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

Several different cellular processes determine the size of the metabolically available nitrate pool in the cytoplasm. These processes include not only ion fluxes across the plasma membrane and tonoplast but also assimilation by the activity of nitrate reductase (NR). In roots, the maintenance of cytosolic nitrate activity during periods of nitrate starvation and resupply (M. van der Leij, S.J. Smith, A.J. Miller [1998] Planta 205: 64-72; R.-G. Zhen, H.-W. Koyro, R.A. Leigh, A.D. Tomos, A.J. Miller [1991] Planta 185: 356-361) suggests that this pool is regulated. Under nitrate-replete conditions vacuolar nitrate is a membrane-bound store that can release nitrate to the cytoplasm; after depletion of cytosolic nitrate, tonoplast transporters would serve to restore this pool. To study the role of assimilation, specifically the activity of NR in regulating the size of the cytosolic nitrate pool, we have compared wild-type and mutant plants. In leaf mesophyll cells, light-to-dark transitions increase cytosolic nitrate activity (1.5-2.8 mm), and these changes were reversed by dark-to-light transitions. Such changes were not observed in nia1nia2 NR-deficient plants indicating that this change in cytosolic nitrate activity was dependent on the presence of functional NR. Furthermore, in the dark, the steady-state cytosolic nitrate activities were not statistically different between the two types of plant, indicating that NR has little role in determining resting levels of nitrate. Epidermal cells of both wild type and NR mutants had cytosolic nitrate activities that were not significantly different from mesophyll cells in the dark and were unaltered by dark-to-light transitions. We propose that the NR-dependent changes in cytosolic nitrate provide a cellular mechanism for the diurnal changes in vacuolar nitrate storage, and the results are discussed in terms of the possible signaling role of cytosolic nitrate.
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PMID:Light-dark changes in cytosolic nitrate pools depend on nitrate reductase activity in Arabidopsis leaf cells. 1590 93

A Rhizobium etli Tn5 insertion mutant, LM01, was selected for its inability to use glutamine as the sole carbon and nitrogen source. The Tn5 insertion in LM01 was localized to the rsh gene, which encodes a member of the RelA/SpoT family of proteins. The LM01 mutant was affected in the ability to use amino acids and nitrate as nitrogen sources and was unable to accumulate (p)ppGpp when grown under carbon and nitrogen starvation, as opposed to the wild-type strain, which accumulated (p)ppGpp under these conditions. The R. etli rsh gene was found to restore (p)ppGpp accumulation to a DeltarelA DeltaspoT mutant of Escherichia coli. The R. etli Rsh protein consists of 744 amino acids, and the Tn5 insertion in LM01 results in the synthesis of a truncated protein of 329 amino acids; complementation experiments indicate that this truncated protein is still capable of (p)ppGpp hydrolysis. A second rsh mutant of R. etli, strain AC1, was constructed by inserting an Omega element at the beginning of the rsh gene, resulting in a null allele. Both AC1 and LM01 were affected in Nod factor production, which was constitutive in both strains, and in nodulation; nodules produced by the rsh mutants in Phaseolus vulgaris were smaller than those produced by the wild-type strain and did not fix nitrogen. In addition, electron microscopy revealed that the mutant bacteroids lacked poly-beta-hydroxybutyrate granules. These results indicate a central role for the stringent response in symbiosis.
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PMID:The stringent response is required for amino acid and nitrate utilization, nod factor regulation, nodulation, and nitrogen fixation in Rhizobium etli. 1603 Jan 99

Continuous operation of a new bioreactor for air pollution control called the foamed emulsion bioreactor (FEBR) has been investigated. The effect of several liquid feeding strategies was explored. The FEBR exhibited high and steady toluene removal performance (removal efficiency of 89%-94%, elimination capacity of 214-226 g/m3h at toluene inlet concentration of 1 g/m3) for up to 360 h, when 20% of the culture was replaced every 24 h by a nutrient solution containing 4 g/L of potassium nitrate as a nitrogen source. This feeding mode supported a high cell activity measured as INT reduction potential and active cell growth without being subject to nitrogen limitation. In comparison, operating the FEBR with the liquid in a closed loop (i.e., batch) resulted in a significant decrease of both the removal efficiency of toluene and INT reduction activity. Operation with feeding active cells resulted in stable and effective treatment, but would require a significant effort for mass culture preparation. Therefore, the continuous process with periodically feeding nutrients was found to be the most practical and effective operating mode. It also allows for stable operation, as was shown during removal of low concentration of toluene or after pollutant starvation. Throughout the study, INT reduction measurements provided insight into the process. INT reduction activity data proved that under normal operating conditions, the FEBR performance was limited by both the kinetics and by mass transfer. Overall, the results illustrate that engineered gas-phase bioreactors can potentially be more effective than conventional biofilters and biotrickling filters for the treatment of air pollutants such as toluene.
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PMID:Continuous operation of foamed emulsion bioreactors treating toluene vapors. 1604 6

The mRNA level of the aconitase gene acn of Corynebacterium glutamicum is reduced under iron limitation. Here we show that an AraC-type regulator, termed RipA for "regulator of iron proteins A," is involved in this type of regulation. A C. glutamicum DeltaripA mutant has a 2-fold higher aconitase activity than the wild type under iron limitation, but not under iron excess. Comparison of the mRNA profiles of the DeltaripA mutant and the wild type revealed that the acn mRNA level was increased in the DeltaripA mutant under iron limitation, but not under iron excess, indicating a repressor function of RipA. Besides acn, some other genes showed increased mRNA levels in the DeltaripA mutant under iron starvation (i.e. those encoding succinate dehydrogenase (sdhCAB), nitrate/nitrite transporter and nitrate reductase (narKGHJI), isopropylmalate dehydratase (leuCD), catechol 1,2-dioxygenase (catA), and phosphotransacetylase (pta)). Most of these proteins contain iron. Purified RipA binds to the upstream regions of all operons mentioned above and in addition to that of the catalase gene (katA). From 13 identified binding sites, the RipA consensus binding motif RRGCGN(4)RYGAC was deduced. Expression of ripA itself is repressed under iron excess by DtxR, since purified DtxR binds to a well conserved binding site upstream of ripA. Thus, repression of acn and the other target genes indicated above under iron limitation involves a regulatory cascade of two repressors, DtxR and its target RipA. The modulation of the intracellular iron usage by RipA supplements mechanisms for iron acquisition that are directly regulated by DtxR.
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PMID:The AraC-type regulator RipA represses aconitase and other iron proteins from Corynebacterium under iron limitation and is itself repressed by DtxR. 1617 44

In this study, four kinetic parameters of autotrophic denitrifiers in fixed-bed sulfur-limestone autotrophic denitrification (SLAD) columns were evaluated. The curve-matching method was used by conducting 22 non-steady-state tests for estimation of half-velocity constant, K(s) and maximum specific substrate utilization rate, k. To estimate the bacteria yield coefficient, Y and the decay coefficient, k(d), two short term batch tests (before and after the starvation of the autotrophic denitrifiers) were conducted using a fixed-bed SLAD column where the biofilm was fully penetrated by nitrate-N. It was found that K(s) = 0.398 mg NO(3-)-N/l, k = 0.15 d(-1), k(d) = 0.09-0.12 d(-1), and Y = 0.85-1.11 g VSS/g NO(3-)-N. Our results are consistent with those obtained from SLAD biofilm processes, but different from those obtained from suspended-growth systems with thiosulfate or sulfur powders as the S source. The method developed in this study might be useful for estimation of four Monod-type kinetic parameters in other biofilm processes. However, cautions must be given when the estimated parameters are used because the measurements of the biomass and the biofilm thickness could be further improved, and the assumption of sulfur being a non-limiting substrate needs to be proved.
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PMID:Evaluation of kinetic parameters of a sulfur-limestone autotrophic denitrification biofilm process. 1628 71

In this communication, we present a genetic analysis of the glnN promoter region of Synechococcus elongatus PCC 7942. luxAB reporter fusions were used to characterize the glnN promoter by deletion and site-directed mutational analysis. Reporter gene expression analysis was performed in S. elongatus wild-type and mutant strains to reveal the role of the global nitrogen responsive transcription factor NtcA and of the P(II) signalling protein on regulation of glnN gene expression. A non-canonical NtcA-binding motif is responsible for NtcA-dependent, nitrogen-responsive regulation of glnN. The P(II) signalling protein has opposing effects on NtcA-dependent glnN expression. Under conditions of nitrate-growth, it depresses expression, whereas under conditions of combined nitrogen starvation, it is required for full induction. Furthermore, sequences upstream of the NtcA-binding site have repressive effect on glnN promoter activity.
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PMID:Analysis of a non-canonical NtcA-dependent promoter in Synechococcus elongatus and its regulation by NtcA and PII. 1631 58

The effects of iron starvation on the growth and physiology of the unicellular cyanobacterium Agmenellum quadruplicatum were studied. Uptake of iron from the medium did not occur at a constant rate. The majority of the iron was removed at two different times, when the cells were initially inoculated into the medium and after the cultures had become quite dense and had stopped growing. Iron became limiting for growth 16 h after transfer to an iron-deficient medium, but cultures retained full viability for at least 212 h. Once iron became limiting, c-phycocyanin and chlorophyll a were degraded concurrently. This was followed by an accumulation of intracellular glucose in place of the c-phycocyanin. Nitrate and nitrite reductase activities were elevated through 50 h, after which they decreased steadily. The photosynthetic unit size also increased through 50 h and then decreased. Once iron was restored to the culture medium, growth resumed. The intracellular pigment levels increased rapidly as the glucose level diminished.
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PMID:Effects of Iron Starvation on the Physiology of the Cyanobacterium Agmenellum quadruplicatum. 1634 59

Azospirillum lipoferum RG6xx was grown under conditions similar to those resulting in encystment of Azotobacter spp. A. lipoferum produced cells of uniform shape when grown on nitrogen-free beta-hydroxybutyrate agar. Cells accumulated poly-beta-hydroxybutyrate and often grew as chains or filaments that eventually lost motility and formed capsules. Within 1 week, vegetative A. lipoferum inocula were converted into microflocs arising from filaments or chains. Cells within microflocs were pleomorphic, contained much poly-beta-hydroxybutyrate, and were encapsulated. Some cells had a cystlike morphology. Up to 57% of the dry weight of encapsulated flocs was poly-beta-hydroxybutyrate, whereas vegetative cells grown in broth with combined nitrogen had only 3% of their dry weight as poly-beta-hydroxybutyrate. Neither encapsulated cells in flocs nor nonencapsulated vegetative cells were significantly desiccation resistant. Under starvation conditions (9 days) only 25% of encapsulated cells remained viable, whereas vegetative cells multiplied severalfold. In short-term germination experiments with encapsulated flocs, nitrate, ammonium, and soil extract promoted formation of motile vegetative cells. Most cells in treatments lacking combined nitrogen eventually depleted their visible poly-beta-hydroxybutyrate reserves without germinating. The remaining cells retained the reserve polymer and underwent size reduction.
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PMID:Floc Formation by Azospirillum lipoferum Grown on Poly-beta-Hydroxybutyrate. 1634 92

Up-regulation of the high-affinity transport system (HATS) for NO(3)(-) and stimulation of lateral root (LR) growth are two important adaptive responses of the root system to nitrogen limitation. Up-regulation of the NO(3)(-) HATS by nitrogen starvation is suppressed in the atnrt2.1-1 mutant of Arabidopsis (Arabidopsis thaliana), deleted for both NRT2.1 and NRT2.2 nitrate transporter genes. We then used this mutant to determine whether lack of HATS stimulation affected the response of the root system architecture (RSA) to low NO(3)(-) availability. In Wassilewskija (Ws) wild-type plants, transfer from high to low NO(3)(-) medium resulted in contrasting responses of RSA, depending on the level of nitrogen limitation. Moderate nitrogen limitation (transfer from 10 mm to 1 or 0.5 mm NO(3)(-)) mostly led to an increase in the number of visible laterals, while severe nitrogen stress (transfer from 10 mm to 0.1 or 0.05 mm NO(3)(-)) promoted mean LR length. The RSA response of the atnrt2.1-1 mutant to low NO(3)(-) was markedly different. After transfer from 10 to 0.5 mm NO(3)(-), the stimulated appearance of LRs was abolished in atnrt2.1-1 plants, whereas the increase in mean LR length was much more pronounced than in Ws. These modifications of RSA mimicked those of Ws plants subjected to severe nitrogen stress and could be fully explained by the lowered NO(3)(-) uptake measured in the mutant. This suggests that the uptake rate of NO(3)(-), rather than its external concentration, is the key factor triggering the observed changes in RSA. However, the mutation of NRT2.1 was also found to inhibit initiation of LR primordia in plants subjected to nitrogen limitation independently of the rate of NO(3)(-) uptake by the whole root system and even of the presence of added NO(3)(-) in the external medium. This indicates a direct stimulatory role for NRT2.1 in this particular step of LR development. Thus, it is concluded that NRT2.1 has a key dual function in coordinating root development with external NO(3)(-) availability, both indirectly through its role as a major NO(3)(-) uptake system that determines the nitrogen uptake-dependent RSA responses, and directly through a specific action on LR initiation under nitrogen-limited conditions.
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PMID:A central role for the nitrate transporter NRT2.1 in the integrated morphological and physiological responses of the root system to nitrogen limitation in Arabidopsis. 1641 11

Experiments were carried out to examine the effects of nitrogen source on nitrogen incorporation into cyanophycin during nitrogen limitation and repletion, both with or without inhibition of protein synthesis, in cyanobacteria grown on either nitrate or ammonium. The use of nitrate and ammonium, 14N labeled in the growth medium and 15N labeled in the repletion medium, allows the determination of the source of nitrogen in cyanophycin using proton nuclear magnetic resonance spectroscopy. The data suggest that nitrogen from both the breakdown of cellular protein (14N) and directly from the medium (15N) is incorporated into cyanophycin. Nitrogen is incorporated into cyanophycin at different rates and to different extents, depending on the source of nitrogen (ammonium or nitrate) and whether the cells are first starved for nitrogen. These differences appear to be related to the activity of nitrate reductase in cells and to the possible expression of cyanophycin synthetase during nitrogen starvation.
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PMID:Effect of nitrogen source on cyanophycin synthesis in Synechocystis sp. strain PCC 6308. 1642 97


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