Nitrogen Assimilation of Micropropagated Strawberry Plantlets during the Transition from Heterotrophy to Photoautotrophy

A study was conducted to determine the implication of nitrate reductase (NR) and glutamine synthetase (GS) during the transition of micropropagated plantlets from heterotrophy to photoautotrophy to document how nitrogen metabolism interfaces with photosynthetic and anaplerotic CO2 fixation. The activity of the two enzymes was determined in different tissues at different organogenic stages during the development of plantlets transferred onto rooting media containing varying quantities of sucrose. Under 3% sucrose, NR activity was much higher in leaves than in crown tissues. When roots are initiating, there is a shift in the proportion of nitrate reduction from leaves to crown. As roots mature, the proportion of nitrate reduction increases in roots. Similar trends were observed under 5% sucrose. In contrast, under 1% sucrose, a higher proportion of the nitrate is reduced in the leaf tissues throughout the culture period. This suggests that nitrate is reduced mainly in leaves in photoautotrophic plantlets, while it is reduced in crowns and root tissues for mixotrophic plantlets. In general, the GS activity follows the pattern of NR, but is always in excess, to enable rapid assimilation of ammonium derived from metabolism and medium absorption.

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Nitrogen assimilation and dissimilation in five genotypes of Brachiaria spp.

Canadian Journal of Botany ◽

10.1139/b81-201 ◽

1981 ◽

Vol 59 (8) ◽

pp. 1475-1479 ◽

Cited By ~ 15

Author(s):

Pedro Antonio A. Pereira ◽

Johanna Döbereiner ◽

Carlos A. Neyra

Keyword(s):

Nitrate Reductase ◽

Field Experiment ◽

Nitrogen Assimilation ◽

Nitrogenase Activity ◽

Nitrate Accumulation ◽

Brachiaria Ruziziensis ◽

Intact Soil ◽

Nr Activity ◽

Better Than ◽

Nitrate Fertilization

Five genotypes of Brachiaria spp. were planted in a field experiment with and without nitrate fertilization. Nitrogen metabolism was evaluated by measurements of nitrate reductase (NR) activity in leaves, nitrate accumulation in stems, and nitrogenase activity and dentrification in intact soil–plant cores. There were differences between genotypes in all parameters and a tendency was observed for genotypes with high NR activity and nitrate accumulation to have low nitrogenase activity and vice versa. Brachiaria radicans (Tanner grass) was representative for the first type and B. ruziziensis (CPI 30623) for the second. Denitrification reached 7% of the applied N within 63 h and was lowest in Tanner grass and highest in B. brizantha (FL 902-4). Brachiaria ruziziensis (CPI 30623) plants were able to withstand N stress better than B. radicans as a consequence, possibly, of differences in nitrogenase activity.

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

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1508412112 ◽

2015 ◽

Vol 112 (45) ◽

pp. E6243-E6252 ◽

Cited By ~ 73

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.

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Nitrogen assimilation in orchids

HortScience ◽

10.21273/hortsci.27.6.680f ◽

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.

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Elevated CO2 concentrations alter nitrogen metabolism and accelerate senescence in sunflower (Helianthus annuus L.) plants

Plant Soil and Environment ◽

10.17221/70/2013-pse ◽

2013 ◽

Vol 59 (No. 7) ◽

pp. 303-308 ◽

Cited By ~ 10

Author(s):

L. De la Mata ◽

P. De la Haba ◽

Alamillo JM ◽

M. Pineda ◽

E. Agüera

Keyword(s):

Nitrate Reductase ◽

Helianthus Annuus ◽

Nitrogen Metabolism ◽

Leaf Development ◽

Nitrogen Assimilation ◽

Nitrogen Availability ◽

Leaf Ontogeny ◽

Transcript Levels ◽

Helianthus Annuus L ◽

Accelerate Senescence

Elevated CO2 concentrations were found to cause early senescence during leaf development in sunflower (Helianthus annuus L.) plants, probably by reducing nitrogen availability since key enzymes of nitrogen metabolism, including nitrate reductase (NR); glutamine synthetase (GS) and glutamate dehydrogenase (GDH), were affected. Elevated CO2 concentrations significantly decreased the activity of nitrogen assimilation enzymes (NR and GS) and increased GDH deaminating activities. Moreover, they substantially rose the transcript levels of GS1 while lowering those of GS2. Increased atmospheric CO2 concentrations doubled the CO2 fixation and increased transpiration rates, although these parameters decreased during leaf ontogeny. It can be concluded that elevated atmospheric CO2 concentrations alter enzymes involved in nitrogen metabolism at the transcriptional and post-transcriptional levels, thereby boosting mobilization of nitrogen in leaves and triggering early senescence in sunflower plants.

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RELATIONS BETWEEN NITRATE REDUCTASE ACTIVITY AND NITROGEN ACCUMULATION IN SOYBEANS

Canadian Journal of Plant Science ◽

10.4141/cjps76-057 ◽

1976 ◽

Vol 56 (2) ◽

pp. 377-384 ◽

Cited By ~ 5

Author(s):

MIR HATAM ◽

D. J. HUME

Keyword(s):

Nitrate Reductase ◽

Nitrate Reduction ◽

Nitrate Uptake ◽

Reductase Activity ◽

N Uptake ◽

Nitrogen Accumulation ◽

Total N ◽

Total Plant ◽

Nr Activity

An in vivo assay for nitrate reductase (NR) activity was adapted to measure total NR activity in soybean [Glycine max (L.) Merr.] plants grown for a 29-day period indoors. Disappearance of nitrate from the nutrient solution, plant nitrate and total plant nitrogen (N) also were measured. Under the conditions of this experiment, nitrate reduction estimated from NR activities agreed closely with actual nitrate reduction. The same assay was used to measure leaf NR activities of field-grown soybeans throughout the 1971 growing season. Leaf NR activities accounted for 77 and 72% of the total N uptake in plants receiving 0 and 280 kg N as NH4NO3/ha, respectively. Measurements of nitrate and ammonium losses from soil under soybeans and under adjacent bare soil at three stages of plant development suggested that in plots receiving no fertilizer N, 86% of N uptake from the soil was in the form of nitrate. The NR activity of field-grown plants agreed well with total plant N derived from soil nitrates. Results indicated that leaf NR activities were proportional to nitrate uptake and might be used to determine amounts and seasonal patterns of nitrate uptake by soybean plants.

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Polyaspartic Acid Improves Maize (Zea mays L.) Seedling Nitrogen Assimilation Mainly by Enhancing Nitrate Reductase Activity

Agronomy ◽

10.3390/agronomy8090188 ◽

2018 ◽

Vol 8 (9) ◽

pp. 188 ◽

Cited By ~ 3

Author(s):

Qingyan Wang ◽

Huihui Tang ◽

Guangyan Li ◽

Hui Dong ◽

Xuerui Dong ◽

...

Keyword(s):

Zea Mays ◽

Nitrate Reductase ◽

Nitrogen Assimilation ◽

Zea Mays L ◽

Reductase Activity ◽

Protein Accumulation ◽

Nitrogen Accumulation ◽

Maize Seedlings ◽

Polyaspartic Acid ◽

Nr Activity

Improvement of nitrogen use efficiency is of great importance in maize (Zea mays L.) production. In the present study, an eco-friendly growth substance, polyaspartic acid (PASP), was applied to maize seedlings grown with different nitrate (NO3−) doses by foliar spraying, aimed at evaluating its effects on maize nitrogen assimilation at both the physiological and molecular level. The results showed that PASP promoted biomass and nitrogen accumulation in maize seedlings, especially under low NO3− doses. Among different NO3− conditions, the most noticeable increase in plant biomass by PASP addition was observed in seedlings grown with 1 mmol L−1 NO3−, which was a little less than the optimum concentration (2 mmol L−1) for plant growth. Furthermore, the total nitrogen accumulation increased greatly with additions of PASP to plants grown under suboptimal NO3− conditions. The promotion of nitrogen assimilation was mostly due to the increase of nitrate reductase (NR) activities. The NR activities in seedlings grown under low NO3− doses (0.5 and 1.0 mmol L−1) were extremely increased by PASP, while the activities of glutamine synthetase (GS), aspartate aminotransferase (AspAT), and alanine aminotransferase (AlaAT) were slightly changed. Moreover, the regulation of PASP on NR activity was most probably due to the promotion of the protein accumulation rather than gene expression. Accumulation of NR protein was similarly affected as NR activity, which was markedly increased by PASP treatment. In conclusion, the present study provides insights into the promotion by PASP of nitrogen assimilation and identifies candidate regulatory enzymatic mechanisms, which warrant further investigation with the use of PASP in promoting nitrogen utilization in crops.

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