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1.
The role of H2O2 in abscisic acid (ABA)-induced NH4+ accumulation in rice leaves was investigated. ABA treatment resulted in an accumulation of NH4+ in rice leaves, which was preceded by a decrease in the activity of glutamine synthetase (GS) and an increase in the specific activities of protease and phenylalanine ammonia-lyase (PAL). GS, PAL, and protease seem to be the enzymes responsible for the accumulation of NH4+ in ABA-treated rice leaves. Dimethylthiourea (DMTU), a chemical trap for H2O2, was observed to be effective in inhibiting ABA-induced accumulation of NH4+ in rice leaves. Inhibitors of NADPH oxidase, diphenyleneiodonium chloride (DPI) and imidazole (IMD), and nitric oxide donor (N-tert-butyl-α-phenylnitrone, PBN), which have previously been shown to prevent ABA-induced increase in H2O2 contents in rice leaves, inhibited ABA-induced increase in the content of NH4+. Similarly, the changes of enzymes responsible for NH4+ accumulation induced by ABA were observed to be inhibited by DMTU, DPI, IMD, and PBN. Exogenous application of H2O2 was found to increase NH4+ content, decrease GS activity, and increase protease and PAL-specific activities in rice leaves. Our results suggest that H2O2 is involved in ABA-induced NH4+ accumulation in rice leaves. 相似文献
2.
Alvarez-Pizarro JC Gomes-Filho E Prisco JT Grossi-de-Sá MF de Oliveira-Neto OB 《Journal of plant physiology》2011,168(14):1617-1626
The effect of external inorganic nitrogen and K+ content on K+ uptake from low-K+ solutions and plasma membrane (PM) H+-ATPase activity of sorghum roots was studied. Plants were grown for 15 days in full-nutrient solutions containing 0.2 or 1.4 mM K+ and inorganic nitrogen as NO3-, NO3-/NH4+ or NH4+ and then starved of K+ for 24, 48 and 72 h. NH4+ in full nutrient solution significantly affected the uptake efficiency and accumulation of K+, and this effect was less pronounced at the high K+ concentration. In contrast, the translocation rate of K+ to the shoot was not altered. Depletion assays showed that plants grown with NH4+ more efficiently depleted the external K+ and reached higher initial rates of low-K+ uptake than plants grown with NO3-. One possible influence of K+ content of shoot, but not of roots, on K+ uptake was evidenced. Enhanced K+-uptake capacity was correlated with the induction of H+ extrusion by PM H+-ATPase. In plants grown in high K+ solutions, the increase in the active H+ gradient was associated with an increase of the PM H+-ATPase protein concentration. In contrast, in plants grown in solutions containing 0.2 mM K+, only the initial rate of H+-pumping and ATP hydrolysis were affected. Under these conditions, two specific isoforms of PM H+-ATPase were detected, independent of the nitrogen source and deficiency period. No change in enzyme activity was observed in NO3--grown plants. The results suggest that K+ homeostasis in NH4+-grown sorghum plants may be regulated by a high capacity for K+ uptake, which is dependent upon the H+-pumping activity of PM H+-ATPase. 相似文献
3.
The influence of NH4+ on microbial CH4 oxidation is still poorly understood in landfill cover soils. In this study, effects of NH4+ addition on the activity and community structure of methanotrophs were investigated in waste biocover soil (WBS) treated by a series of NH4+-N contents (0, 100, 300, 600 and 1200 mg kg−1). The results showed that the addition of NH4+-N ranging from 100 to 300 mg kg−1 could stimulate CH4 oxidation in the WBS samples at the first stage of activity, while the addition of an NH4+-N content of 600 mg kg−1 had an inhibitory effect on CH4 oxidation in the first 4 days. The decrease of CH4 oxidation rate observed in the last stage of activity could be caused by nitrogen limitation and/or exopolymeric substance accumulation. Type I methanotrophs Methylocaldum and Methylobacter, and type II methanotrophs (Methylocystis and Methylosinus) were abundant in the WBS samples. Of these, Methylocaldum was the main methanotroph in the original WBS. With incubation, a higher abundance of Methylobacter was observed in the treatments with NH4+-N contents greater than 300 mg kg−1, which suggested that NH4+-N addition might lead to the dominance of Methylobacter in the WBS samples. Compared to type I methanotrophs, the abundance of type II methanotrophs Methylocystis and/or Methylosinus was lower in the original WBS sample. An increase in the abundance of Methylocystis and/or Methylosinus occurred in the last stage of activity, and was likely due to a nitrogen limitation condition. Redundancy analysis showed that NH4+-N and the C/N ratio had a significant influence on the methanotrophic community in the WBS sample. 相似文献
4.
Different sensitivity of Phragmites australis and Glyceria maxima to high availability of ammonium-N
The ability to cope with NH4+-N was studied in the littoral helophytes Phragmites australis and Glyceria maxima, species commonly occupying fertile habitats rich in NH4+ and often used in artificial wetlands. In the present study, Glyceria growth rate was reduced by 16% at 179 μM NH4+-N, and the biomass production was reduced by 47% at 3700 μM NH4+-N compared to NO3−-N. Similar responses were not found in Phragmites. The amounts (mg g−1 dry wt) of starch and total non-structural carbohydrates (TNC) in rhizomes were significantly lower in NH4+ (8.9; 12.2 starch; 20.1; 41.9 TNC) compared to NO3− treated plants (28.0; 15.6 starch; 58.5; 56.3 TNC) in Phragmites and Glyceria, respectively. In addition, Glyceria showed lower amounts (mg g−1 dry wt) of soluble sugars, TNC, K+, and Mg2+ in roots under NH4+ (5.6; 14.3; 20.6; 1.9) compared to NO3− nutrition (11.6; 19.9; 37.9; 2.9, for soluble sugars, TNC, K+, and Mg2+, respectively), while root internal levels of NH4+ and Ca2+ (0.29; 4.6 mg g−1 dry wt, mean of both treatments) were only slightly affected. In Phragmites, no changes in soluble sugars, TNC, Ca2+, K+, and Mg2+ contents of roots (7.3; 14.9; 5.1; 17.3; 2.6 mg g−1 dry wt, means of both treatments) were found in response to treatments. The results, therefore, indicate a more pronounced tolerance towards high NH4+ supply in Phragmites compared to Glyceria, although the former may be susceptible to starch exhaustion in NH4+-N nutrition. In contrast, Glyceria's ability to colonize fertile habitats rich in NH4+ is probably related to the avoidance strategy due to shallow rooting or to the previously described ability to cope with high NH4+ levels when P availability is high and NO3− is also provided. 相似文献
5.
Lucena MN Garçon DP Mantelatto FL Pinto MR McNamara JC Leone FA 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》2012,161(4):380-391
We examine hemolymph ion regulation and the kinetic properties of a gill microsomal (Na+, K+)-ATPase from the intertidal hermit crab, Clibanarius vittatus, acclimated to 45‰ salinity for 10 days. Hemolymph osmolality is hypo-regulated (1102.5 ± 22.1 mOsm kg−1 H2O) at 45‰ but elevated compared to fresh-caught crabs (801.0 ± 40.1 mOsm kg−1 H2O). Hemolymph [Na+] (323.0 ± 2.5 mmol L−1) and [Mg2+] (34.6 ± 1.0 mmol L−1) are hypo-regulated while [Ca2+] (22.5 ± 0.7 mmol L−1) is hyper-regulated; [K+] is hyper-regulated in fresh-caught crabs (17.4 ± 0.5 mmol L−1) but hypo-regulated (6.2 ± 0.7 mmol L−1) at 45‰. Protein expression patterns are altered in the 45‰-acclimated crabs, although Western blot analyses reveal just a single immunoreactive band, suggesting a single (Na+, K+)-ATPase α-subunit isoform, distributed in different density membrane fractions. A high-affinity (Vm = 46.5 ± 3.5 U mg−1; K0.5 = 7.07 ± 0.01 μmol L−1) and a low-affinity ATP binding site (Vm = 108.1 ± 2.5 U mg−1; K0.5 = 0.11 ± 0.3 mmol L−1), both obeying cooperative kinetics, were disclosed. Modulation of (Na+, K+)-ATPase activity by Mg2+, K+ and NH4+ also exhibits site-site interactions, but modulation by Na+ shows Michaelis-Menten kinetics. (Na+, K+)-ATPase activity is synergistically stimulated up to 45% by NH4+ plus K+. Enzyme catalytic efficiency for variable [K+] and fixed [NH4+] is 10-fold greater than for variable [NH4+] and fixed [K+]. Ouabain inhibited ≈80% of total ATPase activity (KI = 464.7 ± 23.2 μmol L−1), suggesting that ATPases other than (Na+, K+)-ATPase are present. While (Na+, K+)-ATPase activities are similar in fresh-caught (around 142 nmol Pi min−1 mg−1) and 45‰-acclimated crabs (around 154 nmol Pi min−1 mg−1), ATP affinity decreases 110-fold and Na+ and K+ affinities increase 2-3-fold in 45‰-acclimated crabs. 相似文献
6.
Although mineral N generally has a negative effect on legume-rhizobia symbioses, experiments in hydroponic culture in our laboratory (Waterer et al., 1992) have shown that low concentrations of NH+
4 can stimulate nodulation in pea (Pisum sativum L.). The objectives of the current study were to determine the immediate and residual effects of NH+
4 on nodulation and N2 fixation in pea in sand culture. Peas (cv. Express) were exposed to 0.0, 0.5, 1.0, and 2.0 mM of 15N-labelled (NH4)2SO4 for 28 days after inoculation (DAI). From 28 to 56 DAI the plants were grown on a NH+
4-free nutrient solution. Plants were harvested at 7, 14, 21, 28 and 56 DAI and nitrogenase activity was measured by gas exchange at 28 and 56 DAI. Root, shoot, and nodule dry weight (DW) and total N content were obtained, in addition to nodule counts and 15N enrichment of plant composites. The 1.0 and 2.0 mM NH+
4 treatments consistently resulted in higher total plant DW accumulation than the control (0.0 mM NH+
4). At 28 DAI, plants exposed to 1.0 and 2.0 mM NH+
4 had 1.8 to 2.8 times more nodules plant-1, respectively, and plants exposed to 2.0 mM NH+
4 had 1.7 fold higher specific nodulation (nodule number g-1 root DW). However, individual nodule DW was greater in control plants, such that there were no differences in nodule DW per plant among treatments. Ammonium treatment resulted in more nitrogen derived from the atmosphere (NDFA) in peas early in the experiment, but by 28 DAI there were no treatment effects on NDFA. Whole plant and nodule specific nitrogenase activity (µmol H2 g-1 nodule DW h-1) was higher in control plants at 28 DAI. However, by 56 DAI, after an additional 4 weeks of NH+
4-free nutrition, no differences in nitrogenase activity nor whole plant or specific nodulation were detectable. This study indicates that nodulation in pea is stimulated in sand culture while exposed to NH+
4. However, once NH+
4 is removed, relative growth rate, nodulation and nitrogenase activity becomes similar to plants that were never exposed to NH+
4. 相似文献
7.
Various enzymes involved in the initial metabolic pathway for ammonia assimilation by Methanobacterium ivanovii were examined. M. ivanovii showed significant activity of glutamine synthetase (GS). Glutamate synthase (GOGAT) and alanine dehydrogenase (ADH) were present, wheras, glutamate dehydrogenase (GDH) was not detected. When M. ivanovii was grown with different levels of NH
+
4
(i.e. 2, 20 or 200 mM), GS, GOGAT and ADH activities varied in response to NH
+
4
concentration. ADH was not detected at 2 mM level, but its activity increased with increased levels of NH
+
4
in the medium. Both GS and GOGAT activities increased with decreasing concentrations of NH
+
4
and were maximum when ammonia was limiting, suggesting that at low NH
+
4
levels, GS and GOGAT are responsible for ammonia assimilation and at higher NH
+
4
levels, ADH might play a role. Metabolic mutants of M. ivanovii that were auxotrophic for glutamine were obtained and analyzed for GS activity. Results indicate two categories of mutants: i) GS-deficient auxotrophic mutants and ii) GS-impaired auxotrophic mutants.Abbreviations GS
Glutamine synthetase
- GOGAT
glutamate synthase
- GDH
glutamate dehydrogenase
- ADH
alanine dehydrogenase 相似文献
8.
The influence of three nitrogen salts: NH4NO3, KNO3 and NH4Cl on wheat in vitro cultures was investigated. Both NO
3
−
and NH
4
+
ions were indispensable for proliferation of embryogenic calli and development of wheat somatic embryos. It is possible to
obtain wheat somatic embryos when the medium is enriched with NH4NO3 only as a source of inorganic nitrogen. The results of the statistical analysis showed that the level of NH4NO3 and KNO3 in the medium had a great influence on the efficiency of somatic embryogenesis. We observed tendency that calli on media
containing 50 mM NH4NO3 and 0 to 20 mM KNO3 turned out to be more embryogenic than on control MS medium. High concentrations of KNO3- 100 mM inhibited somatic embryogenesis, while 100 mM NH4NO3 did not. The level of total N did not have significant influence on wheat somatic embryogenesis. Ratio NO
3
−
:NH
4
+
also turned out to be not substantial. We observed that mutual connection of concentration levels between NH4NO3 and KNO3 and between NH4Cl and KNO3 was more important. The efficiency of somatic embriogenesis obtained in the experiment with NH4Cl and KNO3 was significantly lower than in experiment with NH4NO3 and KNO3. 相似文献
9.
Corinne I. Rodgers John D. LaBrie R. Meldrum Robertson 《Journal of insect physiology》2009,55(7):599-3216
Stress-induced arrest of ventilatory motor pattern generation is tightly correlated with an abrupt increase in extracellular potassium concentration ([K+]o) within the metathoracic neuropil of the locust, Locusta migratoria. Na+/K+-ATPase inhibition with ouabain elicits repetitive surges of [K+]o that coincide with arrest and recovery of motor activity. Here we show that ouabain induces repetitive [K+]o events in a concentration-dependent manner. 10−5 M, 10−4 M, and 10−3 M ouabain was bath-applied in semi-intact locust preparations. 10−4 M and 10−3 M ouabain reliably induced repetitive [K+]o events whereas 10−5 M ouabain had no significant effect. In comparison to 10−4 M ouabain, 10−3 M ouabain increased the number and hastened the time to onset of repetitive [K+]o waves, prolonged [K+]o event duration, increased resting [K+]o, and diminished the absolute value of [K+]o waves. Recovery of motor patterning following [K+]o events was less likely in 10−3 M ouabain. In addition, we show that K+ channel inhibition using TEA suppressed the onset and decreased the amplitude of ouabain-induced repetitive [K+]o waves. Our results demonstrate that ventilatory circuit function in the locust CNS is dependent on the balance between mechanisms of [K+] accumulation and [K+] clearance. We suggest that with an imbalance in favour of accumulation the system tends towards a bistable state with transitions mediated by positive feedback involving voltage-dependent K+ channels. 相似文献
10.
Rat C6 glioma cells were cultured for 4 days in MEM medium supplemented with 10% bovine serum and Na+,K+-ATPase activity was determined in homogenates of harvested cells. Approximately 50% of enzyme activity was attained at 1.5 mM K+ and the maximum (2.76±0.13 mol Pi/h/mg protein) at 5 mM K+. The specific activity of Na+,K+-ATPase was not influenced by freezing the homogenates or cell suspensions before the enzyme assay. Ten minutes' exposure of glioma cells to 10–4 or 10–5 M noradrenaline (NA) remained without any effect on NA+,K+-ATPase activity. Neither did the presence of NA in the incubation medium, during the enzyme assay, influence the enzyme activity. The nonresponsiveness of Na+,K+-ATPase of C6 glioma cells to NA is consistent with the assumption that (+) form of the enzyme may be preferentially sensitive to noradrenaline. Na+,K+-ATPase was inhibited in a dose-dependent manner by vanadate and 50% inhibition was achieved at 2×10–7 M concentration. In spite of the fact that Na+,K+-ATPase of glioma cells was not responsive to NA, the latter could at least partially reverse vanadate-induced inhibition of the enzyme. Although the present results concern transformed glial cells, they suggest the possibility that inhibition of glial Na+,K+-ATPase may contribute to the previously reported inhibition by vanadate of Na+,K+-ATPase of the whole brain tissue. 相似文献
11.
Chantal Eid Miryana HémadiNguyêt-Thanh Ha-Duong Jean-Michel El Hage Chahine 《Biochimica et Biophysica Acta (BBA)/General Subjects》2014
Background
Dietary and recycled iron are in the Fe2 + oxidation state. However, the metal is transported in serum by transferrin as Fe3 +. The multi-copper ferroxidase ceruloplasmin is suspected to be the missing link between acquired Fe2 + and transported Fe3 +.Methods
This study uses the techniques of chemical relaxation and spectrophotometric detection.Results
Under anaerobic conditions, ceruloplasmin captures and oxidizes two Fe2 +. The first uptake occurs in domain 6 (< 1 ms) at the divalent iron-binding site. It is accompanied by Fe2 + oxidation by Cu2 +D6. Fe3 + is then transferred from the binding site to the holding site. Cu+D6 is then re-oxidized by a Cu2 + of the trinuclear cluster in about 200 ms. The second Fe2 + uptake and oxidation involve domain 4 and are under the kinetic control of a 200 s change in the protein conformation. With transferrin and in the formed ceruloplasmin–transferrin adduct, two Fe3 + are transferred from their holding sites to two C-lobes of two transferrins. The first transfer (~ 100 s) is followed by conformation changes (500 s) leading to the release of monoferric transferrin. The second transfer occurs in two steps in the 1000–10,000 second range.Conclusion
Fe3 + is transferred after Fe2 + uptake and oxidation by ceruloplasmin to the C-lobe of transferrin in a protein–protein adduct. This adduct is in a permanent state of equilibrium with all the metal-free or bounded ceruloplasmin and transferrin species present in the medium.General significance
Ceruloplasmin is a go-between dietary or recycled Fe2 + and transferrin transported Fe3 +. 相似文献12.
The effects of inorganic nitrogen (N) source (NH4+, NO3− or both) on growth, biomass allocation, photosynthesis, N uptake rate, nitrate reductase activity and mineral composition of Canna indica were studied in hydroponic culture. The relative growth rates (0.05-0.06 g g−1 d−1), biomass allocation and plant morphology of C. indica were indifferent to N nutrition. However, NH4+ fed plants had higher concentrations of N in the tissues, lower concentrations of mineral cations and higher contents of chlorophylls in the leaves compared to NO3− fed plants suggesting a slight advantage of NH4+ nutrition. The NO3− fed plants had lower light-saturated rates of photosynthesis (22.5 μmol m−2 s−1) than NH4+ and NH4+/NO3− fed plants (24.4-25.6 μmol m−2 s−1) when expressed per unit leaf area, but similar rates when expressed on a chlorophyll basis. Maximum uptake rates (Vmax) of NO3− did not differ between treatments (24-35 μmol N g−1 root DW h−1), but Vmax for NH4+ was highest in NH4+ fed plants (81 μmol N g−1 root DW h−1), intermediate in the NH4NO3 fed plants (52 μmol N g−1 root DW h−1), and lowest in the NO3− fed plants (28 μmol N g−1 root DW h−1). Nitrate reductase activity (NRA) was highest in leaves and was induced by NO3− in the culture solutions corresponding to the pattern seen in fast growing terrestrial species. Plants fed with only NO3− had high NRA (22 and 8 μmol NO2− g−1 DW h−1 in leaves and roots, respectively) whereas NRA in NH4+ fed plants was close to zero. Plants supplied with both forms of N had intermediate NRA suggesting that C. indica takes up and assimilate NO3− in the presence of NH4+. Our results show that C. indica is relatively indifferent to inorganic N source, which together with its high growth rate contributes to explain the occurrence of this species in flooded wetland soils as well as on terrestrial soils. Furthermore, it is concluded that C. indica is suitable for use in different types of constructed wetlands. 相似文献
13.
In vivo
31P nuclear magnetic resonance (NMR) was used to characterize the effect of the N form (NO3 vs. NH4) and the external pH (4, 6, and 8), on the intracellular pH of root tips (0–5 mm) and root segments (5–30 mm). Ammonium-grown root tips were the most sensitive to changes in the external pH. In vivo
15N NMR was used to characterize the pathway of primary ammonium assimilation in the ammonium-grown roots and to compare the activity of the apical and more-basal root parts. The kinetics of 15NH4
+ incorporation showed that primary assimilation in both root tips and root segments followed the glutamine synthetase (GS) pathway. In agreement with the reported gradient of GS along the seminal root of maize, incorporation of label into glutamine amide was more rapid in tips than in segments. It is suggested that this higher GS activity increases the endogenous proton production and thus contributes to the greater dependence of the cytoplasmic pH on the external pH in the ammonium-treated root tips. 相似文献
14.
Gisela Mäck 《Planta》1995,196(2):231-238
One cytosolic glutamine synthetase (GS, EC 6.3.1.2) isoform (GS 1a) was active in the germinating seeds of barley (Hordeum vulgare L.). A second cytosolic GS isoform (GS 1b) was separated from the leaves as well as the roots of 10-d-old seedlings. The chloroplastic isoform (GS 2) was present and active only in the leaves. The three GS isoforms were active in N-supplied (NH+
4 or NO
3
–
) as well as in N-free-grown seedlings. This indicates (i) that a supply of nitrogen to the germinating seeds was not necessary for the induction of the GS isoforms and (ii) that no nitrogen-specific isoforms appeared during growth of seedlings with different nitrogen sources. The activity of GS, however, depended on the seedlings' nitrogen source: the specific activity was much higher in the leaves and much lower in the roots of NH+
4-grown barley than in the respective organs of NO
3
–
-fed or N free-grown plants. With increasing concentrations of NH+
4 (supplied hydroponically during growth), the specific activity of GS 1b increased in the leaves, but decreased in the roots. The activity of GS 2 (leaf) also increased with increasing NH+
4 supply, whereas GS 1a activity (leaf and root) was not affected. The changes in the activities of GS 1b and GS 2 were correlated with changes in the subunit compositions of the active holoenzymes: growth at increased levels of external NH+
4 resulted in an increased abundance of one of the four GS subunits, and of two of the five GS 1b subunits in the leaves. In the roots, however, the abundance of these two GS 1b subunits was decreased under the same growth conditions, indicating an organ-specific difference either in the expression of the genes coding for the respective GS 1b subunits or in the assembly of the GS 1b holoenzymes. Furthermore, growth at different levels of NH+
4 resulted in changes in the substrate affinities of the isoforms GS 1b (root and leaf) and GS 2 (leaf), presumably due to the changes in the subunit compositions of the active holoenzymes.Abbreviations FPLC
fast protein liquid chromatography
- GHA
-glutamyl hydroxamate
- GS
glutamine synthetase
Dr. Roger Wallsgrove's (Rothamsted Experimental Station, Harpenden, UK) generous gift of GS antiserum is greatly appreciated. 相似文献
15.
Rubio-Wilhelmi Mdel M Sanchez-Rodriguez E Rosales MA Blasco B Rios JJ Romero L Blumwald E Ruiz JM 《Journal of plant physiology》2012,169(2):157-162
Wild Type (WT) and transgenic tobacco plants expressing isopentenyltransferase (IPT), a gene encoding the enzyme regulating the rate-limiting step in cytokinins (CKs) synthesis, were grown under limited nitrogen (N) conditions. We analyzed nitrogen forms, nitrogen metabolism related-enzymes, amino acids and photorespiration related-enzymes in WT and PSARK∷IPT tobacco plants. Our results indicate that the WT plants subjected to N deficiency displayed reduced nitrate (NO3−) assimilation. However, an increase in the production of ammonium (NH4+), by the degradation of proteins and photorespiration led to an increase in the glutamine synthetase/glutamate synthase (GS/GOGAT) cycle in WT plants. In these plants, the amounts of amino acids decreased with N deficiency, although the relative amounts of glutamate and glutamine increased with N deficiency. Although the transgenic plants expressing PSARK∷IPT and growing under suboptimal N conditions displayed a significant decline in the N forms in the leaf, they maintained the GS/GOGAT cycle at control levels. Our results suggest that, under N deficiency, CKs prevented the generation and assimilation of NH4+ by increasing such processes as photorespiration, protein degradation, the GS/GOGAT cycle, and the formation of glutamine. 相似文献
16.
Shyam R. Morar Shaun P. Wilkinson 《Journal of experimental marine biology and ecology》2011,399(2):110-119
The sea anemone Anthopleura aureoradiata (Carlgren), which harbours symbiotic dinoflagellates (zooxanthellae), is abundant on mudflats and rocky shores around New Zealand. We measured the potential for particulate nitrogen uptake from sediment by A. aureoradiata and the subsequent consequences of this uptake on the nitrogen status of its zooxanthellae. Sediment was rinsed, labelled with (15NH4)2SO4, and provided to anemones at low (0.23 g ml− 1) and high (1.33 g ml− 1) sediment loads for 6 h. Both anemone tissues and zooxanthellae became enriched with 15N. Enrichment of anemone tissues was similar at both high and low sediment loads, but the zooxanthellae became more enriched at the lower load. This was presumably because the uptake of ammonium, arising from host catabolism, by zooxanthellae is light driven and because the anemones at the lower load were able to extend their tentacles into the light while those at the higher load were not. The influence of sediment uptake on the nitrogen status of the zooxanthellae was determined by measuring the extent to which 20 μM NH4+ enhanced the rate of zooxanthellar dark carbon fixation above that seen in filtered seawater (FSW) alone; the ammonium enhancement ratio (AER) was expressed as [dark NH4+ rate/dark FSW rate], where ‘rate’ refers to C fixation and a ratio of 1.0 or less indicates nitrogen sufficiency. When anemones were starved with and without rinsed sediment in nitrogen-free artificial seawater for 8 weeks, zooxanthellar nitrogen deficiency became apparent at 2-4 weeks and reached similar levels in both treatments (AER = ~ 2). In contrast, anemones fed 5 times per week for 8 weeks with Artemia nauplii were nitrogen sufficient (AER = 1.03). In the field, zooxanthellae from mudflat anemones were largely nitrogen sufficient (AER = 1.26), while nitrogen deficient zooxanthellae were present in anemones from a rocky intertidal site (AER = 2.93). These results suggest that, while there was evidence for particulate nitrogen uptake, dissolved inorganic nitrogen (especially ammonium) in interstitial pore water may be a more important source of nitrogen for the zooxanthellae in mudflat anemones, and may explain the marked difference in nitrogen status between the mudflat and rocky shore populations. 相似文献
17.
【目的】通过改造谷氨酸棒杆菌JNR中双功能尿苷酰转移/去除酶GlnD,减弱尿苷酰去除酶的活性,增强NH_4~+的转运和利用,提高L-精氨酸的合成。【方法】本文对来源于谷氨酸棒杆菌的突变菌株JNR中的双功能尿苷酰转移/去除酶GlnD进行整合突变,采用同源重组的方法将H_(414)和D_(415)位点突变为两个丙氨酸AA,在此菌株的基础上过量表达PII蛋白GlnK,并对其进行尿苷酰化研究,离子色谱检测摇瓶发酵过程中NH4+的浓度,并对最终的改造菌株进行连续流加发酵分析。【结果】该双功能尿苷酰转移/去除酶在谷氨酸棒杆菌中成功进行整合突变,有效减弱了尿苷酰去除酶的活性;同时过表达PII蛋白GlnK,其酰基化程度明显增强。摇瓶发酵结果表明菌株L4消耗NH_4~+增加,L-精氨酸产量为36.2±1.2 g/L,比对照菌株L3高出22.7%。5-L发酵罐实验结果显示改造菌株L4的L-精氨酸的产量为52.2 g/L,较野生型菌株L0提高了25.3%。【结论】谷氨酸棒杆菌合成L-精氨酸的过程中氮源是必不可少的。减弱GlnD尿苷酰去除酶的活性后,胞内尿苷酰化的GlnK-UMP增加,GlnK-UMP与氮转录调控因子AmtR结合,转运至胞内的NH_4~+浓度提高,促使L-精氨酸产量显著提高。 相似文献
18.
Denis V. Abramochkin Eugenia I. Alekseeva Matti Vornanen 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2013,158(3):181-186
KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea) was developed as a specific inhibitor of the sarcolemmal sodium–calcium exchanger (NCX) with potential experimental and therapeutic use. However, KB-R7943 is shown to be a potent blocker of several ion currents including inward and delayed rectifier K+ currents of cardiomyocytes. To further characterize KB-R7943 as a blocker of the cardiac inward rectifiers we compared KB-R7943 sensitivity of the background inward rectifier (IK1) and the carbacholine-induced inward rectifier (IKACh) currents in mammalian (Rattus norvegicus; rat) and fish (Carassius carassius; crucian carp) cardiac myocytes. The basal IK1 of ventricular myocytes was blocked with apparent IC50-values of 4.6 × 10− 6 M and 3.5 × 10− 6 M for rat and fish, respectively. IKACh was almost an order of magnitude more sensitive to KB-R7943 than IK1 with IC50-values of 6.2 × 10− 7 M for rat and 2.5 × 10− 7 M for fish. The fish cardiac NCX current was half-maximally blocked at the concentration of 1.9–3 × 10− 6 M in both forward and reversed mode of operation. Thus, the sensitivity of three cardiac currents to KB-R7943 block increases in the order IK1 ~ INCX < IKACh. Therefore, the ability of KB-R7943 to block inward rectifier potassium currents, in particular IKACh, should be taken into account when interpreting the data with this inhibitor from in vivo and in vitro experiments in both mammalian and fish models. 相似文献
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Robert D. GrayJonathan B. Chaires 《Biophysical chemistry》2011,159(1):205-209
Formation of DNA quadruplexes requires monovalent cation binding. To characterize the cation binding stoichiometry and linkage between binding and folding, we carried out KCl titrations of Tel22 (d[A(GGGTTA)3]), a model of the human telomere sequence, using a fluorescent indicator to determine [K+]free and circular dichroism to assess the extent of folding. At [K+]free = 5 mM (sufficient for > 95% folding), the apparent binding stoichiometry is 3K+/Tel22; at [K+]free = 20 mM, it increased to 8-10K+/Tel22. Thermodynamic analysis shows that at [K+]free = 5 mM, K+ binding contributes approximately − 4.9 kcal/mol for folding Tel22. The overall folding free energy is − 2.4 kcal/mol, indicating that there are energetically unfavorable contributions to folding. Thus, quadruplex folding is driven almost entirely by the energy of cation binding with little or no contribution from other weak molecular interactions. 相似文献