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.

Salinity and nitrogen fertilization and nitrogen metabolism in rose plants

2001 ◽  
Vol 137 (1) ◽  
pp. 77-84 ◽  
Author(s):  
H. LORENZO ◽  
J. M. SIVERIO ◽  
M. CABALLERO
Keyword(s):  
Nitrate Reductase ◽  
Glutamine Synthetase ◽  
Nitrogen Source ◽  
Nutrient Solution ◽  
Reductase Activity ◽  
Ammonium Uptake ◽  
Mineral Contents ◽  
Sodium Accumulation ◽  
Npk Uptake ◽  
Mineral Concentrations

Rose production is limited by salinity and highly affected by the nitrogen source present in the nutrient solution. The influence of sodium on several aspects of nutrition has been investigated in ‘Lambada' rose plants using different sources of nitrogen in the fertilization treatment. Experiments using a previously defined mono-shoot model plant and a simplified hydroponic culture allowed us to study the effects of salinity v. nitrogen on NPK uptake during the culture period. Mineral concentrations, nitrate reductase (NR) and glutamine synthetase (GS) activities were also analysed. This study showed that rose plants were more sensitive to saline conditions under NH4+ fertilization without detectable effects on growth or in NPK mineral contents in shoots. Parameters affected most were enzymatic activities analysed such as leaf nitrate reductase activity which was reduced under NH4+ nutrition. Leaf glutamine synthetase was also enhanced by saline conditions. The Na/K ratio showed that under NH4+ nutrition, the highest sodium accumulation occurred in roots. Nitrate uptake did not show a clear pattern related to nitrogen source, however, ammonium uptake was affected by salinity when NH4+ was the sole nitrogen source in the nutrient solution. Potassium and phosphate uptake were always lower when NH4+ was present in the nutrient solution.

Impact of low pH and aluminium on nitrogen uptake and metabolism in roots of Lotus japonicus

Biologia ◽  
2007 ◽  
Vol 62 (6) ◽  
Author(s):  
Peter Pal’ove-Balang ◽  
Igor Mistrík
Keyword(s):  
Nitrate Reductase ◽  
Nitrogen Uptake ◽  
Nitrate Uptake ◽  
Reductase Activity ◽  
Lotus Japonicus ◽  
Low Ph ◽  
Ammonium Uptake ◽  
Glutamine Synthetase Activity ◽  
Al Treatment ◽  
Uptake And Metabolism

AbstractThe effect of low pH and aluminum on nitrogen uptake and metabolism was studied in roots of Lotus japonicus grown in hydroponic cultures. The low pH slightly suppressed root elongation, and this effect was accompanied by the suppression of nitrate and ammonia uptake, as well as the nitrate reductase activity. In spite of high resistance of young Lotus plants to short-term Al application, the one-day treatment of Al strongly reduced nitrate uptake and also the activity of nitrate reductase (NRA) in the apical parts of roots. The glutamine synthetase activity was also suppressed by Al treatment, but in lower extent. On the other hand, the ammonium uptake and nitrite reductase activity stayed unchanged by Al treatment and the values were practically the same as in control plants. These results support the view that nitrate uptake and nitrate reduction might be the main processes responsible for Al induced growth retardation in Lotus plants grown in mineral acid soils.

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

HortScience ◽  
1995 ◽  
Vol 30 (4) ◽  
pp. 871A-871
Author(s):  
S. Aquin ◽  
Y. Desjardins ◽  
L.-P. Vézina
Keyword(s):  
Nitrate Reductase ◽  
Glutamine Synthetase ◽  
Nitrogen Metabolism ◽  
Nitrate Reduction ◽  
Nitrogen Assimilation ◽  
Culture Period ◽  
Leaf Tissues ◽  
Root Tissues ◽  
Nr Activity ◽  
Different Tissues

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.

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.

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