Inducible Formation of Glutamate Dehydrogenase in Rice Plant Roots by the Addition of Ammonia to the Media

Section: Resultssupporting

confidence: 78%

Protein Metabolism in Leaves and Developing Grains of Rices Differing in Grain Protein Content

Perez¹,

Cagampang²,

Esmama³

et al. 1973

“…Thus, the high affinity of higher plant GS for ammonia compared with the much lower affinity ofGDH (23) together with observed increases in GDH activity in plant tissues fed exogenous ammonia (5,19,20) led to the suggestion that ammonia assimilation occurs via the GS/glutamate synthase pathway at low ammonia concentrations, while GDH may operate in the asimilation ofhih ammonia concentrations (19) in a manner analogous to the algal NADP enzyme (23). There are no indicatons of any similar alterations in the levels of GS and GDH in barley grown on differet nitrogen sources.…”

Section: Discussionmentioning

confidence: 99%

Ammonia Assimilation in the Roots of Nitrate- and Ammonia-Grown Hordeum Vulgare (cv Golden Promise)

Fentem¹,

Lea²,

Stewart³

1983

to be reached on the pathway of ammonia assimilation. Thus, 15N-feeding experiments with both root (17, 27) and shoot (8) tissues, and studies using 13N (13,22) in which glutamine was initially more highly labeled than glutamate, have been interpreted as being consistent with ammonia assimilation via the GS/glutamate synthase route. Similarly, experiments in which glutamate was initially more highly labeled than glutamine (6, 8) have been interpreted as being at least qualitatively consistent with assimilation via GDH. Such conclusions are, however, speculative in the absence of information on the number and relative sizes of the glutamate and glutamine pools in the tissues concerned.The purpose of these studies was to obtain kinetic labehling data from experiments in which Hordeum seedlings, growing under steady state conditions, were fed '5N-labeled ammonia or nitrate.Attempts were then made to apply a quantitative analysis to the 15N incorporation patterns in ammonia-fed barley roots. MATERIALS AND METHODSNumerous studies have demonstrated that both roots and leaves of higher plants possess the enzymic potential for the assimilation of ammonia either via the direct reductive amination of 2-oxoglutarate, catalyzed by GDH2 or via the combined action of GS and glutamate synthase (23). The now widely held belief that the GS/ glutamate synthase pathway is solely responsible for ammonia assimilation in these tissues (15) Growth of Plants. The growth system used was a 'continuous flow' water culture system. Seeds of Hordeum vulgare L. var.Golden Promise were soaked overnight in running tap water, with aeration, before sowing on sections of Netlon mesh covered with muslin and stretched over the top of lengths of plastic guttering filled with culture solution. Culture solution was cycled through the gutters from a large reservoir by means of a pump. The flow of nutrient solution through the gutters was adjusted to a rate sufficient to prevent the concentrations of nutrient in the gutters differing from those in the reservoir due to uptake by the plants. Seedlings were subjected to a 14-h daylight regime, with a light intensity of 4.95 J cm -2 h-' at the level of the plants, and a constant temperature of 23°C. The nutrient solution used was a modified one-quarter strength Long Ashton solution (4). Nitrogen was supplied either as potassium nitrate or ammonium chloride. The volume of the reservoir was chosen to prevent the concentration of ammonia or nitrate in the culture solution from being reduced by more than 10% over a 24-h period. Labeling studies were performed on 9-d-old seedlings. At the start of a '5N-labeling experiient, the pump was stopped, and the gutters were rapidly drained and refilled with culture solution containing the nitrogen source labeled at 96% 15N atom abundance. The reservoir was exchanged for one containing the labeled nitrogen source, and the pump was restarted. The plants were sampled by removing individual sections of Netlon mesh.Extraction of Soluble Nitrogen Pools. Root and shoot tissues...

“…In rice roots, Kanamori et al (12) reported that chloramphenicol inhibited the production of ammonium-induced GDH by 50%, whereas cycloheximide inhibited the synthesis of the enzyme by 80%. In other studies, puromycin and cycloheximide (24,25), but not chloramphenicol, were shown to inhibit ammonium-induced GDH activity suggesting a cytosolic origin of the ammonium-induced enzyme.…”

Section: Discussionmentioning

confidence: 99%

A Plastidial Localization and Origin of l-Glutamate Dehydrogenase in a Soybean Cell Culture

Bhadula

Shargool²

1991

The subcellular distribution of L-glutamate dehydrogenase (GDH, EC 1.4.1.3.) was studied in SB3 soybean (Glycine max) cells using subcellular fractionation techniques. Compounds that inhibit protein synthesis either on 80s or 70s ribosomes were also used to give a preliminary idea of which subcellular fraction is involved in GDH synthesis. It was found that whereas cycloheximide and puromycin considerably reduced the total amount of protein synthesized by the cells, they did not appear to inhibit the synthesis of GDH. In the presence of chloramphenicol, both GDH activity and protein level in the cells were considerably reduced, suggesting that this enzyme was synthesized in organelles and not in the cytosol. Streptomycin, which inhibits plastid protein synthesis, also inhibited synthesis of GDH, indicating that a fraction of GDH activity was plastidial in origin. This is supported by the data on subcellular distribution of the enzyme, which showed that a major fraction of GDH is found in the plastidial fraction, although some activity is found associated with the mitochondrial fraction also. Since a major fraction of GDH activity was found in the plastidial fraction, we studied protein synthesis using isolated plastids and 35S-methionine. Using antibodies raised against purified GDH, we identified a 35S-labeled 41-kilodalton polypeptide synthesized by plastids as GDH.