (AGS) systems. Herein, we found that compared to graphene nanomaterials (G-NMs), the long-term presence (95 days) of graphene oxide nanomaterials (GO-NMs) resulted in an increased proliferation of filamentous bacteria, poorer sedimentation performance (SVI30 of 74.1 mL/g) and smaller average particle size (1224.4 µm) of the AGS. In particular, the GO-NMs posed a more significant inhibitory effect to the total nitrogen removal efficiency of AGS (decreased by 14.3 %), especially for the denitrification process. The substantial accumulation of GO-NMs within the sludge matrix resulted in a higher level of reactive oxygen species in AGS compared to G-NMs, thereby inducing lactate dehydrogenase release, and enhancing superoxide oxidase and catalase activities. Such excessive oxidative stress could potentially result in a significant reduction in the activity of nitrogen metabolism enzymes (e.g., nitrate reductase and nitrite reductase) and the expression of key functional genes (e.g., nirS and nirK). Altogether, compared to G-NMs, prolonged exposure to GO-NMs had a more significant chronic toxicity effect on AGS systems. These findings implied that the presence of G-NMs and GO-NMs is a hidden danger to biological nitrogen removal and should receive more attention.

Differences in Fatty Acid and Central Carbon Metabolite Distribution among Different Tissues of Alfalfa–Rhizobia Symbiotic System

Fatty acid and central carbon metabolism are crucial energy metabolism reactions. However, to date, few studies have examined their distribution characteristics within the alfalfa–rhizobia symbiotic system. To clarify the distributional differences and accumulation rates of fatty acids and central carbon with this system, we measured the plant phenotype, nodule formation, nitrogen fixation capacity, and key nitrogen metabolism enzyme activities of Medicago sativa ‘Gannong No. 9’ 35 days post-inoculation (dpi) with Sinorhizobia meliloti LL11. Additionally, we employed targeted metabolomics to analyze central carbon and fatty acid metabolites in various tissue samples of symbiotic and control (C.K.) plants, as well as in S. meliloti LL11. We found that plant height; root length; aboveground fresh and dry weights; underground fresh and dry weights; and nitrate reductase, nitrogen reductase, glutamine synthetase, and glutamate synthase activities were significantly higher in the leaves and roots of symbiotic plants than in those of C.K. plants. Compared to symbiotic plants, C.K. plants exhibited higher total central carbon and fatty acid metabolite content, accounting for 38.61% and 48.17% of C.K. plants, respectively. We detected 32 central carbon and 40 fatty acid metabolites in S. meliloti LL11, with succinate (343,180.8603 ng·mL−1) and hexadecanoic acid (4889.7783 ng·mL−1) being the most. In both symbiotic and C.K. plants, central carbon metabolite was considerably higher than the fatty acid metabolite central. Moreover, the carbon metabolites found in symbiotic plants were primarily distributed in pink nodule roots (PNRs), with malate exhibiting the highest content (4,800,612.3450 ng·g−1), accounting for 53.09% of total central carbon metabolite content. Fatty acid metabolites were mainly found in pink root nodules (P.N.s), which are sites of nitrogen fixation. Trans-10-nonadecenoic acid and hexadecanoic acid exhibited the highest contents, comprising >15% of the total fatty acid metabolite content. We found that petroselaidic acid is only present in P.N., which seems to be closely related to the nitrogen fixation reaction in P.N. In general, symbiotic plants transfer central carbon metabolites to nodules via PNRs to drive nitrogen fixation. However, in P.N.s, these metabolites are limited, leading to accumulation in PNRs. Fatty acid metabolites, crucial for nitrogen fixation, are prevalent in P.N.s. Conversely, C.K. plants without nitrogen fixation distribute these metabolites primarily to the stems, emphasizing growth. This study provides new insights into the energy metabolism of symbiotic nitrogen fixation.

Foliar melatonin ameliorates drought-induced alterations in enzyme activities of sugar and nitrogen metabolisms in cotton leaves.

Sugar and nitrogen metabolisms help plants maintain cellular homeostasis, stress tolerance, and sustainable growth in drought conditions. Melatonin, a potent antioxidant and signaling molecule, appears to mitigate the negative impacts of drought on plants. This study aimed to investigate the potential role of foliar-applied melatonin in ameliorating drought-induced alterations in leaf sugar and nitrogen metabolisms' enzyme activities during cotton flowering and boll formation. To date, no study has examined drought-induced sugar and nitrogen metabolisms' enzyme activity changes in cotton treated with foliar melatonin. Drought levels (FC1 = 75 ± 5%, FC2 = 60 ± 5%, and FC3 = 45 ± 5%) were maintained between 3 and 35 days after flowering (DAF), and melatonin (M) concentrations (0, 25, 50, and 100 μmol L-1 ) were applied at 3 and 21 DAF in a completely randomized design. M100 concentrations at low FC levels significantly enhanced leaf sugar and N-metabolic enzyme activities, such as sucrose synthase (65.56%) and glutamine synthetase (55.24%), compared to plants not treated with melatonin; peaking between 7 and 21 DAF and declining gradually with crop growth. Moreover, the M100 concentrations at all FC levels, particularly FC3, significantly increased the relative expression of GhSusB, GhSusC, SPS1, and SPS3 genes, indicating that melatonin improves leaf sugar and N-metabolism enzymatic activities under drought stress. Therefore, applying M100 concentrations to cotton foliage under FC3 conditions during reproductive stages improves leaf water status, sugar, and N-metabolism enzyme activities, demonstrating melatonin's potent anti-stress, osmoregulatory, and growth-promoting properties in overcoming drought stress in cotton crops. Future research into the molecular mechanisms of melatonin-mediated sugar and nitrogen metabolism enzyme activities in cotton leaves may lead to biotechnological methods to improve drought resilience in cotton and other crops.

Comparative evaluation of four Chlorella species treating mariculture wastewater under different photoperiods: Nitrogen removal performance, enzyme activity, and antioxidant response

The nitrogen removal performance, nitrogen metabolism enzyme activities, and antioxidant response of four Chlorella species (Chlorella sp., Chlorella vulgaris, Chlorella sorokiniana, and Chlorella protothecoides) were compared under different light: dark (L:D) photoperiods during treating mariculture wastewater. The increase of light duration in the range of 8L:16D to 16L:8D was beneficial to the chlorophyll synthesis of selected four Chlorella species. Chlorella vulgaris was the most effective to treat mariculture wastewater than Chlorella sp., Chlorella sorokiniana, and Chlorella protothecoides. and its microalgae density, photosynthetic activity, and nitrogen metabolism enzyme activity were higher than those of the other three Chlorella species. An obvious oxidative stress in microalgal cells was under 20L:4D photoperiod, which led to a decrease in photosynthetic activity and nitrogen metabolizing enzyme activity. Among the four Chlorella species, Chlorella protothecoides had the highest degree of light-induced stress and ROS accumulation. This study can provide suitable microalgae and optimal photoperiod for treating mariculture wastewater.

Foliar spray of La2O3 nanoparticles regulates the growth, antioxidant parameters, and nitrogen metabolism of fragrant rice seedlings in wet and dry nurseries.

Nanoparticles (NPs) have been widely used in agriculture, and lanthanum oxidenanoparticles (La2O3) NPs can regulate plant growth. La2O3 NPs treatment was hypothesized to affect the accumulation and distribution of substances in rice seedlings under wet and dry nursery conditions. The objective of the present study was to ascertain the effects of La2O3 NPs foliar spray on the morphology and physiology of fragrant rice seedlings under wet and dry nursery conditions. Seedlings of two fragrant rice cultivars, namely 'Xiangyaxiangzhan' and 'Yuxiangyouzhan,' were grown under wet and dry nursery conditions with La2O3 NPs treatments at three concentrations (CK, La2O3 NPs 0mg L-1; T1, La2O3 NPs 20mg L-1; and T2, La2O3 NPs 40mg L-1). The results showed that the seedling-raising method was significantly associated with La2O3 NPs application (P < 0.05), affecting the leaf area of both cultivars. Changes in plant morphological parameters, such as dry weight and root-shoot ratio, were the reasons for the differences in cultivars in response to La2O3 NPs application. Changes were also observed in the plant morphological and physiological parameters of leaf area, specific leaf area, chlorophyll contents, antioxidant properties, and activities of nitrogen metabolism enzymes. The relationship between morphological and physiological processes in fragrant rice was investigated to test the hypothesis. In both wet and dry nursery methods, the T2 concentration of La2O3 NPs was beneficial for rice seedlings and significantly increased their leaf area due to changes in morphological and physiological parameters. Therefore, the results of this study provide a theoretical basis for expanding the research on La2O3 NPs application in rice, as well as relevant references for strengthening rice seedlings in the nursery, which has a positive effect on the grain yield improvement in fragrant rice.

Exogenous melatonin alleviates apple replant disease by regulating rhizosphere soil microbial community structure and nitrogen metabolism

Apple replant disease (ARD) is a common soil-borne disease afflicting apple plants. Melatonin is a broad-spectrum oxygen scavenger that plays a key role in alleviating stress-induced damage in plants. In this study, we aimed to determine whether adding melatonin to replant soil can promote plant growth by improving the rhizosphere soil environment and nitrogen metabolism. In replant soil, chlorophyll synthesis was blocked, reactive oxygen species (ROS) accumulated in large quantities, and membrane lipid peroxidation was aggravated; this eventually resulted in slow plant growth. However, the application of 200 μM exogenous melatonin enhanced the tolerance of plants to ARD by up-regulating the expression of antioxidant enzyme-related genes and increasing ROS scavenging enzyme activity. Exogenous melatonin also increased the absorption and utilization of 15N by increasing the expression of nitrogen absorption genes and the activity of nitrogen metabolism enzymes. Exogenous melatonin enhanced the soil microbial environment by promoting soil enzyme activity and bacterial richness and decreasing the abundance of several harmful fungi in rhizosphere soil. Mantel test results showed that soil properties (except for AP) and growth indexes were positively correlated with the rate of 15N absorption and utilization. Spearman correlation analysis showed that the above factors were closely related to the richness and diversity of bacteria and fungi, indicating that the composition of microbial communities might play a key role in mediating change in the soil environment and thus affect nutrient absorption and growth. These findings provide new insights into how melatonin enhances ARD tolerance.

Individual and combined effects of heat and drought and subsequent recovery on winter wheat (Triticum aestivum L.) photosynthesis, nitrogen metabolism, cell osmoregulation, and yield formation

Extreme temperatures and droughts are considered as the two main factors that limit wheat growth and production. Although responses of wheat plants to heat and drought stress have been extensively investigated, little is known about the extent to which wheat plants can recover after stress relief. In this study, a winter wheat pot experiment was conducted to evaluate the growth, physiological activities, and yield formation responses of wheat to stress and recovery periods under heat stress (36 °C, daily maximum temperature), drought (45–55% of soil water holding capacity), and combined stress conditions. Heat and drought stress significantly reduced photosynthesis, leaf relative water content (LRWC), leaf water potential (LWPnoon), and nitrogen metabolism enzyme activities and increased electrolyte leakage. These parameters showed significant interactions between heat and drought stress. Beneficial osmoregulation of membrane stability was observed in stressed plants because of the accumulation of proline and soluble sugars. Within a range of stresses, the abovementioned physiological processes of individual heat- and drought-stressed plants recovered to levels comparable to those of the control. The recovery capacities of the physiological traits decreased gradually with increasing stress duration, particularly under combined stress. The recovery of LWPnoon and LRWC contributed to the improved photosynthetic performance after stress relief. The combined stress caused greater yield losses than individual heat and drought stress, which was mainly attributed to low levels of thousand grain weight (TGW), the number of grains per ear, and the grain filling rate. After stress relief, the recovery of proline content, glutamine synthetase activity, photosynthetic rate, and LRWC were closely associated with grain yield and thousand grain weight. Collectively, these findings contribute to a better understanding of the coordinated responses of winter wheat during the combined heat and drought stress and recovery periods.

Potential Assessment of Selenium for Improving Nitrogen Metabolism, Yield and Nitrogen Use Efficiency in Wheat

In wheat production, improving resource utilization and grain yield is the goal researcher have been pursuing. This study aimed to investigate if a regulated nitrogen (N) and selenium (Se) fertilizer management could increase wheat yield and N use efficiency (NUE). This study reports the effects of three N application levels (N0: 0 kg N ha−1, N1: 180 kg N ha−1, N2: 270 kg N ha−1) and a combination of three Se application levels (Se0: 0 g Se ha−1, Se1: 450 g Se ha−1, Se2: 900 g Se ha−1) on N metabolism, NUE and yield in wheat in 2020–2021. Compared with N0, wheat yield increased by 44.76% in N1 and by 54.32% in N2, and the activity of N-metabolizing enzymes increased by 25.15~35.03% in N1 and by 32.01~51.27% in N2. Compared with N1, the apparent recovery efficiency of N, the agronomic N use efficiency and the partial factor productivity of applied N decreased by 15.71%, 28.00% and 28.93% in N2, respectively. Compared with Se0, the 1000-grain weight increased by 3.93% in Se1 and by 4.87% in Se2, and the activity of nitrogen-metabolizing enzymes increased by 4.23~4.91% in Se1 and by 6.65~8.46% in Se2. We conclude that Se could improve the wheat 1000-grain weigh and N metabolism and has the potential to increase wheat yield and NUE.

Changes in the photosynthetic performance, the activity of enzymes of nitrogen metabolism, and proline content in the leaves of wheat plants after exposure to low CO&lt;sub&gt;2&lt;/sub&gt; concentration

The changes in photosynthetic activity, as well as the activity of nitrogen-metabolism enzymes, the intensity of lipid peroxidation, and proline content were studied in <i>Triticum aestivum</i> L. plants after their incubation at a low CO₂ concentration in a sealed chamber for 10 d. CO₂ deficiency (-CO₂) compared to normal CO₂ concentration (control) led to a decrease in the rate of O₂ gas exchange at the plateau of the light curve and quantum yield of photosynthesis. The maximum and effective quantum photochemical yields also decreased. CO₂ deficiency reduced the activity of nitrate reductase, but increased the activities of nitrite reductase, glutamine synthetase, and glutamate dehydrogenase, and promoted proline accumulation. It is assumed that with a lack of CO₂, an excess of nitrogen-containing compounds occurs, which must be removed from metabolic processes. Also, we suggest the partial storage of nitrogen in the form of nitrogen-containing compounds such as proline.

Appropriate and Constant Potassium Supply Promotes the Growth of M9T337 Apple Rootstocks by Regulating Endogenous Hormones and Carbon and Nitrogen Metabolism.

Potassium (K) is an indispensable nutrient element in the development of fruit trees in terms of yield and quality. It is unclear how a stable or unstable supply of K affects plant growth. We studied the root morphology and physiological and molecular changes in the carbon and nitrogen metabolism of M9T337 apple rootstock under different K levels and supply methods using hydroponics. Five K supply treatments were implemented: continuous low K (KL), initial low and then high K (KLH), appropriate and constant K (KAC), initial high and then low K (KHL), and continuous high K (KH). The results showed that the biomass, root activity, photosynthesis, and carbon and nitrogen metabolism of the M9T337 rootstocks were inhibited under KL, KH, KLH and KHL conditions. The KAC treatment promoted root growth by optimizing endogenous hormone content, enhancing carbon and nitrogen metabolism enzyme activities, improving photosynthesis, optimizing the distribution of carbon and nitrogen, and upregulating the transcription levels of nitrogen assimilation-related genes (nitrate reductase, glutamine synthetase, glutamate synthase, MdNRT1.1, MdNRT1.2, MdNRT1.5, MdNRT2.4). These results suggest that an appropriate and constant K supply ensures the efficient assimilation and utilization of nitrogen and carbon.

Interactive Effects of Melatonin and Nitrogen Improve Drought Tolerance of Maize Seedlings by Regulating Growth and Physiochemical Attributes.

Melatonin plays an important role in numerous vital life processes of animals and has recently captured the interests of plant biologists because of its potent role in plants. As well as its possible contribution to photoperiodic processes, melatonin is believed to act as a growth regulator and/or as a direct free radical scavenger/indirect antioxidant. However, identifying a precise concentration of melatonin with an optimum nitrogen level for a particular application method to improve plant growth requires identification and clarification. This work establishes inimitable findings by optimizing the application of melatonin with an optimum level of nitrogen, alleviating the detrimental effects of drought stress in maize seedlings. Maize seedlings were subjected to drought stress of 40–45% field capacity (FC) at the five-leaf stage, followed by a soil drenching of melatonin 100 µM and three nitrogen levels (200, 250, and 300 kg ha−1) to consider the changes in maize seedling growth. Our results showed that drought stress significantly inhibited the physiological and biochemical parameters of maize seedlings. However, the application of melatonin with nitrogen remarkably improved the plant growth attributes, chlorophyll pigments, fluorescence, and gas exchange parameters. Moreover, melatonin and nitrogen application profoundly reduced the reactive oxygen species (ROS) accumulation by increasing maize antioxidant and nitrogen metabolism enzyme activities under drought-stress conditions. It was concluded that the mitigating potential of 100 µM melatonin with an optimum level of nitrogen (250 kg N ha−1) improves the plant growth, photosynthetic efficiency, and enzymatic activity of maize seedling under drought-stress conditions.

Nitrogen Fertilizer Regulated Grain Storage Protein Synthesis and Reduced Chalkiness of Rice Under Actual Field Warming.

Our previous study has shown that nitrogen plays an important role in dealing with significantly increased chalkiness caused by elevated temperature. However, the role of nitrogen metabolites has not been given sufficient attention, and its regulatory mechanism is not clear. This study investigated the effects of high temperature and nitrogen fertilizer on the synthesis of grain storage protein and further explored the quality mechanism under the actual scenario of field warming. Results showed that increased temperature and nitrogen fertilizer could affect the activities of nitrogen metabolism enzymes, namely, glutamate synthetase, glutamine synthetase, glutamic pyruvic transaminase, and glutamic oxaloacetic transaminase, and the expressions of storage protein synthesis factor genes, namely, GluA and GluB, and subfamily genes, namely, pro14, BiP1, and PDIL1, which co-induced the changes of storage protein synthesis in rice grains. Furthermore, the increased temperature changed the balance of grain storage substances which may lead to the significantly increased chalky rate (197.67%) and chalkiness (532.92%). Moreover, there was a significant negative correlation between prolamin content and chalkiness, indicating that nitrogen fertilizer might regulate the formation of chalkiness by affecting the synthesis of prolamin. Results suggested that nitrogen application could regulate the related core factors involved in nitrogen metabolism pathways, which, in turn, affects the changes in the storage protein components in the grain and further affects quality. Therefore, as a conventional cultivation measure, nitrogen application would have a certain value in future rice production in response to climate warming.

Efficacy of Characterized Prosopis Wood Biochar Amendments in Improving Growth, Nitrogen Use Efficiency, Nitrate Accumulation, and Mineral Content in Cabbage Genotypes

This study was carried out to elucidate the impact of Prosopis wood biochar on growth, nitrogen use efficiency, and mineral profile of two genotypes of cabbage (Brassica oleracea L. capitata). The genotypes were grown under four different treatments of biochar: BT0 (control), BT1 (2.5% biochar), BT2 (5% biochar), and BT3 (7.5% biochar). Prior to its application, biochar was characterized to know about its morphological and physicochemical properties by performing scanning electron microscopy–energy dispersive X-ray (SEM-EDX), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), and X-ray diffraction (XRD) analysis. Pre-treated Prosopis-derived wood biochar was found to contain mesoporous structures and diverse functional groups. It was also found to contain considerable amounts of nutrients like carbon, nitrogen, sulfur, and calcium. The results revealed that growth, chlorophyll content, soluble sugar content, soluble protein levels, and nitrogen use efficiency increased following the biochar amendment compared to control. In the leaves of tested cabbage genotypes, the activity of nitrogen-metabolizing enzymes like nitrate reductase, nitrite reductase, and glutamine synthetase was significantly increased by biochar amendment; however, glutamate synthase activity was not significantly increased. Moreover, application of biochar significantly decreased the amount of nitrate in the tissue. Furthermore, biochar significantly increased concentrations of minerals like phosphorus, potassium, calcium, magnesium, iron, and zinc in the leaves of tested genotypes. Together, our study proposes that biochar amendments (2.5–7.5%) can be employed as an effective strategy to improve growth and nitrogen use efficiency by regulating nitrogen-metabolizing enzymes, lowering tissue nitrate levels, and maintaining or improving nutritional quality of cabbage.

Effect of dietary protein‐to‐energy ratios on growth performance, body composition, feed utilization and nitrogen metabolism enzyme of Cirrhinus mrigala

The present study was conducted to encompass the effect of dietary protein-to-energy ratios on growth performance, feed utilization, body composition and nitrogen metabolism enzymes of Cirrhinus mrigala. Five Iso-energetic diets (16 kJ/g) with graded levels of P/E ratios (17.84, 19.79, 22.19, 24.46 and 26.50 mg/kJ) named as A, B, C, D and E were formulated. A total of 300 C. mrigala fingerlings (initial body weight 17.8 ± 0.12 g) were equally distributed into five groups (in triplicate). Each group was fed twice a day at 4% wet body weight with respective P/E ratio diets for 8 weeks. Highest weight gain, specific growth rate, protein efficiency ratio and protein retention efficiency were observed in group C with the lowest, feed conversion ratio, Hepatosomatic index and Viscerosomatic index as compared to other groups. Furthermore, the whole-body and muscle tissue composition were also significantly (p < .05) influenced by the P/E ratios in diets. Among all groups, group C was significantly higher in crude protein and ash contents, with comparatively low lipids level and moisture contents compared to other groups. Additionally, the activities of nitrogen metabolism enzymes, Aspartate amino transferase, Alkaline amino transaminase, Glutamate dehydrogenase and Adenosine 5′-monophosphate deaminase (AST, ALT, GDH and AMPD) were significantly (p < .05) increased with the increasing of P/E ratios in diets. Our results showed that on the basis of second-order polynomial regression analysis of feed conversion ratio, the optimal dietary P/E ratio of C. mrigala (fingerlings) was 22.61 mg/kJ.

Effect of Drought Stress at Reproductive Stages on Growth and Nitrogen Metabolism in Soybean

This study aims to determine variability among soybean (Glycine max (L.) Merr.) cultivars under drought conditions and how nitrogen metabolites, metabolism-related enzymes, and gene expression vary during soybean growth. Three soybean cultivars, Shennong17 (CV.SN17), Shennong8 (CV.SN8), and Shennong12 (CV.SN12), were grown in pot culture and subjected to drought stress at reproductive stages for 45 days. The results showed that long-term drought stress decreased biomass allocation to reproductive organs, weakened antioxidant capacity, and reduced seed weight, effects that were less pronounced in CV.SN12 compared with those in CV.SN8 and CV.SN17. Drought stress decreased the concentrations of nitrogen and soluble protein but increased nitrate concentration in leaves. This was related to the significantly reduction of nitrogen metabolism efficiency, including decreased activities of nitrogen metabolism enzymes, and downregulated expression of GmNR, GmNiR, GmGS, and GmGOGAT. Drought stress increased the concentrations of free amino acid, proline, and soluble sugar in leaves to enhance the osmotic adjustment ability. Furthermore, soybean seed weight showed significantly correlation (p &lt; 0.05) with nitrogen-metabolism-related parameters. Based on the performance of growth, nitrogen metabolism, and yield attributes, CV.SN12 showed the highest tolerance to drought, followed by CV.SN8 and CV.SN17. In addition, these nitrogen-metabolism-related parameters could be used in soybeans to select for drought tolerance.

Indirect effect of different dietary protein to energy ratio of bait fish mori diets on growth performance, body composition, nitrogen metabolism and relative AMPK & mTOR pathway gene expression of Chinese perch

Chinese perch (Siniperca chuatsi) is an important economic freshwater carnivorous fish. Commonly feeds on other live fish or bait fish, and accept an artificial diet only after standard training. The feeding habit of Chinese perch caused high aquaculture costs and consumer prices. However, only a few studies are conducted on Chinese perch live feed (bait fish) or live feed (mori) feeds. Therefore, the present study was conducted to investigate the effect of live feed (mori) and live feed (mori) feeds protein to energy ratio on Chinese perch. Three Iso-energetic diets (16 kJ/g) with graded levels of P/E ratios (19.79, 22.19 and 24.46 mg protein/kJ) each with a protein level of 28.18 %, 31.36 %, and 33.91 % (named A, B, and C) were formulated. Two separate experimental tanks systems were used. In one tanks system, a total of 90 kg live bait fish C. mrigala were distributed into three groups (triplicate tanks (1000 L) for each group) and fed with respective P/E ratio diets. In another tanks system, a total of 270 Chinese perch (30 fish/tank) were divided into three groups (triplicate tanks for each group), distributed into 9 (1000-L) fiberglass tanks and fed with assigned live bait fish at 4 % fish wet body weight, twice a day for 8 weeks. The results showed that P/E ratio in bait fish diets significantly affected bait fish and Chinese perch growth performance, feed utilization, body composition, nitrogen metabolism, protein synthesis, and energy homeostasis. Bait fish in Group A showed significantly lower weight gain (WG), specific growth rate (SGR), and higher Viscerosomatic index (VSI) and Hepatosomatic index (HSI) as compared to other groups. Correspondingly, bait fish in Group A showed significantly low whole-body crude protein and high lipid contents as compared to other groups. Similarly, Chinese perch in Group A, showed significantly lower WG, SGR, protein efficiency ratio (PER) and highest feed intake (FI), feed conversion ratio (FCR), VSI, HSI, and Intraperitoneal fat (IPF), as compared to other groups. Furthermore, Chinese perch in Group A, showed significantly lower whole body and muscle crude protein, and higher lipid contents as compared to other groups. Similarly, the nitrogen metabolism enzyme activities (ALT, AST, GDH, AMPD) and gene expression of GDH and AMPD in Group A of Chinese perch, were significantly lower than other groups. Moreover, the AMPK and mTOR pathways gene expression showed a low energy status and protein catabolism in Group A of Chinese perch as compared to other groups. From our results, we conclude that the P/E ratio in bait fish diet significantly affected bait fish and Chinese perch growth performance and nutrients metabolism.

Characterization of nitrogen metabolism and photosynthesis in a stay-green rice cultivar

A field experiment was carried out in the years 2008–2011 in China to assess the nitrogen metabolism enzyme activities and photosynthetic characteristics in stable-yielding stay-green rice (Oryza sativa L.) cv. Shennong196. The results showed that higher levels of nitrogen content, nitrate reductase activity, and glutamine synthetase activity occurred in leaves of cv. Shennong196 compared with cv. Toyonishiki (control). Leaf color of cv. Shennong196 was positively correlated with nitrogen levels and nitrogen metabolism enzyme activities (P &amp;lt; 0.05). Superoxide dismutase activity and malondialdehyde contents were 18.53 unit/g fresh weight and 3.32 nmol/g, respectively, which were lower in flag leaves of cv. Shennong196 than cv. Toyonishiki. Cv. Shennong196 had a higher level of net photosynthetic rate, stomatal conductance, intercellular CO&lt;sub&gt;2&lt;/sub&gt; concentration, and transpiration rate in flag leaves of diurnal variation of photosynthesis at the ripening stage. The high net photosynthetic rate in cv. Shennong196 was positively correlated with the stomatal density of flag leaves (P &amp;lt; 0.01). Considering the yield-increasing potential and to prevent premature senescence of crop, these traits of cv. Shennong196 are useful for improved rice cultivar.

Effect of Epichloë gansuensis endophyte on the activity of enzymes of nitrogen metabolism, nitrogen use efficiency and photosynthetic ability of Achnatherum inebrians under various NaCl concentrations

This study explored the effects of Epichloe gansuensis endophyte on photosynthetic ability, the activity of nitrogen metabolism enzymes, nitrogen use efficiency, and biomass accumulation of Achnatherum inebrians growing under five NaCl concentrations. A. inebrians plants with (E+) and without E. gansuensis (E−) were grown under different NaCl concentrations. Photosynthetic indexes, NO3− and NH4+ content, nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS) activity, nitrogen use efficiency and nitrogen content were determined. The plant total biomass, NO3− and N content, NR, NiR and GS activity, total N accumulation (TNA), nitrogen utilization efficiency (NUtE) and nitrogen uptake efficiency (NUpE) were higher in leaves and roots of E+ than of E− plants under 300 and 400 mM NaCl concentrations, but NH4+ content was lower in leaves and roots of E+ than of E− plants under 100, 200, 300 and 400 mM NaCl concentrations. However, there were almost no significant effects on these factors between E+ and E− plants under the 0 mM NaCl concentration. The endophyte improved the growth of plants under high NaCl concentration by improving photosynthetic ability, increasing the activity of nitrogen metabolism enzymes and nitrogen use efficiency.

The positive function of selenium supplementation on reducing nitrate accumulation in hydroponic lettuce (Lactuca sativa L.)

High nitrate (NO3−) in vegetables, especially in leaf vegetables poses threaten to human health. Selenium (Se) is an important element for maintaining human health, and exogenous Se application during vegetable and crop production is an effective way to prevent Se deficiency in human bodies. Exogenous Se shows positive function on plant growth and nutrition uptake under abiotic and/or biotic stresses. However, the influence of exogenous Se on NO3− accumulation in hydroponic vegetables is still not clear. In the present study, hydroponic lettuce plants were subjected to six different concentrations (0, 0.1, 0.5, 5, 10 and 50 µmol L−1) of Se as Na2SeO3. The effects of Se on NO3− content, plant growth, and photosynthetic capacity of lettuce (Lactuca sativa L.) were investigated. The results showed that exogenous Se positively decreased NO3− content and this effect was concentration-dependent. The lowest NO3− content was obtained under 0.5 µmol L−1 Se treatment. The application of Se enhanced photosynthetic capacity by increasing the photosynthesis rate (Pn), stomatal conductance (Cs) and the transpiration efficiency (Tr) of lettuce. The transportation and assimilation of NO3− and activities of nitrogen metabolism enzymes in lettuce were also analysed. The NO3− efflux in the lettuce roots was markedly increased, but the efflux of NO3− from the root to the shoot was decreased after treated with exogenous Se. Moreover, Se application stimulated NO3− assimilation by enhancing nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS) and glutamate synthase enzyme (GOGAT) activities. These results provide direct evidence that exogenous Se shows positive function on decreasing NO3− accumulation via regulating the transport and enhancing activities of nitrogen metabolism enzyme in lettuce. We suggested that 0.5 µmol L−1 Se can be used to reduce NO3− content and increase hydroponic lettuce yield.

Effects of potassium on nitrogen translocation and distribution and nitrogen metabolism enzyme activities of sweet potato.

A pot experiment with 15N tracing techniques was designed to study the effect of potassium application on nitrogen transfer, photosynthetic characteristics and nitrogen metabolism enzyme activities in two different growth stages of sweet potato. Results indicated that potassium application significantly increased the shoot 15N distribution rate. Compared with control, the 15N transfer rate of K3 treatment increased by 76.2% and the total accumulation of 15N increased by 92.1% in tuber formation period. Different with tuber formation period, shoot 15N distribution rate decreased from 33.7% to 24.4%, but the root 15N distribution rate increased from 5.8% to 17% with the increase of K application in tuber rapid growth stage. Especially, root 15N accumulation of K3 treatment was 3 times of the CK. During the two growth stages, nitrate reductase, glutamate dehydrogenase, glutamine synthetase, glutamate synthase and net photosynthetic rate all increased with the increase of K application. Stepwise regression analysis showed that nitrogen metabolism enzyme activities (nitrate reductase, glutamate dehydrogenase, glutamine synthetase, glutamate synthase) and Pn were the main factors to affect the 15N transfer and distribution of sweet potato (R1=0.965,R2=0.942). Path analysis showed that nitrate reductase and glutamate dehydrogenase activities were the key factors to influence 15N distribution to the shoot in tuber formation period, while glutamate dehydrogenase, glutamate synthase activities were the key factors to influence 15N distribution to the tuber in tuber rapid growth stage.