Glutamine Synthetase ( GS ): A Key Enzyme for Nitrogen Assimilation in The Macroalga Gracilariopsis lemaneiformis (Rhodophyta)

2019 ◽  
Vol 55 (5) ◽  
pp. 1059-1070 ◽  
Author(s):  
Xiaojuan Liu ◽  
Zhongyan Huan ◽  
Qingfang Zhang ◽  
Mingqi Zhong ◽  
Weizhou Chen ◽  
...  
Keyword(s):  
Glutamine Synthetase ◽  
Nitrogen Assimilation ◽  
Gracilariopsis Lemaneiformis ◽  
Key Enzyme

scholarly journals Nitrogen Regulating the Expression and Localization of Four Glutamine Synthetase Isoforms in Wheat (Triticum aestivum L.)

2020 ◽  
Vol 21 (17) ◽  
pp. 6299
Author(s):  
Yihao Wei ◽  
Xiaochun Wang ◽  
Zhiyong Zhang ◽  
Shuping Xiong ◽  
Xiaodan Meng ◽  
...  
Keyword(s):  
Glutamine Synthetase ◽  
Nitrogen Assimilation ◽  
Vascular Tissue ◽  
Mrna Level ◽  
Triticum Aestivum L ◽  
Kinetic Properties ◽  
High Catalytic Activity ◽  
Root Tips ◽  
Plant Nitrogen ◽  
Key Enzyme

Glutamine synthetase (GS), the key enzyme in plant nitrogen assimilation, is strictly regulated at multiple levels, but the most relevant reports focus on the mRNA level. Using specific antibodies as probes, the effects of nitrogen on the expression and localization of individual wheat GS (TaGS) isoforms were studied. In addition to TaGS2, TaGS1;1 with high affinity to substrate and TaGS1;3 with high catalytic activity were also localized in mesophyll, and may participate in cytoplasmic assimilation of ammonium (NH4+) released from photorespiration or absorbed by roots; TaGS1;2 was localized in xylem of leaves. In roots, although there were hundreds of times more TaGS1;1 than TaGS1;2 transcripts, the amount of TaGS1;1 subunit was not higher than that of TaGS1;2; NH4+ inhibited TaGS1;1 expression but stimulated TaGS1;3 expression. In root tips, nitrate stimulated TaGS1;1, TaGS1;3, and TaGS2 expression in meristem, while NH4+ promoted tissue differentiation and TaGS1;2 expression in endodermis and vascular tissue. Only TaGS1;2 was located in vascular tissue of leaves and roots, and was activated by glutamine, suggesting a role in nitrogen transport. TaGS1;3 was induced by NH4+ in root endodermis and mesophyll, suggesting a function in relieving NH4+ toxicity. Thus, TaGS isoforms play distinct roles in nitrogen assimilation for their different kinetic properties, tissue locations, and response to nitrogen regimes.

Control of nitrogen assimilation in Stichococcus bacillaris by growth conditions

1987 ◽  
Vol 65 (3) ◽  
pp. 432-437 ◽  
Author(s):  
Iftikhar Ahmad ◽  
Johan A. Hellebust
Keyword(s):  
Glutamine Synthetase ◽  
Nitrogen Assimilation ◽  
Continuous Light ◽  
Synthetase Activity ◽  
Glutamine Synthetase Activity ◽  
Dark Cycle ◽  
Continuous Darkness ◽  
Cell Carbon ◽  
Stichococcus Bacillaris ◽  
Mixotrophic Conditions

Stichococcus bacillaris Naeg. (Chlorophyceae) grown on a 12 h light: 12 h dark cycle divides synchronously under photoautotrophic conditions and essentially nonsynchronously under mixotrophic conditions. Photoassimilation of carbon under photoautotrophic conditions was followed by a decline in cell carbon content during the dark period, whereas under mixotrophic conditions cell carbon increased throughout the light–dark cycle. The rates of nitrogen assimilation by cultures grown on either nitrate or ammonium declined sharply during the dark, and these declines were most pronounced under photoautotrophic conditions. Photoautotrophic cells synthesized glutamine synthetase and NADPH – glutamate dehydrogenase (GDH) exclusively in the light, whereas in mixotrophic cells about 20% of the total synthesis of these enzymes during one light–dark cycle occurred in the dark. NADH–GDH was synthesized almost continuously over the entire light–dark cycle. In the dark, both under photoautotrophic and mixotrophic conditions, the alga contained more than 50% of glutamine synthetase in an inactive form, which was reactivated in vitro in the presence of mercaptoethanol and in vivo after returning the cultures to the light. The thermal stability of glutamine synthetase activity was less in light-harvested cells than in dark-harvested cells. The inactivation of glutamine synthetase did not occur in cultures growing either heterotrophically in continuous darkness or photoautotrophically in continuous light. This enzyme appears to be under thiol control only in cells grown under alternating light–dark conditions, irrespective of whether this light regime results in synchronous cell division or not.

scholarly journals Do sex steroids regulate glutamine synthesis with age?

2002 ◽  
Vol 282 (1) ◽  
pp. E215-E221 ◽  
Author(s):  
Lionel Verdier ◽  
Yves Boirie ◽  
Sebastien Van Drieesche ◽  
Michelle Mignon ◽  
Rene-Jean Begue ◽  
...  
Keyword(s):  
Glutamine Synthetase ◽  
Sex Steroids ◽  
Tibialis Anterior Muscle ◽  
Female Rats ◽  
Female Wistar Rats ◽  
Endocrine Status ◽  
Key Enzyme ◽  
Reproductive Endocrine ◽  
Glutamine Synthesis

Glutamine synthetase, a key enzyme in the production of glutamine, is known to be induced by glucocorticoids and preserved in skeletal muscle during aging, but the effect of other steroids, such as sex steroids (progesterone, estradiol), is unknown in vivo. The aim of this study was to determine whether progesterone or estradiol plays a role in the regulation of glutamine synthetase (GS) with aging. The effects of glucocorticoids and sex steroids on muscle GS activity and mRNA expression were measured in adult (6–8 mo; n = 7 in each group) and aged (26 mo; n= 10 in each group) female Wistar rats after adrenalectomy (ADX), ovariectomy (OV), or both (ADXOV) and were compared with those in sham-operated (Sham) control rats. In tibialis anterior muscle, ADX noticeably decreased both GS activity and expression irrespective of age (50–60%; P < 0.05), whereas OV had no effect at either age. Progesterone and estradiol replacement had no effect on the recovery of muscle GS response in either ADX or OV rats, regardless of age. In contrast, heart GS activity was decreased by ADX in aged animals only. These results suggest that the reproductive endocrine status of female rats does not affect muscle GS activity either in muscle or in heart, in young or aged animals, and that the heart GS response to steroids may be differently regulated in aged rats.

scholarly journals The sRNA NsiR4 is involved in nitrogen assimilation control in cyanobacteria by targeting glutamine synthetase inactivating factor IF7

2015 ◽  
Vol 112 (45) ◽  
pp. E6243-E6252 ◽  
Author(s):  
Stephan Klähn ◽  
Christoph Schaal ◽  
Jens Georg ◽  
Desirée Baumgartner ◽  
Gernot Knippen ◽  
...  
Keyword(s):  
Glutamine Synthetase ◽  
Nitrogen Metabolism ◽  
Nitrogen Assimilation ◽  
Nitrogen Sources ◽  
Transcriptome Profiling ◽  
Site Directed Mutagenesis ◽  
Reporter System ◽  
Available Nitrogen ◽  
Mrna Accumulation

Glutamine synthetase (GS), a key enzyme in biological nitrogen assimilation, is regulated in multiple ways in response to varying nitrogen sources and levels. Here we show a small regulatory RNA, NsiR4 (nitrogen stress-induced RNA 4), which plays an important role in the regulation of GS in cyanobacteria. NsiR4 expression in the unicellularSynechocystissp. PCC 6803 and in the filamentous, nitrogen-fixingAnabaenasp. PCC 7120 is stimulated through nitrogen limitation via NtcA, the global transcriptional regulator of genes involved in nitrogen metabolism. NsiR4 is widely conserved throughout the cyanobacterial phylum, suggesting a conserved function. In silico target prediction, transcriptome profiling on pulse overexpression, and site-directed mutagenesis experiments using a heterologous reporter system showed that NsiR4 interacts with the 5′UTR ofgifAmRNA, which encodes glutamine synthetase inactivating factor (IF)7. InSynechocystis, we observed an inverse relationship between the levels of NsiR4 and the accumulation of IF7 in vivo. This NsiR4-dependent modulation ofgifA(IF7) mRNA accumulation influenced the glutamine pool and thusNH4+assimilation via GS. As a second target, we identifiedssr1528, a hitherto uncharacterized nitrogen-regulated gene. Competition experiments between WT and an ΔnsiR4KO mutant showed that the lack of NsiR4 led to decreased acclimation capabilities ofSynechocystistoward oscillating nitrogen levels. These results suggest a role for NsiR4 in the regulation of nitrogen metabolism in cyanobacteria, especially for the adaptation to rapid changes in available nitrogen sources and concentrations. NsiR4 is, to our knowledge, the first identified bacterial sRNA regulating the primary assimilation of a macronutrient.

Studies on possible routes of ammonium assimilation in soybean root nodule bacteroids

1973 ◽  
Vol 19 (12) ◽  
pp. 1493-1499 ◽  
Author(s):  
Stanley D. Dunn ◽  
Robert V. Klucas
Keyword(s):  
Glutamine Synthetase ◽  
Nitrogen Assimilation ◽  
Reductive Amination ◽  
Root Nodule ◽  
Root Nodules ◽  
Ammonium Assimilation ◽  
Kinetic Properties ◽  
Transferase Activity ◽  
Soybean Root

Glutamine amide–2-oxoglutarate aminotransferase NAD+ oxidoreductase (GOGAT), glutamine synthetase (GS), glutamate dehydrogenase (GD), and alanine dehydrogenase (AD) were studied in soybean root nodules. GS, GOGAT, and AD were present in bacteroids at levels that could account for ammonium assimilation, but GD activity was quite low. The total activities of GS and GD were higher in the cytosol than in the bacteroids by factors of 20 and 7, respectively, whereas GOGAT was not detected in the cytosol. GS (transferase activity) was inhibited by alanine, CTP, glycine, and tryptophan at 5 mM but was relatively unaffected by asparagine, aspartic acid, CMP, glucosamine, and histidine at 5 mM. GOGAT activity was unaffected by ATP, ADP, 8-hydroxyquinoline, and 1,10-phenanthroline but was inhibited by EDTA, citrate, and parachloromercuribenzoate. GOGAT activity (reductive amination) was also inhibited 97% by preincubation with 10−4 M azaserine for 30 min but GD activity was inhibited only 13%. The apparent Km values for NH4+ by AD was 7.4 × 10−3 M and by GD was 7.3 × 10−2 M while for glutamine by GOGAT it was 9.3 × 10−5 M. Activities and kinetic properties for these enzymes may suggest potential routes of nitrogen assimilation in vivo.

scholarly journals Remodeling of intermediate metabolism in the diatom Phaeodactylum tricornutum under nitrogen stress

2014 ◽  
Vol 112 (2) ◽  
pp. 412-417 ◽  
Author(s):  
Orly Levitan ◽  
Jorge Dinamarca ◽  
Ehud Zelzion ◽  
Desmond S. Lun ◽  
L. Tiago Guerra ◽  
...  
Keyword(s):  
Phaeodactylum Tricornutum ◽  
Nitrogen Assimilation ◽  
Nitrogen Availability ◽  
Carbon Fixation ◽  
De Novo ◽  
Nitrogen Stress ◽  
Gene Encoding ◽  
Storage Lipids ◽  
Intermediate Metabolism ◽  
Key Enzyme

Diatoms are unicellular algae that accumulate significant amounts of triacylglycerols as storage lipids when their growth is limited by nutrients. Using biochemical, physiological, bioinformatics, and reverse genetic approaches, we analyzed how the flux of carbon into lipids is influenced by nitrogen stress in a model diatom, Phaeodactylum tricornutum. Our results reveal that the accumulation of lipids is a consequence of remodeling of intermediate metabolism, especially reactions in the tricarboxylic acid and the urea cycles. Specifically, approximately one-half of the cellular proteins are cannibalized; whereas the nitrogen is scavenged by the urea and glutamine synthetase/glutamine 2-oxoglutarate aminotransferase pathways and redirected to the de novo synthesis of nitrogen assimilation machinery, simultaneously, the photobiological flux of carbon and reductants is used to synthesize lipids. To further examine how nitrogen stress triggers the remodeling process, we knocked down the gene encoding for nitrate reductase, a key enzyme required for the assimilation of nitrate. The strain exhibits 40–50% of the mRNA copy numbers, protein content, and enzymatic activity of the wild type, concomitant with a 43% increase in cellular lipid content. We suggest a negative feedback sensor that couples photosynthetic carbon fixation to lipid biosynthesis and is regulated by the nitrogen assimilation pathway. This metabolic feedback enables diatoms to rapidly respond to fluctuations in environmental nitrogen availability.

Enzymes of nitrogen assimilation during seed development in normal and high lysine mutants in maize (Zea mays, W64A)

1981 ◽  
Vol 59 (12) ◽  
pp. 2735-2743 ◽  
Author(s):  
Santosh Misra ◽  
Ann Oaks
Keyword(s):  
Zea Mays ◽  
Glutamine Synthetase ◽  
Nitrogen Assimilation ◽  
Glutamate Synthase ◽  
Asparagine Synthetase ◽  
Developmental Sequence ◽  
Normal Variety ◽  
High Lysine ◽  
Rapid Accumulation ◽  
Low Levels

Enzymes involved in nitrogen metabolism in endosperms of a normal variety of maize (W64A) and isogenic high lysine mutants (opaque-2 and floury-2) were examined. Glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), asparaginase, asparagine synthetase, and glutamine synthetase were present in the immature endosperm in all three genotypes; increased in activity just prior to the onset of zein biosynthesis; and remained at maximal levels during the period of rapid accumulation of nitrogen. With the exception of GOGAT trends and levels of activities were similar in all cases. Opaque-2 mutants had higher levels of GOGAT (29 ± 0.5 nmol∙min−1 endosperm−1 at day 20 postpollination) than floury-2 (19 ± 0.07) or W64A (13 ± 0.6). Levels of aspartate, asparagine, glutamate, and glutamine were also higher in the high lysine mutants throughout the developmental sequence. NH4+ in the endosperm rose from low levels at day 5 (0.1 μmol∙endosperm−1) to significant levels (1.3, 1.7, and 1.98 μmol∙endosperm−1 in normal, floury-2, and opaque-2, respectively) between 20 and 25 days and then declined. The decline was less apparent in the mutants. Levels of an endopeptidase increased initially in the control and then declined. In the mutants the decline in activity was less apparent and this resulted in higher levels of protease activities at later stages of development. RNAase activities were higher in the mutants throughout the developmental sequence. Where differences were observed, they were more apparent in the opaque-2 than in the floury-2 mutants.

scholarly journals Nitrogen assimilation in orchids

HortScience ◽  
1992 ◽  
Vol 27 (6) ◽  
pp. 680f-680
Author(s):  
C.S. Hew ◽  
L.Y. Lim ◽  
C.M. Low
Keyword(s):  
Nitrate Reductase ◽  
Glutamine Synthetase ◽  
Ammonium Nitrate ◽  
Nitrate Uptake ◽  
Nitrogen Assimilation ◽  
Solution Culture ◽  
Ion Uptake ◽  
Ammonium Uptake ◽  
Regulatory Role ◽  
Epiphytic Orchids

The uptake of nitrate and ammonium by a terrestial (Bromheadia finlaysonia) and an epiphytic (Dendrobium hybrid) orchid in solution culture has been studied. The rates of nitrate and ammonium were relatively linear, with higher rate of uptake for ammonium. The rates of nitrate uptake in terrestial and epiphytic orchids were 0.4 and 0.9 μmole gm fw-1 hr-1 respectively and they were considerably lower than those of most major crops. SEM studies show that the velamen of Bromheadia was 2 cells thick whereas that of Dendrobium was 8-10 cells thick. It is unlikely that the velamen is the major factor in restricting influx of nitrate or ammonium. Nitrate reductase (NR) and glutamine synthetase (GS) were present in roots and leaves of both orchids. NR was high in roots but low in leaves. The reverse was for GS. The activities of NR and GS was low but high enough to account for the rate of nitrate or ammonium uptake. It appears that the movement of ions across the transfer junction at the exodermis plays a major regulatory role in ion uptake by orchid root.

Sign in / Sign up

Export Citation Format

Share Document