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 The roles of glutamate dehydrogenase, glutamine synthetase and three forms of glutamate synthase on nitrogen assimilation in various organs of Pisum arvense L.

2014 ◽  
Vol 60 (3-4) ◽  
pp. 295-302
Author(s):  
Genowefa Kubik-Dobosz
Keyword(s):  
Glutamine Synthetase ◽  
Glutamate Dehydrogenase ◽  
Nitrogen Assimilation ◽  
Decisive Role ◽  
Glutamate Synthase ◽  
Pisum Arvense ◽  
Age Dependent ◽  
The Individual

The activities of GDH, GS and three forms of GOGAT (NADH, NADPH or ferredoxin-dependent) were studied in the leaves, stems and roots of the <i>Pisum arvense</i>. GS and the individual forms of GOGAT dominated in the leaves of 7 day-old plants which were taking up NO<sub>3</sub><sup>-</sup> or NH<sub>4</sub><sup>+</sup> ions, while NADH-GDH dominated in the roots of these plants. In comparison with HNO<sub>3</sub><sup>-</sup> , NH<sub>4</sub><sup>+</sup> ions stimulated the activity of most of the enzymes of the GS/GOGAT and GDH pathways in stems and roots, while in and leaves this effect was age-dependent. The Fd-GOGAT located in leaves and stems was not regulated by NH<sub>4</sub><sup>+</sup> , which indicates that this enzyme is not likely to be directly involved in the assimilation of NH<sub>4</sub><sup>+</sup> ions that have been taken up. The obtained data indicate that at lower tissue NH<sub>4</sub><sup>+</sup> concentration a decisive role in nitrogen assimilation in leaves and stems is played by the GS/GOGAT pathway, while in the roots-by GDH and in less degree by GS, GOGAT. High amounts of accumulated NH<sub>4</sub><sup>+</sup> ions set off a detoxication mechanism which includes NADH-GDH, common to all tissues. Only in 7 day-old leaves did the detoxication of NH<sub>4</sub><sup>+</sup> take place with the involvement of NADH-GOGAT and NADPH-GOGAT.

Nitrogen Assimilation in Alfalfa: Isolation and Characterization of an Asparagine Synthetase Gene Showing Enhanced Expression in Root Nodules and Dark-Adapted Leaves

1997 ◽  
Vol 9 (8) ◽  
pp. 1339 ◽  
Author(s):  
Lifang Shi ◽  
Scott N. Twary ◽  
Hirofumi Yoshioka ◽  
Robert G. Gregerson ◽  
Susan S. Miller ◽  
...  
Keyword(s):  
Nitrogen Assimilation ◽  
Root Nodules ◽  
Asparagine Synthetase ◽  
Isolation And Characterization ◽  
Enhanced Expression

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.

Ammonia, glutamine, and asparagine: a carbon–nitrogen interface

1988 ◽  
Vol 66 (10) ◽  
pp. 2103-2109 ◽  
Author(s):  
K. W. Joy
Keyword(s):  
Glutamine Synthetase ◽  
Glutamate Dehydrogenase ◽  
Higher Plants ◽  
Amino Nitrogen ◽  
Glutamate Synthase ◽  
Dinitrogen Fixation ◽  
Similar Function ◽  
Metabolic Processes ◽  
Organic Form ◽  
Primary Input

In plants, the primary input of nitrogen (obtained from the soil or from symbiotic dinitrogen fixation) occurs through the assimilation of ammonia into organic form. Synthesis of glutamine (via glutamine synthetase) is the major, and possibly exclusive, route for this process, and there is little evidence for the participation of glutamate dehydrogenase. A variety of reactions distribute glutamine nitrogen to other compounds, including transfer to amino nitrogen through glutamate synthase. In many plants asparagine is a major recipient of glutamine nitrogen and provides a mobile reservoir for transport to sites of growth; ureides perform a similar function in some legumes. Utilisation of transport forms of nitrogen, and a number of other metabolic processes, involves release of ammonia, which must be reassimilated. In illuminated leaves, there is an extensive flux of ammonia released by the photorespiratory cycle, requiring continuous efficient reassimilation. Aspects of ammonia recycling and related amide metabolism in higher plants are reviewed.

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