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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have investigated both the kinetics and regulation of 15NH4+ influx in roots of 3-month-old hydroponically grown Citrus (Citrus sinensis L. Osbeck x Poncirus trifoliata Blanco) seedlings. The 15NH4+ influx is saturable below an external ammonium concentration of 1 mM, indicating the action of a high-affinity transport system (HATS). The HATS is under feedback repression by the N status of the plant, being down-regulated in plants adequately supplied with N during growth, and up-regulated by N-starvation. When assayed between 1 and 50 mM [15NH4+]0, the 15NH4+ influx showed a linear response typical of a low-affinity transport system (LATS). The activity of the LATS increased in plants supplied with NH4+ as compared with plants grown on an N-free medium. Transfer of the plants to N-free solution resulted in a marked decrease in the LATS-mediated 15NH4+ influx. Accordingly, resupply of NH4+ after N-starvation triggered a dramatic stimulation of the activity of the LATS. These data provide evidence that in Citrus plants, the LATS or at least one of its components is inducible by NH4+. Even when up-regulated, both the HATS and the LATS displayed a limited capacity, as compared with that usually found in herbaceous species. The use of various metabolic uncouplers or inhibitors indicated that 15NH4+ influx mediated by the HATS is strongly dependent on energy metabolism and H+ transmembrane electrochemical gradient. By contrast, the LATS is not affected by protonophores or inhibitors of the H(+)-ATPase, suggesting that its activity is mostly driven by the NH4+/NH3 transmembrane gradient. In agreement with these hypotheses, the HATS-mediated 15NH4+ influx was strongly inhibited when the solution pH was raised from 4 to 7, whereas influx mediated by the LATS was slightly stimulated.
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PMID:Characterization and regulation of ammonium transport systems in Citrus plants. 1176 76

Growth and starvation of baker's yeast was monitored by on-line microcalorimetry and cells originating from four different physiological states were stored at low temperature (4 degrees C) for up to 26 days. The different physiological states were designated F (respiro-Fermentative phase of growth), R (initial Respiratory phase of growth), -N (non-growing state because of Nitrogen depletion), and -NC (non-growing state because of both Nitrogen and Carbon depletion). The cells were tested before and after cold storage for their fermentative capacity, and characterised by 2D gel analysis (and subsequent quantitative silver staining and image analysis with software PDQUEST) for their levels of six enzymes of the glycolytic pathway (hexokinase 2 (Hxk2p), fructose bisphosphate aldolase (Fba1p), glyceraldehyde-3-phosphate dehydrogenase (Tdh3p), enolase A (Enolp), enolase B (Eno2p), and triose phosphate isomerase (Tpi1p)) and two enzymes of the fermentative branch (pyruvate decarboxylase (Pdc1p) and alcohol dehydrogenase (Adh1p)). The enzymes Hxk2p, Tdh3p, Eno2p, Pdc1p and Adh1p were down-regulated by 25-80% during the transition between the F and R states. During the transition to non-growing states (-N and -NC states), the levels of Hxk2p, Tdh3p and Eno2p were further reduced. However, after cold storage, the glycolytic and fermentative enzymes of the different physiological states were expressed to the same extent. In contrast, the fermentative capacity differed between the states; the R-state cells were superior compared to cells from the other states tested and preserved more than 50% of their initial fermentative capacity (6 mmol ethanol per gram dry weight and hour). Our data therefore clearly demonstrate that persistence of fermentative capacity during total starvation at low temperature after as long as 1 month is strongly dependent on the physiological state from which the cells originate. However, the level of expression of the glycolytic enzymes could not explain the difference in fermentative capacity of the different physiological states after cold storage.
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PMID:Fermentative capacity after cold storage of baker's yeast is dependent on the initial physiological state but not correlated to the levels of glycolytic enzymes. 1178 28

Ammonia-starved cells of Nitrosomonas europaea are able to preserve a high level of ammonia-oxidizing activity in the absence of ammonium. However, when the nitrite-oxidizing cells that form part of the natural nitrifying community do not keep pace with the ammonia-oxidizing cells, nitrite accumulates and may subsequently inhibit ammonia oxidation. The maintenance of a high ammonia-oxidizing capacity during starvation is then nullified. In this study we demonstrated that cells of N. europaea starved for ammonia were not sensitive to nitrite, either when they were starved in the presence of nitrite or when nitrite was supplied simultaneously with fresh ammonium. In the latter case, the initial ammonia-oxidizing activity of starved cells was stimulated at least fivefold.
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PMID:Nitrite as a stimulus for ammonia-starved Nitrosomonas europaea. 1187 1

An industrial strain of Saccharomyces cerevisiae (DGI 342) was cultivated in fed-batch cultivations at a specific growth rate of 0.2 h(-1). The yeast was then exposed to carbon or nitrogen starvation for up to 8 h, to study the effect of starvation on fermentative capacity and content of protein, trehalose and glycogen. Nitrogen starvation triggered the accumulation of trehalose and glycogen. After 8 h of starvation, the content of trehalose and glycogen was increased 4-fold and 2-fold, respectively. Carbon starvation resulted in a partial conversion of glycogen into trehalose. The trehalose content increased from 45 to 64 mg (g dry-weight)(-1), whereas the glycogen content in the same period was reduced from 55 to 5 mg (g dry-weight)(-1). Glycogen was consumed faster than trehalose during storage of the starved yeast for 1 month. Nitrogen starvation resulted in a decrease in the protein content of the yeast cells, and the fermentative capacity per gram dry-weight decreased by 40%. The protein content in the carbon-starved yeast increased as a result of starvation due to the fact that the content of glycogen was reduced. The fermentative capacity per gram dry-weight was, however, unaltered.
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PMID:Fed-batch cultivation of baker's yeast followed by nitrogen or carbon starvation: effects on fermentative capacity and content of trehalose and glycogen. 1211 Nov 63

Nitrogen starvation and blue light are the two environmental cues that control sexual differentiation in Chlamydomonas reinhardtii. Insertional mutagenesis was applied to generate mutants that still require nitrogen starvation as the initiating signal for gametogenesis but were no longer dependent on irradiation. In one mutant analysed, sequences adjacent to the site of insertion were cloned and used for the isolation of a genomic clone that, upon transformation, could complement the mutant phenotype. The gene identified (LRG6) encodes two mRNAs that appear to be the products of differential splicing. The two putative gene products derived from these mRNAs differ in their C-terminal ends. Both predicted gene products exhibit multiple hydrophobic domains with alpha-helical secondary structure typical for integral membrane proteins. These proteins may form pores, and may function as transporters of as-yet unknown substrates. Since rendering the LRG6 gene non-functional resulted in light-independence of gamete formation, it is suggested that this transporter may inhibit signal flux from the photoreceptor to target genes - either directly by its activity or indirectly by serving as a scaffold for signalling proteins. Shutting off this transporter may be required for the activation of signal flux in this pathway. This concept is supported by the observed reduction in LRG6 mRNA levels during the first phase of gametic differentiation.
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PMID:Knock-out of a putative transporter results in altered blue-light signalling in Chlamydomonas. 1220 48

The effects of nitrogen starvation on photosynthetic efficiency were examined in three unicellular algae by measuring changes in the quantum yield of fluorescence with a pump-and-probe method and thermal efficiency (i.e. the percentage of trapped energy stored photochemically) with a pulsed photoacoustic method together with the inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea to distinguish photosystems I and II (PSI and PSII). Measured at 620 nm, maximum thermal efficiency for both photosystems was 32% for the diatom Thalassiosira weissflogii (PSII:PSI ratio of 2:1), 39% for the green alga Dunaliella tertiolecta (PSII:PSI ratio of 1:1), and 29% for the cyanobacterium Synechococcus sp. PCC 7002 (PSII:PSI ratio of 1:2). Nitrogen starvation decreased total thermal efficiency by 56% for T. weissflogii and by 26% for D. tertiolecta but caused no change in Synechococcus. Decreases in the number of active PSII reaction centers (inferred from changes in variable fluorescence) were larger: 86% (T. weissflogii), 65% (D. tertiolecta), and 65% (Synechococcus). The selective inactivation of PSII under nitrogen starvation was confirmed by independent measurements of active PSII using oxygen flash yields and active PSI using P700 reduction. Relatively high thermal efficiencies were measured in all three species in the presence of the PSII inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea, suggesting the potential for significant cyclic electron flow around PSI. Fluorescence or photoacoustic data agreed well; in T. weissflogii, the functional cross-sectional area of PSII at 620 nm was estimated to be the same using both methods (approximately 1.8 x 102 A2). The effects of nitrogen starvation occur mainly in PSII and are well represented by variable fluorescence measurements.
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PMID:Differential Effects of Nitrogen Limitation on Photosynthetic Efficiency of Photosystems I and II in Microalgae. 1222 11

A malachite green colorimetric assay for glutamine synthetase is described. Glutamine synthetase activity was determined in situ in the marine diatom Phaeodactylum tricornutum Bohlin using cells permeabilized by freeze/thawing. Higher activities were obtained with cells permeabilized in N-2-hydroxyethylpiperazine-N[prime]-2-ethanesulfonic acid compared with N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid, tris(hydroxymethyl)aminomethane, or imidazole, and the optimum pH was 7.9. Activities were higher in cells permeabilized in the presence of reductant, particularly dithiothreitol. Glutamine synthetase activities were markedly decreased in the presence of methionine sulfoximine. In the presence of saturating concentrations of glutamate and ATP, the apparent Km for ammonia was 320 [mu]M, but this value decreased to 110 [mu]M with subsaturating concentrations of glutamate and ATP. The apparent Km values for glutamate and ATP, in the presence of saturating concentrations of ammonia, were 9.7 and 2.9 mM, respectively. Ammonia-grown cells had lower glutamine synthetase activities than did nitrate-grown cells. During nitrogen starvation of both ammonia- and nitrate-grown cells, glutamine synthetase activities increased rapidly during the first 8 h, reaching maximum values after 24 to 48 h. Moreover, the time course for the increases in glutamine synthetase activities and rate of methylamine uptake following the transfer of nitrate-grown cells to nitrogen-deficient medium were very similar. In nitrate-grown cells and cells deprived of combined nitrogen, glutamine synthetase activities and maximum rates of ammonia uptake gave comparable values when measured at the same temperature (20[deg]C).
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PMID:In Situ Glutamine Synthetase Activity in a Marine Unicellular Alga (Development of a Sensitive Colorimetric Assay and the Effects of Nitrogen Status on Enzyme Activity). 1222 76

1. Nitrogen-corrected apparent and true metabolisable energy contents (AMEN and TMEN) of 12 diets, containing different amounts of maize, wheat, barley and rye, barley with beta-glucanase and maize with 0.05 g/kg guar gum were measured using 3-week-old male broilers. 2. The AMEN method involved: 4 d of dietary adaptation, 24 h of starvation, 54 h of ad libitum feeding, 24 h of starvation and daily total droppings collection. TMEN was measured after a 48 h starvation period followed by 2 d of tube-feeding two doses of 15 g of the diets and quantitatively collecting all the droppings after 48 h of starvation. The endogenous energy losses (EELN) were measured after tube-feeding 8 chickens with 30 g of glucose, also over 2 d. 3. The results show that a significant interaction exists between the nature of the diets and the method used to measure metabolisable energy. Differences between TMEN and AMEN values ranged from 1.03 to 1.98 MJ/kg dry matter. These differences were positively correlated with the total pentosan contents of the diet (r = 0.94), the natural logarithm of the viscosities of the water extracts (r = 0.87), the sum of the contents of total pentosans and total beta-glucan (r = 0.85), the calculated total non-starch polysaccharide contents (r = 0.79), the neutral detergent fibre contents (r = 0.76) and the total beta-glucan contents (r = 0.70). Furthermore, a significant interaction was found between diets and the method used to derive lipid digestibility. The differences between apparent and true lipid digestibility ranged from 0.05 percentage points for the wheat diet to 0.20 percentage points for the rye diet. 4. From the results of this trial, it appears that TMEN overestimates the energy value of high fibre diets.
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PMID:Comparison of two direct bioassays using 3-week-old broilers to measure the metabolisable energy of diets containing cereals high in fibre: differences between true and apparent metabolisable energy values. 1236 15

The nucleotide sequences reported in this paper have been submitted to the GenBank(R)/EBI Nucleotide Sequence Databases with accession numbers AF462037 (glutamine synthetase) and AF462032 (glutamate synthase). Nitrogen retrieval and assimilation by symbiotic ectomycorrhizal fungi is thought to play a central role in the mutualistic interaction between these organisms and their plant hosts. Here we report on the molecular characterization of the key N-assimilation enzyme glutamine synthetase from the mycorrhizal ascomycete Tuber borchii (TbGS). TbGS displayed a strong positive co-operativity ( n =1.7+/-0.29) and an unusually high S(0.5) value (54+/-16 mM; S(0.5) is the substrate concentration value at which v =(1/2) V (max)) for glutamate, and a correspondingly low sensitivity towards inhibition by the glutamate analogue herbicide phosphinothricin. The TbGS mRNA, which is encoded by a single-copy gene in the Tuber genome, was up-regulated in N-starved mycelia and returned to basal levels upon resupplementation of various forms of N, the most effective of which was nitrate. Both responses were accompanied by parallel variations of TbGS protein amount and glutamine synthetase activity, thus indicating that TbGS levels are primarily controlled at the pre-translational level. As revealed by a comparative analysis of the TbGS mRNA and of the mRNAs for the metabolically related enzymes glutamate dehydrogenase and glutamate synthase, TbGS is not only the sole messenger that positively responds to N starvation, but also the most abundant under N-limiting conditions. A similar, but even more discriminating expression pattern, with practically undetectable glutamate dehydrogenase mRNA levels, was observed in fruitbodies. The TbGS mRNA was also found to be expressed in symbiosis-engaged hyphae, with distinctively higher hybridization signals in hyphae that were penetrating among and within root cells.
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PMID:Distinctive properties and expression profiles of glutamine synthetase from a plant symbiotic fungus. 1268 51

Nitrogen starvation is generally assumed to be encountered by biotrophic and hemibiotrophic plant fungal pathogens at the beginning of their infection cycle. We tested whether nitrogen starvation constitutes a cue regulating genes that are required for pathogenicity of Colletotrichum lindemuthianum, a fungal pathogen of common bean. The clnr1 (C. lindemuthianumnitrogen regulator 1) gene, the areA/nit-2 orthologue of C. lindemuthianum, was isolated. The predicted CLNR1 protein exhibits high amino acid sequence similarities with the AREA and NIT2 global fungal nitrogen regulators. Targeted clnr1- mutants are unable to use a wide array of nitrogen sources, indicating that clnr1 is the C. lindemuthianum major nitrogen regulatory gene. The clnr1- mutants are non-pathogenic, although few anthracnose lesions seldom occur on whole plantlets. Surprisingly, cytological analysis reveals that the clnr1- mutants are not disturbed from the penetration stage until the end of the biotrophic phase, but that they are impaired during the setting up of the necrotrophic phase. Thus, through CLNR1, nitrogen starvation constitutes a cue for the regulation of genes that are compulsory for this stage of the C. lindemuthianum infection process. Additionally, clnr1- mutants complemented with the Aspergillus nidulans areA gene are fully pathogenic, indicating that areA is able to activate the C. lindemuthianum suited genes, normally under the control of clnr1.
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PMID:CLNR1, the AREA/NIT2-like global nitrogen regulator of the plant fungal pathogen Colletotrichum lindemuthianum is required for the infection cycle. 1269 11


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